Impressive U values for the eco lodge floor

Ian has finished calculating the thermal insulation value (the U value) for the floor of the new eco lodge. Well, it’s not quite finished yet, as the picture shows, but here’s the plan.

The U value measures the overall ability of a wall/roof/floor to prevent heat loss. It’s measured in Watts per square metre per degree Kelvin (W/m2.k) and takes into account all the thermal conductivity (k values) of the components of the structure, as well as other factors that affect how heat is lost from the building. Until recently, building regulations required floors to have a U value of 0.7 or below. That’s now been brought down to 0.22 W/m2.k. So how do we fare?

The floor will be high-proportion recycled aggregate, then 150mm insulation (Kingspan, for it’s exceptional insulation value, which we think outweighs it’s only light-green manufacturing process – well they have been trying at least), then another 150mm of concrete made of 70% ash cement and recycled aggregate. Because it’s above the insulation, this layer becomes part of the thermal mass of the building, acting as a heat store to help regulate temperature. On top of that we’ll be putting down larch floor boards sourced locally (8 miles) from Mike Moser’s oak woodland restoration project.

Overall, that will give us a U value of 0.11 W/m2.k – twice as good as the 2010 building regulations.