Suspended floor insulation

juraj.kecso

Hi All,

I am thinking of insulating my ground floor.

I haven't looked under the floorboards yet, so not sure what the actual situation is. At this stage I am just contemplating different options.

So far I've gathered that you can use either foam boards like Kingspan or Celotex supported by battens or mineral wool (the type normally used for lofts) supported by netting. If I am not mistaken, you need 100mm thick foam boards or 200mm thick mineral wool.

Purely from a cost perspective, I am inclined to go with mineral wool as it is about a quarter or a fifth of a price of foam boards making it very attractive option. However, at 200mm thick, there is a good chance of the wool being quite a bit thicker that joists. Would that be a problem?

I know that building regs require certain U value, but if I only use say 100mm wool to make sure that parts of the joists are still exposed for ventilation, who will ever know?

What about vapour barrier? Is that necessary and if so, where will go? Between joists and floor boards or between floor boards and laminate flooring? I was thinking of buying the gold foild underlay as a vapour barrier.

TheCyclingProgrammer

Vapour barrier goes on the warm side, breather membrane on the cold side. You need to ensure you have good ventilation too.

Personally I’m not convinced the effort is worth it. How much heat do you think you’re losing through the floor?

juraj.kecso

Hi, I am not sure how much heat is lost through the floor but it does get quite cold to touch (it's a laminate flooring).

At the very least I am considering the gold-foiled underlay, which my friend swears by (he has it on a concrete floor).

My question really was whether the mineral wool can be thicker than a joist as you'd need 200mm wool and most joists are around 150mm thick. Would that present a risk to joists?