Insulating loft - Question re the last bit between roof and outside walls?

andre_xs

Dear All,
I plan to re-insulate the loft soon. As far as I know, in the last corner, where the angled roof meets the outside walls, a gap needs to be kept for the air to circulate. However, this is also the point where insulation (in our house) is sometimes missing (to leave the gap) and cold spots occur on the ceiling plasterboard in the upstairs bedroom, just lining the ceiling along the outside wall.

Thus, my question is:
How can I make sure the insulation is covering the full ceiling and part of the outside wall (to avoid the cold spots causing mould) and at the same time retain enough space to the roof so that the air can circulate?

I've read somewhere that they put in short bits of air duct. Would you screw them somewhere, or just push them against the roof by squeezing the mineral wool from below? If so, how many ducts between two joists? As many as possible (= more expensive) or just one? Or is that not a good idea?

I've also thought about using expanding foam (from a can) for the last bit /corner between roof and floor, with a temporary board put in place which makes sure there's a gap for circulation (so that the expanding foam would form a kind of wedge).

Best wishes,
Andre

MikeJXE

The roof rafters sit on a wall plate that sits on the inside wall. You need to leave an airflow between the rafters. 

Eves trays 

https://www.amazon.co.uk/Manthorpe-Continuous-Eaves-Metres-Ventilation/dp/B074DFHSBB/ref=asc_df_B074DFHSBB/?tag=googshopuk-21&linkCode=df0&hvadid=430958423258&hvpos=&hvnetw=g&hvrand=15418119480019238561&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1006482&hvtargid=pla-908215572391&psc=1&tag=&ref=&adgrpid=97419445822&hvpone=&hvptwo=&hvadid=430958423258&hvpos=&hvnetw=g&hvrand=15418119480019238561&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1006482&hvtargid=pla-908215572391

andre_xs

Ahh, perfect, I didn't know something like this existed. Although the linked above is meant to be installed before the roof is installed, I presume I can still install it now as well, and somehow stick it between or staple it to the rafters.

I guess this would be an alternative: https://www.amazon.co.uk/dp/B09N9PJHK4/

 

MikeJXE

andre_xs said:

Ahh, perfect, I didn't know something like this existed. Although the linked above is meant to be installed before the roof is installed, I presume I can still install it now as well, and somehow stick it between or staple it to the rafters.

I guess this would be an alternative: https://www.amazon.co.uk/dp/B09N9PJHK4/

 

Yes it's normally fixed by the roof tilers but a simple job to do yourself, cut it into pieces the width of the rafters and wedge it down between the rafters and the wall plate in the eves, it will hold itself up 

That is an alternative but may be more expensive for the same job

Chickereeeee

Aha, I was just looking into how to insulate the top of the inner leaf of the cavity wall, to prevent a cold bridge. Any ideas how you actually get the insulation to stay in place, in contact with the verticle wall, without gravity to help?

andre_xs

Do you mean the bit which in the picture looks a bit liked a rolled/curvy sheet?

https://m.media-amazon.com/images/I/71kDA1-dVvL._AC_SL1500_.jpg

Chickereeeee

andre_xs said:

Do you mean the bit which in the picture looks a bit liked a rolled/curvy sheet?

https://m.media-amazon.com/images/I/71kDA1-dVvL._AC_SL1500_.jpg

Yes, that is the bit I meant!