Home DIY

Whether the boards are nailed or (unlikely) screwed to the joists, it's heavy work to pull up the boards and you'll end up damaging a lot of them. Better to lay your insulation (eg 3 mm expanded foam) over the existing boards and fit extra floor covering over. It's still a lot of work (you will probably have to trim all the doors) but I bloody well wish the neighbours above me would do it.

I did it. Took the entire ground floor up (tongue & groove 1930s pine boards), cleaned out all the crap underneath (sacks and sacks of rubble), put mesh over the airbricks, rebuilt some of the dwarf walls the joists rested on, took out two hearths, built up the fireplace with a new dampcourse and added joists to support the gaps for the boards to sit on.

Then I hung some plastic netting between the joists and suspended about 5" of wool insulation before laying tyvek breathable roofing membrane on top, sealed all the seams with airtightness tape and used the same tape to seal it to strips of plywood fixed all around the room behind the skirting.

Then I had to relay the floorboards and add some extra from a reclamation yard to make up for a few that broke and the extra area where the hearths used to be. This involved a couple of thousand screws which were all countersunk beneath the surface and then covered with 2 part wood filler which needed sanding flush with the boards. Finally we sanded the boards, then filled some of the worst gaps with a mix of sawdust & PVA (don't use this - use a proper filler, it's horrible to sand). Then finally sanded once more with a finer grit and oiled with a couple of coats of Osmo.

Bear in mind you (technically) require building regulations approval if you're renovating more than a certain percentage of your floor area and there are certain U values you're supposed to achieve. Also you should ensure there is adequate volume of air beneath the insulation and be aware of how moist it gets in the subfloor. Our subfloor was concrete so no real dampness do deal with from the ground at least.

Oh and of course we found that there was loads of old wiring and gas pipe and crumbly mortar on the brickwork beneath the floor so we took all that out and repointed where the walls we particularly bad.

So you can do it, but don't underestimate the amount of work to do it 'properly'