Subfloor Issue - Advice Needed

[MichelleH]

Hello,

I have moved into a converted bungalow in Jan. Some of the property is about 7 years old, some from the 70's and part from 1900's.

The problem is with the 1900 part. The 2 older rooms are very cold and the air is moist. We found green mould under the mattress in our bedroom which has prompted us to take action.

The bungalow in this part is covered in harling of sorts outside, then about 2 ft stone walls, then as part of the conversion has been finished in plasterboard. Upon inspection last night, we found that the plasterboard had no insulation. They had left a large gap between with stone and plasterboard for ventilation, but no insulation. We have decided to remove this and have it insulated.

Then, upon removing some hatches in the flooring, we found that our bedroom had no space for ventilation beneath i,e the concrete rubble and joists were tight against the flooring. It also felt a little damp, which we are assuming is because there is no ventilation.

There is no room for ventilation so I was wondering what to do? Do we have to dig out the floor or should we raise or do something else?

Any advice would be greatly appreciated.

Thanks

 

[jeds]

Depends how much work you want to do and how far you are prepared to go. The walls are easy. Hack off the plasterboard and replace with thermal plasterboard direct to the walls. Skim finish and job done. There are different thicknesses of insulation and also different grades - price up a range of options and go for the highest/thickest you are prepared to pay for. The floor is more tricky. If you are happy to raise the floor you could insulate on top and re-board but I would be concerned about lack of ventilation. If you are prepared to go the whole way I would take the floor up, reduce levels and replace. You've got two options - suspended or solid. Suspended is more work and I would only consider it if you can introduce adequate ventilation. Otherwise go for a solid floor on a good amount of insulation.

 

[MichelleH]

Thanks John.

After lots of reading, it was my understanding that a gap should be left for airflow between the stone and plasterboard. Also, I had thought insulation between the struts with a layer of plastic/vapour barrier plus foil backed plasterboard?

The floor has no option for ventilation, so if keeping at the same height, what about a rubber sealing concrete poured on top with polythene?

If raising the floor, would that mean building regs etc?

Thanks

 

[jeds]

The method you describe is fine but it is important to get the details right. It is really a case of personal preference but in my opinion, which comes from a long experience of specifying this sort of stuff, direct fix thermal laminate boards is the simplest and easiest method and is very effective. The vapour barrier is built into the boards so you just cut the boards to size and fix them - done!

Just in case you decide to go with a cavity; It is important to seal the cavity completely, otherwise you will create a condensation issue. In practice that is quite difficult to achieve.

Not sure what you mean by rubber sealing concrete? What I pictured you've got at present is a timber floor sat more or less directly on sub-floor rubble. It wouldn't be a good idea to pour anything concrete like on top of that. And in any case I don't think it would add much in terms of thermal performance. If you want to raise the floor just lay PIR insulation over the top and 22mm t&g chipboard on top. That will give you a warm floor but the trouble is it will also increase the condensation risk. So I wouldn't actually advise doing that without also introducing some sub-floor ventilation. From what you describe that isn't going to be easy. The only other alternative is leave it as is or take the floor up.