Gaz1892a Posted September 13 Share Posted September 13 Good Morning, So I'm doing a big project on my house and just about to put the slab in. Ive got room to put 150mm insulation in even though only 100mm has been specified by the engineers. my question is : - a - is it worth the extra 50mm on the insulation and will it make a difference? b - what does everyone use? Jabolite or celotex or similar? Thanks in advance Also one final question - ive got 3 course of engineering up to dpc, does anyone put weep vents in for airflow in the cavity? they've not been specified but how an earth does the cavity dry out if moisture gets in? Cheers Gaz Link to comment Share on other sites More sharing options...
JohnMo Posted September 13 Share Posted September 13 More insulation the better. Go PIR for all of it at 150mm. So Celotex or similar. Tape all joints, foam all gaps, add a 25mm minimum upstand all round. Prior to screed a thin polythene membrane on top to keep the cement in the screed away from the aluminium on the insulation. 1 Link to comment Share on other sites More sharing options...
Chanmenie Posted September 13 Share Posted September 13 Get prices for 150mm 100mm and 50mm I put 200mm Celotex in mine, 2 layers of 100mm was cheaper than one layer of 200mm and far easier to cut. Cutting any PIR thicker than 100mm is a challenge so consider 2 layers, stagger all the joins and as JohnMo said tape all the joins and use expanding foam where necessary. Link to comment Share on other sites More sharing options...
G and J Posted September 13 Share Posted September 13 If one has two layers of PIR with staggered joints is taping and foaming really needed? Link to comment Share on other sites More sharing options...
JohnMo Posted September 13 Share Posted September 13 5 minutes ago, G and J said: taping and foaming really needed? Gaps make the insulation a waste of time, bit like a cup with a hole in it. You will be amazed, you have to knock the insulation in place because you have made it a tight fit, next time you look you will see gaps. Taping is belts and braces, if screed does get under the poly sheet and into a gap the whole floor insulation can lift. End result, screed under insulation. Link to comment Share on other sites More sharing options...
Super_Paulie Posted September 13 Share Posted September 13 26 minutes ago, G and J said: If one has two layers of PIR with staggered joints is taping and foaming really needed? I did. For the extra time it takes at least id know i did all that i could. Link to comment Share on other sites More sharing options...
G and J Posted September 13 Share Posted September 13 Ok, I get that taping is needed to give a second layer of protection to help stop screed infiltration. But what does foaming bring to the party? Link to comment Share on other sites More sharing options...
joe90 Posted September 13 Share Posted September 13 (edited) 4 minutes ago, G and J said: But what does foaming bring to the party? Glueing and making it tight (no air gaps). I always preferred to cut undersized and foam to fit. Edited September 13 by joe90 Link to comment Share on other sites More sharing options...
G and J Posted September 13 Share Posted September 13 18 minutes ago, joe90 said: Glueing and making it tight (no air gaps). I always preferred to cut undersized and foam to fit. Is the foam flexible enough to continue to fill the gap after shrinkage? Link to comment Share on other sites More sharing options...
saveasteading Posted September 13 Share Posted September 13 1 hour ago, JohnMo said: polythene membrane on top to keep the cement in the screed away from the aluminium on the insulation. I don't think that matters. The aluminium does nothing for insulation levels. Tiny gaps don't matter really. They are closed air pockets. Screed getting through will harm the insulation properties....and floating pir is a disaster.. hence the top poly. The question....yes add the 50mm in pir. Eps is half the benefit, perhaps more than that if on the bottom. Link to comment Share on other sites More sharing options...
saveasteading Posted September 13 Share Posted September 13 2 minutes ago, G and J said: the foam flexible enough to continue to fill the gap after shrinkage? Ii it any better than an air pocket? If the gap is 2mm or less, leave it. If 2 to 10mm, insert a sliver. If over 10mm , try harder. I would like to make the use of foam for anything forbidden unless agreed by the project manager in writing. It has its uses but is usually for bodges. Link to comment Share on other sites More sharing options...
G and J Posted September 13 Share Posted September 13 1 minute ago, saveasteading said: It has its uses but is usually for bodges Sadly I’m also saddled with that belief. I just can’t see why I would design it in. 1 Link to comment Share on other sites More sharing options...
joe90 Posted September 13 Share Posted September 13 10 minutes ago, saveasteading said: It has its uses but is usually for bodges. I disagree, I found it invaluable for filling uneven spaces and gripping surrounding materials. Yes anything can be used as a bodge. Link to comment Share on other sites More sharing options...
SteamyTea Posted September 13 Share Posted September 13 29 minutes ago, saveasteading said: It has its uses but is usually for bodges I have never measured a sheet of foam insulation across the diagonal, how accurately are they cut. Most 'foams' will shrink over time. Link to comment Share on other sites More sharing options...
Super_Paulie Posted September 13 Share Posted September 13 Illbruck FM330 foam was the game-changer for me. 1 Link to comment Share on other sites More sharing options...
saveasteading Posted September 13 Share Posted September 13 47 minutes ago, joe90 said: , I found it invaluable But you are the PM and made a considered decision I assume. I have read on here of 'professionals' deliberately cutting pir well short of rafters and foaming it in place. My gut feeling is that this is wrong, perhaps emphasised by how wrong it is to insulate whole roofs with foam. 1 hour ago, G and J said: just can’t see why I would design it in. What a good point. I can't recall ever seeing a spec that included expanding foam. Even the much lauded Illbruck, 1 Link to comment Share on other sites More sharing options...
joe90 Posted September 13 Share Posted September 13 29 minutes ago, saveasteading said: have read on here of 'professionals' deliberately cutting pir well short of rafters and foaming it in place. My gut feeling is that this is wrong, perhaps emphasised by how wrong it is to insulate whole roofs with foam. +1. 1 Link to comment Share on other sites More sharing options...
JohnMo Posted September 13 Share Posted September 13 (edited) 1 hour ago, saveasteading said: The aluminium does nothing for insulation levels. Correct, but does form hydrogen so you get small bubbles of hydrogen form. That's the only reason you do it. It also prevents the ham fisted screed operator getting screed under the insulation. Edited September 13 by JohnMo Link to comment Share on other sites More sharing options...
saveasteading Posted September 13 Share Posted September 13 1 hour ago, JohnMo said: screed under the insulation. I have seen pir float and that was with 30N concrete, not screed. This was 20 odd years ago and ufh was unheard of. Our plumber insisted on organising the pour and got it badly wrong. I happened to be there. I then realised I was quite good under stress and people will listen. Concrete blocks as weights. Sorted. There must have been concrete in the gaps still though. Moral...I always personally check the polythene cover and sealing before the pour. I can now add aluminium hydrogenating (?) to the reasons. Would bubbles of hydrogen be a problem? Link to comment Share on other sites More sharing options...
SteamyTea Posted September 13 Share Posted September 13 1 hour ago, saveasteading said: I can now add aluminium hydrogenating (?) to the reasons. Would bubbles of hydrogen be a problem? I don't think so as there is only a tiny amount of hydrogen produced. If aluminium and concrete produced lots of hydrogen, the worlds energy crisis would be over. I would think that the biggest problem is liquid water, it is not called the universal solvent for nothing. This will, in time, break down near enough all materials, with polyurethanes being one of the faster ones. I don't think this is a problem for housing though. Link to comment Share on other sites More sharing options...
JohnMo Posted September 13 Share Posted September 13 3 hours ago, SteamyTea said: aluminium and concrete produced lots of hydrogen, the worlds energy crisis would be over Except the energy required to make the concrete. Link to comment Share on other sites More sharing options...
JohnMo Posted September 13 Share Posted September 13 3 hours ago, SteamyTea said: aluminium and concrete produced lots of hydrogen Never said lots - a short read https://www.concreteconstruction.net/how-to/concrete-production-precast/how-does-contact-with-aluminum-affect-concrete_o Link to comment Share on other sites More sharing options...
mike2016 Posted September 13 Share Posted September 13 Am doing weep vents into cavity just below dpc which is 150mm min above ground level as specified. Link to comment Share on other sites More sharing options...
Dave Jones Posted September 14 Share Posted September 14 22 hours ago, joe90 said: +1. gapotape. Link to comment Share on other sites More sharing options...
G and J Posted September 14 Share Posted September 14 44 minutes ago, Dave Jones said: gapotape. Just looked that up. Is it just for the ends of PIR sheets? Link to comment Share on other sites More sharing options...
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