An extension to Kelbrook House, an eighteenth-century listed house in Amersham Old Town in Berkshire, has been completed as an all glass box over a steel frame.
The columns are 100mm x 50mm channels with roof supports formed from 102mm x 125mm T-beams. The roof members have been sized to take the loading as well as being sufficient to fix the exterior glazing framework. The steelwork was located to +/-2mm tolerances at the base fixing point and +/-0mm tolerances on overall diagonals. All steelwork is galvanised and powder-coated white.
The 1,620mm x 1,781mm doubleglazed flat roof panels comprising 12mm toughened upper pane, 12mm cavity and 10.8mm lower pane and are strong enough to walk on.
The roof is laid at a fall of 1 in 100 towards the existing building. The gap formed by the bowed existing brickwork (95mm deformation) and the new construction accommodates the gutter.
The walls are single glazed in 12mm toughened glass to avoid the visual interruptions caused by spacers and framing.
The bottom sits in a channel and the top is fixed back to the steel structure with stainless steel bolts.
The south-facing aspect and low-lying surroundings mean that a significant proportion of the solar energy is incident on the new structure. To avoid uncomfortable internal temperatures, an automaticallycontrolled motorised blind has been fitted;
activated by a solar cell. The high short wave radiation reflectivity of the blind means it reflects back about 50 per cent of the radiation striking it.
Approximately 10-12kWhrs of energy is taken in through the roof. The heat loss is anticipated to be 21kWhrs per day when the average outside temperature is 5 degrees C.
The solar benefit is therefore intended to compensate for about half of the heat loss.