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Terraced house refurbishment, Mottingham, London by ECD Architects

The Mottingham house before refurbishment

The Mottingham house before refurbishment

Considered use of products should ensure that ECD Architects' retrofit of a social-housing property achieves an 80 per cent reduction in carbon emissions.

Refurbishment of existing housing stock is often cited as the panacea to our carbon woes. According to the Energy Saving Trust, the average household can save up to 25 per cent of its annual carbon emissions through energy efficiency, and retrofitting is one way to achieve this.

ECD Architects' retrofit of a terraced house in Mottingham, south-east London, due to complete later this month, is aiming for a reduction of more than three times that figure, targeting 80 per cent. The project could have a far-reaching impact on how properties owned by Registered Social Landlords (RSLs) are transformed to reduce carbon emissions.

Nondescript terrace
This Hyde Housing Association property is a nondescript brick terraced house built in the 1930s, with a flat-roofed rear extension added in the 1980s. 'We needed a house that was representative of [Hyde's] stock,' says ECD associate director Mark Elton. 'The idea being that lessons learnt from this project can be rolled out on a larger scale.'

The target od an 80 per cent reduction in carbon emissions was adopted because it is the figure proposed for the UK's existing housing stock by Brenda Boardman, of the University of Oxford's Environmental Change Institute, in her Home Truths report. The SAP (Standard Assessment Procedure) rating system, against which the project will be measured, is a scale from 0 (inefficient) to 100 (highly efficient).

'The fact that it is a brick cavity wall has actually made the job harder than if we'd been given a solid-wall Victorian property [because the former is inherently more energy efficient],' says Elton. 'The SAP for the existing building was around 60, and the national average is 48, so getting the 80 per cent reduction has proved quite a challenge.'

PassivHaus standard
The German PassivHaus standard (AJ 28.02.08), which Elton sees as more accurate than the SAP, was used to double-check emissions.
The budget for the project is £80,000 including design fees, but, as Elton points out, this is not a representative figure. Both ECD and main contractor Mears are working at less than cost, and many products are being supplied free of charge or at a discount. A table of predicted costs will be collated and made public at a later date.

On completion, a week of launch events will take place before the house is handed over to the tenant. Parity Projects, a consultancy that works to reduce the environmental impact of existing buildings, will then monitor the performance of the building for two years, periodically publishing the results.

During this period, social housing consultancy (and ECD's sister company) PPCR will interview the tenant and a control tenant in an existing similar property. 'It's a great opportunity for everybody involved to actually put the techniques and materials to
the test,' says Elton. 'Hyde is committed to reducing carbon emissions from its stock, and this project will allow it to identify the most cost-effective measures and apply them.'

  • Author: Cathy Strongman.

Choosing products
'The key driver of product selection is the 80 per cent carbon reduction,' says Elton. 'We shouldn't get too hung up on the embodied energy of products in a refurbishment scheme until we've cracked the bigger problem, which is the operational energy use.'
ECD therefore rejected more expensive solutions such as ground-source heat pumps in favour of standard solutions like glazing and condensing boilers. The project adheres to PassivHaus-standard U-values of 0.15W/m2K for external walls and 0.1W/m2K for the roof, and has an airtightness value of 3. New homes are expected to achieve a value of 10 to meet Part L of the Building Regulations.

Elton often uses GreenSpec  for product research, and
is increasingly wary of the BRE's Green Guide. 'There's hardly anything in there that isn't A or A+ rated. When PVC windows have an A rating, I begin to wonder,' he says.

The choice of products was partially dictated by the appointment of main contractor Mears – the firm entered the job with Travis Perkins backing it on the supply side and Kingspan on technical issues.

mottingham_solarthermal

Solar-thermal panels: Solimpeks
ECD opted for flat-plate solar-thermal panels rather than an evacuated tube system, because they are cheaper and more robust. Kingspan advised ECD
to install Solimpeks' Marvel Dual system (for which Kingspan is UK distributor), so there is one 2m2 panel on either side of the pitched roof, and the system automatically switches the water flow to the hottest panel. The panels feed into a 250-litre thermal store, and Solimpeks claims it will provide up to 70 per cent of the building's hot water.

mottingham_kingspan200

Insulation: Kingspan Insulation/Knauf
ECD has used two different forms of insulation: Kingspan phenolic lining boards to the walls of the main house, and, in the 1980s extension, 100mm of Kingspan phenolic external insulation with a silicone render by Wetherby Building Systems. Some of the cavity walls have existing blown insulation, but the coverage is patchy. ECD is topping it up with Knauf Crown Supafil blown glasswool, and is using Knauf's Crown CarbonZero glasswool in the two eaves.

mottingham_multifoil

Breathable multi-foil insulation: Web Dynamics
TLX Gold, a waterproof, breathable multi-foil from Web Dynamics, is being installed between the rafters in the roof and on the party walls. The 33mm-thick, seven-layer laminate consists of a top layer of breathable roofing membrane, a bottom layer of reflective film laminate, and a core of PET wadding alternated with gold film. 'In combination with Kingspan insulation laid horizontally, we can get our 0.1 U-value and still have enough room in the roof for storage and the water cylinder,' says Elton.

mottingham_pvpanels

Photovoltaic panels: Solar Technologies
Solar Technologies is supplying photovoltaic (PV) panels for a timber loadbearing structure positioned on the flat roof of the extension. The 170W polycrystalline units will provide a total of 1.36kW peak of electricity. 'Even with the mechanical ventilation and heat recovery that we are installing, we'd struggle to reach the 80 per cent reduction in emissions without the PV,' says Elton. 'The system is grant-funded, but this is an element of the retrofit that might not prove affordable in future projects.'

mottingham_led

LED lighting: GreenLED
GreenLED is supplying 100 per cent LED lighting throughout the house. 'We are installing six per room, but each light is 2W, compared to a 50W halogen bulb,' says Elton. 'These LEDs are a lot more expensive, costing around £20 each, but they have
a lifespan of 50,000 hours and we've calculated
that a typical tenant won't have to replace them for 20 years.' However, the capital cost of the lighting comes down to the RSL instead of the tenant,
which could hinder future application.

mottingham_window

PassivHaus-standard windows: NorDan
ECD is working to the PassivHaus-standard target U-values for windows of 0.8W/m2K. 'There are a few products available in the UK, but we have gone with NorDan because it is arguably the biggest UK importer and is most likely to be able to gear up to a roll-out programme with the RSL,' says Elton. NorDan NTech Passive windows are triple-glazed, with argon-filled cavities, and low-emissivity coated glass with split frames and a polyethurane core. They have a whole window U-value of 0.7W/m2K.

mottingham_sustdrawing

Rainwater harvesting: Parity Projects
'Rainwater harvesting systems are controversial when applied to single houses,' says Elton. '[Some] scientific studies show the energy savings don't stack up. On our bespoke system there is no pump, no costly maintenance, and the system is made entirely from off-the-shelf components.' The installation, designed by Russell Smith of Parity Projects, is in a boxed-out void over the staircase. Rainwater flows directly from the downpipe, through a filter into a 318-litre tank, and is fed to the dual-flush toilets by force of gravity alone.

CREDITS
Start on site date July 2008
Contract duration 10 weeks
Gross external floor area 98.7m2
Form of contract Exchange of letters only
Cost £80,000, but the true costs based on a roll-out programme will be delivered at the end of the project
Client Hyde Housing Association
Architect ECD Architects
Quantity surveyor/planning supervisor/CDM co-ordinator Keegans
Main contractor Mears  
Annual C02 emissions 9kgCO2/m2 according to SAP


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