How Do You Reduce the Impact of a Solid Floor? – Can I Just Ask? | Ep.28

Solid floors are one of the more involved elements of a whole-building retrofit, and the approach taken here is designed around two principles: managing ground moisture without relying on a conventional damp proof membrane, and building a floor construction that can be fully deconstructed and reused rather than ending up in landfill. The foundation of the system is recycled foam glass, compacted directly onto the subsoil. Unlike a sheet DPM — which is inherently discontinuous where it meets the walls and can displace moisture rather than manage it — foam glass acts as a capillary break while simultaneously providing insulation. It’s lightweight, low-carbon to transport, taken directly from the waste stream, and can be dug out and reused indefinitely.

Above the foam glass, a vapour control membrane is laid — functioning primarily as an airtightness layer at floor level rather than a moisture barrier per se — followed by a levelling layer of mineralised wood chip to create a flat, stable surface. Two layers of wood fibre board go over that, and then Lithotherm: an interlocking screed-replacement tile system into which underfloor heating pipes are laid, finished with a floating timber floor above. The entire build-up is dry and deconstructable — no wet trades, no curing time, and no tonnes of concrete screed releasing moisture into the building during construction. A conventional 60–100mm screed introduces a substantial and prolonged moisture burden on surrounding elements, including variable diffusion membranes in timber frame walls, which are forced open by the drying load.

The broader point is that while individual components like foam glass and Lithotherm carry a reasonable embodied energy figure on their own, the ability to disassemble and reuse them repeatedly across multiple building lifetimes dramatically reduces their whole-life impact. A screed, by contrast, can’t be reused — it gets broken up and sent to landfill, with all the carbon cost that entails. For a domestic floor where the structural loads are modest, there’s no functional reason to use wet construction at all — and good reason not to.