Replacing timber floor with concrete/UFH in a Victorian ground floor flat

Hi Poppy. A suspended floor like yours needs ventilation but this can also cause draughts and vermin to come up through the boards, as in your case. Before starting the job, ensure your final floor finish level (FFL) would be level with that in the rest of the flat if not all the floor is being removed. It should also take into account FFL at door openings. For a solid floor, you would need to start about 300mm below FFL. Option 1 The best but most expensive solution would be; to remove the floor boards, cut out the joists and build up a solid floor. Starting from the lowest point you would prepare the base to ensure a solid substrate, either with a layer of 100mm concrete, or compacted hardcore of 100mm. On this, you would lay a blinding of sand (for hardcore) of approx. 25mm and then a damp proof membrane (DPM), dressed up the wall. For concrete, no blinding of sand is required, just the DPM. Next would be a layer of Celotex / Xtratherm or Kingspan of 75mm minimum. On this, lay another DPM also dressed up the wall. You should also have an expansion joint around the edge of the room of approx. 25mm to prevent thermal bridging. On top of the insulation, lay wet underfloor heating pipework which would have a flow and return back to the boiler via a manifold. Then, pour a 75mm concrete screed over this. Make sure that the floor finish level and amount of concrete screed allows for your floor finish level and the depth of the boards / tiles / carpet that you intend to lay. You will probably need to allow for new skirting boards and architraves around the doors to be fitted. Option 2 A cheaper option is to keep the boards or replace them over the existing joists, lay a breathable membrane over them that will reduce draughts into the living space. Over this, a layer of insulation sheet can be used for better thermal performance. An electric underfloor heating system is a more cost-effective way of heating a smaller space and this will need to be compatible with a boarded floor and the floor covering. Consult manufacturers and suppliers to determine the types of electric under floor heating that would be appropriate. For the cheaper option, make sure that the floor joists are sound as sometimes they rot where they are pocketed into the walls. This is especially the case if ventilation is inadequate or if there is not clear space between the joists and the soil beneath them. One test is to jump on the boards and see if there is any 'bounce' in them. To stop rising damp in the walls, first ensure that externally, gutters and downpipes are working properly and also that the external ground level is not higher than the internal floor finish level. It should be 150mm lower and the water should be able to run away from the walls and foundations. If there is still a problem with dampness in the walls, it might be best to use a specialist damp proofing company that will provide a 25 yr. guarantee on any work they carry out. Please get in touch if you want further information. Tom