The Nottingham Ecohome. Part L1 (2002) in existing dwellings

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1 The Nottingham Ecohome Part L1 (2002) in existing dwellings

2 The Nottingham Ecohome is a refurbished Victorian house situated in West Bridgford, Nottingham, which incorporates a variety of eco-friendly features, including very low U-values and the use of renewable energy. Front (south) facade In order to upgrade the solid brick wall at the front facade without adversely affecting the appearance of the Victorian exterior, two layers of zero ozone-depleting phenolic foam and plasterboard were applied to the inside of the (215 mm solid brick) front wall using a continuous layer of adhesive. The plasterboard-foam sandwiches consisted of 12.5 mm of plasterboard bonded to 40 mm of phenolic foam, which is quoted by the manufacturer to have a thermal conductivity of W/m 2 K. The overall thermal transmittance (U-value) of the wall has been calculated to be 0.20 W/m 2 K. This value is considerably lower than the current guidance for new-build properties in Approved Document L1 of 0.35 W/m 2 K and is also lower than the 0.27 W/m 2 K elemental value suggested in the proposals for the 2005 revision of Approved Document L1. However, this thickness of the insulating material (phenolic foam), despite its very low thermal conductivity, only just achieves the suggested new-build standard for the following revision of the Approved Document (2010) of 0.20 W/m 2 K. As this thickness of insulation is unlikely to be practical in many dwellings, it suggests that new-build standards would be very difficult to achieve in the future unless there is further development of insulating materials. The house, showing the brick external facade at the front and external insulation at the gable wall and back wall. Notable are the bevelled edges to the external insulation which improve the general appearance. Side (east) wall and back (north) wall External insulation consisting of 140 mm of expanded polystyrene was applied to the 215 mm (9 ) solid brick side wall and back wall giving a wall U-value of 0.23 W/m 2 K. Prior to the application of the external insulation, the occupiers tended to find the ground floor rooms colder than the upstairs rooms. This was especially true for the cold north facing bedroom on the ground floor. It is too soon to say whether the application of insulation on these walls will help to even out the temperature distribution in the house. Prior to application, some sections of the wall were re-pointed and in some areas of the wall 15 mm of plaster was applied internally to the existing brickwork. For aesthetic reasons, there are 45 bevelled edges on the external insulation on the side and back walls with 30 bevelled edges at the front end of the side wall. Both the internal and external wall insulation systems are given an A rating in the BRE Green Guide to Housing Specification for refurbishment of insulation. Attic/Roof The roof construction consists of tiling on battens, breathable roofing felt, 400 mm thick cellulose between deep (400 mm) rafters and 12.5 mm plasterboard, giving a U-value of 0.10 W/m 2 K, which is equal to the aspirational level for the 2010 revision of Approved Document L1. The roof was overhauled and renewed because the existing roof had no felt beneath the battens and the occupiers were concerned that the new insulation, once installed, could be vulnerable to wetting. Plywood rafters were attached to the existing rafters in order to provide the 400 mm thickness, the plywood provided a thinner profile and a greater depth than could be achieved using solid 2

3 Internal insulation at junction between front wall and gable wall, showing how the internal insulation overlaps part of the external insulation in a relatively unobtrusive way. The cornicing in the ceiling has been adjusted in order to blend with the surroundings wood. This helped to reduce thermal bridging. There is a polythene membrane applied between the bottom of the plywood rafters and the sloping plasterboard, which helps to improve air tightness. Between each pair of rafters a strip of breathable cellulose board was fitted in order to form a restraint for the loose-fill cellulose insulation and to create a gap beneath the breathable waterproof membrane. Despite the attic rooms being wedge-shaped they still have reasonable head height. The roof windows have deep internal reveals, owing to the 400 mm thick cellulose roof insulation at rafter level. The attic rooms were found to be comfortable during the winter of despite the absence of insulation in the east wall at that time. Partly to compensate for the depth of the internal reveals at the roof windows, the window reveals are tapered to maximise the amount of natural daylight. Floors The floors above the unheated cellar were insulated between the joists (at 400 mm centres) with 100 mm of Thermafleece sheep s wool and 60 mm wood fibreboards were fixed to the bottom of the floor joists, giving a U-value of 0.24 W/m 2 K, which is lower than the new-build elemental value of 0.25 W/m 2 K. An air-tightness membrane was fixed to the underside of the joists before fixing the wood fibre board. A membrane was also sealed to the walls behind the downstands at the wall-floor junction. A solid floor in another part of the house was insulated with 150mm of polystyrene below a 100mm concrete slab, giving a U-value of 0.18 W/m 2 K - lower than the aspirational elemental new-build value for the 2010 revision of Approved Document L1 of 0.20 W/m 2 K. Internal insulation at skirting board level, showing that an overlap between internal and external insulation can be achieved in a relatively unobtrusive way. Thermal bridging At the junction between the internally-insulated front wall and the externally-insulated gable wall, thermal bridging was reduced by providing an overlap of insulation. Internal insulation was continued some 450 mm along the internal surface of the gable wall and tastefully tapered at the end (see photographs). The 450 mm internal insulation along the gable wall consists of 12.5 mm plasterboard bonded to 40 mm of phenolic foam. Interestingly, the presence of the internal insulation at this point is hardly noticeable and could easily be mistaken for an architectural feature. Overlapping was also used near the foot of the stairs to avoid thermal bridging at ground floor level. 3

4 Windows The windows consist of either low-emissivity double glazing or triple glazing with wood or PVC frames. The double glazing had a lowemissivity coating with argon fill, with a manufacturer s quoted U-value of 1.1 W/m 2 K. The triple glazing had low-emissivity coatings and Predicted temperature distribution for the junction between the front wall and the side wall. It is notable that the minimum internal surface temperature is above 17.5 C, giving a surface temperature factor of This is well above the recommended minimum surface temperature given in IP17/01 indicating that the thermal bridging is acceptable and there is no undue risk of surface condensation. krypton fill, with a manufacturer s quoted U-value of 0.6 W/m 2 K. The manufacturer s U-values are centre-pane measurements and BRE have calculated that the U-values for the whole window fitment would be in the order of 1.7 W/m 2 K and 1.3 W/m 2 K for the double and triple-glazed windows, respectively. The thermal conductivities that were assumed for the numerical modelling calculations. Although the thermal conductivity for the phenolic foam (internal insulation) was quoted by the manufacturer to be W/m K, the conductivity of the foam in this model was given a conservative value of W/m K. The occupiers have generally used triple glazing on any replacement glazing on the north facade and low-emissivity glazing for any replacement glazing on the east or south facade. The wood frames are better from a sustainability point of view with an A rating in the BRE Green Guide ; the PVC frames are rated C, but disposal of sound, existing PVC frames is also poor practice from a sustainability point of view This image shows the predicted heat flow lines, indicating the direction of heat flow at different points. The results indicate that, as expected, there is lateral heat flow along the wall between the internal insulation and the external insulation, and shows that the 450 mm extension to the internal insulation is having a significant effect. 4

5 Ventilation The ventilation is provided by several heat recovery ventilation fans in the kitchens and bathrooms, linked to humidity sensors. The heat recovery fans recover heat from outgoing air and transfer the heat to incoming air with a heat recovery efficiency of 80%. The occupiers considered installing whole-house ventilation but chose not to because of the difficulty of retrofitting the ductwork. Space heating and hot water The house is heated in winter by a wood-burning boiler, coupled to a large (1100 litre) water-filled thermal store; the boiler can use either scrap wood or pellets. The occupiers affectionately refer to the thermal store as the big cheese on account of its appearance. During the winter, the thermal store is used to retain excess heat from the solid fuel burner and to release heat when it is needed. The full seasonal efficiency of the boiler is unknown, but it is thought to operate at about 86% efficiency once up to full temperature and using dry wood. The disadvantage of the boiler is that it has to be stoked by hand. There is also a large solar thermal panel (area 4m 2 ) on the roof which is estimated to provide around 50% of the annual hot water needs. Low energy spotlighting The solid fuel heating system and thermal store shown together General The occupiers have spent some six years gradually applying insulation and other energy-saving features to their house to reach its present state. They note that while there were no incentives from public funding bodies for installing energy saving features when they started, they have this year been able to take advantage of two grants. Both the New Energy Foundation and the Clear Skies schemes have been instrumental in enabling the first biomass boiler of its type to be installed in their house, which is located in an urban area and is a smokeless zone. The occupiers believe that solar thermal energy is the most costeffective of the renewable energy systems and consider it to be a financially sound and environmentally sound investment for households. There is currently no accurate way for the occupiers to assess the proportion and quantity of renewable energy used in their house but as a result of the improvements which they have carried out they perceive a tangible improvement in thermal comfort levels. Owing to the high insulation levels the boiler consumption is low and, as the wood which is burned is mostly off-cuts, the electricity bill is expected to be cut to about a fifth this winter (compared with previous electricity bills). 5