Having and extension built roof has dormers in it. I want it well insulated. Building inspector says there must be a gap between the tri iso
10 and the plasterboard on the sloping parts of the ceiling?? ie triiso10 stapled to the rafters then a batten of inch be inch nailed over that onto which the plasterboard will be nailed....... surely the conducted heat from the back of the plasterboard will just vent into the ceiling space?!
I also said id like some rockwool (150mm) above the tri iso 10 as I'm not
100% convinced by it, she said (the buildings inspector) that if i do this it will invalidate tri iso's guarantee!
If you wanted 'well insulated', you wouldn't use Tri-Iso (or any other multi-foil insulation). It works by the liberal use of magic pixie dust.
If you're using the material as intended and as per the nearest thing that purports to be a test, you do need that cavity on either side of it. The manufacturers claim (but can't prove) that it gets its marvellous properties from the high emmissivity of the materials, in other words, by reflecting the heat off the silver foils.
You could of course save yourself the bother, expense & fuel by using polyisocyanurate (PIR) insulation instead (e.g., "Kingspan", "Celotex", "Xtratherm", etc.). You'll find that you need a slightly less thickness of that than the multi-foil with 25mm battens either side to get the same result.
If you're using TLX (AFAIK the only one so far that's gone to the bother of a legitimate test), you also need 70mm PIR between the rafters.
For multilayer foil insulation to even pretend to work (see below) it has to have a still (absolutely still) air gap on either side (is it 2" each or 1", can't remember) so you need another wind barrier on the outside which you can then ventilate.
The chuff is that these so called insulation products are worthless, to properly insulate a dormer you need kingspan, celotex et al with the edges sealed absolutely air tight with foam and tape. You could use rockwool but you'd need twice the thickness for the same level insulation.
ed. Building inspector says there must be a gap between the tri iso 10 and = the plasterboard on the sloping parts of the ceiling?? ie triiso10 stapled = to the rafters then a batten of inch be inch nailed over that onto which th= e plasterboard will be nailed....... surely the conducted heat from the bac= k of the plasterboard will just vent into the ceiling space?! I also said i= d like some rockwool (150mm) above the tri iso 10 as I'm not 100% convinced= by it, she said (the buildings inspector) that if i do this it will invali= date tri iso's guarantee! Chuff, what's going on!? Steve
Isn't the point here that foil is held against the rafters by CROSS batteni= ng so that there is not a continuous contact between the rafter and the pla= sterboard? I've only used this stuff in conjunction with 'solid insulation= between the rafters' with ventilation by permeable membrane.
Multilayer foil is useful for at least one thing. If you sew it up into a hat and place it on your BCO, you can keep the evil mind control rays inside and make then think that you've insulated something. If you have an old property, you want to improve insulation but you can't meet full modern standards without ridiculous effort (and making the room smaller), then a homeopathic lamination of Magic Pixie Foil can keep everyone happy.
Some building control departments wont accept "triiso's" figures anymore. Or that's what a head of building control told me. As the figures don't actually appear to make sense I expect its true.
To get anywhere near the quoted figure you have to have a layer of still air on both sides, that adds about 20 mm of air to the insulation. Just like double glazing can have 10 mm of still air either side if there are no draughts. This would explain the requirement for battens, I still think the insulation figures are miss-leading though. At least you can "seal" (you would still need breathers) the cavities better so have some chance of avoiding draughts that strip off the insulating layers.
It has its uses, and it has a particular resistance value, but the problem I have with the particular product in the OP is that they steadfastly stick to their claim that it gives the equivalent of 200mm of mineral fibre, when all recognised tests have failed to come close to that figure. Some other multi-foils haven't even gone that far; they've taken Tri-Iso & just copied it.
The conventional way to test insulation is what is called a "hot-box" test. In essence, heat is applied to one side of a material & the results measured on the other. Tri-Iso claim that this method doesn't replicate their products unique abilities, but haven't come up with a reproducible alternative.
TRADA's test on which they place so much stall was to compare the heat loss from a small building in the south of France insulated with their product against one insulated with 200mm mineral fibre. They reportedly used the same amount of energy to heat these two buildings. This was rebuffed in an Advertising Standards judjement against them.
Real world testing was carried out on a number of buildings insulated with this product (by a PIR insulation manufacturer as it happens), using infra-red thermography. The results were strikingly close to those that would be expected using the conventional hot-box test, and roughly equivalent to 40-50mm of conventional PIR insulation in a non-bridging layer.
TLX from a company called Web Dynamics has gone to the expense of actually having a recognised, scientifically verifiable test carried out, and market on the basis that it gives a provable resistance value. This would need additional insulation, which is shown in their installation instructions, to achieve the U-values needed for material alterations or the renovation of a thermal element.
If you can't insulate with 40mm of PIR without reducing the floor area down by 15%, then a) you're insulating a broom cupboard, and b) having multi-foil & 2 x 25mm battens ain't gonna be any better, and any BCO should recognize that.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.