roof vents?

[katherine45]

Hi
Looking to insulate a pitched roof space above a ground level extension. Have to get the ceiling reboarded and skimmed so thought we should use the opportunity to insulate. Have been advised that cheapest and easiest way is for us to cut hole and put in rockwool style insulation leaving a 6" space near the very edge of the roof. Was concerned about possible condensation once roof is insulated and the builder suggested he puts a couple of roof vents in. Does this sound right? have cut small hole in ceiling for a look and it seems very draughty up there ( I can see that the roof is felted under the slate tiles). My concern is that roof vents are either unneccessary or will allow in rainwater. Any advice on this one would be much appreciated.
Thanks.

 

[catlad]

Is this a resent extension? why does it not have insulation already, and what do you intend cutting holes in?

 

[katherine45]

Hi and thanks for a quick reply.It's probably around 1950 but not sure. the slates look old and well weathered. Just cut larger hole in plasterboard ceiling (which is going to be reboarded anyway) and had a proper look. No insulation at all but a very low pitch and lots of beams. Reckon the only way to get access to insulate with rock wool will be to cut a hole at the end of each space between rafters and push it through! this seems like a nightmare job so am now wondering whether it's worth insulating at all - the ceiling is above half of a large dining room and is about 8 x 13 feet. The other half of the room has a bedroom above it.

 

[catlad]

Re board with insulated plaster board then.

 

[katherine45]

Thanks catlad. Did wonder about that but have no experience of insulated boards and it looks like there's a lot of choice out there. Didn't know whether I'd need to consider condensation or moisture membranes (is that right?). Any suggestions would be very welcome.

 

[catlad]

Have a look at the celotex web site, I think it is the PL4000 that has a built in vapour barrier.

 

[katherine45]

Will check that out. Thanks so much for your help.