cavity insulation

[dormermike]

Hi

This is how my cavity looks, am assuming its insulating properties not too effective like that and it shouldn't be open? I am planning closing the top off with rockwool would that be ok, or likely to cause problems?

Untitled

• dormermike
• 17 Nov 2013
• 1

Also as its only 25mm board but the gap is much larger, is it feasible to stick another 25mm board down? It is doable in places, just wondering if it worth it.

Thanks

Edit: inner leaf is nearest (bottom of frame) and that's a screengrab from a movie, apologies for poor quality

 

[Burnerman]

Personally I'd leave that one.....the whole purpose of a cavity being that any water ingress shouldn't pass from the outer leaf to the inner leaf.
If the cavity is bridged then water could theoretically pass over.....so if the cavity is filled, its a good idea to keep the outer wall in good order.
John

 

[tony1851]

Is the polystyrene board firmly fixed to the inner skin? If not, it won't be effective.
Polystyrene is not normally used as partial cavity fill anyway - it's nowhere near as good as the PIR/PUR boards.
And no, don't try to pack more in unless you want damp patches.

 

[dormermike]

No, its not firmly fixed against inner skin, there is a 10-30mm gap between the inner leaf brickwork and the insulation board. The board itself doesn't move its just not tight against the inner skin. The heat presumbly, escaping through that gap. I was going to lay insulation across the top of the cavity primarily - is that a bad idea? Surely the cavity should be closed anyway? Cavity is 75mm wide.

Appreciate stuffing more down into the cavity probably not a great idea.

 

[tony1851]

If it's not firmly against the inner skin, then it's useless as the warm air on the cavity-side of the inner skin will just rise up.
Jut try and block the top of the cavity with some glass wool.