Only real choice is over rafter insulation then. Strip roof, save tiles boards or planks, insulation counter-battens, breather felt, batten and re-tile.

Posted By: jamesingram
I know your suppose to leave a 50mm air gap for ventalation above the insulation , if you put it in between the rafters
but if you use one of the board insulations (PUR etc) and push it right up to the battons and foam/tape the edges to make it air tight ,is this not almost a warm roof
only the top of the rafter will be exposed. No doubt the answers why not, is simple , i was just wondering. I'm no expert

cheers
Jim

Jim, the reason is this: In a warm roof the structural timbers are inboard of the insulation, ie, inside the conditioned space. Any water vapour able to migrate through the insulation cannot condense in a location where it can cause damage to the structural timbers. This can happen [depending on the choice of sarking felt] where insulation is between them, and a 50mm space is not left outboard to ventilate it away. The gap is considered unnecessary where a suitable breather membrane is used, though choosing the correct membrane and detailing it correctly is key. I have always gone for the 50mm ventilated gap AND breather membrane myself.

1 other thing what is a warm roof and what is a cold roof?
Thanks
Michael

Posted By: Michael11 other thing what is a warm roof and what is a cold roof?
Thanks
Michael

Warm roof: Insulation outside the structure of an unventilated space. [Edit: at least not in the way a cold roof is ventilated]
Cold roof: Insulation somewhere within the structure. Commonly above ceilings in a ventilated loft space or between the rafters with a ventilated space directly above.

No probs, nice photo by the way - wish I owned it

Hi Tony,
I shall only take off the tiles and any timber that needs replacing which I shall do my best to use reclaimed timber. I was trying all sorts of ways to avoid taking the roof off but its the best way to do it and it will make it easier to seal it up. And now that we have decided to remove the roof I shall be able to do a better job with replacing the metalwork in the timbers that can be seen in the photo.
Thanks all for advice,
Michael.

Yes, that's the theory.

Hi Skywalker,

When cutting between rafters I deliberately leave a gap of around 10mm either side. I use a few battens at say 1m ctrs fixed horizontal to, and underneath the rafters to support the insulation. Also temporarilly wedge the insulation with timber cut wedges. Then fill the gaps in stages with expanding foam. Remove battens, trim foam, polythene barrier, plasterboard and skim. I gave up trying to cut them tight a few years ago.

Heres a picture of what I mean:

skywalker do you use the foam gun or straight out of the can
the guns much better and you can make an adjustable nozzle with a taped on silcon nozzle , cutting it down to the size you want , hammering it flat for tight holes

leave it on , once the foams gone off , unscrew the nozzle as it leave a thread created out of the foam to fit a new nozzle to.
always leave the can on til its finished , then stick a new one on , dont bother cleaning it unless your not intendingto use it for a long time

cheers Jim

Where are you using the foam? and also what type of foam is it.
Michael

Its polyurethane expanding foam , similiar to celotex/kingspan PUR boards material , it come in a aerosol can and expand to about 10x its size over 15 minutes then forms a hard crust which can be cut back , not very green at all , but great at filling gap
place to use it;
fitting windows/doors, between the walls and frame, some people dont even bother screwing them anymore as it make such a strong bond
getting a good fit for insulation board in between rafter
filling any gap under or behind skirting ,stopping draugths
filling round pipes were they enter the building
fitting door liners/ electricial back boxes
they've got one now for fixing dry lining as well , though i'm a 2 coat plaster fan myself
basically anywhere thats hard to fill or make air tight in the building structure by a more conventional method
I think its benifits out way its negative if your trying to improve the airtightness of a building

http://www.screwfix.com/prods/65927/Sealants-Adhesives/Expanding-Foams/Expanding-Foams/Dow-Window-Door-Fixer-Kit;jsessionid=F5LLQAZX1V1ROCSTHZPCFFI

OOh

The guns look good, foam cheaper too!

Top, top tips.

I will still try to be econmical with it though it is evil stuff. I guess by the end of all this I will have gained the judgement of how much to squeeze in. Although I find big differences between the own brands and the branded stuff. Branded stuff definitely more expansive and more even (smaller) bubble size.

Thanks chaps

S.