Insulating a sloped roof which has slates & felt

quietsailor

I've been reading all the threads on insulating roofs but I'm still unsure of the correct method of insulating a slated and felted roof. My brother is hoping to slab the ceiling of his attic to use it as living space, what I've picked up so far is,

1. There has to be a minimum of 50mm between the insulation and the felt from the eaves to pitch of the roof for ventilation purposes.

2. A vapour barrier has to be between the plasterboard and the insulation.

Q - are the two statements above correct?

Q - Can the vapour barrier be normal builders plastic or should he use some special plastic?

Q - What plasterboard should he use. Are normal 1/2" slabs sufficent or should he use a) foil backed slabs, taping the joints or b) polystyrene backed slabs (inch thick white insulation stuck to the back of the slab)

Any and all advice would be greatly appreciated as we want to make the room as warm as we can.

Supertech

Yes both statements are correct. Vapour Barrier should be 500guage with sealed laps. 12mm (1/2") plasterboard slabs are fine as long as your rafters are not more than 600mm apart.

RKQ

Refurbishment / Conversion:

Along slope of rafters:-
Friction fit foil backed high density insulation between rafters, up to 100mm if possible, depending on depth of rafters. 2 x 50mm sheets.

Maintain 50mm gap between felt & insulation.
25mm insulation to underside of rafters.

500 guage vapour barrier, stapled to rafters, lap & tap joints.
It is possible to buy an "airtight" paper / plastic, but it is more expensive.

Plasterboard slabs with skim coat or tape & fill joints.

300mm fibre glass to horizontal ceiling, should be fine.
100mm fibre glass to vertical walls, if any.(Purlin / stud walls):)

quietsailor

Supertech and RKO, thank you from the bottom of my brothers heart . I showed him the post just now and he knows exactly what to do to finish the job.

sinnerboy

don't overlook this

remember that 50mm vent space between bottom of felt and top of sloped insulation - it must be actively ventilated

you need to make sure that soffit ( flat part of roof overhang ) has at least a 25mm wide continuous strip - you will need to cut these vent strips front elevation and rear

also

you need the equivalent of a 5mm vent strip all along the ridge line
this can be achieved by inserting ventilation tiles at 2000mm c/c close to the apex

this is a pain in the swiss i know because it's high level external work - but you risk condensation rotting your roof timbers if you don't grasp this nettle

Supertech

Spot on Sinnerboy - this is often overlooked.

Nulty

Hey

See: http://www.boards.ie/vbulletin/showthread.php?t=2055433120

I'm doing this right now, actually for two weeks now, trying to get the correct information as it applies to my roof. The roofers I spoke to have overlooked what you have said and what i suspected all along. Im going to do the ridge and hip vents soon and appreciate the conforming opinions you've posted here. The last thing i want is to do all the work only to turn around and find its all wrong.

head wrecked!:mad: