GF Suspended Floor Insulation

[padstar]

I am finishing off internally to the small extension. I have a suspended timber floor that i need to insulate. Is PIR or mineral wool the best option?

 

[^woody^]

One is about twice as efficient for a given thickness.

One may cost more per m2

They are installed differently

One has a potential greater fire risk that needs to be managed

You need to pick your criteria to decide which is best

 

[padstar]

I have 100mm of joist depth and am looking for the easiest install which I guess would be mineral wool.

I will also be routing a few cables through the void in the future so ease of removal also a consideration.

Its a small area so efficiency is more important than cost. I know PIR is more efficient but for its use will I notice the difference?

 

[^woody^]

You will notice the difference. But just as important would be sealing any gaps to stop draughts coming up

Does this need to conform to building regs? As 100mm of quilt wont conform.

Putting the cables in now would be wiser.

It seems like 80-100mm of foil backed insulation would be best

 

[padstar]

100mm PIR it is then. I have been looking at a product called Gapotape to ensure there are no gaps to the perimeter. It seems to have good reviews.

 

[^woody^]

I have been looking at a product called Gapotape

Also look at a product called duct tape. Might be cheaper.

But above all, accurately cut the insulation to fit, and if need be, cut slithers to fill gaps, to only leave a very thin joint.

 

[padstar]

Chaps I have everything cleared and ready to go. Is it best to sit the 100mm PIR towards the bottom of the joist leaving a void for pipes between the insulation and floorboards or at the top of the joists with the services below?

 

[endecotp]

You want hot pipes on the warm side of the insulation so their heat loss heats the room; for cold pipes you don’t want them to freeze but on the other hand you don’t want warm water coming out of the cold tap. Insulate the pipes separately in any case.

Regarding fitting, I’ve found it easiest to cut 5-10mm undersize and then seal in place with expanding foam. If you aim for a “perfect” fit you get gaps that are too small to get the foam gun nozzle into. I guess it depends on how straight your joists are.

Edit: have you read Kingspan’s floor insulation guide? It’s full of detail. They say the insulation should be flush against the floorboards, but they don’t say anything about pipes. See: https://www.kingspan.com/gb/en-gb/p...rds/insulation-boards/therma/thermafloor-tf70 and click on the download button for the product brochure.

 

[JP_]

Also look at a product called duct tape. Might be cheaper.

and expanding foam, to flll those inevitable gaps.

I found the nicest solution for my retrofitting was to put down 50mm insulation boards first (held in place with thin battens running under the joists) and 50mm mineral wool on top - easy to fit, cheaper, and the wool is great to ensure no drafts sneaking in. Although in bathroom I just did 100mm kingspan.

 

[padstar]

and expanding foam, to flll those inevitable gaps.

I found the nicest solution for my retrofitting was to put down 50mm insulation boards first (held in place with thin battens running under the joists) and 50mm mineral wool on top - easy to fit, cheaper, and the wool is great to ensure no drafts sneaking in. Although in bathroom I just did 100mm kingspan.

I like the sound of this. Are there any issues with running pipework within the mineral wool?

 

[JP_]

I like the sound of this. Are there any issues with running pipework within the mineral wool?

I don't see why not, but all my pipes run under the joists rather than through.