a multi-stage approach to low carbon housing ... - plea 2014 · the prices were found online, and...

Marianna Rosa Arpano is a former MSc SBPD student, in the Department of Architecture, Oxford Brookes University, Oxford, UK.

Paola Sassi is a senior lecturer and program leader at Oxford Brookes University, Oxford, UK.

A Multi-Stage Approach to Low Carbon

Housing Renovations

Marianna Rosa Arpano, MSc Paola Sassi, PhD

[Oxford Brookes University] [Oxford Brookes University]

[email protected] [email protected]

ABSTR ACT HEADING

In 2009 the European Union approved “Roadmap 2050” to reduce greenhouse gasses by at least

80% below 1990 levels by 2050. In 2012 the Danish Government established to achieve 100% autonomy

from fossil fuels by 2050 by implementing a strategy that included reducing energy demand of existing

housing that accounts for about 40% of the national gross energy consumption. A mass retrofit of the

existing housing stock could lead to 75% reduction of energy use and carbon emissions. However due to

the cost and disruption of retrofits that can radically improve energy performance of buildings,

strategies that address both disruption and cost have to be considered. One such potential strategy

examined in this paper is a staged approach, which involves different elements of a building to be

upgraded over several years, thus spreading the capital cost of the work and enabling the occupants to

remain in their homes. Applied to the Danish context this approach can also benefit from financial

incentives currently in place. Adopting a case study approach in conjunction with IES modelling, a cost

analysis and interviews with industry experts, this research examines the energy savings, capital cost,

cost savings of a selection of energy improvements measures, and the implications of undertaking the

building work on the occupants of typical Danish detached houses built between 1850-1930. It

concludes by proposing a decision matrix for home owners to achieve the most cost-effective and least

disruptive approach to undertaking radical energy upgrades.

INTRODUCTION

Background

In 2009 the European Union approved “Roadmap 2050” to reduce greenhouse gasses “by at least

80% below 1990 levels by 2050” (Roadmap 2050). In March 2012 the Danish Government established a

new, ambitious Energy Policy, to achieve a 100% autonomy away from fossil fuels by 2050. The

strategy adopted to reach such results involves a consistent reduction of the energy demand. According

to the Danish Energy Policy Report (Ministry of Climate, Energy and Building, 2012), the existing

building stock accounts for about 40% of the total energy consumption; more specifically in 2010 the

69% was related to the housing sector, and the 36% to non-residential buildings (IEA, n.d.; Agency

Danish Energy Agency, 2011). Thus, the biggest savings could be achieved by improving the energy

performance of the less efficient housing stock. However, this mass-retrofit meets two barriers,

involving the government and the private owners: one is financial (Kragh and Rose, 2011, p2252) and

30th INTERNATIONAL PLEA CONFERENCE 16-18 December 2014, CEPT University, Ahmedabad

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one is practical (Thorpe, 2010, p.2). The first requires financial help from the government to the private

owners, and second one requires a solution to prevent the occupants from moving to a temporary home.

A multi-stage or “stepwise” (Galiotto et al., 2012) approach to energy efficient retrofits could address

these issues.

Aim of the research

This paper investigated a staged retrofit strategy as feasible solution to finance a national mass

retrofit; to make an expensive housing retrofit more financially sustainable and more practical. Smaller

and less disruptive works carried out in several stages could distribute the total investment in more than

one transaction; they could also allow the occupants to stay in their homes and avoid additional expenses

to rent a temporary accommodation.

METHODS

Due to time limitations this research has focused on a specific category of detached houses, built

between 1850 and 1930. Detached houses were identified as most diffused and the worst performing

housing type; they account for the 52% of the entire housing stock (Statistics Denmark), and for more

than 330,000 units ( 53%) with EPC labels between D and G and a heating consumption requirement

above 240 kWh/m2/yr (Aggerholm et al., 2010)-.

The construction details and materials of the housing type analyzed were sourced from the Danish

report for TABULA Project (Wittchen and Kragh, 2012). The reference retrofit measures used were

collected from a previous research by SBi, the Danish Building Research Institute (Galiotto et al., 2012),

by VTT, the Technical Research Institute of Finland, (Häkkinen et al., 2012) and Larsen et.al (2011).

IES- VE was chosen as dynamic simulation tool to test the effect of several retrofit measures on the

building performance. A 3d model of a real detached house from 1917 and located in Copenhagen was

built in IES. It was used an average floor, window and floor area; average construction, materials and

shape; the U-values, infiltration rate, boiler type were conformed to those specified in the TABULA

project report (Wittchen and Kragh, 2012). The NCM heating, appliances and occupants’ profiles were

used. The details of the model created and the average building described in TABULA are shown in

Table 1.

Table 1. Multi-Stage Plan. Number of Years for Each Stage.

Average building Example building

U-values Area m2

Wall 1.6 W/m2K 1.6180 W/m

2K 88

Roof 0.6 W/m2K 0.5724 W/m

2K 86

Ground Floor 1.5W/m2K 1.6078 W/m

2K 47

Windows 2.7W/m2K 2.7 W/m

2K 15

Door 2.29 W/m2K

ACH 0.45 0.45

Boiler Old non condens. Old boiler Ɛ=55%

Fuel Oil-gas Oil - gas

Area 112 m2

122 m2

Windows area 15.1 m2 15.1 m

2

Wall area 88 m2

Roof area 86 m2

Slab 47 m2

Ceiling Height 2.5 2.1 (basement, first floor) 2.7

(ground floor)

Location DK Copenhagen

Age of construction 1850-1930 1917

Heating

consumption

263 kWh/m2 yr 265 kWh/m

2 yr


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ANALYSIS

IES modelling

A first series of simulations was carried by introducing one variable at a time in the model’s

building construction; such as wall, slab or roof insulation, new windows, mechanical ventilation,

heating system. All the measures were previously collected from other research. The results were

organized in reduction of the heating consumption (%), the reduction of Carbon Emissions (%), the

grade of disruptiveness and invasiveness of each measure (low- medium and high). Table 2 shows the

percentages of reduction achieved by the measures belonging to the different building’s systems.

Table 2. Heating Consumption (%) and CE reduction (%) of the Building’s System tested in IES-VE.

Measure Heating reduction CE reduction

External wall insulation 51,2% 39,7%

Slab’s insulation 16-20% 12-22%

Mechanical ventilation

combined with

airtightness of

0.15ACH

10% 7%

Windows 5-7% 4-6%

Roof and ceiling

insulation

6-8% 4-5%

Heating system 0% 7%

Cost Analysis

In order to identify the most cost-effective and less invasive measures, it was important to compare

the costs, the savings and their grade of disruptiveness. The comparison was carried only for wall and

slab’s insulation as the measures tested varied for thickness, type of material and strategy adopted

(internal or external insulation).

The prices were found online, and on Spon’s Architects’ and Builders’ Price Book 2013, available

at the University’s Library (Langdon, 2013). The Danish prices were available on V&S Prisdata,

provided by Byggecentrum, with an annual price. For this reason, the labour prices were searched in

Spon’s, while the materials‘ costs were found on the sellers’ websites (listed in the references), and by

asking quotations to the manufacturers.

The external insulation of the wall with demolition of the cavity wall, and cavity insulation +

internal insulation were excluded from the feasible measures because highly invasive and disruptive, less

effective than the external insulation, and more expensive. Thus, the most cost-effective solutions with

the shortest payback period are the insulation of the cavity wall and an additional external insulation,

which can be between 50 and 160 mm., as shown in Fig. 2.

As shown in Fig.3 the ceiling insulation seemed to be most cost-effective than the roof insulation

because it involves a smaller surface to cover, thus lower material costs, but similar savings to the roof

insulation (6% reduction of heating demand in both cases, 4% reduction of CE for 200mm insulation and

5% for 400mm insulation). Also the ceiling insulation can be less disruptive than the roof insulation,

which would involve a disassembly of the roof cover and waterproof layer. Such measure is suggested

only in case the roof needs to be updated because it would solve a problem of thermal bridging in the

junction between the roof and the external wall.


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Figure 2 Investment, Saving with Waste Heat and Saving with Natural Gas for Wall Insulation

Measures (£).

Figure 3 Investment, Saving with Waste Heat and Saving with Natural Gas for Roof and Ceiling

Insulation (£).

A second series of simulations was run to estimate how much the heating demand could be

reduced, once all the retrofit measures are completed. For this purpose any possible combination of

measures was tested. The ACH used were 0.3 (a medium value); in such old leaky houses a value of 0.25

ACH is hardly achievable. Among 127 simulations the heating demand varied from a maximum of 39

kWh/m2/yr, to a minimum of 20.7 kWh/m

2/yr; both results are lower than the established goal of 44

kWh/m2/yr (Danish energy class 1).

According to the results of all the IES simulations, the multi stage plan should follow the next

order: cavity insulation, external wall insulation, slab insulation, mechanical ventilation, roof and ceiling

insulation, windows and heating system.

However these dynamic simulations cannot considerate the fact that the single measures are part of

a staged plan and cannot preclude further works in the future (Thorpe, 2010).

Interview

For this reason a semi-structured interview was conducted with a NIRAS’ engineer specialized in

energy efficient retrofits. During the interview, the installation of an automatic heating control system

was recommended as first measure on the list, being a cheap and very effective solution. In fact, further

simulations confirmed that.

The time-temperature control and the time control can both lead to a 38% reduction in space

heating demand; while the temperature control only a 10% reduction. The carbon emissions were

reduced by 31% with the first two controls, and by 9% with the third one.

The engineer also evidenced how changing windows can be a priority for the occupants to enhance

0 5000 10000 15000 20000

Ext. Ins. Rockwool 50 mm…

Rockwool 100 mm

Ext. Ins. Rockwool 160 mm…

Ext. Ins. Rockwool 300 mm

Ext. Ins. Kingspan TW55-PIR

Int. Ins. Spacetherm 50 mm…

Savings with Waste Heat Savings with natural gas Investment

0 500 1000 1500 2000 2500 3000

Roof Rockwool 300mm

Roof Eco wool 300mm

Ceiling Rockwool 200mm

Ceiling Ecowool 200mm





Savings with Waste Heat Savings with natural gas Investment


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the thermal comfort, and avoid air-drafts.

Besides, it was suggested to consider windows and external insulation as a whole package; indeed,

if the external insulation is applied first the windows should be moved to the outer layer of the wall to

avoid thermal bridges. Thus, the windows could be changed when moved, avoiding extra installation

costs.

At last, the mechanical ventilation cannot be considered as measure unless an airtightness test

proves that the infiltration rate is lower than 1,5 ACH50.

The limitations of a multi-stage retrofit were also discussed during the interview. Not all the

construction details can be solved during a multi-stage retrofit (certain thermal bridges) and these

limitations need to be accepted and explained to the owners not to create too high expectations. In fact,

the savings obtained by large scale and less expensive retrofit (nearly 80%) can still make a big

difference in reducing the gross energy consumption and the CO2 emissions of a Country.

Multi-stage plan

Based on these suggestions and considerations the final multi-stage plan was organized in 11 stages

and the measures of each stage were classified in low-medium and high budget (Table 3), The intent was

to produce a flexible scheme that leaves to the single owners the choice of the best measures for their

budget.

Table 3. Multi- Stage Retrofit Plan

Low budget Medium budget High budget

1 Automatic

heating control

Boiler control

Boiler and

time/temperature

control

Boiler, time and

temperature control

2 Cavity

insulation

75mm Phenolic

foam

75mm Eco bead

Platinum

75mm Bio-foam

3 Windows Double-glazing

1.25

Double-glazing low-e Triple glazing

4 External

insulation

50mm mineral

wool, EPS, PIR

100mm mineral wool,

EPS, PIR

160mm mineral wool, EPS,

PIR

5 Roof insulation 300mm Rock

wool, Ecowool

400mm rock wool,

Ecowool

Renovation of the whole

roof and placement of 340-

400mm insulation on the

external side of the roof.

6 Basement

insulation

200mm

Rockwool,

Ecowool,

cellulose

insulation

300mm Rockwool,

Ecowool, cellulose

insulation

400mm Rockwool,

Ecowool, cellulose

insulation

7 Slab insulation 160mm XPS

insulation on top

of the existing

slab

250mm XPS

insulation under the

new slab

300mm XPS insulation

under the new slab

8 Basement

insulation

50mm insulation 100mm insulation

9 Insulation/new

external doors

50mm insulation New insulated doors

10 MVHR High efficiency Most efficient MVHR

model

11 Heating system Gas boiler District heating Ground Source heat pump


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The list of measures was accompanied by a scheme, shown in Fig.4, with questions and answers

(yes/no) that show which is the first stage to undertake and which should follow. For each stage there is

a corresponding color, that remands to the first scheme of measures.

Figure 4 Guiding Scheme to House owners.

Possibilities to finance energy efficient retrofits

If the financing barrier is to be overcome, the annual cost of energy renovation investment should

at least be equal to the annual savings on energy (Kragh and Rose, 2011), and at the moment, even with

the increased energy price, the payback period for energy retrofits is still too long.

In this research an existing tax deduction was used to abolish or reduce the difference between

investments and energy savings as shown below :

𝐴𝑛𝑛𝑢𝑎𝑙 𝐼𝑛𝑣𝑒𝑠𝑡𝑚𝑒𝑛𝑡 = 𝐴𝑛𝑛𝑢𝑎𝑙 𝐸𝑛𝑒𝑟𝑔𝑦 𝑆𝑎𝑣𝑖𝑛𝑔𝑠 + 𝐴𝑛𝑛𝑢𝑎𝑙 "𝐴𝑟𝑡𝑖𝑠𝑎𝑛 𝐷𝑒𝑑𝑢𝑐𝑡𝑖𝑜𝑛"

The so called “artisan deduction” consists of about £2000 per salary/yr, to deduce for installation

and craftsmen costs, but not for materials and devices costs (SKAT), which account for half of the total

investment. In this research it is assumed a modification of the tax scheme, allowing the homeowners of

a specific category to deduce also materials and devices’ costs.

Another assumption is that the annual savings on energy are cumulated and saved in a bank

account with exclusive use for the next stage, until the whole retrofit is completed.

In Denmark detached houses are often occupied by one or two families, in which case there could

be two, three or four salaries that could bring £3496-£5244 of tax deduction per year/house.

A scheme showing the investment, the energy and carbon savings and the tax deduction for 1,2,3

and 4 salaries was created to verify the workability of the new “artisan deduction” and the cumulated

energy savings. The final equation is:

𝐴𝑛𝑛𝑢𝑎𝑙 𝐼𝑛𝑣𝑒𝑠𝑡𝑚𝑒𝑛𝑡 = ∑ 𝐸𝑛𝑒𝑟𝑔𝑦 𝑆𝑎𝑣𝑖𝑛𝑔𝑠

𝑛

𝑛−1

+ Artisan Deduction

n=number of the years since the first retrofit stage


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Where the result is negative, the investment is paid back in the same year of realization, through the

monetary savings obtained by reducing the energy demand and the incentives. When the difference is

positive, the incentives and the monetary savings are lower than the initial investment. In the first case, it

could be possible to carry one or more measures during the given year, depending on how much of the

incentive is left. In the second case the measures too expensive to be paid in one year, should be carried

out in two or more years (i.e. windows can be changed one at a time). Another solution is to wait a

couple of years, save the money not spent for heating, and use it to pay in a single shot the works.

In order to estimate the number of years necessary to carry on the whole retrofit, every time the

difference was negative, a new calculation was done adding the cost of the next measure and the savings

achievable from that. If the difference was still negative the two or more measures could be carried out

the same year.

In all cases the first two steps can be completed in one year. The window replacement can require

one or two years with one salary, and one year for the other three cases. Only with four salaries per

household the windows could be replaced at the same time when adding external insulation. The next

steps can be completed in five years with one salary, for a total of seven years, in case the house is

connected to the district heating; and twelve years if there is a heat pump. In case the salaries in the

house are two, the retrofit could be completed in six-seven years. if there are three salaries four-five

years could be enough to complete the retrofit; four with the district heating and five with a heat pump.

Table 1. Multi-Stage Plan. Number of Years for Each Stage.

1 2 3 4 5 6 7 8 9 10

Year of

retrofit

Automatic

Control

Cavity

Ins.

Window Ext.

Ins.

Roof

Ins.

Slab Door MV Boiler Heating

System

1 salary Yr 1 Yr 1 Yr 2-3 Yr 4 Yr 5 Yr 5 Yr 5 Yr 6 Yr 7 Yr 7-12

2 sal. Yr 1 Yr 1 Yr 2 Yr 3 Yr 3 Yr 4 Yr 4 Yr 4 Yr 5 Yr 6-7



Incentives plan to retrofit the detached houses built between 1851 and 1931 by 2030

Supposing the national mass retrofit starts in 2015 detached houses between 1850 and 1930, all the

houses with three or four salaries could be completed in 4-6 years. In 2020 the next stage of the mass

retrofitting could start with the houses built between 1961-1972. By 2027 the first stage should be

concluded and the 11 % of the whole Danish housing stock retrofitted (Fig.5) with 80% energy

reduction. As shown in Fig.69 this group of houses accounts about the 31% of the energy used by

detached houses, so the 80% reduction would be equal to 24% reduction of detached-houses’ energy use.

CONCLUSIONS

This paper has investigated the possibility of using a multi-stage plan to overcome economic and

practicality barriers to energy efficient housing retrofit. The research results have shown that the

integration of dynamic simulations and the practical experience of specialists can lead to multi-stage

retrofit plans for each housing type.

A financing scheme was proposed to equal the annual investment for retrofit, to the derived energy

savings; however, a similar model would be burdensome for the national tax system; which would see

the national tax income considerably reduced. On the other hand, without a significant help from the


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government, only a few house owners would invest their own savings in such housing retrofit, as “one of

the main barriers in renovation” is “financing” (Kragh and Rose, 2011, p. 2252).

Figure 5 Sample of Mass Retrofit Organization.

Most of them would probably decide to upgrade something, not aware of what they could actually

do to have an energy efficient house. In conclusion this research suggests that government guidance is

essential as government funding schemes. The proposal of recouping a percentage of the monetary

savings achieved by the house holders to help the government to finance the second step could make the

scheme unpopular, if the advantages derived from such help are not well stated. Nevertheless, this

scheme does not require any investment to the owners, which have only to pay upfront.

Educating the householders about the long term and non-monetary advantages is critical to their

acceptance of the scheme. This research has shown how tax-related schemes can encourage retrofit

initiatives and how technical solutions can help reduce the cash flow and capital cost. Other technical

solutions and financial incentives could address these and other barriers to retrofit initiatives and should

be further investigated. In addition, all incentive schemes need to be supported by effective information

and this area could also benefit from further research.

AKNOWLEDGMENT

This paper is based on a dissertation for the MSc in Sustainable Building Performance and Design,

offered by Oxford Brookes University.

We would like to thank those who have taken part in the project, Andrew Ferguson Dunn, Jørgen

Søndermark , Diana Ricco, Hu Du.

2015

year 1

•The "artisan deduction" includes the material costs only for the owners of detached houses built between 1851-1930.

•This housing stock starts being renovated at the same time.

2019-2021

year 4-6

•The houses with 3-4 salaries should be completed.

•The house owner of the renovated houses give a percentage of the annual energy savings back to the government.

2020

year 5

•The "artisan deduction" for the completed houses is back to the original formula.

•Houses built between 1961-1972 start being renovated with the percentage of the savings from the houses already renovated.

2022

year 7

•Most of the houses are renovated if the district heating is preferred to the ground source heat pump.

•As long as the houses are completed the next category of houses is gradually renovated following the previous scheme.

2027

year 12

• 23% of detached houses should be renovated, saving about 80% of the energy.

•11% of the total existing housing stock would be retrofitted.


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http://www.ens.dk/en-us/info/factsandfigures/energy_statistics_and_indicators/annual%20statistics/sider/forside.aspx

http://www.ens.dk/en-us/info/factsandfigures/energy_statistics_and_indicators/annual%20statistics/sider/forside.aspx

http://www.dst.dk/

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