I live in the UK in a typical '1930's semi' house. It is built with two layers of good old bricks and a cavity wall inbetween them. In my hallway, there is currently no carpet or hardwood flooring - just the original timber floor, which has gaps in. I happened to notice the sun shining in through the floor recently when the sun was at a low angle in the sky. I could then tell that the 'airbrick' or vent in the brickwork outside, was allowing air directly in and under this floor. This explains why the hallway is so cold in the winter, with cold air coming directly underneath this floor. I have several more of these airbricks around the house, and I suspect they are all letting cold air directly into the house and making it like a sieve in the winter. Im trying to make the house more thermally efficient to save on gas bills etc and to make it bit more environmentally friendly. Ive done triple glazing and insulated the loft. But Ive got cold air coming directly in here so I need to do something about these vents. My question then is - can I just remove them and put a normal brick in, and get away with it? Will I end up with condensation / damp afterwards? How do you make these 1930s style houses really thermally efficient? Any tips much appreciated, thanks.


No, you cannot just block those air vents.

If you do you will cause condensation problems.

You need to investigate some cavity insulation systems - which would be more effective with your money compared to the triple glazing - think about the area of the walls and the areas of the windows. Whatever system of insulation is used, there must be some compensating air ventilation - good windows tend to have small air vents built into the top of them for exactly this.

  • Thanks Mike. Out of interest - I can obviously see why theres ventilation into that first row of bricks. But why can I see daylight directly under my floor? Is it standard to have another ventilation brick in line with the outside brick, on the inside brick wall too? I would have guessed that a vent in the outside bricks would ventilate that gap, but ventilation on the inside too? – Luke Smith May 2 '19 at 11:10
  • As most old houses had open fires, there were ventilation bricks fitted to make sure sufficient air was available. – Solar Mike May 2 '19 at 11:29
  • So perhaps I do need the external wall vent brick - but less so the internal wall vent brick, eh? the air just needs to get into the cavity - not into the house. Perhaps I could lift the floor, replace the internal vent brick and leave the external one? – Luke Smith May 2 '19 at 13:05
  • Or you could have windows with vents as I suggested... There are other options, including pipes under the floor to come up in front of the fire... – Solar Mike May 2 '19 at 13:29

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