Peter Napier and Co
CHARTERED BUILDING SURVEYORS
9 Ashford Park, Pontesbury, Shrewsbury
The brief from the client for this 4 bedroom house was for a budget that did not exceed the cost of a traditional Building Regulations standard house. It was agreed that the house would be designed to provide the best thermal performance within this brief.
The plot had the benefit of a planning permission dating back to the building of the surrounding houses in the 1960s (see photo in margin). The planners agreed to a new design provided that it respected the designs of the existing houses and with a ridge height comparable with other dormer bungalows on the estate.
External walls were originally to be timber framed but the lowest tender allowed for a traditional cavity wall of two skins of concrete blockwork and a 250mm wide cavity filled with mineral wool quilt. This gave a U value of 0.13 W/msqK compared with a Building Regulations requirement of 0.35W/sqmK.
Suspended concrete T beams and polystyrene blocks which wrapped beneath the T beams were used for the ground floor. This gave a U value of 0.11 W/msqK compared with a Building Regulations requirement of 0.25W/sqmK.
The roof construction was provided by attic trusses insulated with Kingspan between the rafters and insulated plasterboard beneath. This provided a U value of 0.11W/sqmK compared with a Building Regulations requirement of 0.25W/sqmK.
Air tightness provided by wet plaster to ground floors and air tight membrane with taped joints to upper floor and roof.
Air tightness of 2.4cum/sq m of envelope per hour at 50Pa was achieved although this was less than hoped the house is performing well. The Building Regulations minimum standard is 10 cum/sq m of envelope per hour at 50Pa.
Controlled ventilation through MVHR (mechanical ventilation and heat recovery) with underfloor heating on the ground floor, no heating on the first floor and with an electric boiler providing hot water to underfloor heating and to a heater battery in the MVHR incoming air duct.