farm boy Posted March 20, 2021 Share Posted March 20, 2021 I have a natural vented house with some short sloping ceilings on the first floor with 100mm pir between the rafters, then 50mm pir/ plasterboard and skim coat over the top. Is it worth me sealing the joints between the rafters and the pir with foil tape before putting the 50mm/board layer on or is this a bit over the top. Link to comment Share on other sites More sharing options...
nod Posted March 20, 2021 Share Posted March 20, 2021 It wouldn’t do any harm But not necessary Link to comment Share on other sites More sharing options...
tonyshouse Posted March 20, 2021 Share Posted March 20, 2021 I would fit a combined airtightness/vapour barrier on the warm side of the insulation, seal it to adjoining similar layers before plasterboard Link to comment Share on other sites More sharing options...
nod Posted March 20, 2021 Share Posted March 20, 2021 (edited) 1 hour ago, tonyshouse said: I would fit a combined airtightness/vapour barrier on the warm side of the insulation, seal it to adjoining similar layers before plasterboard Why? No air will get through the tape and skim and the insulation should be cut tight against the joists Edited March 20, 2021 by nod Link to comment Share on other sites More sharing options...
Thorfun Posted March 20, 2021 Share Posted March 20, 2021 2 hours ago, nod said: Why? No air will get through the tape and skim and the insulation should be cut tight against the joists I wonder if this is why self-builds generally cost more to do, not because of cutting corners by non-selfbuilders (or self-builders that are in the trade like yourself @nod) but more that a self-builder will do stuff 'just in case' it's needed. so are very much more belt and braces as they don't have the build experience to know that what you say is correct so over-engineer solutions. I know that when I do the insulation, VCL, taping, plasterboard etc I will definitely be using more material that is probably required just in case it needs it. it will cost me more but I'll know that it will definitely be enough! 1 Link to comment Share on other sites More sharing options...
ProDave Posted March 20, 2021 Share Posted March 20, 2021 2 hours ago, nod said: Why? No air will get through the tape and skim and the insulation should be cut tight against the joists Relying only on plasterboard and skim for air tightness is a very bad idea. It is a "normal" occurance for me when I unscrew a light switch or a socket I am greetid with a howling gale of icy cold air. Air tightness should be a planned well detailed layer before plasterboard and finishes go on. And don't rely on solid insulation fitted between joists or rafters being a tight fit. Experience from what I see suggests in a great many cases it is anything but well fitted. This is where a self builder can make a difference, by ensuring the detail is done properly and carefully. 3 Link to comment Share on other sites More sharing options...
Cpd Posted March 20, 2021 Share Posted March 20, 2021 2 hours ago, nod said: and the insulation should be cut tight against the joists 8 minutes ago, ProDave said: And don't rely on solid insulation fitted between joists or rafters being a tight fit. I have done a lot of rigid insulation and it’s one area I always go OTT on even if the PIR look tight I still jam the foam gun into the joint between timber and insulation and give it a squirt every inch or so along the joint.... cut back any snots and then I tape it carefully. I realise it’s a bit crazy but when it gets covered over I sleep easy knowing I did the best I could. The reason for this crazy detailing is that I live in a VERY exposed location where I have felt the wind wind blowing through less than 1mm gaps. The foaming of tight joints is totally impractical on a commercial build but I am only dealing with 3 buildings all of which I never intend to sell... and I’m just playing around at the end of the day ! 1 Link to comment Share on other sites More sharing options...
Oz07 Posted March 20, 2021 Share Posted March 20, 2021 I undercut all around and foam in with inbetween fitting. Easier and better job IMO. I use foil tape if I have to do pir over top of joists/rafters. In my layman brain it completes the foil vapour barrier. Link to comment Share on other sites More sharing options...
nod Posted March 20, 2021 Share Posted March 20, 2021 Your probably better fixing a visqueen vapor barrier to the joists Then simply board over it Link to comment Share on other sites More sharing options...
farm boy Posted March 20, 2021 Author Share Posted March 20, 2021 Thanks for the replys. The prognosis is to seal it. I think this also means that I had better tape the joints on the loft side of the foil backed plaster board on the horizontal first floor ceilings as well. Link to comment Share on other sites More sharing options...
PeterW Posted March 20, 2021 Share Posted March 20, 2021 As others have said, when you tape stuff it’s belt and braces but you also spot the detail - @Cpd is spot on that you find the gap and shove the foam gun in it. You will get to know your house much better, and you’ll slowly remove all the potential issues. Foil tape isn’t expensive - get some 100mm rolls and you’ll be soon ensuring the whole place is airtight and you’ll benefit for years to come. Link to comment Share on other sites More sharing options...
Pocster Posted March 20, 2021 Share Posted March 20, 2021 (edited) Pir and foam between joists Then pir over all of that equally with foam where required . Then foil tape every joint . That’s what I did - yet to feel a draft Edited March 20, 2021 by pocster Link to comment Share on other sites More sharing options...
Johnny Jekyll Posted May 15, 2021 Share Posted May 15, 2021 (edited) Good thread this. Can anyone recommend a good quality foil tape for taping insulation please? A link would be great thanks. I'm using full fill 100mm Cavity Therm PIR insulation. Edited May 15, 2021 by Johnny Jekyll Link to comment Share on other sites More sharing options...
farm boy Posted June 4, 2021 Author Share Posted June 4, 2021 I have been using the 100mm aluminium foil ultratape, been getting it from toolstation or ebay. I always wipe the surface with a damp methylated spirt cloth beforehand to get good adhesion. Nothing will stick to dirt or dust. 1 Link to comment Share on other sites More sharing options...
SteamyTea Posted June 5, 2021 Share Posted June 5, 2021 (edited) On 04/06/2021 at 11:46, farm boy said: Nothing will stick to dirt or dust. I have a pair of trousers that stick to them both. No idea what is special in them, maybe @pocster knows. Edited June 5, 2021 by SteamyTea 1 Link to comment Share on other sites More sharing options...
JOE187 Posted June 5, 2021 Share Posted June 5, 2021 On 15/05/2021 at 21:42, Johnny Jekyll said: Good thread this. Can anyone recommend a good quality foil tape for taping insulation please? A link would be great thanks. I'm using full fill 100mm Cavity Therm PIR insulation. This tape with the scrim seems to be very strong and stick well! https://www.ebay.co.uk/itm/302772723552?hash=item467ea91f60:g:ubMAAOSwo9VbI84~ 1 Link to comment Share on other sites More sharing options...
Johnny Jekyll Posted June 6, 2021 Share Posted June 6, 2021 Thanks very much for the replies. Much appreciated. Link to comment Share on other sites More sharing options...
Faz Posted June 6, 2021 Share Posted June 6, 2021 I am just doing it now - as said above use gun grade foam in any gaps then I am taping up with this stuff - Gocableties Aluminium Foil Adhesive Insulation Tape 50metres x 100mm (4") Silver Premium Metal Roll: Amazon.co.uk: DIY & Tools Bit of a pain getting the backer off but no biggie. 1 Link to comment Share on other sites More sharing options...
Mr Punter Posted June 6, 2021 Share Posted June 6, 2021 1 hour ago, Faz said: I am just doing it now - as said above use gun grade foam in any gaps then I am taping up with this stuff - Gocableties Aluminium Foil Adhesive Insulation Tape 50metres x 100mm (4") Silver Premium Metal Roll: Amazon.co.uk: DIY & Tools Bit of a pain getting the backer off but no biggie. Don't tear or cut through the paper and foil both at once. Leave the paper longer than the foil. 1 Link to comment Share on other sites More sharing options...
Faz Posted June 6, 2021 Share Posted June 6, 2021 It is pretty thin but worth a go. Cheers. Link to comment Share on other sites More sharing options...
TonyT Posted June 6, 2021 Share Posted June 6, 2021 Insulation installers use a belt larger than their waist and put the tape through the belt so it’s always to hand and as Mr Punter says keep the backing longer when ripping the tape off. rope or wire around the waist also works. 1 Link to comment Share on other sites More sharing options...
Johnny Jekyll Posted June 7, 2021 Share Posted June 7, 2021 Thanks again for all the replies. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now