Airbricks in cavity wall

29 Jun 2008
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United Kingdom
Hi I'm currently building an extension on the side of my house. The ground floor is a garage with a bedroom above.

My question is this.
The existing external house wall has 4 airbricks inserted in it directly below the DPC across its length.
I want the garage floor level to be above the level that these airbricks are which would mean either running channels through the floor and putting new airbricks in the new side wall. or covering them up.

I have been looking into the purpose of these airbricks and do not understand why they are there.
All our internal floors are solid concrete built off the ground and our cavities are filled with insulation.
I have had a look into one of the airbricks and as far as i can see they are channeled through the cavity but then close at the inner wall.

Is there a purpose to these airbricks and would it cause a problem if they were covered over.

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was there ever a baxi solid fuel fire within the house at any time?

the garage floor is required to be at least 100mm below the habitable floor. it is common to fit them 150mm below, bringing them more in-line with the external ground/paving height.

so, by laying the garage floor at the 'correct' height, leaves these air bricks unmolested, no?
Doesn't the garage floor level need to be 100mm below habital floor level only if you have internal access to the garage to prevent spills/fumes passing through the threshold.

I won't have internal access to the garage so can't my floor level be higher. The problem I've got is the garage access at the front is quite a bit higher than the floor would be if I had to lay it below the airbrick. This would mean having to landscape my drive which I would like to avoid if possible.

And no, there has never been any solid fuel fire in the house. Its only ten years old and has only ever had a gas fire and gas boiler.
Doesn't the garage floor level need to be 100mm below habital floor level only if you have internal access to the garage to prevent spills/fumes passing through the threshold.

quite so.

so what you are saying is the ground around the front of your house is 150mm too high?
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O.k Had another look at it and i guess I can keep my garage floor level just below the airbricks. I guess I was being greedy and trying to get an even transistion between garage floor and drive. I'll have to make do with a small step / incline.

But..... Another query if I may be so bold.

If I settle for the garage floor level to be below the airbrick (which is in the course directly below the DPC) How do I get the DPM from the garage floor to overlap the internal wall DPC without it being left exposed. As I see it there would be a one course strip round the edge of the garage floor. Also would I have to chase the DPM into the existing wall DPC (and therefore covering the airbrick!).

Is it viable to have the DPC on the inner leaf lower than the outer leaf to accomodate this or am I missing something obvious.

Please excuse my ignorance in this matter...

i garages we don't bother lapping to existing, for the exact reasons you have highlighted.

it would be visible, ugly and end up getting damaged anyhow. we do fit the dpm then trim it to floor finish level, after the floor has hardened.
Thanks for your help in this. I can now at least see in my head what needs doing and in what order.

Again many thanks
Just to update anyone reading through this thread. :idea:

The Building Regs guidance (Approved Document B, Vol 1) actually made a change in respect of the required floor levels arrangement, referred to above, as of April 07.

It is now acceptable to simply lay the garage floor with a fall to the outside, from the location of any door into the house. A 100mm step is still the alternative to that if you want a level floor.
There is no specification for the amount of fall required, save that fuel spills should drain to the outside.....
See page 34 of this pdf (or page 32 of the original document) -
just wanted to say is it possible that your house floor is beams and blocks with a screed on top if it is building control might not be very happy with you leaving the air bricks exposed because of carbon monoxide getting into the house sounds silly but i ve come across this afew times with building control.
yes, he has been out today to look at it and sure enough the airbricks do go down a telescopic into a void so must be beam and block.
He has said he wants the existing airbricks to be channeled under the new floor and through the new external wall to vent in fresh air and not the garage for the reasons you stated.

As a result i've had to have a total rethink on my levels.

strange this as our local council some years ago had to put in cavity wall insulation upon completion they sealed up every vent into the house then rebored one as all the houses where on solid fuel heating , i bought one of the houses but noticed in the corner of the hall way under the stairs there was always a smell of damp . on the outside wall was a single air vent i drilled out the cement from some years ago on this and another close by vent , within a few weeks the damp smell had subsided plus the wall felt warmer and drier

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