How to insulate a wimpy style chalet house flat roof?

[927465]

I have a house similar to the image below.

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• 927465
• 5 Jan 2009
• 2

The apex roof space and the top of the flat sections is all as one. i.e. the same air flows in both and I can put my hand between the plasterboard ceiling and flat roof top(from the loft).

I will be replacing the felt covering on the flat sections in the summer. However, I would really like some advice on insulating the flat roof. There is basically no ventilation in the roof space at all(so I need to provide ventilation as well, because it gets all damp from condensation(unsurprisingly))

I don't want to remove either the ceiling plasterboard or the wood top of the flat sections. To make matters worse currently there is 25mm glass fibre insulation stapled to the underside of the wooden flat roof along with various batons going across the top side of the plasterboard between the joists. Making it very difficult to stuff any insulating product down the gap properly.(Believe me I've tried)

I'm getting cavity wall insulation installed shortly to the house by EAGA, but they didn't have any suggestions on how to insulate the flat roof.(Apart from saying make the roof pitched). If making the flat roof section pitched and using ordinary wool insulation was the cheapest option I would go with that, but I suspect it isn't. Also I think it would look rubbish unless I could get my neighbour to do it as well. Also, things like Super Quilt or foam board are bloody expensive and will be very hard to install correctly.

Suggesting an inverted roof, isn't any help either as my cold roof construction is part of my apex roof(i.e. my loft)

So I'm looking for some inspiration.

 

[PaulJR]

If you are re-covering the flat section this summer, then fix some PUR (Celotex/Kingspan etc.) on the roofing and felt over it.

This will remove the need for ventilating the flat roof space.

Seal off the ceiling void from your loft - so that the cold air doesn't get into he ceiling.

PUR is expensive, but it's a one off job.

You may find your roof boards need replacing if your felt has been leaking , in which case you can insulate the ceiling void, with lower cost insulation.

 

[927465]

When you say seal off. Does it have to be air/vapour tight? Or would blocks of wood do the trick?

I suspect this is what I will do, however do I have any other options. At the moment I can tell there is a leak before too much damage is caused. With a Hot roof construction I won't know until it starts leaking through the ceiling and has caused(potentially lots of damage)

 

[PaulJR]

When you say seal off. Does it have to be air/vapour tight? Or would blocks of wood do the trick?

Yes, you need to stop air movement into this warm zone.

I suspect this is what I will do, however do I have any other options. At the moment I can tell there is a leak before too much damage is caused. With a Hot roof construction I won't know until it starts leaking through the ceiling and has caused(potentially lots of damage)

If you want to know about leaks quickly then use a single membrane roofing system, like Sarnafil, I am sure there are other manufacturers that aren't quite so painful on the wallet. The big problem with built up felt systems is that by the time t drips into the room, the roof deck is usually rotten. It is also close to impossible to find a leak in multi layer systems.

 

[chappers]

[ It is also close to impossible to find a leak in multi layer systems.

But they are less prone to damage and leaking