In your ‘How to deal with damp’ article it says “Where a floor has a modern damp-proof membrane (horizontal barrier or DPM) that is displacing moisture to the bottoms of walls, it may be sensible to replace this completely with a breathable construction or to at least provide a breathing zone for evaporation around the perimeter of the room”. Please can you explain how exactly to provide a breathing zone for evaporation around the perimeter of the room?


  • Lindsey Davis

    Hello Charlotte,

    Here is an explanation from David who wrote the article:

    The breathing zone only needs to be 18"/450mm wide. The modern floor in the required breathing zone will have to be broken up and removed. Some people lay timber floorboards on joists over the gap and insert air vents through the bottoms of the walls to ventilate below the floorboards. This can work well but you need to have at least two outside walls for the ventilation. It is often easier to lay a limecrete floor in the breathing zone. This would require a breather membrane over the exposed earth, a layer of coarse hardcore (or nowadays often insulating nuggets), another breather membrane, a limecrete slab and limecrete screed. To stop the remaining modern floor overwhelming the limecrete with moisture, a vertical damp proof membrane should be run down the sides of the modern concrete, and the top of the hardcore/nuggets forming the base of the breathing zone should be above the bottom of the concrete.

    We hope this is helpful,

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