Cavity Wall + Fixed Vent - GOT A PROBLEM

[zappastix]

Hi

On one wall in the bedroom there is a regular metal vent (that you can slide on or off with a small grip).

This vent is positioned about 8" off the ground.

The strange thing is, there are 'no outside' vents on this side of the property to provide free flowing air into this vent.

When you get down on your knees near the 'inside vent' there is a distinct musty smell.

About a year ago we had cavity wall insulation done (the cheap 'blown in' fibre type).

Not thinking at the time - this cavity insulation would block any air reaching this bedroom vent.

The bedroom where the vent is, is on an extension that is about 15 years old.

The property is a bungalow, all the floors are concrete BUT on the extension they have fitted that Green Chipboard over the concrete floor, leaving around a 3" gap between the chipboard and solid floor.

I think the floor is called 'floating'

I HAVE 3 QUESTIONS

1) Is it normal for a vent to be fitted like this - i.e. not to have an outside vent to furnish it?

2) Have you ever seen a vent fitted to a cavity wall (other than for a kitchen cooking on gas)?

3) Any thoughts on what I might be able to do, to stop this smell that might get worse, if left.

Many thanks, Stephen

 

[stem]

It does sound unusual. I would expect the vent to have a sleeve that bridges the cavity with a airbirck or vent on the external side. The sleeve stops warm air from the house condensing in the cold cavity and also prevents the vent being blocked by loose insulation.

Cavities often do smell damp as a single external brick course does let some moisture through, the original idea for the cavity was to prevent the transmission of damp from the outer skin to the inner skin. It's only later that the insulation started to be added.

If your extension was constructed 15 years ago it should have already have had cavity wall insulation installed when it was built anyway and not needed it adding with the rest of the house.

It's a longshot here, but it's not part of a disused chimney pre-extension is it? Disused chimneys need ventilation to avoid damp so they often have an airbrick inside at low level and a cowl or airbrick outside at higher level to keep a flow of air through the chimney.

I would answer your questions as follows:

1. No, unless it's a disused chimney

2. Yes, airvents are frequently installed in rooms with open chimneys where gas appliances are installed, (particularly a lounge with a gas fire & back boiler) also in older houses in bedrooms as night vents, & bathrooms before the widespread use of extractor fans.

3. Take the grille off and have a look what's behind. Maybe it just be used cosmetically to cover up a hole that was made for some other purpose. if you don't need the airvent brick it up. If you do want to keep it sleeve it and put a vent on the outside.