Insulating internal cavity wall

[Tim Streater]

Our house (1930s) has what used to be an external wall, but which has become an internal one, due to various extensions done before our time.

I haven't been into the attic to have a look, but I'm assuming that the cavity is just open to the attic. We had cavity insulation done elsewhere to the house, but is then any benefit to trying to get that remaining wall done? That wall always feels quite cold in winter, particularly in windy weather. What would be a good approach - does it need the cavity wall insulation stuff pumped in from the top or would strips of celotex jammed in at the top to seal it suffice?

[Tim Watts]

On Wednesday 16 January 2013 11:23 Tim Streater wrote in uk.d-i-y:

If it's just wind blowing down it from the attic, capping off teh top should be enough.

You could stuff a small amount of crumpled newspaper down the first few inches then run some expanding foam along the top inch which would seal it tight.

[Bob Minchin]

If both sides of your wall are in rooms heated to a similar temperature, then there will be minimal heatflow and no need to insulate the cavity in full however closing off the top edge is a good idea to minimise internal air currents. I expect that the wall feels cold as it never really warms up - especially if you don't run the heating all day.

Dry lining the wall on both sides would help in this case.

[harry]

You will probably find that both leafs of the cavity wall go all the way up to the roof. It could be that cold air is circulating within. If so, it would be benificial to prevent this.

[Andrew Gabriel]

The company who did my parents' house claimed they had to fill such walls when doing the cavity insulation for various reasons which I can't recall now (one was that the fill from elsewhere could slump into that space if it wasn't filled).

[bert]

Is sealing a cavity with air trapped inside a good idea? Would it not encourage condensation? I would have though either fill it completely or not at all. The only heat loss is by convection currents caused by the small amount of heat coming through the wall.