For many years, the energy efficiency spotlight has been on improving the performance of walls and roofs. But there’s another area of the superstructure that merits close scrutiny – and you might be surprised to learn that, in many existing houses, around 10%-15% of the heat generated is lost through the floor.
The Building Regulations are fairly relaxed when it comes to thermal performance of upper storey floor structures – although you will need to consider fire safety and acoustic insulation. It’s really only with ground floors that conserving energy becomes a major design factor.
In new homes, Part L of the regs specifies a threshold U-value (a measure of heat loss) of 0.25 Watts per metre square Kelvin (W/m2K). If you’re providing new thermal elements in an existing home (eg as part of an extension), the limit is 0.22 W/m2K – unless there’s a heritage-related reason this can’t be achieved. Bear in mind these backstop levels vary slightly in Wales and Scotland. And in practice, most self builders will achieve a significant improvement on this. Indeed, the government’s own guidance for a notional dwelling suggests a target of 0.13 W/m2K.
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