Warm Roof

Does anyone know how to convert a cold vented at the eves roof with tiles and sarking, to a warm roof? Is sealing up the air vents, installing insulation and putting a layer or two of vapour barrier enough? A vapour barrier under plasterboard should prevent any warm moist air getting to the sarking.

thx

Reply to
timegoesby
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The first thing is that you don't want to seal the vents at the eaves. You will still need the airflow past the rafters to avoid rot. Assuming 100mm rafters, I'd use 50mm Celtoex between them, with another 50mm of Celotex fixed to the rafters, and with joints sealed. Then plasterboard. I'd also include ridge vents at the apex of the roof.

Cheers Clive

Reply to
Clive Summerfield

But that's not a warm roof. Warm roofs have all the insulation above the rafters, and ventilation and vapour barriers are unnecessary. That means stripping and relaying the tiles and battens.

Reply to
Peter Taylor

On this subject, has anybody used "Framefoil" which is sold by Sheffield Insulations. It is a series of thin silver foils and felt (11 layers I believe) which is fixed (stapled?) to the underside of rafters, before then fixing the plasterboard. This eliminates the cutting of the Celotex/Kingspan to fit between the rafters, and then huge amount of waste; ever noticed the amount of Celotex in the skip outside a loft conversion? It's still a cold roof, but I'm surprised it's not used more often.

IanC

Reply to
River Tramp

On 15 Jan 2004 09:39:56 -0800, a particular chimpanzee named snipped-for-privacy@my-deja.com (timegoesby) randomly hit the keyboard and produced:

This is virtually the worst thing you can do for the roof. What you suggest is not a warm roof, it's a cold roof with inadequate ventilation. A warm roof is one with the insulation (or the majority of it) above the rafters to maintain them at a temperature above dew-point, and the only way you can do this is to strip the tiles and felt.

A vapour barrier can _reduce_ the amount of moisture getting to the structure, but it will not eliminate it entirely. You don't say whether your existing roof is a pitched roof, and whether the insulation is currently laid between horizontal ceiling joists, but if so, insulation between the rafters will need to be quite thick to give anything like the U-value you can get from a reasonable thickness of Rockwool.

The question is, why would you want to do this?

Reply to
Hugo Nebula

On Thu, 15 Jan 2004 19:13:49 -0000, a particular chimpanzee named "River Tramp" randomly hit the keyboard and produced:

It sounds very similar to Tri-Iso Super 9.

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It has been accepted in my area on loft conversions, despite not having a BBA certificate (nor any european equivalent). It has a (questionable) test certificate from TRADA as having the equivalent U-value to 200mm Rockwool.

Reply to
Hugo Nebula

Argh, you're right. Always get that one wrong. Would a warm roof therefore be something like the following:

Tiles Tile battens Sarking Insulation Supporting boarding? Rafters

Cheers Clive

Reply to
Clive Summerfield

This Framefoil also does not have a BBA certificate, I believe it's Finnish or Norwegian, but as you say, its been accepted as achieving the 0.3 loft conversion standard, and (I suppose sheeplike) I've also been accepting it.

RT

Reply to
River Tramp

Clive Summerfield wrote

That's about it Clive. Usually the insulation is a rigid board, so there's no need for supporting boarding. It's also usual to fix vertical battens over the insulation on the line of the rafters, then the breather membrane, followed by the horizontal battens and tiling. This creates a gap under the horizontal battens to allow the membrane to sag, which is necessary for proper drainage.

Remember, a "warm roof" is where the whole of the timber structure and any decking is on the warm side of the insulation. The idea started with flat roofs, where the insulation board is always above the decking, either between a vapour barrier and the roofing membrane or, as in the "upside down roof", where the insulation is exposed above the roofing membrane and ballasted down with stones. In either case there is no likelihood of condensation forming on the roof timbers or the decking, so there is no need for ventilation. But a vapour barrier IS required on the warm side of the insulation in the first example in order to stop condensation forming under the roofing membrane - this is the prime reason for flat roof failure. Usually the insulation is well wrapped up between the layers of felt and/or asphalt.

Peter

Reply to
Peter Taylor

Hugo Nebula

Whilst I mostly agree with you Hugo, the OP's suggestion is not all that different (and maybe marginally better) to wall panels in timber frame construction, where the insulation is packed between the studs and the only ventilation is in the cavity, on the outside of the plywood. Is there a double standard here?

Peter

Reply to
Peter Taylor

I looked at the web site. Is there any independent tests on this stuff? Is it cheaper than Kingspan? The left hand picture is the normal roof arrangement. It looks easy to fit by pining to the rafters, batons and then plasterboard. It doesn't mention if the eves vents should still be there. If this stuff works then this is the way to go for loft conversions.

Reply to
IMM

The sarking would have to be Tyvek in this case, which doesn't allows water in on the top side and allows vapour out through the other.

Reply to
IMM

In article , River Tramp writes

I was going to say smoke & mirrors, quite appropriate really as all the foil based insulations seem to work by reducing radiated losses and need a significant airgap (without air movement) to achieve their 'results'. So fine if you can create an even, sealed airgap _and_ the foil retains it's mirror like finish over the years.

Reply to
fred

When first I came across it in a loft conversion, I couldn't find out much about it, so via Sheffield Insulations spoke to their supplier (the details are at work) and they informed me of the either Finnish or Norwegian tests it had undergone. I should have followed this up, but didn't have time - will have to get one of our trainees on the case. If I get an answer I'll post it here.

The guys who are using it seem to think everybody will be using it soon, because of the ease of fixing, no cutting and no waste, but I don't know about comparitive costs with Kingspan or Celotex.

RT

Reply to
River Tramp

IMM wrote

The eaves vents are still required for the under-rafter application as this is a cold roof. (The Building Regs don't take vapour barriers into account, so the timbers are likely to collect condensation in their eyes). The over-rafter application is a warm roof and does not require vents, although there will still be a risk of condensation on the tiles and battens!!

What always worries me a lot about the foam insulants is their behaviour in fire - they must give off tons of toxic smoke, or am I wrong? I imagine this foil/foam combination only 25mm thick has got to be better in this respect. I am certainly very interested in finding out more about it.

Peter

Reply to
Peter Taylor

On Thu, 15 Jan 2004 22:08:44 -0000, a particular chimpanzee named "Peter Taylor" randomly hit the keyboard and produced:

The OP mentioned nothing about a breather membrane above the insulation, so I assumed it was a bitumen felt. A timber frame would incorporate a breather membrane (or building paper) on the cold side of the insulation.

Reply to
Hugo Nebula

It has been around for at least 5 years, in differing forms.

Reply to
IMM

So if you cut away the sarking from inside with a Stanley knife, exposing the timbers to the outside air, staple this Actis stuff on, battens, plasterboard with vapour barrier behind (I assume the Actis stuff is also a vapour barrier) and block up the vents, then that should do it.

Reply to
IMM

Hugo Nebula wrote

Ah, that's OK then. Because Regulation F2 only refers to roofs it's perfectly acceptable to have unventilated cold surfaces in timber walls. And please don't call me a chimpanzee!

Peter

Reply to
Peter Taylor

IMM wrote

Technically yes, as long as there is adequate air passage through the tiling, but try telling that to a BCO who doesn't have any guidance on unfelted tiling to refer to in his bible. But what's the point of doing this? You could just leave the felt and the vents as they are.

Reply to
Peter Taylor

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