Warm Roof

[IMM]

I thought the thread was about making a warm roof and blocking up loft vents.

[River Tramp]

Is there any of these similar products with a BBA Certificate?

regards

[Peter Taylor]

IMM wrote

Look, either you're being incredibly stupid or you're winding me up. In the faint hope you're basically a decent bloke who wants to understand I will keep my cool and explain one last time. I thought we had cleared this up over a year ago.

If you had read all the messages on the thread you would have understood the thread was about providing insulation underneath and in between the rafters. This does NOT create a warm roof. The word "roof" means just the timber structure, not the loft, roofspace or roof void whatever you want to call it. So a "warm roof" is where the timber structure is completely inside the insulation. Anything else is a cold roof, even if the loft is as hot as a sauna. Please try to get this in your head once and for all - a warm roof has ALL the insulation outside the timber structure.

The Building Regs do not require ventilation to warm roofs as there are no cold timber surfaces on which condensation is likely to form. But ventilation IS required to cold roofs in order to evaporate any condensation forming on cold surfaces. If the rafters have insulation fitted between them then part of their surface is cold, so the Regs require that an air gap of at least 50mm must be left above the insulation, with vents at the eaves and possibly the ridge.

Fitting insulation under the rafters creates a warm LOFT, but not a warm roof. The roof (remember - this means the structure) is still cold, as it is on the outside of the insulation. So it needs to be ventilated. If you already have eaves vents then these will do the job nicely, so why block them up?

If you still can't get your head round this you're a d*****ad. Please show me you're not, otherwise I will treat you as such from now on.

Peter

[IMM]

OK, a well insulated roof on the rafters and the vents blocks off. I personally see no point in insulating rafters when a gale is coming in at the eves bring in air at less than 0C. To me that sounds very dumb indeed. A warm loft is what many people want, whether it is termed warm roof or loft, the end result is still the same.. ...no vents at the eves and a well insulated loft (at the rafters).

The OP wanted to do it from the inside from what I gleaned, so that would preclude a "warm" roof which means ripping the roof off. read what he wrote and you will see that he didn't want vents and the loft well insulated. You have an inability not to get the big picture, immediately delving into technicalities.

[Peter Taylor]

IMM wrote

???

No, the OP wanted to know how to convert his cold roof to a warm roof. I quote: "Does anyone know how to convert a cold vented at the eves roof with tiles and sarking, to a warm roof?" That seems clear enough to me.

???

Ah well, I did try.

[RichardS]

Welcome to the wonderful world of IMM....

-- Richard Sampson

email me at richard at olifant d-ot co do-t uk

[IMM]

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

[PoP]

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.

[Andy Hall]

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

To email, substitute .nospam with .gl

[IMM]

Who would want to send one?

[IMM]

It is obvious you haven't a clue what you are on about.

[Andy Hall]

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

To email, substitute .nospam with .gl

[Hugo Nebula]

On Sat, 17 Jan 2004 11:04:04 -0000, a particular chimpanzee named "River Tramp" randomly hit the keyboard and produced:

No. Actis (who make Tri-Iso) admit that the product won't meet the standard BS hot-box test for insulation, but claim that the test is a load of cack and doesn't show the benefits of their product.

[Hugo Nebula]

On Sat, 17 Jan 2004 08:40:06 -0000, a particular chimpanzee named "Peter Taylor" randomly hit the 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).

[Peter Taylor]

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

[IMM]

Hit the roofing nail on the head though.

[IMM]

Roof vs. timber frame wall. Plywood on the outside of stud in a wall: if this was on a roof with out any sarking above (or Tyvek), if a tile fails the plywood would get wet and fail. That scenario in a wall (bricks let in water), would not cause the ply wood to fail, and it is highly unlikely the plywood would ever get wet. That is pretty obvious.

[The Natural Philosopher]

How many people are you IMM?

We know you hear voics...

[The Natural Philosopher]

Not in this NG, no. He is unique.

I have met one or two others around the net tho, that vebear a startling resemblance.

[The Natural Philosopher]

Yes, that is precisely how my timber farmed walls are done.

Plasterboar, studs/insulation, then ply facing, then breathable membrane, then battens/aigap, then mesh, then render.

There is a gap at the base behind the drip bead so any moisture that gets in can indeed get out, and presumably enough breathing via the render and said gap to keep the battening dry.