Eaves ventilation on 60's re-furb?

[Watshot]

Hi,

As part of a loft conversion on my 1963 bungalow, I'm upgrading the original 40° cut pitched roof. It's a warm roof detail to allow for maximum headroom inside. The specs of that are all good, no problems, however, that system finishes at the wallplate on the inner leaf. The top layer of Celotex extends to the eaves and as a result I end up with a closed void between the inner and outer leaves (the cavity is back filled with stone, so the wall is considered to be solid in practise).

Non of this has anything to do with the new warm roof, that's just detail, but I'm wondering if the void behind the eaves would normally benefit from ventilation (through the soffit). This has nothing to do with ventilating the roof, it won't do that, just the small void above the soffit and back over the wall to the inner leaf which rises about 18" above the solid part of the wall.

I was also going to line the inner leaf with a cavity batt style fibre insulation just to help at the top of the ground floor walls. Nothing I can do about the cavity itself, as I said it's solid.

So questions are: is there any reason that I shouldn't put insulation here, and, should this void be ventilated? Obvious answer is probably to vent anyway, but I've already bought solid soffits so trying not to waste anymore cash if there's no need! Diagram attached. Many thanks.

 

[freddiemercurystwin]

Have I interpreted your drawing correctly?

Assumed

• freddiemercurystwin
• 23 Sep 2015

If so then adding some insulation where you have proposed will be fine though adding to the inside of the wall would be slightly better.

The breathable membrane normally goes underneath the counter battens.

 

[Watshot]

Hi FMT, thanks for replying.

Yes, the drawing is as you have seen it. The manufacturers state that the breathable membrane can go either above or below the c/batten, and above (as shown) works better. It means it will exit into the gutter (via some 5m eaves felt) easier. Fitted below the c/batten makes this awkward.

I can't add the insulation inside as it would mean re-doing the whole of the ground floor walls (The ceiling height is at the top of the wallplate for 'downstairs'.) May be a project for another time!

If it won't cause any problems in the void, then I'll go ahead with the insulation. Any thoughts as to whether the void should be vented or not?

Cheers.

 

[freddiemercurystwin]

I think you're over thinking it. I guess some vents would not do any harm but not necessary IMO.

 

[Watshot]

I think you're probably right! You read so much stuff on the web, trying not to go wrong, and it gets in your head!

Cheers.