G and J Posted October 16 Share Posted October 16 In the beginning there was plan A; and plan A was marmite because plan A used PIR and thus got us a decent average wall u-value (circa 0.15W/km2) for a thin-ish wall and at a sensible cost and lo, we thought it was good - but there are those who though of PIR was the anticrust. And behold, the heathen (G&J in this case) listened and paid homage to the almighty (Jeremy) spreadsheet and asked it for guidance. At which point we realised that given how airtight we were going to be and the insulation levels in floor and attics the precise wall insulation level didn't really make that much difference, within reason. So, that means we could contemplate relaxing to a wall u value of circa 0.18. Which means we can contemplate mineral wool instead of PIR. (Plan A is: 120mm foil backed PIR in frame 25mm PIR layer VCL 20mm service void OSB, then finally plasterboard and skim.) Off to Ubakus we went to play with 140 Frametherm32 in the timber frame plus..... what exactly? We could do as plan A but with a thicker PIR layer inboard of the frame. But how about we put yet more mineral wool inboard? Something like: 140 Frametherm32 in frame VCL (is this condensation I see before me?) 50mm battens with 50mm mineral wall between, then OSB, Plasterboard and skim. Is this a good plan? Will we get a wet VCL? Will the service void be OK filled with wool? Is it better to do the 50mm battens horizontally to reduce bridging? Is there a better alternative to mineral wool for the inboard layer? (I probably should apologise for coming back to the forum for yet more help with our wall build ups, but in reality it is the cumulative affect of BH groans at my planning to use PIR that has driven this, so in a way, it's BH's own bloody fault lol) Responses and thoughts gratefully received..... Link to comment Share on other sites More sharing options...
Iceverge Posted October 16 Share Posted October 16 Good to see you following the numbers. They don't lie. Frametherm 32 is expensive though. Do the calcs on cellulose (my favourite insulant!) and mineral wool with a k value of 0.035W/mK. Much more bang for your buck. 4 hours ago, G and J said: Is this a good plan? Will we get a wet VCL? Will the service void be OK filled with wool? Is it better to do the 50mm battens horizontally to reduce bridging? Is there a better alternative to mineral wool for the inboard layer? Yes. No. Yes. Yes. No. Link to comment Share on other sites More sharing options...
stu w Posted October 16 Share Posted October 16 Don't rule out rockwool nyrock frame slab, I have used it several times now and an excellent product Link to comment Share on other sites More sharing options...
G and J Posted October 16 Author Share Posted October 16 2 hours ago, Iceverge said: Yes. No. Yes. Yes. No. OK, that's good to know, thank you. Link to comment Share on other sites More sharing options...
G and J Posted October 16 Author Share Posted October 16 2 hours ago, Iceverge said: Frametherm 32 is expensive though. Do the calcs on cellulose (my favourite insulant!) and mineral wool with a k value of 0.035W/mK. Much more bang for your buck. If I have a wall build up with Frametherm that hits u=0.18, changing to a mineral wool which has a lambda of 0.035 changes that into a wall u=0.19! Ouch. I think that's another 15mm of mineral wool to compensate. But I do like to save cash so will look into it. Link to comment Share on other sites More sharing options...
G and J Posted October 16 Author Share Posted October 16 3 hours ago, Iceverge said: Do the calcs on cellulose (my favourite insulant!) Is there an easy rule of thumb for the cost per area/volume of this and will I need more than the VCL to contain it while it sets, as if it needs another layer of OSB inboard then it will hurt. Link to comment Share on other sites More sharing options...
G and J Posted October 16 Author Share Posted October 16 42 minutes ago, stu w said: Don't rule out rockwool nyrock frame slab, I have used it several times now and an excellent product Will investigate. Ta. Link to comment Share on other sites More sharing options...
Gus Potter Posted October 16 Share Posted October 16 7 hours ago, G and J said: and at a sensible cost and lo Was this the cost of the material or did you take into account labour installation cost, buildability, wastage and how complex it would be to make air tight. Often when I design the insulation I look at these things and think.. yes the higher spec insulation may give a better U value but getting it properly installed on site properly is going to cost much more overall. For self builders there is often no point in trying to be smart. If you get too technical a lot of local builders will either not do what you want them to do.. then you have a barny or they charge a premium.. and then still not deliver the quality of workmanship required for some of the high spec insualtion. Service voids are handy, the spark will love you for that as they don't like cables buried in insulation. Start with your structural TF stud depth. Then think about who / what kind of contractors are avialable / how much you are going to do yourself. Look at the structure of your TF.. does it have loads of dense clusters of cripple studs, noggings and so on.. then think about the spacing and wastage of the insulation, air taping etc. Keep it simple and buildable then use Ubakus say to add weight to your common sense assumptions and understanding. 1 Link to comment Share on other sites More sharing options...
G and J Posted October 16 Author Share Posted October 16 51 minutes ago, stu w said: Don't rule out rockwool nyrock frame slab, I have used it several times now and an excellent product 8 minutes ago, G and J said: Will investigate. Ta. On the face of it it looks like the same lambda but only 75% of the price. - So, thank you. Link to comment Share on other sites More sharing options...
G and J Posted October 16 Author Share Posted October 16 2 minutes ago, Gus Potter said: Was this the cost of the material or did you take into account labour installation cost, buildability, wastage and how complex it would be to make air tight. Materials. The insulation and VCL and maybe the inner layer of OSB we will be doing. 3 minutes ago, Gus Potter said: Often when I design the insulation I look at these things and think.. yes the higher spec insulation may give a better U value but getting it properly installed on site properly is going to cost much more overall. For self builders there is often no point in trying to be smart. If you get too technical a lot of local builders will either not do what you want them to do.. then you have a barny or they charge a premium.. and then still not deliver the quality of workmanship required for some of the high spec insualtion. Understood - but we are prepared to invest the time (2 retired types here) so that does change things, but it is a point well made. We built in '91 in 5 months when we were both working full time and still found the time to do stuff ourselves (some including labouring, electrics, plumbing, roofing, painting) and whilst we don't want to take forever we aren't going to push it through as quickly this time as we are older and we don't have to. (We had two mortgages going at once back then - v stressful!). Link to comment Share on other sites More sharing options...
Gus Potter Posted October 16 Share Posted October 16 2 minutes ago, G and J said: but we are prepared to invest the time (2 retired types here) so that does change things It does. You have experience so play to your strengths. There is nothing like fitting the insulation yourself as you will get it right, builders are working against the clock. DIY insulation.. often delivers better quality of workmanship / air tightness which is a key requirement. You've obviously got a grasp of the basics on keeping a house warm while avoiding / mitigating condensation risks. In terms of using software... unless you really know your onions and understand the limitations of any software then trust your common sense... which it seems you have. As an SE / Designer I use a lot of different software design tools but always carry out a "sense check" as ultimately I'm responsible for what I design. Jeremy produced a great spread sheet which I've interrogated. It's a great tool to get folk enthused.. he did a great job here and a service to all. The spread sheet has it's has limitations but you can't knock Jeremy for that. At the end of the day I think it will boil down to buildability and what suits your skill set rather than the cost difference in the various types of insulation delivered to site? Remember that one day of a good trades person that you don't have to stand over can cost £200 -250 a day say. 1 Link to comment Share on other sites More sharing options...
Iceverge Posted October 16 Share Posted October 16 57 minutes ago, G and J said: Is there an easy rule of thumb for the cost per area/volume of this and will I need more than the VCL to contain it while it sets, as if it needs another layer of OSB inboard then it will hurt. @Nickfromwales might have a contact? For walls it needs to be 60kg/M3. So approx £135/m3 plus install inc VAT. 1 Link to comment Share on other sites More sharing options...
Iceverge Posted October 16 Share Posted October 16 1 hour ago, G and J said: If I have a wall build up with Frametherm that hits u=0.18, changing to a mineral wool which has a lambda of 0.035 changes that into a wall u=0.19! Ouch. I think that's another 15mm of mineral wool to compensate. But I do like to save cash so will look into it. Do the sums on heat loss for the house. believe it or not 0.01W/m²K isn't as consequential as you might imagine. Link to comment Share on other sites More sharing options...
Iceverge Posted October 16 Share Posted October 16 1 hour ago, G and J said: will I need more than the VCL to contain it while it sets, as if it needs another layer of OSB inboard then it will hurt. Nope. Normal stapled VCL is fine. Link to comment Share on other sites More sharing options...
G and J Posted October 16 Author Share Posted October 16 12 minutes ago, Iceverge said: @Nickfromwales might have a contact? For walls it needs to be 60kg/M3. So approx £135/m3 plus install inc VAT. Not sure but I think that means it’s circa £16/m2 (exc.) at 140mm which is the same as I found nyrock frame slab for, and that has no installation costs (as a little old and round bald guy will be running round fitting the nyrock for free!). I'm guessing the shredded stuff would be good for deeper frames but looks like the bats will work well for me. Next question though is what do I use for the 50mm inboard of the frame. I’m assuming rolls would be better to reduce gaps. Is there a clear market leader? Link to comment Share on other sites More sharing options...
Iceverge Posted October 16 Share Posted October 16 As the living ghost of @SteamyTea would say ....... "Beware the units, BEWARE!!!" m³ Vs m² Cellulose is about £19/m² plus install. I have a feeling an installed price from a supplier would be much the same as they buy in bulk. Don't forget the airtighess benefits it offers too. Link to comment Share on other sites More sharing options...
Nickfromwales Posted October 17 Share Posted October 17 15 hours ago, Iceverge said: @Nickfromwales might have a contact? I just recommended Gordon from Bridgend (iirc) who does a lot of MBC Timberframe’s insulation work. He blows all the cellulose stuff in. For PIR / other sheet insulation try Seconds&Co for big discounts on nearly perfect but ‘seconds’ insulation materials. Spoke to their chap at the NSBRC weekend event and they said they can also supply insulated plasterboard too. ”Save money on your insulation, buy more beer”……sign me up!!! Link to comment Share on other sites More sharing options...
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