Calling for builders advice - air bricks

matty_hunt

Hi. Im looking for some advice please. Im having damp issues in a flat and it was suggested that the air bricks may be incorrectly set up. Ive (hopefully) attached a picture of the current arrangement. 9" air brick on external wall feeds into the cavity. Behind that a hole is knocked into the internal wall to allow air to the sub floor space. Holes have been drilled in the skirting board, through the wall into the cavity for air to feed the room. Is this right, wrong, needs changing, makes any difference?

https://flic.kr/p/pmHK3U

Building is a converted 1890s house, into flats.
Any thoughts much appreciated.
Thanks.

Doozergirl

An 1890s house wouldn't usually have a cavity. It could have an early type. They did at some point use perhaps one or two cavity air bricks.

Air bricks should ventilate the sub floor area and stop the joists from rotting in a damp atmosphere so they should go through to the area under the joists. It sounds like someone has bodged one for you as the building is perhaps lacking, particularly if it is an early type cavity. There should be plenty of these to back front and side of property wherever possible, creating a through draft.

The holes in the skirting are not accepted practice to serve a genuine purpose.

What are the symptoms of damp that you're experiencing? That's what will provide the diagnosis.

DRP

I'm not a builder but have been doing a lot of research for my (c1901) house and have recently had additional airbricks fitted. YOur diagram looks a little weird:

Are you sure there's a cavity? unusual for a property that age. Also, if there is a cavity there should be a conduit through to the inner wall and into the room i.e. so the airbrick would not be venting the cavity

The airbricks are installed to vent the underfloor and the room above is in theory separate, so i'm not sure why the skirting is involved? Ideally the airbrick would be located below the joists

matty_hunt

Thanks for the replies. There is definately a cavity. Could be I got the age older than it is though. Basically I have mould on the inside of all external walls, mainly from floor level up, and all the way up in the corners. Lifestyle causes have been addressed, Ive taken one air brick out, (there is a couple for every room). The cavity had lots of rubble and sand in it which I cleared out and is how I know there is a cavity and that the air bricks vent straight into it. At some point a previous owner has drilled holes into the skirting and screwed a vent over them to provide air flow into the room. In one external corner I see the joists and parts of floor boards have been replaced so clearly an issue for some time.

Doozergirl

So, you need lots of proper airflow under the floorboards, definitely, a system of airbricks, not just one.

Is there a chimney breast in the room? Used? Double glazing? Does that have trickle vents?

matty_hunt

Doozergirl wrote: »

So, you need lots of proper airflow under the floorboards, definitely, a system of airbricks, not just one.

Is there a chimney breast in the room? Used? Double glazing? Does that have trickle vents?

Thanks. There is a sealed chimney in a bedroom, with a vent in it. Also its the room with the worst mould but might be expected being a bedroom. There is double glazing but some pains are misted. No trickle vents but when I looked into retro fitting some I was told by guys who sell cleaners and anti-mould paint chemicals not to bother as they dont really do anything.

Southend1

Are you sure you're not confusing a brick structure on which the joists are sitting with the internal wall of a cavity wall construction?

matty_hunt

Southend1 wrote: »

Are you sure you're not confusing a brick structure on which the joists are sitting with the internal wall of a cavity wall construction?

Hi. The drawing I provided is accurate. I had the floor up today to double check and that is exactly the set-up.
Cheers

Southend1

matty_hunt wrote: »

Hi. The drawing I provided is accurate. I had the floor up today to double check and that is exactly the set-up.
Cheers

Are you sure that the internal "wall" extends above floor height though?

Doozergirl

As well as sub floor ventilation, open the fireplace back up. Either as a working one (which would be the nicest option and keep you warm) or by putting a period fireplace in for show. You'll be able to buy one on ebay or gumtree. The chimney will provide important airflow, much better than a wall vent and infinitely more attractive than holes in the skirting?!

The seals have gone on your DG units. It isn't part of this problem but they are very easy to replace in uPVC and cheap. Trickle vents are useful on helping airflow without you freezing. In a house with condensation, they will certainly do more good than harm.

We cannot seal up Victorian houses, which are an intrinsic part of the design, and expect the house to cope. We had a mould problem years ago in a ground floor Victorian flat. We opened up the fireplace and the problem literally disappeared. It was the right ventilation and had been on our list anyway!

matty_hunt

Thanks for all the previous replies and apologies for delay in the follow up. I have finally taken an air brick out of the wall and taken some photos (not totally sure how to do this so hope this works...there are 4 photos in same album as link in first post) https://flic.kr/p/pziDcq
Thanks