Warm Roof

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You are in your world and we are not, so no welcome for us.
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IMM wrote:

How many people are you IMM?
We know you hear voics...

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You hear my voice in your sleep.
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wrote:

He lives in a world? You mean there are more like him?
PoP
Sending email to my published email address isn't guaranteed to reach me.
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Who would want to send one?
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PoP wrote:

Not in this NG, no. He is unique.
I have met one or two others around the net tho, that vebear a startling resemblance.

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..a great thinker.
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On Sat, 17 Jan 2004 17:33:02 -0000, "Peter Taylor"

Yes you did, Peter, and everybody else understood your explanation.
The point about the precise definition of what constitutes a warm roof is an important one and is clearly used throughout the industry. Since many of the manufacturers provide application notes on how to use their products but assume an understanding of these meanings then this becomes very important.
It would be all too easy to follow IMM's confused advice on this topic, block up all the vents and create an unventilated cold space with very serious risk to the timbers.
.andy
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It is obvious you haven't a clue what you are on about.
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So you believe that it is OK to block up vents that were designed into the structure of a building to ventilate the timbers?
Perhaps timber doesn't decay in your world....
You wouldn't be one of those silicon based life forms that they had in Star Trek once, would you? These things ate their way through rock and when one was injured, the doctor healed it using Polyfilla.

.andy
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On Fri, 16 Jan 2004 11:13:14 -0000, a particular chimpanzee named

Several loft conversion companies use it. They say it's dearer that Celotex, but you don't have to cut it to fit between the rafters which makes it quicker to install, and there's less waste.
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Hugo Nebula
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You
100mm
also
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
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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
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Celotex
the
means
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.
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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?
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Hugo Nebula
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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
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On Thu, 15 Jan 2004 22:08:44 -0000, a particular chimpanzee named
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.
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Hugo Nebula
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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
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On Sat, 17 Jan 2004 08:40:06 -0000, a particular chimpanzee named
keyboard and produced:

Last point first: my introduction message is standard on all my follow-up messages. It's meant to be humourous, alluding to the idea that one of an infinite number of monkeys randomly tapping away on an infinite number of keyboards will produce the works of Shakespeare. It wasn't aimed at you personally, and I certainly wasn't 'having a go' at anyone.
The cavity of a timber framed wall should be ventilated, and in essence the resistance to moisture and control of condensation is the same as a cold roof. A vapour control layer on the inside (underside) of the structure, with insulation between the studs (rafters), a sheathing (sarking) layer (optional) with a breathable membrane on the outside (above), the space outside (above) this is then ventilated, and finally a weatherproofing layer of brick (tiles or slates).
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Hugo Nebula
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Hugo Nebula wrote:

don't
Accepted, even though you did it again!

I totally agree

Ah, but the difference between roofs and wall panels is that in walls there is a sheet of plywood fixed on the cavity side of the studwork. The inside face of this plywood, and the surfaces of the studs on the cold side of the insulation are subject to condensation but are not ventilated. All that saves them is the vapour control layer.
My point, and I apologise for going round the houses to get to it, is that if a vapour control layer is accepted as being an alternative to ventilation in walls, why is it not acceptable in roofs? (See AD F2 1995 Page 15, Para 2.7).
It's anomalies like this (and the question of ventilation of roofs without sarking felt) that made me lose respect for the AD's a long time ago, especially when they made all those errors and had to issue an erratum document. I know you don't write them Hugo, but maybe you can explain why BCO's defend them to the letter against all logic and common sense? I'm just very thankful they are not the actual regulations.
Peter
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