Low airbricks advice

[kalmap]

Hi,

Our survey flagged up some low airbricks that vent suspended floors and I didn't really think about it at purchase time. There are airbricks at sensible heights under the DPC on all sides of the (1960s) property except one.

That side has 2 airbricks (rubbish pic attached) basically at ground level right under DPC, adjacent to block paved driveway. There is no visible drainage here, other than a very slight slope, towards a bigger slope taking water away. There is maybe a 1.5cm gap between the wall and the paving, which looks to have sand/soil in it. This is also the gable end, so roof water doesn't hit here at least.

I have no visible signs of damp and the survey flagged nothing of concern. I'm really wondering if I should take any action to address these? As far as I can tell they've been in place for decades, so part of me thinks if it was a problem then damp would have manifested?

I can't look under the suspended floors, as they are all tiled. One thing i might do is scrape a few cm's of the sand out the gap just so it can't immediately flow into the brick if it builds up?

Does anyone think it's worth the cost of doing something with or can I just ignore and keep the vents clean and get on with life?

Depends how much effort you want to put in, we have a 1920s property and most of the air bricks were either blocked or as yours are, and the floor plates were rotten in many places, because they used to use slate as a damp proof course which is more damp resistant than damp proof when bedded in lime mortar. So they were relying heavily on the air flow to keep them dry.
In your case it will be something slightly more modern, but without looking you won't know the state. If something does go wrong you'll have to take up the tiles anyway, so maybe the best solution is to leave it until you're doing some other work, then get it sorted then. We did a lot of repairs when insulation the floors and during the extension.

Difficult to tell exactly what's going on from the photo. In a standard cavity wall, the dpc (usually a visible black line in the mortar) is normally a min of 2 brick courses above ground level to stop water rising up the external brickwork. Air bricks are underneath the dpc so 1 brick above the ground. Looks like the paving on your house has raised the ground level. If the air bricks are not actually blocked they will still be venting the space under the floor. Also good that the ground slopes away from the house. As long as the dpc is above the air brick, it will probably be fine. The only thing you could do to improve the situation is to remove a strip of paving from next to the house, dig a small trench then fill with gravel to a brick course below the airbrick.

the aitbricks aren't low, the paving is too high. No doubt some idiot has put a layer of paving (maybe more) on whatever was already there, raising the level. Such idiots are very common.

In your pic it looks as if the idiot has blocked the airbrick wil silicone sealant or something.

You will certainly get rainsplash, but maybe you are lucky and the new paving is sloped so that water runs away from the house. Otherwise the wall will become damp. As a start you could have the blocks beside the airbrick taken up to fully expose it so that air can flow. Dig the pit lower than the airbrick and put pebbles at the bottom so that any water can drain away without flowing into the void.

As Tattypoo says, if necessary you will have to excavate a french drain beside the house wall to preven it getting damp.

If anybody suggests a chemical injection...

Don't.

Ok thanks, I think I will do as you say and remove the row of horizontal pavings and maybe put them the other way around to create space for a gravel bit there. The bricks just have a wire mesh on the front of them, I dont think they are blocked otherwise.

One other question - and I don't understand how this is possible but one of the airbricks looks to be full of cavity insulation balls, behind the wire mesh on the front of it. Any idea how that happens? Surely it should be venting through the cavity into the floor space. I guess there's no point in me even trying to clean that out?

measure to see if it is above floor level. Look to see if there is another airbrick higher up the wall. At one time the cavities in cavity walls were ventilated. This makes them colder.

It might otherwise be a building defect.

pebbles, not gravel. Small stones can pass damp by capillary action. Large stones don't.