I've decided to do the under floor insulation in my new house. I recon I can get the materials for about £600. £700 if I have to replace all
the skirting boards. The builders wanted £3600+VAT for the work.
I'll be using battens to support the foil faced foam insulation boards, but I want to make it airtight by putting some sealant between the foam
and the joists and noggins. What sealant should I use?
My brother in law did this in his old house and simply made the insulation board a relatively tight fit to cut out drafts rather than trying to seal the floor boards. It worked OK for him and saved time, money and effort doing the job.
I helped a friend do this 7 years ago on a house refurb. All we did was hammer lines of nails in the joists to support the insulation. Cut the
insulation so it was 10-15mm narrower than the gap, dropped it in on top of the nails and then sealed both sides with expanding foam. After the
expanding foam had set the nails wernt really doing anything. I dont know for sure if that method is the best, but it worked fine and was very quick.
House is very warm
As said the standard method is to make it a tight fit. Use a length of offsaw on top of the insulation at the edge and hammer on the offsaw when
pushing between joists to avoid breaking up the insulation edge. Usually cut 2 to 3mm or so oversize. If you mismeasure usually the joists are
slightly different spacing so it will fit elsewhere and by the time you get to the end you will have sussed out the cutting.
Its easier if you use two insulation boards and stagger the joints to avoid airgaps. As you are cutting up its worthwhile getting second quality
boards which are usually slightly off dimension which is a pain when butting large areas but irrelevant in your application.
Cheers!
quote:
Originally posted by smart51
I've decided to do the under floor insulation in my new house. I recon I can get the materials for about £600. £700 if I have to replace all the skirting boards. The builders wanted £3600+VAT for the work.
I'll be using battens to support the foil faced foam insulation boards, but I want to make it airtight by putting some sealant between the foam and the joists and noggins. What sealant should I use?
quote:
Originally posted by Toprivetguns
quote:
Originally posted by smart51
I've decided to do the under floor insulation in my new house. I recon I can get the materials for about £600. £700 if I have to replace all the skirting boards. The builders wanted £3600+VAT for the work.
I'll be using battens to support the foil faced foam insulation boards, but I want to make it airtight by putting some sealant between the foam and the joists and noggins. What sealant should I use?
£3600+VAT!!!!!!! I should of been a builder.
Nice tight fit with the insulation and foil tape all the joints to seal it
Good suggestions, thanks. I like the idea of nails rather than nailing battens to support the panels. I'll look into tape rather than using
caulk too.
quote:
Originally posted by nick205quote:I think that relies on the fact that many people don't know what to do or can be bothered to do it themselves. Being a Locoster I'd imagine "smart51" is more inclined like the rest of us to do the work himself and use the cash elsewhere.
Originally posted by Toprivetguns
£3600+VAT!!!!!!! I should of been a builder.
Tight fit between joists and rafters is how we could do it on site if we were doing roofs.
We lay it straight across the floors but obv thats with the recessed floor to suit. If you really wanted to seal joints then you can buy insulation
tape that goes between joints. we use it on some cavity walls to win extra building control brownie points.
I would just tight fit it as other have said. the tape or "bridging" wont have any thermal performance really and will just create a thin
lump over the joists.
Regards,
JM (Quantity Surveyor)