bmj1 Posted April 22, 2023 Share Posted April 22, 2023 (edited) Our structure is fully erected. We've got 150mm deep cavities (for deeper reveals), and they are currently filled with 100mm of Rock wool 032 cavity wall insulation, and 50mm void. I'd like to increase our u value of our cavity walls... Lining on the inside would be gutting as we would lose space. Can I blow in more rockwool insulation to fill the 50mm void ? Any reasons not to do this ? Thank you in advance Edited April 22, 2023 by bmj1 Link to comment Share on other sites More sharing options...
nod Posted April 23, 2023 Share Posted April 23, 2023 Lining the interior would be better Would loosing 25 mil really make so much difference to your life Link to comment Share on other sites More sharing options...
Dave Jones Posted April 23, 2023 Share Posted April 23, 2023 100mm of rock wool slab isnt enough to pass building regs for a new build. is yours a new build ? who did the SAP calcs specifying whats needed ? Link to comment Share on other sites More sharing options...
bmj1 Posted April 23, 2023 Author Share Posted April 23, 2023 (edited) 14 minutes ago, Dave Jones said: 100mm of rock wool slab isnt enough to pass building regs for a new build. is yours a new build ? who did the SAP calcs specifying whats needed ? Yes. FYI we're under previous version of building regs as planning granted in first 2021 so not quite as tight. However, 150mm of rockwool would obviously work much better. We had a SAP consultant do the design, was originally spec'd as 100mm K108, but taking out the existing rockwool would be a mammoth task, so that's why I'm trying to think creatively here... 14 minutes ago, nod said: Lining the interior would be better Would loosing 25 mil really make so much difference to your life We're in London, so price per square foot means we'd be much better filling the cavity if at all possible. I'm not ruling out some kind of thermal lining, but this is last resort. I'll be grateful for any further thoughts. Edited April 23, 2023 by bmj1 Link to comment Share on other sites More sharing options...
JOE187 Posted April 23, 2023 Share Posted April 23, 2023 Kooltherm K108 is an advanced partial fill cavity wall insulation solution. It has a thermal conductivity of 0.019 W/mK and can achieve the same wall U-value as alternative products with a much thinner profile. Its low thermal conductivity can maximise usable internal floor space. Did the Sap consultant mean you to use this product? Link to comment Share on other sites More sharing options...
nod Posted April 23, 2023 Share Posted April 23, 2023 19 minutes ago, bmj1 said: Yes. FYI we're under previous version of building regs as planning granted in first 2021 so not quite as tight. However, 150mm of rockwool would obviously work much better. We had a SAP consultant do the design, was originally spec'd as 100mm K108, but taking out the existing rockwool would be a mammoth task, so that's why I'm trying to think creatively here... We're in London, so price per square foot means we'd be much better filling the cavity if at all possible. I'm not ruling out some kind of thermal lining, but this is last resort. I'll be grateful for any further thoughts. Your going to be lining the walls with PB anyways Using a thermal board will only add 20% to the labour Link to comment Share on other sites More sharing options...
Dave Jones Posted April 23, 2023 Share Posted April 23, 2023 34 minutes ago, bmj1 said: Yes. FYI we're under previous version of building regs as planning granted in first 2021 so not quite as tight. However, 150mm of rockwool would obviously work much better. We had a SAP consultant do the design, was originally spec'd as 100mm K108, but taking out the existing rockwool would be a mammoth task, so that's why I'm trying to think creatively here... We're in London, so price per square foot means we'd be much better filling the cavity if at all possible. I'm not ruling out some kind of thermal lining, but this is last resort. I'll be grateful for any further thoughts. why wasn't the k108 boards used ? You've got little choice now other than to overboard and lose 25mm. Link to comment Share on other sites More sharing options...
bmj1 Posted April 23, 2023 Author Share Posted April 23, 2023 56 minutes ago, nod said: Your going to be lining the walls with PB anyways Using a thermal board will only add 20% to the labour Ok. But does it add to the wall build up in terms of thickness ? Link to comment Share on other sites More sharing options...
bmj1 Posted April 23, 2023 Author Share Posted April 23, 2023 46 minutes ago, Dave Jones said: why wasn't the k108 boards used ? You've got little choice now other than to overboard and lose 25mm. Why do you rule out blowing additional insulation into the cavity ? Link to comment Share on other sites More sharing options...
Iceverge Posted April 23, 2023 Share Posted April 23, 2023 Do you have an exact spec of the rockwool product used in the wall? Link to comment Share on other sites More sharing options...
nod Posted April 23, 2023 Share Posted April 23, 2023 7 minutes ago, bmj1 said: Ok. But does it add to the wall build up in terms of thickness ? You can use a 37 mil insulated board Which would add 25 mil to each exterior wall Link to comment Share on other sites More sharing options...
bmj1 Posted April 23, 2023 Author Share Posted April 23, 2023 11 minutes ago, Iceverge said: Do you have an exact spec of the rockwool product used in the wall? I'll get it tomorrow. Which spec details would be helpful ? R value ? U value ? Link to comment Share on other sites More sharing options...
Iceverge Posted April 23, 2023 Share Posted April 23, 2023 Yeah, or the product name or a pic of the label. Link to comment Share on other sites More sharing options...
bmj1 Posted May 20, 2023 Author Share Posted May 20, 2023 On 23/04/2023 at 10:41, Iceverge said: Yeah, or the product name or a pic of the label. I believe we've got Rockwool 032 in there. I've come across this product, as an option for dry lining. What would be even more ideal would be 15mm of this PIR product, bonded onto 3mm of MGO board. Any thoughts on how I might procure such a thing ? Or ideas for alternatives ? Link to comment Share on other sites More sharing options...
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