The house has 65m2 of triple-glazed, argon-filled VELFAC 200 aluminium windows on the south elevation, shaded from the midday summer sun by a first floor balcony. Smaller glazed areas on the remaining facades provide adequate daylighting. "The thermal performance of these windows allowed us to have generous glazed areas without comprising on heat loss", says Kerry. "Many high performance windows have chunky wooden frames whereas the VELFAC system looks contemporary. We particularly liked the fact that there is no visible difference between the fixed and opening frames". The slim frames and mullions also allowed for a greater percentage of glass resulting in high Ff (glass ratio) value and therefore superior daylight levels".
The glazing provides 92kWh of solar gain per day in September, 57kWh per day in October and 60kWh per day in May. When combined with heat created by occupant activity and appliances this solar gain means the house only requires minimal heating from November to April.
The dense plaster blockwork walls, highly insulated external envelope and thermally massive slab, which is coupled with slate flooring in the south-facing rooms, provide thermal mass and enable the building to retain heat for long periods during the winter. The solar shading and ventilation system prevents overheating in the hotter months.
Passive stack ventilation
A double-storey winter garden comprising double-glazed, argon-filled VELFAC units has been attached to the west elevation. This has been designed to draw warm air from the house in the summer, while air entering through trickle vents and open windows on the northern facade cools the building down. On sunny days in the colder months a destratifyer pumps warm air from the top of the winter garden to the bottom allowing it to then enter the house. The automated opening vents within the winter garden facade employ actuators concealed within the VELFAC windows. An integrated WindowMaster control system operates this ventilation system, opening and closing windows in response to temperature sensors within the building.
The quantity of glazing and the height of the units of the south elevation meant that the lack of maintenance required by VELFAC composite frames when compared to solid timber frames was a key consideration in their specification.
Additional green measures
The house has an impressive range of sustainable technologies including a manually operated log-burning boiler and stove, a solar thermal array, a rainwater harvesting system and LED and fluorescent lighting.
Yet, the greatest energy savings have been implemented through the design of the building, which through the clever use and positioning of glass can almost exclusively heat and cool itself.
"The glazing was critically important to both the performance of the building and the architectural merit of the project," says Kerry. "It was essential that we got it right".