1940's bungalow - cavity walls

[dormermike]

Got a late 1930's or possibly early 1940's bungalow - brick with cavity walls and no insulation. The cavities are vented to the outside on the front bays beneath windows, and into the roof space as the cavity itself is open to the roof.

Would it be worthwhile sealing the top of the cavities and should I seal the vents off or leave them open?

Thanks!

 

[Ivor Windybottom]

Suspended or solid floor? If below floor vents then they need to stay.

Normal practice is to seal above-floor vents, get cavity wall insulation and leave the top open.

You'll also get some bonus loft insulation when it's blown in!

 

[dormermike]

Solid concrete floors throughout.

 

[^woody^]

Vented cavity walls are an old and outdated concept.

It would not do any harm closing the vents and sealing the cavity at the eaves as long as the cavity is relatively free of debris, and the roofspace is not getting ventilation via the cavities.

If you are to have blown CWI, then the eaves should be sealed.

If you do seal the cavity keep an eye on the roof space for condensation issues.

 

[Ivor Windybottom]

Our 1950s bungalow had CWI blown in before we bought it and has airbrick vents a course down from the soffits, just into the cavity. These have been left open, which will compromise the insulation slightly but it seems sensible to keep them open to left the loft have some air. They weren't ducted at all, it looks like the insulation has all settled to below the vents anyway.

Modern houses don't have them but they do have breathable roof membranes. Older houses have bitumen so are completely sealed other than these wall vents.

When I put new soffits in I'll fit ventilated ones. Then I'd be happy to seal the vents up.

I would expect issues if the loft is completely sealed.

 

[noseall]

I would expect issues if the loft is completely sealed.

Why do you have this propensity to refer to the loft when discussing the (wall) cavity? Did you know that some architects ask for cavities to be sealed at eaves level? Others recognise the more beneficial detail of the cavity insulation uniting with the loft insulation.

No architect recognises a vented cavity, especially one that is meant somehow to add ventilation to loft.

 

[Ivor Windybottom]

I don't understand what point you're trying to make.

Architects design new homes, which have breathable roofing membrane. Usually a vented ridge too, possibly other ventilation too. Obviously a sealed cavity is normal for a new house, standard even.

Many older houses often have vents into the top of the cavity, specifically to ventilate the loft. Probably not a good idea to cut off the air to a loft that's otherwise airtight.

I can post some photos of ours if you are having difficulty understanding.