whole life costs

8/10/2019 Whole Life Costs

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Dr Gillian MenziesInstitute for Building and Urban Design

Heriot Watt University, Edinburgh

Timber, modified timber andaluminium clad timber windows


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Stage one report

SLP and WLC analysis completed for Wood Window Alliance productsmanufactured from timber, modified timber and alu-clad frames, and for PVC-U.

Key findings:

Service Life Planning years

WWA timber frames: 56-65

WWA modified timber frames: 68-80

WWA alu-clad timber frames: 71-83

PVC-U: 25-35

Whole Life Cost PVC-U has the lowest initial cost

WWA timber frames have the lowest lifetime cost for urban/suburban properties Modified timber and aluminium-clad timber frames have a lower lifetime cost for

high rise buildings or severe exposure conditions


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Derivation ofService Life Planning

Based on ISO 15686-8 methodology

Builds on and confirms earlier work on timber windows reported byImperial College London

Research extended to include modified (acetylated) wood and aluminum-clad wooden frames

Derived by applying design, manufacturing and maintenance factors toestablished Reference Service Life in accordance with ISO 15686-8


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Reference Service Life

35 year RSL for WWA timber windows* and for timber-derived frames 30 year RSL for PVC-U windows

Based on research references:

* WWA members meet TWA (Timber Window Accreditation) schemecriteria as a minimum criterion of membership


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Modifying factors(ISO 15686-8)

Five categories considered asmodifying Reference Service Life:

!"#$%& (%)*+,*-. /"$0.%&,

! #$%&'&$( )&'*+',-$.&

/ 0&123$

4 5-$6*-.(6'2$3 1(-$7-'71

8 89(&'$-: &$;2'+$,&$(

< 5-2$(&$-$.& :&;&:

Manufacturing criteria play a strong rolein extending service life: Choice of sustainable, defect free,

engineered timber Window design elements such as rounded

edges, water shedding angles on cills and

beads, and joint and end-grain sealing Flexible, micro porous protective paint Factory controlled glazing and coating

systems


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Modifying factors:maintenance and exposure

Mild(sheltered or partly sheltered -under porch or set back in thewall - non-coastal, lowaltitude)

Moderate(not sheltered or partlysheltered, non-coastal, lowaltitude; sheltered or partlysheltered, exposed or within0.5 miles of coast)

Severe(not sheltered, exposed orwithin 0.5 miles of coast; orpartly or not sheltered, highaltitude, exposed coastal)

WWA timber

Modified timber

Alu-clad timber

8

12

30

6-7

9

30

4-7

6-9

20-30

Maintenance frequency (years) for factory finished joinery derived fromexposure categorisation described in (BS EN 927 1)


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Service Life Planning:Summary

Summary of Service Life Planning ISO 15686 8 analysis Cumulative for all factors under WWA control A, B, C, E, G


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WLC cost assumptions

Capitalcost

Install cost Maintenance frequency(years)

Cost/event Glazingp.a.

Mild Mod Severe

WWAtimber

ModTimber

Alu-cladtimber

PVC-U

290

340

362

280

84

84

84

84

8

12

30

n/a

6

9

30

n/a

4

6

20

n/a

20

24

30

n/a

9

9

9

9

Costs based on average contract prices for a 1230 x 1480 mm casement window with asingle side opening light


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WLC price comparisonin mild environments

60 years 80 years 100 years

Cost Index Cost Index Cost Index

WWA timber 590 87 632 92 639 91

Mod timber 626 92 657 95 663 94

Alu-clad timber 622 92 634 92 657 93

PVC-U 678 100 689 100 706 100


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WLC price comparisonin moderate environments



WWA timber 644 95 659 96 667 94

Mod timber 639 94 677 98 684 97

Alu-clad timber 622 92 658 95 663 94

PVC-U 678 100 689 100 706 100


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WLC price comparisonin severe environments



WWA timber 685 96 703 94 710 94

Mod timber 669 93 714 96 722 96

Alu-clad timber 633 88 674 90 680 90

PVC-U 717 100 747 100 753 100


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SLP and WLCResearch summary

The research compares the expected Service Life and Whole Life Cost of fourwindow frame materials: timber, modified timber, aluminium-clad timber and PVC-U

The research concludes that timber windows made to WWA specifications have anexpected Service Life of around 60 years, compared to 30 years for an equivalentPVC-U frame; modified timber and aluminium-clad timber frames have an expectedlife of over 70 years

PVC-U windows have the lowest initial cost; WWA timber windows have the lowestlifetime costs in typical urban/suburban environments; modified timber andaluminium-clad timber windows have a lower lifetime cost in high rise buildings or insevere exposure conditions

A second report, comparing the environmental impacts of the four material will bepublished later this year, allowing specifiers to make a comprehensive comparison ofthese frame materials against a full range of service life, cost and environmental

considerations .

whole life costs

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