Underfloor insulation

My lounge has a cellar underneath it and gets cold in winter.

Thinking of moving the radiator but have a bit of Kingspan Kooltherm slabs I got for free.

The room is carpeted but am going to try insulation.

Should I cut the slabs to fit between the floor beams allowing the beams a small amount of space to breathe (uses more insulation / more wastage) or just attach the slabs directly to the floor beams (more insulation efficient but no ventilation to beams).

Is the difference the same as laying insulation in the loft over the roof beams without any ventilation to the beams? The cellar is damper so seem to think allowing the beams to breathe is more important than just laying insulatio over beams in the loft

Does your cellar have a ceiling finish?

I am assuming your cellar is an unheated space. If so, you may want to think about heating it somehow, but that depends on what you use it for.

I would suggest just fitting it between the joists as the cold bridging through the joists will be fairly minimal and putting them below the joists would require a vapour control barrier of some kind, assuming that the cellar is unheated and damp.

wrong forum halfwit

Are the joists & floorboards damp?
Friction gripping the insulation in between the joists will give far better performance & cut down on some of the draughts (ventilation)

The Kingspan is a PIR board so should not transfer damp but best results would be tight between joists & snug under the floor boards IMO.

If you have damp then you need to get rid of it anyway
It would be worth putting in a breather membrane between the insulation & the floor boards.

Hope this helps

Cellar is unheated and damp. The kooltherm has a metallic coating, but the vapour barier effect cannot be confirmed, but I would consider putting vapur barrier sheet in place as it would be cheaoer than the wastage in cutting the boards to fit between the boards.

I guess the question is – If I put the boards onto the beams to act as a ceiling (there's nothing there now)will there be vapour issues (i guess so which would require a vapour barrier) or will there be a ventilation issue for the beams (which means if I add the insulation as a ceiling I'll need to add ventilation gaps thus negating the insulation).

I'd ask on a DIY forum but they're useless – I may get a response in a month or so. However a DIY forum is no good for getting information about Biking

ROFL Harris – Member
wrong forum halfwit

does it really matter???
i just look at the forum summary and don't really care if it's in bike or chat forum.

Beams and floorboards not damp.

How would a breather membrane work between floorboards and insulation if the insulation boards are foil 'enveloped' and therefore not breathable themselves?

flatfissh – it was a cheap dig at will who was taking the piss out of me on another forum

k

Fill the joist gaps with rockwool roof insulation then stick the Kingspan on the joists. Dont worry about vapour barriers if the joists are dryish.
The vapour barrier wont work very well through floorboards and carpet.

It could be worse you could have that idiot Racing Ralph comming out with some clueless comment

Does the lounge get very cold in the winter or do you mean the cellar??

The big thing is would there be much benefit with kingspan I have the same query but fortunatly no damp issues

The theory is that I'm losing heat from the lounge into the cellar as its a colder room underneath the lounge (even though heat rises – convection(?) currents are circular meaning I may lose heat).

The lounge does get cold despite every other room in the house being warm / hot and the radiator is hot as well. The cellar is cold too.

Some people have done it and noticed a difference, some haven't. The insulation is free so thought I'd give it a shot but I know that if I cut it to fit between the beams I haven't got enough, but if I fix it to the beams (as if you were over-boarding a ceiling with plaster-board) I might have enough.

Moving the radiator / fitting a bigger one may help but that will cost money.

The kingspan website shows this type of insulation installed between the joists.

You should have a damp proof membrane between any material that can transfer water and the timber joists, so if you fit it below the joists then a vapour control layer should also be installed.

I would seriously look at both heating and ventilating your cellar area to get rid of the damp problem.

Bear – That sounds like a plan. As the Celllar is a 'working space' (storage for bikes, tumble dryer) I should go for non-itch / recycled plastic bottles and then use the boards to hold it in palce?

Is the most important thing getting the insulation as close to the floorboards as possible?

Ventilating the cellar is on the worksheet – however increasing ventilation will also increase draughts underneath the floorboards thus increasing heat loss?

Therefore increase ventilation into the cellar but reduce heatloss by putting rockwool / kingspan(equivalent) up against the floor boards as close as possible to the floorboards?

How about putting the Kingspan between the joists and then fitting 12mm of Celotex TB3000 to the underside of the joists This will minimise any thermal bridging as well as acting as a vapour control layer.

I've got a limited amount of the Kingspan.

What I'll try is cutting it to the width of the floor beams and frictin fit (as close as possible) up to the floorboards. The father in law has a few more boards I can use, otherwise I'll fill in with non-itch rockwool.

Damnit, I knew the leftovers from the attic 'might' have come in useful at some point, but its already gone to the tip.