I'm repairing blown render on my 60's bungalow, and decided to cut out and replace the three airbricks as the rendering was very shoddy around them and years of paint have reduced the hole sizes considerably. The house is 12m across the wall, the airbricks on either side are deep ones that go through to the inner skin to ventilate under the suspended floor.
However, the middle airbrick (which is one course higher than the others) is a shallower one and is only ventilating the cavity (which has very old cavity wall insulation in it)
I'm seeing conflicting advice and I'm not sure if if I need an air brick just to vent the cavity or if I can fill it in and put one or two new vents into the course below and sleeve them through to the suspended floor void.
Thanks for any advice.
I can't see any benefit from venting a wall cavity if it's fully filled with insulation, so I would go with your plan of improving the ventilation of the subfloor void. Maybe just check that the new airbricks don't provide a pathway for surface water to enter.
Is it possible there has been a rearrangement of the room layout in the house? We had a similar air brick set up to you, the third, highest, one went into a room that was originally the kitchen but now a bedroom I left the brick but covered it from the inside within the wall.
Hello,
I don’t think you would need to vent the cavity if it’s a 60s build, I would assume you have fibrous insulation, ridged PIR boards need venting. If in doubt I would add in another air brick to vent the suspended floor. Venting the suspended floor is essential and getting cross flow ventilation is ideal.
If you use clay air bricks and sleeves they will be more robust and easier to retro fit than the plastic ones.
Hope that helps. Always happy to help with more info if required.
Thanks guys.
No change to layout. Wall insulation is a blown fibre/wool type stuff that was blown in via roughly 1" core drills in the centre of the bricks, which were then filled, textured and coloured to make them practically invisible until you know to look for them!
I'm going to go with blocking the shallow central one up and create two new ones (so there are two per room). The cavity one can't be important as I think its the only one on the house. Probably a lazy install as one of the others only has a half brick opening and an aborted attempt to stitch drill through the rest of the brick.
