Insulating Sloped Roof - Ventilation Issue

[cbyr1983]

3 bed end of terrace house.

Ceilings upstairs are sloped downwards at external walls.

The roof slopes down in these parts as well, meaning that there is only minimal space between roof and ceiling, and the space is fairly inaccessible, except perhaps that an arm could extend down into the space from above in the attic.

Has anyone tried to insulate this part of an attic. These types of houses are all over Dublin 8.

I'm afraid that I will block up the ventilation coming from the eaves if I insulate but if I don't I have significant areas of ceiling that are uninsulated, so major heat loss.

 

[cbyr1983]

Photo five at website below shows example from below. You'll need to add

daft.ie/


searchsale.daft?id=536811

 

[davidoco]

You do need to be careful not to block air circulation in the attic so stuffing fibreglass down the gap is a no no.

How long in the slope? The only real effective option is to remove the plasterboard ceiling, insert fibreglass/other insulation between rafters leaving 50mm gap to underlay of roof, then fit insulated plasterboard back to the ceiling.

edit
Viewed photo 5. That really is a small amount of sloped ceiling, therefore buy a packet of xtratherm Thin-R XT/RLOC Rafterloc Pitched Roof insulation and cut to length of slope plus another 300. You should find it easy to push that down the slope from above, use a 2 x 1 put down the slope first to keep the board down against the plasterboard. Once you have that done fire away with 300 mm fibreglass over the rest of your ceiling (the 300 extra on the rafterloc will act as a eaves vent to keep the fibreglass from blocking the air.

 

[cbyr1983]

Looked up that stuff - sounds like it will do the job nicely - thanks

What thickness rafterloc do you recommend, though I think I'll have to get up and measure the depth and width of the rafters.

 

[davidoco]

What thickness rafterloc do you recommend, though I think I'll have to get up and measure the depth and width of the rafters.

Strictly speaking you need to leave a 50 mm air gap if you have the old style felt. Rafterloc only comes in 100mm (I think) so leaving a 25mm gap so as long as you are careful and keep it down tight on the plasterboard it should be fine. It is very important that you get a snug fit as any air circulation around the board ruins the insulating properties.