Underfloor insulation

ccluedo

theoretica said:

If you are going for a solid insulation be careful that you don't set up a microclimate with trapped moisture against your wood floor.  A relative had the wrong sort or wrong installation of insulation lead to rotting.

Tnx, I thought it would be quite simple but it's a bit of a minefield.  Maybe we will just replace the chipboard with well fitted and glued T&G edges moisture board chipboard and leave it like that. If it ain't broke.....

Jeepers_Creepers

theoretica said:

If you are going for a solid insulation be careful that you don't set up a microclimate with trapped moisture against your wood floor.  A relative had the wrong sort or wrong installation of insulation lead to rotting.

That is certainly worth considering. Perhaps safer going for loft-type insulation after all, as this will breathe - just like it does in lofts. You'll then need some way of supporting it in place. FB's is seemingly the easiest solution - drape lightweight 'chicken wire' fencing with large holes (50mm?) over the joists, pressing it firmly down each side, across, and back up the next. That'll then take the insulation, nice and squashily.

Jeepers_Creepers

grumbler said:

 AFAIK, about 8 - still dramatically.

Yes, this I agree with.  Extra 1 inch will reduce the loss 'just' by a factor of ~2 compared to the first 1 inch. Not as dramatical, but not "teeniest improvement" in terms of the heating bill.

Now a see what you mean.

You should know by now that I am prone to exaggeration. :-)

FreeBear

Jeepers_Creepers said: 50mm Celotex/Kingspan-type rigid insulation. Two reasons why this thickness; one, it's easy to cut using a snap-off bladed craft knife or similar (you don't want to be sawing it as it's dusty and 'orrible)

Use a sharp serrated kitchen knife - I use a Kitchen Devil, brilliant little knife, and gives a real clean cut without any dust.

If you have any dwarf walls supporting the joists, do pay attention to air flow. You don't want to be compromising airflow across the under side of the floor.

Oh, and when using expanding foam, use a gun rather than the cans with a flexi spout on the top. A gun will allow you to lay down a precise & controllable bead without any waste.

DRP

Agree with 50mm celotex or similar as recommended above. I used 100mm foil tape to seal all the edges between insulation boards and walls etc as a belt n braces approach. A lot of the cold feeling in the room will be down to drafts, so you really want to make sure you eliminate these. 

DRP

(I also used a kitchen devil bread knife - very handy)

OilyByker

STOP..... we have a floating floor with only 275 mm gap to the foundations and massive 10x 8 wall vents along the outside wall. Not fun when we are elevated from the road, and in direct wind.
The carpets were always cold in winter, but due to dry rot years ago all essential. 
Recently had nech technology fabric OVER floor insulation fitted between the boards and underfelt and carpet. Only 4mm thick and 200% warmer,,,,,, camy believe it. wasn't cheap but works

ccluedo

OilyByker said:

STOP..... we have a floating floor with only 275 mm gap to the foundations and massive 10x 8 wall vents along the outside wall. Not fun when we are elevated from the road, and in direct wind.
The carpets were always cold in winter, but due to dry rot years ago all essential. 
Recently had nech technology fabric OVER floor insulation fitted between the boards and underfelt and carpet. Only 4mm thick and 200% warmer,,,,,, camy believe it. wasn't cheap but works

Do you have a link to more detailed info /what you used pls?