Creative & client-focused architectural practice
Installation of a PV (Photovoltaic) solar array has been completed at our nZEB house, now reaching completion.
The system comprises an 8-panel, 2.4 kW photovoltaic array mounted within the concealed roof valley, and produces enough electricity to offset nearly all of the residual space heating and hot water energy demand of the house.
Initial Blower Door Air Tightness Test has been carried out this week on our nZEB (nearly-Zero Energy Building) house in Dublin 8. The contract specification set a Q50 target of 1.0 m3/hr.m2 (at 50 Pascals pressurisation), roughly equivalent to the Passive House ‘EnerPHit’ standard for the retrofitting of existing buildings. The refurbished and extended dwelling has achieved an initial air permeability result of 0.8 m3/hr.m2 @50Pa. To put this in context – the maximum permitted air permeability level (for new dwellings) under the current Building Regulations is 7.0 m3/hr.m2 @50Pa, so the nZEB house is achieving an air-tightness standard nearly 10 times that required under the current Regulations.
This ambitious level of structural air-tightness is a vital component of the overall low-energy strategy for the dwelling – reducing to a minimum heat losses occurring through uncontrolled air-infiltration (drafts and air-leaks), whilst also minimising risks of interstitial condensation (moisture vapour passing through the building fabric and condensing on concealed surfaces within the structure). Achieving a high standard of air-tightness was also essential in order to deliver optimum efficiencies from the dwelling’s combined heating and ventilation system – an Exhaust Air Heat Pump, which recovers heat from extracted air and recycles it to provide space heating and domestic hot water.
The airtightness level has been achieved by robust detail design, together with careful and diligent execution by the Main Contractor and Sub-Contractors on site. An almost continuous air-tight layer is achieved through the use of wet plaster (walls), double-seals to windows and doors, concrete layers (floor), intelligent air-tight membranes (roof), and with all junctions sealed with air-tight tapes, seals and grommets. A services zone was created to all walls and ceilings to eliminate any chasing or penetrations of the air tight layer.
200mm of high performance EPS external wall insulation (Conductivity 0.031 W/mK) being fitted to walls of our nZEB house currently under construction. Rockwool mineral wool insulation is being used to provide vertical fire-stopping / fire-breaks.
The external walls are built using low-conductivity ‘Thermal-Liteblock’ concrete blocks, and there will also be an additional internal layer of 50mm mineral wool insulation together with a wet-plaster airtightness layer. The U-Value of the complete wall construction has been calculated at less than 0.12 W/m2K (Floor U-Value: 0.09 W/m2K, Roof U-Value: 0.11 W/m2K, Windows U-Value: 0.75 W/m2K)
The wall insulation layers are designed to be continuous with the floor and roof insulation in order to eliminate thermal bridges at junctions. This is important both to prevent additional heat losses that would occur otherwise at the junctions of the wall, floor and roof planar elements, as well as to ensure interior surface temperature factors (fRsi) are sufficient to avoid cold spots and potential condensation (& mould growth) risks. A specially designed threshold detail has been developed for the fixing of the large format glazed doors and screens using stainless steel bracket support angles, faced with 180mm of XPS (extruded polystyrene) carried down to foundation level.
