Page 115 - Rural Housing Association Design Guide
P. 115
Design guide for social housing in rural Northern Ireland Creating rural places: Designing appropriate buildings Building fabric and performance A sustainable rural house should encompass the Passive House principles, where the building is designed and built to a very high standard to achieve a healthy and stable internal environment. An effective building fabric is essential for this. 1 THERMAL MASS AND INSULATION Thermal mass will store heat and a well insulated envelope will minimise heat loss and contributes to comfortable conditions all year round. A Medium Weight Dwelling (blockwork inner walls with concrete ground floor) can out-perform a Light Weight Dwelling (timber stud inner walls with concrete ground floor) by around 7%. Thermal mass also reduces the risk of summer overheating by reducing peak temperatures. The thermal mass area should be around six times the size of windows. Regarding insulation, the basic rule is to wrap the building continuously on all sides, including the ground floor slab with insulation which will need to be 150mm PIR Insulation Board in walls and 4 floor, and 300mm to 400mm in the roof (at current Building Control Regulation Standards). 2 AIR TIGHTNESS AND VENTILATION Even if a dwelling is very well insulated, heat will be lost if there are gaps in the building fabric where air can escape. 3 2 To comply with the current Building Regulations, dwellings with an as-built air leakage test of less than 3m³/hr/m² require additional ventilation to be installed whereas dwellings designed to have air leakage of less than 5m³/hr/m² also require whole house mechanical ventilation installed. Mechanical heat recovery systems can recover heat lost through ventilation by extracting heat from exhaust air and using it to pre-heat incoming air, and work better in dwellings with very low 1 air leakage rates (around 3m³/hr/m²). The designer must choose a ventilation and air tightness strategy from the outset, taking into account their effectiveness, controls, future maintenance and running costs. Single room depth dwellings have the ability to achieve cross ventilation and give more flexibility in placing and sizing windows to take advantage of solar gain. 3 GLAZING “A” rated windows allow more free energy into the dwelling than is lost through the window. As most of this heat is generated in the summer when it is not needed, triple glazing windows with a lower u-value perform better. 4 ACOUSTICS Party walls with 150mm dense blockwork cavity walls can achieve sound reduction levels twice those of the Building Regulations whilst allowing walls to be chased for the installation of services. The combination of these party walls and triple glazed windows to isolate external noise will A dwelling at the notional scheme at Attical, Co.Down, demonstrating the key features of good building fabric and greatly enhance the occupant’s comfort. performance in new-build rural social housing. 114 115
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