External vents - needed?

[dormermike]

Hi

I have a double bay fronted bungalow and there are vents on the outside but not the inside - no real evidence that the internal vents might have been plastered over at some point either, and the vent itself just opens into the cavity.

Circa 1939 I believe.

Are these cavity vents needed? The reason I ask is there is condensation at bottom of the wall on the inside where it meets the concrete floor. The cavity in the bays are not insulated, and the temperature at the wall/floor junction is about 10-12c with the heating on. I wondered if the constant breeze coming through the vents was keeping the inner leaf colder than necessary.

Any thoughts/ideas most welcome - thanks!!!

EDIT: The vents are at the bottom of the wall btw (on the outside), near to where the condensation is appearing internally.

 

[Static]

Could they be air bricks allowing air flow under your property?
Anyways condensation is normally caused by lack of ventilation not too much.. open a window and let the room dry out

 

[dormermike]

No its a solid concrete floor, and the vent is above the level of the floor anyway.

The dampness is underneath the DPM layer in the brickwork - the concrete floor is about 1.5-2 inches beneath the DPM.

This is all behind the skirting by the way, which is currently removed.

Initially I thought this was rising damp, but it doesn't seem to be affected by rain and indeed there seems to be little pattern to it. However I bought a IR thermometer and when the damp is worst (its a tiny spot btw) the concrete is coldest, hence my conclusion about condensation. As the airvent is behind the damp patch (or very near to it) i wondered if there is a link.

Incidentally, so i can see into the cavity i currently have some of the mortar removed - there is a good breeze coming through into the room from these openings (approx 1 inch square holes) so this part of the room is well ventilated.

The inside of the cavity is bone dry too, or at least the inside wall of the outer leaf is.

This is a long standing issue i've been trying to fix the last 18 months. The skirtings were rotten. Behind the skirtings was compressed sawdust and other material which was containing the moisture (wood block floor been sanded at some stage).

Sorry for War and Peace but its a conundrum.

Cheers