Printable Version | Subscribe | Add to Favourites
New Topic New Poll New Reply
Author: Subject: sealant for under floor insulation
smart51

posted on 10/5/16 at 10:16 AM Reply With Quote
sealant for under floor insulation

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?

View User's Profile View All Posts By User U2U Member
nick205

posted on 10/5/16 at 10:39 AM Reply With Quote
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.






View User's Profile View All Posts By User U2U Member
dinosaurjuice

posted on 10/5/16 at 11:56 AM Reply With Quote
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

View User's Profile E-Mail User View All Posts By User U2U Member
v8kid

posted on 10/5/16 at 12:09 PM Reply With Quote
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!





You'd be surprised how quickly the sales people at B&Q try and assist you after ignoring you for the past 15 minutes when you try and start a chainsaw

View User's Profile E-Mail User Visit User's Homepage View All Posts By User U2U Member
Toprivetguns

posted on 10/5/16 at 12:13 PM Reply With Quote
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.





Only drive as fast as your angel can fly... !

View User's Profile View All Posts By User U2U Member
nick205

posted on 10/5/16 at 01:02 PM Reply With Quote
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.



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.






View User's Profile View All Posts By User U2U Member
mark.s

posted on 10/5/16 at 05:41 PM Reply With Quote
Nice tight fit with the insulation and foil tape all the joints to seal it
View User's Profile View All Posts By User U2U Member
smart51

posted on 11/5/16 at 09:49 AM Reply With Quote
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 nick205
quote:
Originally posted by Toprivetguns
£3600+VAT!!!!!!! I should of been a builder.
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.

I'll do any kind of building work that you can't see when its finished. Especially for that kind of money. I suspect the price is partly because they don't want to do it and partly beacuse they haven't done it before so were putting some aside for risk.

View User's Profile View All Posts By User U2U Member
Jeano

posted on 11/5/16 at 10:39 AM Reply With Quote
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)





Location: Essex
Drives: MK Indy F20c with hairdryer

View User's Profile E-Mail User View All Posts By User U2U Member

New Topic New Poll New Reply


go to top






Website design and SEO by Studio Montage

All content © 2001-16 LocostBuilders. Reproduction prohibited
Opinions expressed in public posts are those of the author and do not necessarily represent
the views of other users or any member of the LocostBuilders team.
Running XMB 1.8 Partagium [© 2002 XMB Group] on Apache under CentOS Linux
Founded, built and operated by ChrisW.