devondumpling Posted February 10, 2023 Share Posted February 10, 2023 Hi, We had a new roof put on with a breathable membrane under the slate. We've opted for celotex insulation between joists/rafters and a second layer on top to get it up to spec. I had my suspicions and took a piece of the top layer off and sure enough none of it is either cut to friction fit not have the gaps been foam filled. I can fit my fingers in the gaps. Builders are telling me this fine.... I don't think it is. Am I right? Link to comment Share on other sites More sharing options...
Redbeard Posted February 10, 2023 Share Posted February 10, 2023 No, absolutely not fine! But depressingly common. I have had a contractor tell me the same thing, but being told it is fine does not make the insulation value any better. If the 2nd (under-side) layer is not completely tight to the first (between-rafter) layer, and the ventilation is working as it should, then you may even get thermal by-pass - cold ventilation air getting between the layers of the sandwich and effectively negating the effect of the between-rafter layer. 2 1 Link to comment Share on other sites More sharing options...
Kelvin Posted February 10, 2023 Share Posted February 10, 2023 You’re right. Builders are wrong. They either know they are wrong and fobbing you off or they don’t understand how insulation works. 1 Link to comment Share on other sites More sharing options...
TerryE Posted February 10, 2023 Share Posted February 10, 2023 5 minutes ago, devondumpling said: Builders are telling me this fine.... I don't think it is. Am I right? No it's not fine. You are right. These sorts of gaps are enough to allow air circulation within the panels and this will drop the effective U value. It would only have added a few mins per panel to use filler foam to seal the gaps. Sloppy workmanship, plain and simple. Link to comment Share on other sites More sharing options...
devondumpling Posted February 10, 2023 Author Share Posted February 10, 2023 Thank you! Blimmin knew it 😑 Link to comment Share on other sites More sharing options...
Kelvin Posted February 10, 2023 Share Posted February 10, 2023 Have you paid all of it? Link to comment Share on other sites More sharing options...
devondumpling Posted February 10, 2023 Author Share Posted February 10, 2023 (edited) Sadly the vast majority. I'm asking for some back (yeah wish me luck) but I will threaten to go all over their social media and trustatrader etc accounts with pictures if they don't cough up. Edited February 10, 2023 by devondumpling 1 Link to comment Share on other sites More sharing options...
Kelvin Posted February 10, 2023 Share Posted February 10, 2023 Is it just those bits or is it like that all over. If it’s just those bits fix it yourself without the Tetris approach and move on. Link to comment Share on other sites More sharing options...
devondumpling Posted February 10, 2023 Author Share Posted February 10, 2023 4 minutes ago, Kelvin said: Is it just those bits or is it like that all over. If it’s just those bits fix it yourself without the Tetris approach and move on. It's all over. I've asked for £1500 back to get someone else in to fix it as work is currently crazy busy. I doubt I'll get it but if you don't ask, you don't get. Link to comment Share on other sites More sharing options...
eandg Posted February 10, 2023 Share Posted February 10, 2023 If you've time it's easily DIYable. We did all our insulation ourselves for this reason - knew trades would be half-arsed and have no attention to detail. Nothing a bit of foam and some foil tape won't sort. 1 Link to comment Share on other sites More sharing options...
ToughButterCup Posted February 10, 2023 Share Posted February 10, 2023 55 minutes ago, devondumpling said: Hi, We had a new roof put on with a breathable membrane under the slate. .... Builders are telling me this fine.... I don't think it is. ... Simple way of telling ...... Frosty morning: ice on the roof. Pools of melt-water on the roof when the rest of the roof is still frozen? Not OK. Link to comment Share on other sites More sharing options...
MikeGrahamT21 Posted February 10, 2023 Share Posted February 10, 2023 Yeah seems about right for a lot of tradies, a shame when all that energy has gone into making the product. Also, your timber has signs of woodworm, has it all been treated? Link to comment Share on other sites More sharing options...
ProDave Posted February 10, 2023 Share Posted February 10, 2023 This is one reason why I am not a fan of rigid insulation, it needs to be detailed WELL. Rockwool / frametherm /batts type insulation cut slightly over sized and squashed to be a snug fit is less hard to mess up like this. Tell the builder ALL the joints want foaming and taping, ALL of them, at their expense. 2 Link to comment Share on other sites More sharing options...
SimonD Posted February 10, 2023 Share Posted February 10, 2023 7 minutes ago, ProDave said: This is one reason why I am not a fan of rigid insulation, it needs to be detailed WELL. Rockwool / frametherm /batts type insulation cut slightly over sized and squashed to be a snug fit is less hard to mess up like this. Tell the builder ALL the joints want foaming and taping, ALL of them, at their expense. Yes, absolutely. It's sadly so common to see this. I've done work at two extensions in the last couple of weeks where there are clear gaps in the insulation. It must be ignorance on the part of the trades, mustn't it? Link to comment Share on other sites More sharing options...
Iceverge Posted February 10, 2023 Share Posted February 10, 2023 If 99% of the time 99% of people cannot get it right the system is wrong. Rigid insulation between timbers is a bad idea. Every bloody time. In fact between anything, cavity walls etc. That's why we used blown bead in the walls and cellulose in the roof. @devondumpling, sorry to hear about this. What stage of the build are you at? Is it plasterboarded? maybe we can collectively come up with a good solution. Link to comment Share on other sites More sharing options...
joe90 Posted February 10, 2023 Share Posted February 10, 2023 I concur, crap workmanship, all gaps need filling with expanding foam. Link to comment Share on other sites More sharing options...
devondumpling Posted February 10, 2023 Author Share Posted February 10, 2023 11 minutes ago, Iceverge said: If 99% of the time 99% of people cannot get it right the system is wrong. Rigid insulation between timbers is a bad idea. Every bloody time. In fact between anything, cavity walls etc. That's why we used blown bead in the walls and cellulose in the roof. @devondumpling, sorry to hear about this. What stage of the build are you at? Is it plasterboarded? maybe we can collectively come up with a good solution. We've got a lot of mice where we live so that's why we opted for rigid insulation as they made nests in the rock wool and other stuff. Woodworm is old. It's not plasterboarded yet thankfully. It will be a matter of taking the top layer off and foaming everything underneath and replacing and retaping the top layer. In theory it shouldn't take too long but it's the ball ache of it and it shouldn't be like that in the first place. Link to comment Share on other sites More sharing options...
devondumpling Posted February 10, 2023 Author Share Posted February 10, 2023 56 minutes ago, eandg said: If you've time it's easily DIYable. We did all our insulation ourselves for this reason - knew trades would be half-arsed and have no attention to detail. Nothing a bit of foam and some foil tape won't sort. Yeah it's not that difficult to fix but we've either got the time or the money and never the two shall meet. Currently have neither 🙄 Link to comment Share on other sites More sharing options...
Pocster Posted February 10, 2023 Share Posted February 10, 2023 Foam fill and tape joints . Wonder what else the builders have ( or haven’t ) done ? Link to comment Share on other sites More sharing options...
Iceverge Posted February 10, 2023 Share Posted February 10, 2023 27 minutes ago, devondumpling said: We've got a lot of mice where we live so that's why we opted for rigid insulation as they made nests in the rock wool and other stuff. Unfortunately rigid insulation isn't rodent proof either. Best to keep them out altogether, or install a cat. 28 minutes ago, devondumpling said: It's not plasterboarded yet thankfully. It will be a matter of taking the top layer off and foaming everything underneath and replacing and retaping the top layer. That's good, it'll soon be a long forgotten memory. A diligent amateur would surely take up the task if offered a few ££. Just retain the cost from the builder and document all the poor workmanship to ensure they have no comeback. Don't cheap out on the foam either. Something that remains flexible and doesn't shrink. 1 Link to comment Share on other sites More sharing options...
devondumpling Posted February 10, 2023 Author Share Posted February 10, 2023 17 minutes ago, pocster said: Foam fill and tape joints . Wonder what else the builders have ( or haven’t ) done ? Thankfully haven't got them to do anything else as the rest we pretty much DIY 1 Link to comment Share on other sites More sharing options...
Pocster Posted February 10, 2023 Share Posted February 10, 2023 23 minutes ago, devondumpling said: Thankfully haven't got them to do anything else as the rest we pretty much DIY I guess that’s a blessing ! . DIY whilst maybe not the prettiest ( depending on your skill level ) is frequently done better than the alleged professionals 😁👍 1 Link to comment Share on other sites More sharing options...
Spreadsheetman Posted February 10, 2023 Share Posted February 10, 2023 (edited) 7 hours ago, ProDave said: This is one reason why I am not a fan of rigid insulation, it needs to be detailed WELL. Rockwool / frametherm /batts type insulation cut slightly over sized and squashed to be a snug fit is less hard to mess up like this. Tell the builder ALL the joints want foaming and taping, ALL of them, at their expense. Exactly. I used semi-rigid rockwool rwa45 on my recent dormer chalet downstairs ceiling insulation job as it is very easy to cut and friction fit. It also stays in place against gravity and doesn’t need netting to hold it between ceiling joists before the plasterboard goes up. Another plus was I didn’t want to add a vapour barrier in a place that didn’t have one before (there was loose glass fibre wool stuffed in there originally and I knew that wasn’t causing an issue) so I stayed with something breathable. I did add sections of rigid insulation between joists (slightly undersized and foamed in) and that took much longer to do properly. I’d not have trusted a builder to do the insulation job I did. It was a weeks work and very tedious, so the temptation to cut corners would have been massive. Edited February 10, 2023 by Spreadsheetman Link to comment Share on other sites More sharing options...
Dave Jones Posted February 11, 2023 Share Posted February 11, 2023 the builder wouldn't have costed in the time needed to tape every slab on insulation, if he had he wouldn't have used 600 centres either for the trusses as it results in massive waste of PIR. You need LOTS of http://www.gapogroup.com/ tape, get busy. Link to comment Share on other sites More sharing options...
Sparrowhawk Posted February 12, 2023 Share Posted February 12, 2023 I saw that Gapogroup tape at NSBRC, one of those "why didn't I think of that?" moments. Feels like a thin latex foam with sticky foil over it. I do wonder how many decades it will last & stay springy. Link to comment Share on other sites More sharing options...
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