design strategies

Space heating strategy Re-use existing (<5yr old) gas condensing boiler serving small radiators, generally sized 300 to 400 Watts for each room. Total heating load for whole house calculated as 2.8kW. 5kW wood burning stove in living room.
heating strategy
New 250 litre mains-pressure, indirect twin coil hot water cylinder. Primary heating (initially) will be from boiler. Eventually, flat plate solar collectors will be added to supplement hot water, but budget is being concentrated on fabric improvements first.
Fuel Mains gas for heating and cooking; mains electricity
Renewable energy Solar thermal only being considered.
Large amount of glazing (70%) to rear (east) allowing good winter solar gain.
House faces east/west with approx 70% glazing using high quality triple glazed units. These have a double low-e coating and offer a good degree of solar control. Lower ground floor (new kitchen) will has approximately 1 metre overhang from balcony above, with planting. Live/work from home – window management is key in summer.
Daylighting House is very well day-lit as many mid-century homes tended to be. Glazed area has reduced slightly with the extension/renovation, but occupied rooms have a daylight factor >3, which means that do not need electric lighting during the day.
Ventilation strategy Whole house heat recovery ventilation system with frost coil. Ducted via rigid steel ducting. System provides 220 m3.h-1 in normal mode and 270 m3.h-1 in boost. Summer vent has the option of summer bypass, which will be managed (switched off) in conjunction with window opening.
Airtightness strategy Wet plaster coating to interior walls. Render under-/slurry-coat applied to outer brick layer prior to applying EWI. Airtightness detail around window and door openings and junctions between floors, walls and roofs, by use of airtightness membranes and tapes. Around openings, an adhesive-backed airtightness tape will be fitted to surrounding structure. Existing intermediate floor joists (penetrating the cavity) will be individually sealed using proprietary air barrier sealant and/or membranes and parging.
thermal bridges In general, wrapping the house in 120mm of external wall insulation will eliminate many of the existing thermal bridges. Extending insulation in the extension to foundation level reduces psi-values to negligible levels (<0.02 W.mK). Existing concrete balcony and concrete gutters being cut-off, primarily to reduce thermal bridges from 0.41 to 0.08 W.mK. Positioning of windows and doors at the centre line of the insulation layer. Expect that existing thermal bridges in house will be reduced by some 80%.
INSULATION 120mm external wall render insulation system to extension and majority of existing house. South elevation has external concrete stairs and EWI will not be possible. Internal wall insulation (100mm) will be fitted to this elevation at ground/lower ground. Roof will be 400mm Warmcell, cellulose insulation. Extension roof, tapered PIR, min 100mm. Extension floor 100mm PIR; existing floor 100mm mineral insulation between joists.