Nic Posted June 18 Share Posted June 18 Hi building a small timber frame house in Devon. Was looking at the MBC passive spec and they like to use blown in cellulose. What are the pros and cons over say earthwool for example? Or anything else? Link to comment Share on other sites More sharing options...
SteamyTea Posted June 18 Share Posted June 18 Blown cellulose is excellent and sound deadening (because it is more dense, usually). For the same U-value wall, you will not notice and measurable thermal difference. While cellulose does have a higher heat capacity, and is more dense (usually), there is not enough mass there to dampen out major temperature swings. 1 Link to comment Share on other sites More sharing options...
Nic Posted June 18 Author Share Posted June 18 Is cellulose generally more sound deadening than earthwool as well ? Link to comment Share on other sites More sharing options...
SteamyTea Posted June 18 Share Posted June 18 24 minutes ago, Nic said: Is cellulose generally more sound deadening than earthwool as well ? Yes. Earthwool is just a mineral fibre type insulation. Most insulation works by trapping air into small pockets. It is the low thermal conductivity of air that does the work, not the material that is trapping it. Having said that, some materials have lower conductivity than others, and some can total stop air movement (closed cell foams). It is the ratio between air volume and solid material volume that sets the overall thermal conductivity. (It is more complicated than this as energy is transferred by photons being absorbed and re-radiated at different energy levels/frequencies) 1 Link to comment Share on other sites More sharing options...
saveasteading Posted June 18 Share Posted June 18 5 minutes ago, SteamyTea said: It is more complicated than this as energy is transferred by photons Go on, we can take it.... I've never liked the term earthwool, implying green credentials, when it is made using a lot of energy. Clever marketing though. to their credit, Knauf now say this... we have decided to discontinue Earthwool® from all of our branding. 1 Link to comment Share on other sites More sharing options...
Nic Posted June 18 Author Share Posted June 18 So blown cellulose recommendation for installers in the West Country please Link to comment Share on other sites More sharing options...
SteamyTea Posted June 18 Share Posted June 18 10 minutes ago, saveasteading said: Go on, we can take it. For another day I think. But in brief, if you raise a material's temperature, the electrons get further from the nucleus. Two things can happen then. The electron drops back down towards the nucleus and emits a photon, that then can cause another atom to raise up in temperature, causing the same thing to happen, but at a lower, overall temperature. This is why as you travel through the insulation from the hot side to the cold side, the temperature drops. The other thing that can happen is that the electron is hot enough to break free, this leaves an electron shell with a hole in it. That hole needs to be filled with either another free electron, or the remains of the atom combines with another atom, creating a new compound i.e. oxidisation, carbonisation, hydrogenation. At higher temperatures still, things burn, which is just the above affects happening rapidly (frequency) and violently (intensity). 1 Link to comment Share on other sites More sharing options...
IanR Posted June 18 Share Posted June 18 (edited) 3 hours ago, Nic said: building a small timber frame house in Devon. Was looking at the MBC passive spec and they like to use blown in cellulose. What are the pros and cons over say earthwool for example? Or anything else? Blown cellulose improves airtightness and doesn't require solid studs to be squeezed between - it's good at fully filling irregular shaped cavities. I'm not sure how you'd fit earthwool in a twin-stud structure, and the wider gaps between the webs of an I-Joist structure may leave earthwool lose. Blown cellulose has excellent acoustic properties, helped by fully filling the void. I know earthwool does as well but I'd expect extra care would be needed to ensure no gaps are left as any good sound deadening material will fail if there are gaps for the sound to pass directly through. MBC's twin-stud "cassettes" don't necessarily take the full benefit of blown cellulose's airtightness properties as while each cassette will have good airtightness, you've still got to seal the joints between the cassettes which is I guess why MBC still use an airtightness membrane (afaik), whereas with a stick built I-Joist structure, filled with blown cellulose you can do away with the membranes. I believe earthwool offers similar decrement delay, so both are good for a lightweight timber structure that's not combined with a masonry skin and will give a better temp phase-shift than a PIR/PUR insulation. Edited June 18 by IanR 1 1 Link to comment Share on other sites More sharing options...
Nic Posted June 18 Author Share Posted June 18 36 minutes ago, IanR said: Blown cellulose improves airtightness and doesn't require solid studs to be squeezed between - it's good at fully filling irregular shaped cavities. I'm not sure how you'd fit earthwool in a twin-stud structure, and the wider gaps between the webs of an I-Joist structure may leave earthwool lose. Blown cellulose has excellent acoustic properties, helped by fully filling the void. I know earthwool does as well but I'd expect extra care would be needed to ensure no gaps are left as any good sound deadening material will fail if there are gaps for the sound to pass directly through. MBC's twin-stud "cassettes" don't necessarily take the full benefit of blown cellulose's airtightness properties as while each cassette will have good airtightness, you've still got to seal the joints between the cassettes which is I guess why MBC still use an airtightness membrane (afaik), whereas with a stick built I-Joist structure, filled with blown cellulose you can do away with the membranes. I believe earthwool offers similar decrement delay, so both are good for a lightweight timber structure that's not combined with a masonry skin and will give a better temp phase-shift than a PIR/PUR insulation. I think blown cellulose is what I’d like to do are you says an I -joist structure is better for this . The external has to be a render ( as has to match a next door property Link to comment Share on other sites More sharing options...
IanR Posted June 18 Share Posted June 18 (edited) 1 hour ago, Nic said: I think blown cellulose is what I’d like to do are you says an I -joist structure is better for this . The external has to be a render ( as has to match a next door property Twin-stud cassettes/panels and stick built I-Joist are almost identical in their performance, I'm not suggesting one is better than the other. From what I see MBC's twin-stud does need extra membranes to perform to the same level, but if that costs you around the same then it's not a problem. When I priced up a Touchwood I-Joist structure v. an MBC Twin-stud the I-Joist was 10% cheaper, but others have here have commented the opposite, so there's really not much in it. If you were putting the frame up yourself I'd expect the I-Joist structure would be cheaper, when you look at the build-up there's just less layers and less labour. But, if you're paying for an install then it depends on margins and how much detail they put into the quote. You could argue that a twin-stud structure can achieve a fully thermal bridge free wall-to-floor joint with a simpler (and therefore hopefully cheaper) insulated raft foundation. I did take some of the "saving" in the cost of the I-Joist timber-frame and spent it on slightly more complex perimeter detail on the raft, but if I did it again I probably wouldn't do the same as it's tiny improvements that are being achieved once your at that level of performance. Cullen Timber Design do an excellent service for designing and engineering a PassivHaus-type I-Joist Structure. They can supply a full cutting list to the likes of JJones I-Joists and Assembly drawings to show you how it goes together, or I can thoroughly recommend Wilkinson Passiv Homes (previously Touchwood), as their knowledge and experience of erecting a CTD I-Joist structure will deliver sub 0.2 ACH @50Pa Edited June 18 by IanR 1 Link to comment Share on other sites More sharing options...
Iceverge Posted June 18 Share Posted June 18 Mineral wool is mega itchy. Cellulose, not so much. Link to comment Share on other sites More sharing options...
joe90 Posted June 19 Share Posted June 19 (edited) 10 hours ago, Iceverge said: Mineral wool is mega itchy. Rockwall batts I found to be non itchy not like the old loft insulation roll stuff. Edited June 19 by joe90 Link to comment Share on other sites More sharing options...
ADLIan Posted June 19 Share Posted June 19 Modern mineral wool formulation is much nicer to handle. Older types, normally yellow colour, tend to be worse Link to comment Share on other sites More sharing options...
Kelvin Posted June 19 Share Posted June 19 10 hours ago, Iceverge said: Mineral wool is mega itchy. Cellulose, not so much. The Knauf stuff I used was quite pleasant to use. No itchiness or dust. Easy to cut too. Link to comment Share on other sites More sharing options...
TerryE Posted June 19 Share Posted June 19 (edited) We've got an MBC twinwall with a blow cellulose filler. We were impressed with the choice and its implementation. I found the thermal characteristics great: a good balance of low conductivity and good specific heat which gives a very stable environment with low decrement delays through the walls. It is pretty solid with no voids. It is essentially a product made from recycled newspapers, etc. with some added fire retardants and insect repellants. I liked the idea of using a recycled product with low environmental impact. It is a plant-based rather than mineral product, so it does need additives, but this isn't a potential health issue for the occupants -- so long as your build includes a proper vapour barrier inside the fill. The fill process is a bit disgusting for those doing it. TBH I felt that our MBC crews were a little sloppy IMO when it came to things like personal HSE, and only used them when necessary rather than on a precautionary basis. However, the blowing process was notable in that they were fully kitted in masks, respirators and dust suits for this. Definitely not something to do DIY, IMO. So they have their pros and cons, with cellulose winning on eco credentials and slightly on thermal performance, but less suitable for DIY installation. Edited June 19 by TerryE Link to comment Share on other sites More sharing options...
joe90 Posted June 19 Share Posted June 19 1 hour ago, TerryE said: but less suitable for DIY installation. I found it impossible to hire the kit to DIY blown cellulose, even a customer of mine in the hire trade could not find a machine to hire. I have read that in the USA if you buy enough product they lend the machine FOC. Link to comment Share on other sites More sharing options...
IanR Posted June 19 Share Posted June 19 5 minutes ago, joe90 said: I found it impossible to hire the kit to DIY blown cellulose, There was one sold between forum members a few years back... Link to comment Share on other sites More sharing options...
Kelvin Posted June 19 Share Posted June 19 I couldn’t find anyone local to do it until the air tightness test guy turned up and he said he’d started doing it. Too late by then. Link to comment Share on other sites More sharing options...
joe90 Posted June 19 Share Posted June 19 3 minutes ago, IanR said: There was one sold between forum members a few years back... Yes I saw that but too late for my build. Link to comment Share on other sites More sharing options...
Patrick Posted Tuesday at 13:46 Share Posted Tuesday at 13:46 On 19/06/2024 at 14:59, joe90 said: Yes I saw that but too late for my build. I think the guy who bought it still has the machine and doing a few houses/barns with it. Worth digging it up and getting in touch - just to see if he fancies renting it out. all together between me, simon and the rest of the guys it was a pretty good deal Link to comment Share on other sites More sharing options...
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