chapter 9 durability and treatment

8/18/2019 Chapter 9 Durability and Treatment

1/17

Chapter

Durability and treatment

ntroduction

Timber has a multitude of widely differing uses, each representing

particular service conditions and expectations of longevity. ew

Zealand does not have a range of species that will meet all end

use needs with naturally durable timber. Historically the choice of

species was not particularly wide and the range of naturally durable

indigenous species

is

now very small. Internationally, availability

of naturally durable to highly durable timbers

is

poor and

is

usually

associated with tropical areas.

Timber does not deteriorate through age alone, although

some

changes may take place during the life of timber members in a

structure. n service, the timber components of a structure will

be exposed to a variety of forces and hazards which may operate

continuously or intermittently, consecutively or concurrently, and

which may change in nature or intensity during the lifespan of the

structure. By classifying these hazards and defining the parameter

which describe their effects, it

is

possible to estimate the useful life of

treated or untreated timber in a new structure. n older structures, this

knowledge is essential for assessing the costs and consequences of

taking no action, instituting remedial treatments with minor repairs or

undertaking a major reconstruction.

Wood preservation extends the useful life of timber by modifying

its resistance to detrimental agents. Effective and economic wood

preservation relies on a thorough knowledge of the properties and

availability of appropriate timber species, an appreciation of the in

service hazards and the means of reducing their severity, as well a

the properties of wood - preserving chemicals and their application.

Fortunately, in ew Zealand, the principal construction timber,

radiata pine,

is

very easy to treat with preservatives and can be made

very durable.

This chapter guides designers towards specifying timber to match the

desired lifespan of the product or building element.

Regulation

Timber treatment and its application for building purposes

is

a

regulated activity

in

ew Zealand. While designers and specifiers

are free to call up preservatives and levels

of

preservative retained

in

wood, these are specified for Building Code acceptability

in

various

documents and departure from them

in

alternative solutions bring

a need to demonstrate performance. These documents are outlined

later in this chapter.

77


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Assessment of compliance with treated timber manufacturing

standards is a key feature of regulation of this industry and , while

it is not compulsory for producers to have independent oversight of

their product, it

is

normal practice and independent quality assurance

systems are established. The standard for wood preservation and its

auditing by Quality Assurance systems is intended to apply not only at

the plant gates but also at the time

of

delivery to building sites.

The

New

Zealand Timber Preservation Council and

the

WOODmark™

The New Zea land Timber Preservation Council (TPC) is a quality

assurance agency established by the timber industry to estab lish and

maintain the standards for quality

of

treated timber. The Council

has registered the WOODmark™ as a mark of quality indicating

compliance with treatment specifications with its use being limited

to treatment plants holding a licence, which requires the ability to

perform and maintain records

of

compliance and regularly testing by

independent laboratories.

Agriquality

Agriquality operates as an alternative quality assurance

scheme

for

timber treatment using its own laboratories for testing and assessment.

Certified plants are licensed to use the Agriquality registered

assurance mark.

New Zealand Building Code

requirements

What

s

durability?

The word durable

is

defined

in


Handbook , section B2NM I, AS I as resist nt to wear nd decay

either durable nor durability are defined

in

Clause E2 , where they

are used as an adjective or a noun with connotations of lastingness,

longevity, or persistence

of

time.


Durability is covered in the

New

Zealand Building

Code (NZBC)

in

Section 82 - Durability, and Section E2 - External Moisture. The

durability clause requires that materials, components and construction

methods allow the building to function for its

specified inte

nd

ed

li f

e

of not less than 50 years for structural and inaccessible elements .

Accessible elements where failure can be detected such as exposed

cladding, plumbing

in

a crawl space, interior linings and coatings may

have a shorter specified life

of

5 or 5 years.

The NZBC Approved Documents are guidance documents under the

Building Act 2004 giving means of compliance with the performance

criteria of

the Building Code. In accordance with the Building Act,

the Building Code requirements can be achieved

in

any one

of

three

different ways:

I .Verification Method

2. Acceptable Solution

3.Alternative Solution

A Verification Method

is

an approved calculation method, generally

consisting of well established codes

of

practice for design. Many of

8

these codes have existed much longer than

the Building Act, so are called up with

or

without modifications.

The Acceptable Solution is a cookbook of

prescriptive measures which are a deemed

to satisfy solution to the requirements

of

the

Bui lding

Code

.

For specia l designs which do not fit the

above two options, the Building Act allows

an Alternative Solution to be offered. This

solution may be accepted by the Territorial

u t ~ o r i t y (TA) if they are persuaded on

reasonable grounds that the solution meets

the requirements of the Building Code.

Timber retaining wall requires a high level of

preservative treatment

Clause

8

Durability

In the

New Zea

land Building Code, Clause

B2 Durability sets down as its objective th at

a bui lding wi ll throughout its li fe

continue to satisfy the objectives of the

Code, and that building elements, with

only

nonnal

maintenance, will continue

to satisfy the performance requirements

of

the

Code

for the specified intended

li f

e

of the building.

The standard times used for element life are

50 years, 5 years and 5 years. According to

Verification Method B2NMI durability may

be verified by proof of performance, using

• in-service history,

• Laboratory testing, or

• Comparable performance of similar

building elements

Such factors as the local environment,

intensity of use, material composition, the

degradation mechanism are evaluated for an

element

within a specified system inc luding

fixings, flashings etc.


3/17

cceptable Solution

Arising from Clause B2 the NZBC has as an

Acceptable Solution B2/AS I for durability

and performance requirements

of

timber

building elements. In the Acceptable Solution,

ew Zealand standards are approved for a

variety

of

construction materials. For timber

the main standards are ZS

3604:1999

Timber Framed Buildings

and

NZS

36 2 :2003 Timber and Wood-based Products

for use

in

Building. NZS 3602 includes

the

required level of chemical treatment

for different levels of hazard, and

is

also is

referenced for E External Moisture.

Treated

wo

od being

removed from

pressure

linder on the left

with previously

treated

wood on the right.

NZ3602:2003 Timber

an

d Wood-based

P

roducts for

Use in Buildi

ng

is a primmy

reference standard (an Australian term) in

ZBC Clause B2. This standard (and specific

amendments to it) are listed

in

Clause B2 and

are recognised as an

Acceptable Solution

by

building consent authorities and designers.

The 2003 revision to NZS3602 was driven

by concerns about the frequency of leaking

buil dings in New Zealand and was written in

haste

to

address these. In particular the intent

was to

enhance the robustness of framing

timbers where proven deficiencies in design

and material perforn1ance were resulting in

moi sture penetration and decay. This standard

gives the requirements for timber so that

building elements can be expected to give

acceptable performance during the life of the

building.

t

covers not only the individual

building elements but also aspects of design

and construction, and it references another

Approved Document, E External Moisture.

ZS

3602 gives requirements for timber:

• for particular uses

• for particular species or type

• for particular grades

• for particular in-service moisture

conditions

• for levels of treatment (i.e. hazard levels) to NZS3640 or AS/

NZS 1604(3) (plywood only)

NZS3640:2003 Chemical

Preservation of Round and

Sawn

Timber is a secondary reference standard

in

that it is not referenced

in

B2 Durability

but is

referenced

in

NZS3602.

t

was written

at

the

same

time as, and

in

association with

NZS3602

, to

set

out

requirements for the preservative treatment

of

timber to provide

protection from insect attack and fungal decay and marine borer

attack. The standard

is

a process standard intended both for use by

treatn1ent plants, and to apply at the plant gate.

AS/NZS

1604 .

3:2004

Specification fo r

Prese

r

vative

Trea

tm

ent

-

Plywood

is a secondaty reference standard as is

NZS3640

and

applies to plywood.

lt

has marginal differences from

NZS3640 in

that the HI and H3 hazard classes have not been subdivided. There is

therefore no H3.1 and H3 .2 plywood, it uses H3 only.

lternative solutions

The Acceptable Solution B2/AS I was not intended to exclude

other solutions which can be offered as alternative so lutions.

There

is

such a solution for applications and uses relating to H 1.2

components that was appraised and Codemark accred ited by the

former Building Industry Authority. This accreditation was reviewed

by the Department of Building and Housing and was not withdrawn.

It was the subject of a sustained attack in the media and died as a

commercial product, although all the test data showed its efficacy

to be proven and there was no evidence of non-performance. As

an

outcome

it is unlikely that there will be alternative solutions

around timber treatment

in

the foreseeable future.

c c e p t a n c e

an

alternative solution

is usually supported by expert opinion such as

from Scion and

BRANZ

.

Recent history

Following the introduction of perfonnance based regulation in the

early I990s, poor practice crept in due to concurrent deregulation of

the building industry and introduction of the non-prescriptive code

with poor detailing and poor construction, mostly with monolithic

sheet claddings. By 1999 there were serious calls for improved

practice. Water penetrated the cladding of balcony structures and

poorly sealed building envelopes

of

a large number

of

residential

units , and without adequate wall ventilation this caused decay of the

framing and serious structural risk.

In 1995 an amendment was made to the New Zealand Standard for

timber treatment (referenced in Acceptable Solution B /AS I in 1998)

allowing untreated kiln-dried timber in dry conditions. For buildings

with poor weathertightness, this resulted in severe and rapid timber

decay of timber framing where water was trapped against the timber

in a relatively warm environment. Within two years a number of

significant durability failures resulted in a public outcry and repair

estimates of between NZ$120M to

NZ

I .8Billion. While this was

quickly dubbed leaky buildings

in

the news media it was often

incorrectly attributed to the use of untreated radiata pine timber

framing timber.

This problem led to a legal procedure for resolving disputes

(Weathertight Homes Resolution Services Act 2002), changes to the

Building Act in 2004, a major change to the government regulating

79


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bodies and a requirement for all carpenters to be certified. Territorial authorities went through a period

of

adjustment when

the performance based approach was introduced in 1991 and again in 2004 following the leaky buildings problem, so that

they now have greater levels of responsibility and work more closely with the Department ofBuilding and Housing. A new

conservatism in detailing for weathertightness has become the norm for exterior claddings, with a requirement for chemical

treatment of almost all radiata pine framing timber. [t is interesting to note that e Compliance Document for t e New

Zealand Building Code Clause

£

External Moisture (a prescriptive solution for exterior detailing) was expanded from

28 pages in 2000 to 184 pages in 2005.

azard classes and preservative options

The

design

of

timber buildings must aim at preventing deterioration

of

timber by providing adequate protection

or

by using

durable materials. Australia and New Zealand have adopted simi lar hazard classification systems. In

ew

Zealand, various

end uses have been classified into eight classes with two subclasses. These are shown in Table 9.1.

The

hazard classe

are linked to treatment specifications which enable timber members to perform satisfactorily for their expected life, as

specified in NZS3640:2003. The hazard classes are generally

common

with Austral ia except that Australia does not have a

split in the HI and H3 classes which were introduced in

Z

in 2003. There is no equivalent to the

H

1.2 class in Australia.

The

hazard classes are described in terms of service exposure and biological hazard . A larger list together with preservative

options

in

each class and a

brief

mention

of

environmental and on-site issues

is

given

in

Table 9.2.

Table 9 1

Hazard classes in New Zealand and Australia

Hazard

clas

s Biolog ical hazard Serv ice cond it ions Typical

uses

Dry conditions , not exposed

to

weather or

Roof,

wall and floor framing , flooring,

Untreated

Borers interior timber, wall frames clad with

ground atmosphere.

masonry veneer. Refer to NZS3602

H1.1

Roof wall and floor framing, sub floor

(Was the H

Borers

Dry conditions. Not exposed to weather. framing, where dry use timber is

class before the

Not

in

contact with the ground.

installed wet, or dry rough sawn for

2003 revision)

interior dry use.

Protected from the weather but with a risk

Borers, and short term

of

moisture content conductive to decay

Wall and roof framing

in

situations

H

.2 decay fungi in a leaking wall

as a result

of

moisture penetration

of

the

situation

building envelope.

complying with NZBC E2/AS1 .

Not

in

ground contact

H2

Not exposed to weather, exposed to

(Only Australia, Termites and other borers Framing timber

in

Australia .

not NZ.)

ground atmosphere in dry conditions .

Periodic wetting in water shedding Painted cladding trim, framing

H3.1 Decay fungi and borers situations , such

as

exterior wall framing at for exterior walls at serious risk

risk to leaking cladding (greater than H1.2). of moisture penetration. Refer

to

Not in contact with the ground. E2/AS1.

Cladding and trim (painted or

H3.2

Decay fungi and borers

Periodic wetting in situations not shedding unpainted) , exterior structural and

water. Not

in

contact with the ground. decking and exposed timber uses

in

farming and horticulture.

H4

Decay fungi and borers In water or in the ground, permanently wet.

Posts, fencing , bridge decks,

landscaping .

In

water or

in

the ground, permanently wet,

Piles, poles, foundations, retaining

H5 Decay fungi and borers and where 50 year durability is expected

for building purposes. walls, line poles

H6

Decay fungi and marine

In estuarine ground or immersed in

Marine timber piles

borers seawater.

8


5/17

selection and specificati

on of

treatment levels

Guidan ce

on

specifying timber for particular

hazard

s or uses is given in NZS: 3602:2003

and in NZTPC literature. For residential

and other tim ber framed construction, NZS:

3604:1

999 is

an

Acceptable Solution for the

z

Building Code approved Document B I

truc

ture, permitting the use

of

timber or

wood

-based products specified or protected

in

accordance with NZS 3602. There are

many

situatio

ns

outside the scope

of ZS

3604

, where specific design on the basis

ofNZS3603:

1993

generally is applicable,

includ

ing specifically designed buildings,

civil

engineering construction, and temporary

work

s

The following commentary on the use

of

hazard

ratings

is

a guide

to

designers and

pecifi

ers:

ntreated or Hl l or H1 2?

Achoice between untreated timber or

HI

treated

timber will depend

on

the expected

use.

Dry

, interior structural components for

buildin

gs are not subject

to

decay, and are

rarely

if ever subject

to

insect attack and

damage in

New Zealand. Exceptions

to

this

might be when the timber

is:

• Adjacent

to

damp unventilated ground or

•

Used

in

association with heavily infested

older native timber or

• Exposed

to

unexpected wetting

Resistance

to

insect attack can be provided by

any one of the following:

• Using naturally resistant timbers e.g. kiln

dried untreated radiate pine or Douglas fir

in

interior dry situations, or

• Using heart timber

of

certain indigenous

species traditional use), or

• Using H

1.1

or H

1.2

treated timber or

• Applying a surface coating

of

insecticide,

particularly appropriate for large glue

laminated members.

Plyw

ood and particle board are considered

to

be naturally resistant in interior dry s i t u a t i o n ~

With

outdoor timbers and temporary works

untreated radiata pine timber may be

accept

able for short life applications- say

up

to two

years out

of

ground contact).

In

the

case

of

timber

for

temporary work that

is to be

reused,

e.g., scaffold planks and comparable

comp

onents, the service conditions are not

usuall

y considered a hazard risk requiring

treatment

in

the case

of

Douglas fir and radiata pine, provided that

storage

is

not

in

damp conditions or

on

the ground.

Hl

l

is an insect resistant hazard class only. t was widely used in

the period 1990 - 2003 under the descriptor HI and was discontinued

from application in external wall framing as awareness grew

of

the increased frequency

of

leaking buildings.

1t

is probably not

commercially available at the time

of

writing.

H

l

2

is a recently created hazard class introduced

as

a result

of

concerns about the durability of external wall framing where

it had

become apparent that limitations

of

design, material performance

or workmanship have created a risk

of

moisture penetration and

retention conducive

to

decay. The expectation is that the resistance

to

decay will enable the moisture penetration issue

to

be remedied and a

durability performance period is not specified although some writers

have associated a two year period with

it.

A very high level

of

treatment

is

needed for timber members in

contact with sea water

The introduction

of

risk matrix computations with claddings and

building envelopes and the emphasis on Acceptable solutions refer

Approved Document

E2

External Moisture and E2 /

AS

I has taken

away options around timber treatment and effectively made the use

of H

1.2

mandatory in many external wall framing designs. However

note the following:

• Masonry veneer external cladding has a good track record such

that

it

can generally be used in association with untreated timber

framing.

• Internal wall and floor framing and unlined buildings can be

framed in untreated timber.

• Roof trusses and roof and ceiling framing except skillion and flat

deck roofs) can be untreated timber.

The requirement in NZS:3602 for H

1.2

and H3 . l .in association with

various cladding and design situations has led a number

of

truss and

frame suppliers

to

avoid holding stock

of

H 1.2 and

to

supply

H3.1

wherever treated framing is required.

8


6/17

Table 9 2

Hazard classes

and

preservative

options

Hazard

Preservative

options

Health and

Environmental

Class

and

colour

coding

safety

issues issues

Site issues Disadvantages

(Notes 1 2)

Develops sap stain and

mould when wetted and

Untreated Note 4

Nil

staying wet.

Association with leaky

Cost effective

in

dry

buildings .

situations

Boron getting

Little decay

a) Boron compounds

in

resistance .

H1.1

Note4

to waterways at

Use has almost ceased

water, supplied wet.

treating sites.

Used

in

the leaky

building period.

(Was

H1

pre

b) Permethrin in solvent ,

Solvent

VOC release at

Association with lea

ky

the 2003

supplied dry

emission

treatment.

Nil decay resistance

buildings .

revision)

Note4

No decay resistance.

H1 .2

a) Boron compounds-

Boron getting

Wet timber shrinking on

Dry framing availability

aqueous (pink), supplied

Note4

to waterways at limited.(Note 3)

wet or dry after treating.

treating sites.

drying.

Shrinkage issues.

b) Boron compounds

Moisture content Moisture

with diffusion agent,

measurement a problem measurement. Rapid

aqueous(pink) , treated

Note4

with resistance meters

uptake of moisture if

supplied dry

if glycol as the diffusion diffusion agents are

agent. hygroscopic

Odour, solvent allergy, tin

Odour.

c)TBTN or TBTO

in

Solvent

Tin as a

allergy.

Lack of reliable spot

solvent (white spirit) ,

allergy.

pollutant.

Use with adhesives.

test. Moisture meter

(blue), supplied dry

Tin contact

VOC release at

Residue disposal.

unreliability. OSH

treatment. concerns re solvent

No satisfactory site test.

exposure tin safety.

Odour, solvent allergy.

Odour.

No site test for

OSH concerns re

d) IPBC Permethrin

Note4

VOC release at

preservative.

solvents.

in

solvent (white spirit),

Solvent allergy

treatment

NB: Additives to solvents

IPBC performance.

(blue), supplied dry

modifying (c) and (d) to

reduce odour are possible

Identification of treated

but may

effe t

efficacy.

wood difficult.

H2 Refer AS 1604:2005

N

IAin

NZ N

IAin

NZ NI

Ain

NZ

NIAin

NZ

CCA

(Australia not

ACQ

Z)

Permethrin ( variations)

H3.1

a) Boron compounds with

diffusion agent, aqueous, Cut ends to be primed ,

See also

supplied as dry paint

Note4

product needs to be

preservatives

primed cladding and trim

painted.

listed for

only.

H.3.2 (wet

Odour, Solvent and tin

or dry after

allergies.

Odour, lack of spot

treatment)

b

TBTN or TBTO in

Solvent allergy

test (needs lab test).

Tin as pollutant. Residue disposal.

solvent (white spirit) ,

Tin contact

VOC release at Reliability of spot tests

OSH tin solvent

green colour, supplied

safety concerns.

dry

Note 4

treatment mi measurement.

mi

measurement

Compatibility with

reliability

adhesives

c) Propiconazole plus Odour, solvent allergy

Cost, not easily

tebuconazole in solvent

(white spirit)(plywood ,

Solvent allergy

VOC release at

Not used structurally

in

NZ

verified for presen

ce

speciality products)

Note4

treatment

No site test for presence

or retention of

supplied dry

(2006)

preservative

d) Copper Napthenate

Solvent

Copper as Colour, odour, solvent

Colour, odour, gluing

(green) in solvent (white

emission

pollutant. allergy. Corrosive, staining

Bleed through of

spirit) , dry cladding and

VOC release at

of paint.

colour.

exterior trim

Note 4

treatment. Comoatibi litv with a ues.

82


7/17

H3 .2

Note --CCA.

Only if eaten

Copper loss

ACQ

, CuAZ

a) CCA

in

water, supplied

(normal

(negligible

Residue disposal ,

Fear of As component

can be

dried

wet

precautions)

compared to

corrosive.

in personal contact

other Cu based situations.

after

to

order.

Notes 4 5

preservatives).

Cost vs. CCA.

b)

ACQ in water, supplied Notes 4 5

Copperas

Residue disposal , High loading of

wet pollutant.

corrosive.

copper.

Copperas

Cost

vs.

CCA.

c)

Copper Azole in water,

Notes 4 5

Residue disposal,

High loading

of

supplied wet

pollutant.

corrosive .

copper.

d) Copper Naphenate

in

Solvent allergy

Copper as

Odour, solvent allergy,

colour, corrosive , staining

Odour and colour

solvent, supplied dry

Notes 4 5

pollutant.

of paint

Bleed through paint

N Ain NZ

(Note

6

CQ or Copper Azo/e on

Depends on

N Ain

NZ

N AinNZ N Ain

NZ

a dry

t

dry basis

solvent

a) CCA in water, supplied

Normal

Slight copper Residue disposal,

H4

precautions

wet

Notes 4 5

loss in water. corrosive.

b)ACQ in water, supplied

Note4

Copperas Restdue disposal , Cost and efficacy vs

wet

Pollutant. corrosive. CCA. High Cu loading.

c) Copper azole

in

water,

Copperas

Residue disposal,

Cost and efficacy vs

supplied wet

Note 4

pollutant. corrosive.

CCA. High Cu loading.

Normal

Slight copper

H5

a) CCA

in

water, supplied

precautions

Residue disposal ,

wet

loss

in

water. corrosive.

Notes 4 5

b) ACQ

in

water, supplied

Notes 4 5

Copper as Residue disposal,

Cost and efficacy vs

wet pollutant. corrosive . CCA. High Cu loading.

c) Copper azole

in

water,

Notes 4 5

Copper as Residue disposal, Cost and efficacy vs

supplied wet pollutant. corrosive. CCA. High Cu loading.

CCA in water, supplied

Normal

Slight copper Residue disposal,

H6

precautions

wet

t ~ s 4 . S

loss

in

water. corrosive.

Notes

1)

This column lists preservatives

in

general use at the time

of

writing and covered by NZS3640, the liquid carrier, plus whether supplied

wet

or

dry.

Some development possibilities are

in

italics.

2)

Colour codings are for framing for timber framed buildings as specified

in

NZS3604. For H1 .2 pink or red are optional.

3)

The boron based surface applied system that was accredited by BIA (and later endorsed by DBH) as

an

accredited alternative for

H1

.2

with an orange colour code is excluded from this table.

4) All fine wood dust is a hazardous component and wood processing should involve protection

to

eyes, respiratory systems and skin .

5)

The need for protection as indicated

in

Note 4

is

emphasised with reference to hazard classes

H3

.2,

4,

5, 6 where there are additional

carcinogenic aspects associated with metallic components .

6)

Potentially (as a future development) a dry

H3

.2 could become available on the basis of wood being taken from dry stock and treated

through a non-aqueous process with either ACQ or CuAz.

Glossary: ACQ =Alkaline Copper Quarternary, CCA = Copper Chromium Arsenic, CuAZ Copper Azole, TBTN = Tri-butyltin Napthenate,

TBTO= Tri-butyltin Oxide, VOC =Volatile Organic Compound, DBH = Department of Building and Housing, OSH = Occupational Health

and

Safety.

H1 2 or H3 1

framing

At

the time

of

writing the logic around the

pecification

of

treatment and reasons for

having either H 1.2

or H3 1 is

hard to identify.

It

is simplest

to

say an exterior exposure

classification was applied to a situation

where a decay resistance rating should have

been used.

t

the time when NZS3602 and

3640 we

re

written

in

2003, relative decay

resi

stance ratings as shown

in

Table 9.5 were

not

known. The assumption was that

H3 1

would have to be a significant step up from H1 2 . In particular with

boron preservatives this is not the case and the same factor of safety

against fungal decay

is

present with H 1 2 boron) and

H3

. 1

The

current advice

is

that Table I D

in

NZS3602:2003

is

the

Acceptable Solution and those arbitrary treatment levels apply.

H3 1 or H3.2 exterior exposure

The

reason for dividing

H3

into two subclasses arose from the

different performance

of

the

CC

and the tin based preservatives.

As result the H3 1 hazard class

is

restricted to exterior situations that

shed water - typically claddings, fascia, trim etc and

H3

.2 applies to

83


8/17

situations where a more robust level of decay resistance

is

expected

- e.g. decking and exterior structural uses (but not ground contact).

H3 2 or H4?

A choice between H3 and H4 hazard ratings internally can sometimes

be difficult. For timber

in

contact with the ground, H4 is the

minimum rating. For timber out

of

ground contact, H4 treatment

should be used for very wet situations, particularly for important

structural components. In industrial plants where high humidity and

temperatures are expected, the moisture content of the timber will be

such that H3.2 preservation leve ls should be used. Only in the most

exceptional conditions, which will be wet as a result

of

condensation,

rather than high EMC as a result of humidity, will H4 be required.

H4 or HS?

Both

of

these hazards are described for ground contact . Both can

app ly to round and to sawn timber.

The

key question for building

purposes is

how

critical is the component?

ln

the case

of

agriculture

or horticulture the question is linked to severity of attack and ease of

replacement. These are discussed separately.

Timber

in

the ground supporting buildings can be very difficult to

replace. Proprietary branded timber building piles (whether round or

square) wi

ll

be treated to H5 requirements for

NZBC

comp

li

ance.

Where non-specifically identified timbers are used as building

foundations they should be specified and ordered with H5 treatment.

In the case

ofroundwood

this

is

particularly important because both

treatment levels are in regular use. For short life structures ,

h o r i n g

fences, walls etc. , the same considerations are not applicable and H4

treatment will be satisfactory. Poles are typically supplied with H5

treatment but they should be specified as such.

Fence and horticultural support (round

or

square) posts are almost

always H4 treated. Strainer posts can be

H4

or

H5 depending on the

producer. In the case

of

tension structures

in

vineyards or orchards,

where progressive collapse would be unacceptable H5 anchor posts

are recommended.

H6

This is the highest level

of

preservative loading to resist what can

be severe attack initiated in short time intervals. The lifespan of

H6 treated timber

in

marine environments can vary considerably

depending on the nature

of

the marine borers present and there

frequency. The presence or absence of si lts discoloration or pollutants

will not give any indication of likely severity

of

attack.

esign and detailing

Timber building design, both

in

its concept and detail should aim to:

• Protect untreated timber from direct sun and rain.

• Avoid details that trap moisture

• Avoid condensation points for moisture by insulating or isolating

timber from sources

of

moisture

• Provide mechanical barriers to water or to termites

(if

this hazard

exists)

In realizing these aims, detailed design considerations for untreated

timber should involve the following:

8

• Building sites should always be graded

to provide positive drainage away from

foundation walls.

• All exposed wood surfaces should be

pitched to assure rapid runoff

of

water.

Construction details that trap moisture

in end grain must be avoided . The

prevention

of

decay

in

walls and roofs

relies largely on designs that prevent the

entrance and retention of rain water. A

wide roof overhang with well designed

gutters and downpipes

is

desirable.

• Wood in contact with concrete near the

ground should be protected by a moisture

proof

membrane such as heavy asphalt

paper, and preservative treatment i

advisable even

if

a membrane

is

present.

Openings

in

masonry walls for support

of

timber girders and joists should be

big enough for air space around the sides

and ends of the wood members, and ,

moisture-proofing

of

the outer face

of

th e

wall

is

essential if the members are below

the outside soil level.

• Adequate separation of wood from known

sources

of

moisture (including soil and

concrete) is always necessary to prevent

absorption of moisture and to allow

periodic inspection . When it is impossible

to provide adequate separation, the

wood must be correctly treated with a

preservative or a naturally durable species

be used.

• Unventilated, inaccessible spaces under

buildings should be avoided , because

wetting of untreated

wood

or H I .I

treated wood by condensation may resu

lt

in serious decay damage . A ventilated

crawl

space

with at least a

450

mm

clearance should be left under all wood

joists

and girders . Condensation can

be reduced by

providing

openings on

opposite sides of the foundation walls for

cross ventilation or by laying a plastic

membrane on the soil , or both.

Exceptional circumstances

Porches, decks, fences, patios, pergolas

and other weather-exposed items present a

decay hazard that cannot be fully avoided

by construction practices . t is advisable to

use preservative-treated wood or naturally

durable wood for all exterior situations.

Where highly humid conditions are present

inside buildings, as

in

textile mills, pulp

and paper mills, cold-storage plants and


9/17

swimming pools, preservative treated timber

hould be used.

spection

To supplement good design and construction

practices, periodic inspections of a structure

will

provide assurance that decay-preventive

measures are being maintained and that

additional decay hazards are not present.

It should be emphasized that damage from

deca

y sometimes develops slowly. Periodic

inspections are important, therefore, to reveal

early indications of moisture penetration or

condensation, and once they are detected,

corrective measures can be taken in time to

avoid significant damage. Decay and insect

attack create irreversible damage . Prevention

is mu ch easier than repair.

e

aky

u

ildings

The 1990s

saw

the construction of significant

numbers of buildings that admitted moisture,

resulti ng

in severe decay to parts

of

the

building framing. This was particularly

true in multi-residential developments but

not confined to these. The leakiness was a

particular problem in some buildings with

monol ithic claddings (insulated stucco

construction) but not confined to these. An

outcome has been a major overhaul of the

building controls system in New Zealand

tarting with the 2004 revision

of

the Building

Act the abolition of the Building Industry

Auth

ority, and the resumption

of

direct

government intervention through the new

Depa rtment

of

Building and Housing.

Some

tandards, codes

of

practice, and acceptable

solutions were rewritten in haste, which

resulted in

some

errors which are currently

being revisited and amended. This will be an

ongoing process.

gents causing

deterioration

Timber durability is largely a matter of

design. Permanent timber structures should be

built not only to be structurally safe but also

to be durable, with minimum maintenance.

In common with other structural materials,

uch as steel, concrete, glass

or

plastic, timber

will deteriorate

if

subjected to destructive

agencies. n understanding

of

the variou

destructive agencies is helpful when devising

efficient means

of

delaying or avoiding

natural deterioration. Fire

is

a special case

which is dealt with in Chapter

12.

The behaviour of timber in service

is

affected by both environmental

and biological factors. Usually, outdoor exposure gives the worst

conditions because climatic variations are widest and of greatest

impact, but severe conditions may also occur indoors due to

hazardous artificial environments or poor construction details .

A noteworthy example

of

indoor decay during the 1990s in New

Zealand was external wall envelopes without drainage which, when

water

got

in , resulted in a significant decay hazard situation where

H l. l

or

the old HI) treatment was ineffective.

Considerable variations in climate make some factors insignificant

and others important, such as temperature and humidity. The

longevity

of

timber in service will be directly related to the balance

between destructive agencies and the resistance

of

the timber. This

ection describes the agents that cause deterioration in timber and the

most cost effective means

of

combating them.

The main agents causing deterioration are:

• Insects and marine borers

• Fungi

• Moisture fluctuations

• Ultraviolet light

• Bacteria

• Mechanical abrasion

• Chemicals

Insects and marine borers

Insects are

among

the most successful life-forms on earth, so there

is considerable literature about them. In their life-cycle, all insects

undergo a complete metamorphosis

of

four stages:

I .egg- laid by the fertilised adult, sometimes singly, sometimes in

large numbers;

2.larva

or

grub- for most wood-boring species this

is

the feeding

stage causing damage in the form of tunnels or galleries in the

wood;

3. pupal stage- which

is

non-feeding and essentially non-mobile.

The pupa is encased

in

an impermeable membrane so may

occasionally survive vacuum-pressure impregnation

in waterbome

preservative solutions;

4. imago or adult which emerges from the pupa and

is

highly mobile,

being able to fly to seek fresh feeding sites.

The

primary concern in

New

Zealand

is

with Anobium and Lyctus

wood-boring insects,

or

borer . There are a few species

of

native

termites

but

these are confined to forested areas and are extremely

slow acting, compared to the voracious varieties that have flourished

occasionally (and briefly) after importation of infected timber.

The

heartwood of most species is naturally resistant to Lyctus and

Anobium which establish most readily on rough sawn surfaces of

green sapwood. They prefer the timber at a moisture content between

18 and 25%. High temperature kiln drying, planking, painting and

chemical treatment all reduce the likelihood

of

attack by borer.

Radiata pine that

is

kiln dried and used dry

is

virtually never attacked

by borer in either sapwood or heartwood. Douglas fir and macrocarpa

heartwood

is

generally resistant to borer. Air-dried sapwood

of

rimu

and

some other

native species is often attacked.

85


10/17


11/17

are in sheepyard gratings and compost bins.

These bacteria appear to be highly tolerant

of the preservative loadings

of

the wood.

Th

eir tunnelling and eroding activity causes

ome degree of mechanical weakening and

is believed to reduce the decay resistance of

pr

eservative treated timbers.

Chem icals

ron oxides interact with wood causing a

breakdown known as iron sickness which

will accompany the corrosion of steel in

contact with timber. Wood

is

generally

resistant to most other chemicals, making it

a desirable structural material in corrosive

environments.

Natur

al

durability

Timbers vary enormously

in

their natural

resistance to insect

or

funga l attack.

Some

peci es, like ironbark, teak and redwood

(Sequoia) are very resistant to both fungi and

in

sects, and are known as durable species.

Oth ers such as radiata pine have very little

natural resistance to fungal attack and are

regarded as being non-durable or even

perishable. Sapwood

of

most species has very

littl

e natural resistance to fungal attack, so

all sapwood should be regarded as perishable

unle

ss

it is

properly treated with a wood

preservative.

The

natural durability of a timber species

is

usually

rated by the resistance

of

the mature heartwood to insect and fungal

attack.

Sapwood and heartwood

Sapwood is the outer zone of wood

in

a log, which conducts sap

in

the

li

ving tree. Heartwood is the zone

of

older wood inside the

apwood, which has been slowly converted to heartwood in the

li

ving tree by the deposition

of

toxic chemicals and waste products.

These toxic chemicals deposited in the heartwood ce

ll

s provide some

resistance to funga l and insect attack which varies between species

and within species, depending on density and rate of growth.

Resistance to decay

Testing of timber durability, including treated timber,

is

done by

embedding

stakes in selected plots of ground (called graveyards)

and eva lu ating the progress

of

decay ove r many years. Table 9.3

lists the durability

of

the heartwood

of

so

me New

Zea land-grown

timbers in ground contact. This is not a full list

of

commercially

available species, or complete for native species, and a more

comp lete list

is

given by Hughes (see Further Reading).

Of

those

classed as moderately durable, macrocarpa a

nd

some euca lypts are

commercially available in New Zea land. Hardwoods imported from

Australia and Asia may be obtained to meet requirements for high

natural durability.

Resistance

to

insect tt ck

Based on natural durability, the untreated heartwood

of

most species

is unlikely to be seriously attacked by insects, but sapwood

is

often

able 9 3 Durability of untreated heartwood

of

New Zealand grown timbers

Perishable Non-durable Moderately

durable

Durable

Very durable

(25 years)

Hardwoods

Alder

E.regnans

5

E.globulus

5

E.muellerana

5

Robinia

2

·

Black poplar hybrid Hinau E.sieberi E.saligna

2

Kamah

i

Oak' Black beech

2 3

Hard beech

2

Kanuka Osier Willow ' Silver beech

2

Mountain beech

2

Silver birch Pukatea

Red beech

2

Tawa

Southern rata

So ftwood s

Cosican pine

Radiata pine

Macrocarpa

2

Silver pine

Ponderosa pine

Douglas fir

2

Californian redwood

European larch

2

Rimu

Kauri Kaikawaka

Western

red cedar Lawson's cypress

Tanekaha

No

tes

:

1.

Re

presented by posts only, durability of heartwood alone may be higher.

2. Species exhibiting a range of durability have been assigned to the class representing their average range.

3. Unusually variable

(perishable-

durable) .

4. Robinia specimens have not been installed long enough for an accurate assessment of their durability, but they are at least in the

Durable class and more probably in the very durable class.

5. E. means Eucalyptus .

87


12/17

susceptible to some attack. The likelihood of attack decreases with

decreasing moisture content, with surface smoothness and with surface

coatings or paints. Table 9.4 lists the natural susceptibility

of

the

sapwood

of

the more common timber species, to four species

of

borer.

Table

9 4

u ceptibility to borers of untreated sapwood of some NZ

grown timbers

Tim ber Borer species

spec ies

Anobium

Ambeodontus Leanobium Lyctus

common

two-tooth silverspot powderpost

house borer) borer) borer)

borer)

Radiata pine

1**

Douglas fir

2

Rimu 1

1

Macrocarpa

3

Redwood 1

Kahikatea

1 1 1 1

Taw a

1

-

Notes:

1 =average susceptibility

2 = ound in very dry localities

3 =particularly susceptible, but macrocarpa logs are nearly

ll

heartwood,

Blanks indicate very

low

susceptibility

Susceptibility of radiata pine to anobium

is

significantly reduced by

high temperature

kiln

drying.

Native species

Native species will be found

in

older buildings and in recycled

timber. As shown

in

Table 9.3 some are moderately durable to durable

including the heartwood ofkauri , matai and rimu and totara and these

will be found

in

exterior joinery sashes. Similarly kauri , matai and

rimu will be found

in

floor joists, subfloor and general framing. They

re not available commercially as new timber.

Pinus species

Pinus species are the most frequently grown plantation timber in

New Zealand and all have perishable sapwood. All the preservative

options listed in Table 9.2 can be used in conjunction with some of the

pinus species. Thus Corsican pine and Radiata pine can be converted

from perishable or non-durable to being very durable with chemical

treatment, i.e. up to H5 and H6. Radiata pine is subject to insect attack

when

damp

or wet and also as growing trees in the forest. However

Radiata and other pinus species that are kiln dried and used dry are

virtually never attacked by borer (anobium)

in

either sapwood or

heartwood.

Imported

species

Imported species will be found in older buildings and in recycled

timber.

Some

of

this in older industrial buildings from Australian

hardwoods can be very durable but identification can be difficult.

Douglas fir from North America can be found in older commercial

or industrial buildings and houses and can be of high quality. Jn new

construction, imported timber includes:

• Hardwood decking.

It

can be difficult to identify species and

durability. Some

is in

the durable class and some

is

not. Suppliers

should be required to identify the species and origin.

88

• Baltic Pine (pinus sylvestris or spruce

from Northern Europe)

is

being imported.

The susceptibility of spruce to anobium

attack is not know, but is likely to be

a problem. Pinus sylvestris should be

considered similar to New Zealand grown

pious species.

Preservatives and carriers

Preservatives are chemicals that are toxic to

fungi or insects or both. They are not benign

to humans but the level of toxicity varies.

There was a tradition of categorising them

by the type of carrier or solvent. This seems

obsolete so here they are classified by the

main active element.

They

are grouped as

follows:

• Boron compounds

• Copper based systems

• Tin based systems

• Other metallic compounds

• Non-metallic organics

The basis of timber treatment in New Zealan d

is NZS3640:2003 hemical reservation of

Round and Sawn Timbe : Table 9.2 gives a

list of preservative options in each class, with

a

brief

mention of environmental and on-site

issues.

Boron compounds

Mixtures of borate or boric acid formulati ons

have a long history of use as wood

preservatives and are significant because of

their relative low cost and low level of human

toxicity. They are effective against both fungi

and insects. Their insecticidal property re sults

from the effect they have on the enzymes in

the gut of wood eating larvae.

The

borates

and boric acid are water soluble and do not

become fixed in the wood structure, so they

will leach out in the presence

of

free water. At

the retention levels now in place for Hl.2 they

are a robust preservative at constant elevated

moisture contents and temperatures.

Historically boron was associated with wet

framing. l t diffused readily into wet wood,

both radiata pine and Douglas fir. With th e

demand changing to dry framing there are

now techniques for getting the H 1 2 retention

and penetration with dry wood. This

is

facilitated by the addition of a diffusing agent

to an aqueous system.

The

resulting product

has a modest moisture content increase wh ich

can be tolerated through the framing process.

Typically the diffusing agents are inert to


13/17

other in-contact building elements and to

insects and fungi)

pper based systems

CCA -

principally salts

or

oxides

of

cop

per

,

chromium

a nd arsen ic)

Copper chrom ium and arsenic in an aqueous

carrier are fixed insolubly

in

the wood and

are

res istant to leaching

in

free or running

water. They are effective against a broad

range

of

fungi and insects. Using pressure,

high retentions

of

and penetration of

CCA

can

be

achieved. CCA has now about 70 years of

field

tests and is probably the best performer

of

the ground contact products . In uses where

there are multiple small components, eg

crib walls, where a few

component

failures

can

be tolerated, there are expectations

of

a

service life of I 00 years or longer, from H5

level treatment.

The NZBC

puts H5 treated

poles and piles in the 50

year

durability

classification.

CCA

is approved for all hazard

classes, but is not usual be low H3. See

The

CCA

Debate below.

AC Q Alkaline Copper Qu ate

rn

a ry)

ACQ is approved for hazard classes H3 to

. This is a mixture of

copper

carbonate

usuall y and an organic

compound

didecyldimethyl

ammon

ium chloride in

an alkaline aqueous solution. lt is high

in

copper salts and has an elevated pH making

it corrosive. t has not the history of use of

CCA

but indications are that it will not have

the longevity

of

that preservative. lt

is

an

option for uses where it

is

desired to not have

the arsenical component. t

is

treated

in

a

pressure cylinder using similar processes to

CCA

. The fixity

of

the copper component is

less

effective than for

CCA

and the copper

level s

in

exposed situations will decline with

leaching.

Co

pper Azote CuAz)

Copper Azo le is approved for hazard classes

H3 to H5. t is a mixture of amine copper

and an emulsion

oftebuconazole

in aqueous

solution.

t

also has a higher loading of

copper than CCA but is not as alkaline as

ACQ . It is a second option to

CCA

where

a non

-arse

nical preservative is required.

Because the

copper

will leach it is unlikely

to

ha

ve the longevity

ofCCA.

As an aqueous

solution it is treated in a pressure

cy

linder as

for CCA. The fixity of

copper

is also less than

forCCA.

Copper

Napthenate

C

uN)

Copper

Napthenate is approved for H 1.2 and H3.1 and H3 .2 . t is

copper

napthenate in a light organic solvent carrier - typically white

spirit.

t

has a characteristic bright emerald green colour and has

been used for many years as a brush-on for cut ends.

The

napthenic

acid

component

needs to be carefully monitored . Copper napthenate

is not neutral to a variety

of

other building components particularly

elastomeric rubber based) glues. It is

also used as a brush-on

protection for exposed cut ends.

Tin compounds

T r i-bu tyltin O xid e TBTO )

Tri-butyltin Oxide is approved for use in H 1.2 and H3.1 . This is an

organic tin compound in a light organic solvent, usually white spirit.

In addition to the solvent

odour

there is a separate odour from the tin

compound.

t

is colourless and not compatible with perrnethrin type

insecticides .

Tr i-bu ty ltin Na p thenate T BTN)

Tri-butyltin

Napthenate

is approved for use in H 1.2 and H3. 1, in

a light organic solvent carrier, usually white spirit. lt has similar

properties to

TBTO

but is used because it is compatible with the

insecticide perrnethrin. This other component is a requirement in H3

in

Australia and plants ex porting to Australia will hold the TBTN

in

preference to TBTO. lt

is

odourless. Its use resu lts

in

a dry timber

product. see The Tin Debate below).

Other metallic compounds

Zinc napthenate is used as a colourless brush-on to wood that is

exposed as

cut

ends or similar. It is not listed

in

approved preservative

lists but seems effective as end grain protection. t is desirable

because it is colourless and does not affect paints or glues.

Non metallic organic compounds

IP C

lPBC

is an organic compound used in association with permethrin

plus a combination of waxes and resins and is approved for H 1.2

See its relative performance rating in Table 2.2). t is used in a light

organic solvent carrier, usually white spirit. lt is colourless and is very

difficult to identify and analyse for in treated wood. There are no spot

tests for it.

New

Zealand seems to be the only country in the world

th

at

approves its use as a fungicide in this way.

t

also has a history of

use as a mouldicide additive to preservative systems.

Propiconazole plus Tebuconazole

Propiconazole plus Tebuconazole is approved for use in the H3 .1

class. ft is used as a solution in light organic solvent, usually

white spirit. t is coming

in

to greater use as a dry wood product

preservative for situations where health and safety concerns have

lead to rejection ofTin based dry preservative systems. Some export

destinations of premium wood products will require this preservative

where metallics particularly tin are not acceptab le.

Creosote

Creosote

is

a mixture

of

chemicals, mostly phenols, resulting from

the coking

of

coal. These are effective preservatives that were once

widely used but there are now no commercial plants

in

New Zealand .

89


14/17

Table 9 5 Hazard classes

and

preservative performance ratings .

Hazard level

Active

preservative

Carrier

note 1)

Permethrin LOS

H1.1

Note 5)

Boron Note 4) Water

IPBC + Permethrin LOS

H1 .2

Water

oron Note

4)

TBTN

LOS

H3 .1

LOS

zoles

CuN

LOS

H3 .2

CCAJACQ/CuAz

Water

H4

CCAJACQ/CuAz Water

NOTES

1. LOS = Light organic solvent typically white spirit).

Insect resistance

rating

2

2

2

Decay resis tance Permanence rating

rating Note 2) Note 3)

0 0.5

0.5

1.5

2

1+

2

2

2 2

3 3

3 3

4 4

2. Decay resistance rating is based on performance

in

the M. Hedley decay protocol evaluations at Scion Forest Resea r

ch)

Rotorua .

3.

Permanence rating

is

used

in

the context of resistance

to

leaching associated with damp

H1

.1, H1.2) or periodic or

frequent wetting or, in the case of the tin compounds, resistance to degradation as a result of UV and weathering.

4. This table

is

not comprehensive and only refers to the preservatives

in

common use

in

2005. E.

g.

the option of CCA or

TBTN for H1 is ignored.

5.

H1

.1

was the H1 Hazard Level and specification in MP3640 in the 1988-2003 period.

They were former ly approved for H3 to H6 but are no longer in

ZS3640 although they are still used in Australia. They have a

long hi story

of

use and good performance but are difficult to handle

health and safety issues particularly around skin contact) and have a

characteristic

odour

They were typically carried in oil and the use of

black

or

brown oils associated creosote with dark colours although in

its pure form it is almost colourless. Although approved for up to class

H6 and having long service life history, life cyc le analysis shows that

they ultimately break down into relatively harmless organic materials

as compared to the metallic residues from other preservatives.

ummary of

preservatives

Table 9.5 compares and assigns a rating to various hazard levels and

preservatives that are used for timber framed buildings. The purpose

of this table is to describe the progression

of

performance, in relative

terms, in relation to the cause

of

deterioration and resistance to

leaching. A higher number indicates a better rating, but these are only

relative, so that performance of rating 2

is

not twice the performance

of rating I. This tab le

is

included for comparative purposes, largely

based on unpublished information using

judgement

of

the author.

Unfortunately there is no correlation that can be quoted between

the durability ratings of Table 9.3 and the hazard and preservative

classifications ofTable 9.5.

Preservation processes

• Diffusion

This was the historical process for producing wet boric treated

H

1 2

timber. Fresh sawn wet wood was dipped in a borate or borax

solution which was stacked , and diffusion in the wet wood took place

over some

weeks , depending on temperature. lt appears that it can

now be done with dry wood, in association with diffusion agents , to

achieve H 1.2.

90

• Pressure Processes

There are several pressure processes

incorporating combinations

of

pressure and

vacuum cycles

in

a pressure vessel. These

are typically required for the copper based

aqueous preservatives. For large section

timbers and poles they

may

be accompan ied

by steaming to partially dry the timber befo re

treating. Pulling a strong vacuum

at

the end

of the cycle will result

in

less drip and a dry

surface.

• Vacuum Processes

The preservatives borne by light organic

solvent do not need the high pressures of the

aqueous systems. There is not the need f

or

pressure vessels and hence the plants have

lighter engineering.

They

work on the basis

of pulling a vacuum, flooding, drawing and

pulling another vacuum. The

same

system

can be applied to dry wood, using an aqueous

preservative with a diffusion agent.

arriers

• Water

Water

is

the traditional carrier for aqueous

preservative systems.

• Light Organic

Solvent

LOSP)

White Spirit is the standard light organi c

solvent LOSP) in general use.

It is

a

combination of petroleum fractions with

boiling points from about 160 degrees C

to 240 degrees C. They have a distinctive


15/17

aromatic odour that comes from the heavier

fracti

ons. There

is

widespread

belief

and

trong evidence that there are health problems

associated with the volatile emissions from

these so lvents. There are Occupational Safety

and Health (OSH) requirements in relation to

flash-

off

and filleting

of

LOS P treated wood.

At the time

of

writing the Environmental Risk

Man

agement Authority

ERMA)

and OSH

are scrutinising the use of such solvents in the

timber treatment industry.

Kerosene is no longer in use as a LOSP

carrier. Other new solvents may come into use

as the pr ice

of

petroleum-based solvents rises.

The driver will be the ability to condense and

reco ver so lvents rather than flash-off to the

atmosphere.

Glulam

beams performing well in the severe

env ironment of a urea storage shed

Th

e A deb te

Coming initially from concerns in the USA

there has been a lengthy debate on the safety

of

CCA treated wood.

The

scare factor is

the presence of an ars enical

component

in

the preservative system and the concern that

this component could be eaten by chi ldren.

These co ncerns have been fully investigated

and found to be unjustified. A conclusion

from the Environment Protection Agency

EPA ) in the USA is that it cannot identify

any

ri

sk to health from treated wood when

used correctly. While the EPA has regulated

its use in residentia l situations it has not

listed CCA treated

wood

as a hazardous

substance

in

the USA.

The

arsenical content

is

no t readily available from the wood and

on it

ems s uch as decking dislodgeable

arsenica

ls

are at such low levels that they do

not pose a health risk.

There

has been no ban

or requ irement to remove such equ ipment

from use. Significantly a conclusion

in

the

USA

was that compared to natural sources

of arsen icals, any coming from treated wood

was not s ignificant, and everyday exposure

from natural sources such as food is

much greater than any contact

with treated wood.

In Australia the

APVMA

has adopted a cautious approach.

In

Australia

CCA

treated timber is not permitted for handrails , picnic

tables children s play equipment, domestic decking on the basis that

any risk from such sources is easier to eliminate than to quantify.

In

New

Zealand ERMA has adopted the position that, used correctly,

CCA

treated wood is safe.

There

is concern that end-of-life disposal

of treated wood is unresolved and may be the subject of future

regulation with a focus on recycling.

The Tin debate

The

organic tin

compounds

as used for timber preservation in New

Zealand and Australia are not pennitted for this purpose

in

USA

or

Japan and their usage

in

the EU

is

uncertain. These preservative

products originated in Europe to extend the life

of

specia

li

ty wood

products particularly exterior joinery.

The

extension

of

their use in to

large volumes

of

building framing

is

peculiar to Australia and

New

Zealand . Approval for use in Europe may have been withdrawn or

may vary between countries.

There are concerns around organic tin for two reasons. It may be

a human health hazard and is known to be a hazard to aquatic life.

In New

Zealand its use as marine antifouling is now restricted

to international shipping to limit the loss of tin into marine

environments . It is known that with uncoated treated wood, tin

leaches and

is

reduced to inorganic tin through time and exposure to

sunlight. ln Queensland, Australia, a move to elevated tin levels for

H3

was not adopted in their legislation and may never be adopted .

In New Zealand,

TBTN

/

TBTO

treated timber

is

not classified as

hazardous.

Conclusions

Good durability with timber can be obtained by designing to avoid

destructive agencies.

A few naturally durable timbers exist. Preservative treatment can give

adequate durability to naturally non-durable species.

Radiata pine is very

easy

to treat for a wide

range of

hazard classes.

Methods of timber treatment and regulations regarding their use are

constantly evolving.

91


16/17

Further reading

I

Service Tests

o

Wood Preservatives M.E. Hedley, What s New

in Forest Research, No. 34, Forest Research Institute, 1976.

2 The Natural Durability

o

Untreated Timbers C

Hughes, What s

New

in Forest Research, No. 112, Forest Research Institute, 1982.

3

Wood Preservation

in

New Zealand M.E. Hedley, NZ Journal of

Timber Constmction

Vol

4, No. I, 1988, pp. 18-21.

4 Corrosion

o

Metal Fasteners Embedded

in Timb

e

r J.

R

Duncan. BRANZ Reprint No. 68, Building Research Association of

ew Zealand, 1986.

5 The Compliance Document for the New Zealand Building Code

Clause E2 External Moisture. Department of Building and Housing.

www.dbh .govt.n:zJUserFiles/File/Publications/Building/Compliance

documents/clause-e2.pdf

6

Timber Treatment Requirements: Notes for Builders. Department

of Building and Housing. www.dbh.govt.n:zJUserFiles/File/

Publications/WHRS/pd f/timber-treatment-reguirements.pdf

7

NZ

Timber Preservation Council, www.nztpc.co.nz

A list

of

timber-related

New

Zealand standards

is

given

in

Chapter 15

Treated radiata pine in severe outdoor environment

9


17/17

Further reading

1

Service Tests

o

Wood Preservatives M.E . Hedley, What s ew

in Forest Research, o. 34, Fore t

Re

earcb Institute, 1976.

2

The Natural Durability

o

Untreated Timbers C Hughes, What s

ew

in Forest Research , No.

112

, Forest Research

In

titute, 1982.

3

Wood

Preservation

in

ew Zealand M.E. Hedley, Z Journal

of

Timber Construction

Vol

4,

o

I, 1988, pp. 18-21.

4

Corrosion

o

Metal Fasteners Embedded in Timb e

r

J. R

Duncan. BRA Z Reprint o. 68, Building Research A sociation

of

ew Zealand, 1986.

5.

The

Compliance Document for the New Zealand Building Code

Clau e

E2

External Moisture. Department

of

Building and Housing.

www.dbh.govt.nzJUserFiles/Fi le/Publications/Building/Compliance

documents/clau

e e2.pdf

6. Timber Treatment Requirement : otes for Builders. Department

of Building and Housing. www.dbh.govt.nzJUserFi les/Fi le/

Publications/WHRS/

pd f

/timber-treatment-requirements.

pdf

7 Z Timber Preservation Council, www.nzt.pc.co.nz

A list of timber-related

ew

Zealand standards

is

given

in

Chapter 15

Treated radiata pine

n

severe outdoor environment