Case Study: nZEC - Energy refurbishment of the Gaymer Memorial Cottage in Station Road, Attleborough, UK

Short Description

Built in 1948 by the Gaymer Cider Company (a major local employer until 1990), the cottage was a single storey, two bedroom end terrace of four similar almshouses properties. The property was void. It was off the gas network with reliance on coal and electric storage heaters. It was poorly insulated with very poor thermal performance. It was assumed to be of solid wall and floor construction (during the retrofit it was found to be part solid, part cavity wall). It had single glazed steel Crittall windows. The layout didn’t meet the needs of the older resident who would be moving into the property post-retrofit.

The project concerned the deep retrofit of a 1940s alms cottage, held in trust by Hastoe. The cottage had local historical significance, however was not listed. It mirrored common problems of many homes in the UK – age, build type, lack of thermal comfort and poor energy efficiency. In 2010 Hastoe successfully submitted a proposal for the retrofit of Gaymer Memorial Cottage to the Technology Strategy Board (TSB) ‘Retrofit for the Future’ competition. The retrofit used a mixture of tried and tested measures and products, along with testing cutting edge technologies. Hastoe was awarded £150,000 from TSB. The retrofit was one of 86 funded social housing projects in the UK.

The retrofit approach focused on energy saving and CO2 reduction: minimise heat loss from the thermal fabric and ventilation method; supply space and water heating using replicable, low carbon technology; minimise lighting and appliance energy demand; and, the opportunity to significantly improve the life of resident. It was also an opportunity to upskill our staff and partners. The retrofit also looked at replication potential. The works Included external landscaping and the provision of outdoor store for mobility scooter. Key changes to the property included: super-insulation to all building fabric elements; significantly improving the air-tightness; complete new services which are easy/ intuitive to use; new finishes and fixtures; relocated bathroom and drainage; extended kitchen; general improvement to external works.

Key Elements

Certification

The property was rated G in terms of energy efficiency pre-retrofit. This was improved to a B rating post retrofit.

Project Management

Project management was undertaken by ECD Architects. A multi disciplinary project team was convened at the start of the planning stage to shape the project through to completion. The team included the architect/designer, the contractor, Hastoe Housing Association and the future resident. The role of the architect/design team was to supervise/oversee construction and sign off works.  The project was relatively trouble-free with only minor defects arising post-completion.  The project finished eight weeks late, however this was largely due to the late delivery of the external doors with procurement of vacuum insulated panels causing significant delay. Otherwise the project was generally well managed and quality control was good, resulting in very impressive air-tightness results (despite the fact that for planning reasons traditional Crittall steel frame windows had to be used). This success was in large part due to the diligence of the Site Agent who was particularly keen to ensure that air tightness was maintained.

Capacity Building

As indicated above, the resident was very much a key part of the project and helped to determine the end result, such as changes made to the layout to provide a living environment that met her needs. The resident also chose key finishing elements such as the kitchen, bathroom, tiles and carpets. The contractor, Roalco, did not have any previous experience in undertaking retrofits and wanted the use the project as an opportunity to upskill their staff.

Work with Residents

As indicated above, the resident was central to the retrofit right from the outset, and the resident engagement is recognised as one of the stand out aspects of the project. The resident was a key part of the project team and was consulted on every aspect of the retrofit. The resident lived close to the site and built up and excellent rapport with the contractor. Extensive support was provided to the resident once she had moved into the property to ensure that it met her needs and that she could achieve the optimum benefit from living in the retrofitted property.  Her key goal at the outset was to be provided with a warmer home with a layout that met her needs. The environmental aspect was not a key consideration at the outset; however through the course of the retrofit she really bought into this aspect and strives to adopt a greener lifestyle.

Energy efficiency was a key objective to the project. The resident was looking to achieve significantly improved energy costs. The project team ensured that on moving in that the resident was fully aware of how to use the features of the cottage, such as the ventilation system, and the Wattbox innovative controls for the air source heat pump heating system. The resident was provided with face to face training on using the systems along with a short, simple, homes user guide.   Hastoe Housing Association continues to provide ongoing support to the resident.

Carbon footprint advice is focused on the energy efficiency advice to the resident. The resident is in her 80s with energy use being the biggest impact.

Funding

The project cost £167,000 (VAT exclusive).  The project received funding of £150,000 from the Technology Strategy Board ‘Retrofit for the Future’ competition.

 Retrofit Costs:

Thermal Insulation

Internal insulation was required for planning reasons. The maximum improvement in U values was achieved (0.13 achieved). The design ensured that reduction in floor area was limited, along with maintaining and/or improving access to services. It was also important to avoid the risk of interstitial condensation.  Insulation used: existing solid ground floor was covered with Aerogel Spacetherm C – 18mm chipboard with a Spacetherm blanket backing; 80mm Aerogel spacetherm P dry-lining insulation to be applied to front, flank and rear internal walls with additional cavity wall insulation installed wherever possible, resulting in a U Value of 0.11 W/m²K. (Note: The original specification was written in accordance with manufacturers’ guidance, i.e.: void between insulation and internal face of external wall.  Given the risk of interstitial condensation at the perimeter of the boards it was agreed to fix these directly to the internal face of the exposed wall with an internal void instead thereby reducing risk and also improving future adaptability by providing a zone for services). Loft – blown loft insulation laid at 420mm achieving a U-value of 0.1 W/m²K.

Air Tightness

The pre-retrofit air-tightness was 4.94M3/M2/Hr, with a post retrofit target of 3.0M3/M2/Hr. The role of the site foreman was key in ensuring the building as built achieved the design targets. Programming and coordination of works were designed to avoid excessive and unnecessary penetration of membranes.  The understanding of all trades of the importance of air-tightness and how this is achieved was key.  Regular testing of air-tightness was undertaken at key stages. The final air-tightness achieved was 1.97M3/M2/Hr.

Windows and Shading

High performance steel windows (to match existing) with secondary glazing (local Building Control would not permit triple glazed windows as the windows were required to match the original Crittall windows). Bespoke insulated Heatsaver roman blinds with sealed perimeter framing were installed at each window.

Ventilation

EnergiVent Q humidity-responsive, filterless mechanical heat recovery ventilation with a retrofit airtightness strategy installed in loft.

Heating and Hot Water

Air Source Heat Pump (ASHP) powered by solar panels, along with a solar thermal system.

Solar Thermal

Solar thermal back-up to Air Source Heat Pump providing hot water when possible.

Solar Photovoltaic

Low profile in-line 1.05 KW photovoltaic panels that power Air Source Heat Pump.

Electricity Saving Products

Prototype Wattbox with intelligent controls for heating and hot water. 90% efficient LED lighting throughout. A+ (or better) rated appliances – cooker, washing machine and dishwasher.

Main Results

The SAP rating increased from the pre-retrofit level of 15 to 84, raising the environmental rating from G to B. The energy spend before the retrofit was £900 to 1000 which reduced post-retrofit to £300-400. Carbon emissions reduced from 327 Kg CO2 per m2 to 26.7, representing a 92% reduction. Air permeability reduced from 4.97 m3/(h.m2) to 1.97. The target primary energy reduction of the retrofit was 91.7%, in practice 88% was achieved. The target carbon reduction was 94.9%, with 92% achieved.

Lessons learned

Lack of appropriate contractor skills in the construction industry is a challenge however the excellent airtightness results were achieved due to one member of the contractor team being supported to take ownership and responsibility for airtightness throughout the retrofit process. The supply of the right materials and products was a challenge with long lead in times and delays, however this is improving. Resident engagement was absolutely key to achieving the successful buy-in to the project and to ensure adoption of green measures and lifestyles. ‘Simple’ technologies were not always as simple as intended and we need to provide as much support as required to residents and support staff. Unfortunately the Wattbox eventually malfunctioned and had to be removed, however this was all part of testing the technology. Due to this the quality of the data achieved during the monitoring phase was not as good as hoped.  Hastoe monitors the energy usage and costs for the resident through the regularly review of bills.

Additional Information

Going beyond exemplar – The three remaining properties in terrace were retrofitted in 2011/12. They were of the same building type and experienced the same poor thermal performance. It was the same resident group (with two void properties). The cottages are a one one-storey end of terrace property with two two-storey mid terrace properties with very steep stairs, unsuitable for elderly residents. The kitchens and bathrooms did not meet modern standards. There were reduced funding options for the retrofit (no external funding) however Hastoe spent over £80,000 per property to bring them up to a similar level to the exemplar retrofit. Measures included: insulation to cavity walls, loft and solid floor; window replacement (double glazed Crittall); complete rewire and new central heating via radiators with low temperature air source heat pump; new Part M compliant staircases; relocated and extended kitchens and bathrooms. Headline results of the retrofit include 71.5% reduce in carbon emissions and a primary energy saving improvement of 75%.



Ms Lauren Gee
NHF - The English National Housing Federation
E-mail: lauren.gee@housing.org.uk
Web: www.housing.org.uk