Insulation between roof beams?

Rotor

I'm reroofing a garden building and want to put insulation between the beams. Beams are 4" . With modern breathable fabrics under the slates do I still have to leave 2" gap between the top of the insulation and the slates to allow condensation to dry or can I put the full 4" of insulation in, touching the fabric?

Thanks

savemoney

I wondered this too. I got a integral garage which hosts boiler, freezer, washer and storing tins etc

Roof is almost flat with EDPM felt. Its really cold in there and I do have a radiator in there.

Before big freeze I bought some cheap British gas insulation for a £1 a roll. I was planning on putting in on inside on roof and then using some plasterboard to hot it in as its cheaper than using wood

I was even planning on insulating the garage metal door for Winter only my making a wooden frame around the edge of the door then making a couple of large wooden sheets which have insulation in between and fasten it in

sorry to bump on your thread but similar situation

ams13

This is an interesting thread, as I too have a similiar situation my garden building has plastic corrugated roofing. So could i use insulation and overbard it with plasterboard. Or would I need some sort of ventilation gap.

I am also sorry to jump on your thread lets just hope someone with some knowledge posts!

tomfun

You could use 50mm Kingspan, it would be the most expensive way of doing things but it is easier to work with and would be equivalent to about 200mm fibreglass.
That would give you your 2" gap.

The ventilation gap in an garden building is not a requirement i.e building regs .
Just make sure to tape all the joints if using Kingspan.

Another way would be to use some foil backed insulation http://www.screwfix.com/prods/21112/Building/Roofing-Insulation/Airtec-Double-Insulation-1-05m-x-25m

It is very easy to install ,just staple it to your rafters

Rotor

Thanks for the reply tomfun; I had hoped to put the insulation between beams because the roof in loft is already very low and i didn't want to take a further 2" out of the headroom.
That pitch roof insulation might be a good idea - pricey though ; guess i'll have to dig deep.

Tucker

I would have thought 50mm kingspan with air gap above and possible consider a vapour barrier before any finishing layer?

Is plasterboard wise in an unheated out buidling? It's surely going absorb any moisture and eventually go moldy and smell?

Thin exterior ply or upvc cladding would seem a better finish?

ams13

Thanks for the replies.
I have already got the fibre insulation left over hence the idea. I hadn't thought about plasterboard absorbing moisture? so may have to consider a different covering and then painting. If i was to fill the gap with insulation then cover with waterproof membrane and seal the insulation so it was basically locked between to waterproof layers would that be ok. As surely no liquid could get in.
thanks

Tucker

I would imagine it will need to breath above the insulation, as you won't eliminate moisture from the air gap by sealing it, as moisture will simply get trapped in.

I would want to vent it still myself somehow.

savemoney

My garage the beams are not very deep and just enough space for roof insulation and then some boarding to hold it in place. The roof itself is rubber EPDM and has those large sheets of wood like below HERE underneath