If there is plenty of soffit ventilation, I think you may just get away with it, although I suspect some BCOs might want to see ridge vents.
Shame you've got sarking, though! Without it, you could fully fill the rafters and just put in breathable membrane next time the tiles/slates need changing.
Christian.
hmm, I may have completely the wrong term for this - I can't see the underside of tiles, there's a plastic membrane underneath them (& over all the rafters) - the kind that is reinforced with an internal mesh.
There's no requirement for BCO involvement in this is there? It isn't a loft conversion, just a boarded loft. Well, at the moment, but if it does get converted that'll obviously require the whole Building Control enchilada.
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
Actually, I've just had another thought.
I'd been wondering how I would hold the insulation between the rafters. It strikes me that if I get another lot of kingspan/celotex of about 20mm thickness (if the cost doesnt prove prohibitive), then I can install that over the top of the rafters (well, on the underside - ie on the loft-space side) and that would hold the between-rafter stuff in place. As well as giving me a nice ledge near the apex that the top horizontal insulation can sit on & a nice smooth internal finish to the whole loft. Are there any vapour-condensation issues for cold roof rafters so-covered?
That'd also give me 40% extra insulation (there will only be space for 50mm of insulation between the rafters - I've just measured it).
I'm sure they won't be, but insulation products such as this damned well ought to be VAT zero rated.
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
Yes. It is this stuff (which would not be original) that prevents you fully filling. That's unless you can read the make and it happens to be a breathable membrane.
Probably not. I just mean that there might be some difference in opinion on whether soffit ventilation is sufficient for an apex roof. It may be particularly troublesome if there is a rear "extension" with a valley join, as is common on Victorian houses, as there will be no through ventilation on those sections, particularly on the rear apex section between valley and ridge.
Christian.
just had to go up and recheck that! you reminded me that there is an extension (from where I am typing at this very moment, so can't very well forget it!) but the construction of the house is such that the apex of this extension is substantially lower than the main roof apex, which also means that I am presented by a complete sloping face of the roof on that corner, with no access into the extension roof.
I'm actually beginning to look forward to doing this job now.
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
Indeed. Doing so is strongly recommended, and verging on the compulsory for new build/loft conversions. Keep the lower layer of insulation at or below the thickness up the upper layer to avoid condensation issues. I would put
50mm between and 50mm underneath. Ensure that the top layer is foil covered to give a reflective surface for radiated heat from the tiles (you'll probably find that the boards come fully foiled anyway).Note that you should cover the entire lot in 12.5mm plasterboard. This not only provides an aesthetically pleased surface, but has other benefits, such as making the space lighter and providing much needed fire protection to the insulation.
Your proposed solution is OK for condensation, provided the roof timbers are ventilated to the cold space. This is why you must leave the 50mm gap. If you had no membrane, or it was breathable, you could fully fill the cavity and assume that the timber is still ventilated through its upper surface to the tiles/slates.
Christian.
Yes, some have a valley join, whilst some have lower floors and ceilings in the "extension" to avoid the expensive roofing shenanigans required. Mine is definately the former, whilst my mum's house has the latter.
Christian.
Thanks, Christian. After reading the Kingspan K7 product pdf it seems that the 12.5mm plasterboard can be substituted by Thermawall TW56 zero ODB boards, which would solve the vapour barrier issues and fire protection requirements & provide me with that extra insulation in one go.
Loads of diagrams on that pdf, and that's just confirmed all that you've said.
Of course I haven't got around to pricing this lot up yet, so plans may well change!!
Now, if I can just convince my wife that this is hell of a lot better solution than one of those bloody silly portable air conditioners that she wants at the moment, then I'm onto a winner all round.
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
No, just invite Tony round for professional consultation....
This is one of the Celotex recipes - i.e. some insulation between the rafters and some on top.
But isn't this to create a "computer facility" for your servers?
A reasonable business expense, I think.
Now that is damned good thinking! I'll run it by my (very cautious) accountant. Just as long as it couldn't have any business-rates implications (it shouldn't have - the loft remains very much shared use, as do all other rooms in the house).
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
Although everyone talks about Kingspan and Celotex, you will often find if you look for other less well known brands (and seconds rather than A1 sheets for that matter) you can reduce the price to under a third.
At Jewson prices for Celotex, I was looking at 2 to 2.5k for the insulation for my loft conversion. A local firm did Ecotherm sheets to the same spec for 700 all in.
Yes, in fact I was only talking about Kingspan as a well-known brand - would have investigated Celotex et al and almost certainly the seconds merchants before buying the stuff.
I'll look up Ecotherm, though. Thanks.
-- Richard Sampson
email me at richard at olifant d-ot co do-t uk
BCO insisted on it on my roof, and impermeable membrane sarking.
Makes it bloody draughty up there I can tell you - way overkill IMHO.
Cut it a mill oversize, wedge or use nails, and cover the rafters and the kingpsan with aluminium tape that the kingspan supplier will sell you for this very purpose. Obnec bioarded it can't fall down anyway.
You may car3 to fill any small gapos with an acrylic style sealer as well.
It
The kingspan is foil coated.
Do it.
snip
Be sure to ask your accountant about the implications of capital-gains- tax on the (future) sale of a building that's not just only your principal (sole-use) residence! Remember that accountants tend to provide an answer to the question you ask - not to the question you should have asked. Gordon now controls both the Customs (VAT) but the Revenue (income, and Capital Gains tax (plus others too numerous to mention).
Do a search through yell.com for insulation wholesalers or simmilar.
I was able to get A1 45mm Cellotex for only £3 / sheet more than "seconds" from the well known on-line supplier and that included free delivery.
I bought enough to cover 65m Sq which was about £500 all in IIRC.
When I got mine they did not have any seconds available for 50mm sheets, but the new price was 2 quid extra. However at 14 quid a sheet it was less than half the celotex price at Jewson.
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