Where to put air bricks

mlotito

Hello all,


I have just bought an 1870s end of terrace. I recently took the floorboards up in the downstairs living room to fix a gas leak. While I was there, I noticed a rotting joist, which I have repaired.



I'm now keen to put floorboards back down. As we're just going for bare wood (the old carpet was worn out), I plan to insulate between the joists with Celotex, thickness as per current regulations.


One thing I have noticed though, is that there are no air bricks under there. There's no particular damp problem down there, as things seem pretty dry on the whole. The joist was just rotting where it touched the bare brickwork, and was the original. But I know that insulating normally exacerbates damp issues.



I asked a builder in to quote, and he said although he could install air bricks, there would be little point, as they could only go into one wall. The 4 corners of the room are (anticlockwise): front of the house, into ginnel (under the hallway floorboards), into dining room which has a concrete floor, into a brick workshop.



He seemed like a good guy, and he could have just taken my money and done the work, but I'd like a second opinion. Would it be pointless to just install air bricks into one wall? Does air need a crossflow, or will the pressure difference cause the warm, humid air to force its way out, and cold dry air to work its way in, equalising the whole underfloor space?


Any suggestions much appreciated!

TheCyclingProgrammer

I wouldn’t just stick celotex between the joists. Insulating a ground floor - particularly in older buildings - needs special consideration or you may well end up with damp issues.

https://historicengland.org.uk/images-books/publications/eehb-insulation-suspended-timber-floors/

FreeBear

Under floor ventilation requires a cross flow of air. Attention needs to be paid to sleeper walls and along with any partition walls. Care needs to be taken in positioning air bricks to avoid any dead spaces where air can't or won't circulate.

The property has stood for nearly 150 years, and the absence of air bricks hasn't caused any significant issues - On that basis, I wouldn't bother trying to retrofit any. I'd also be cautious about adding insulation. The heat from the room will warm up the underfloor void and help reduce damp & condensation.

Mistral001

If you want to have a crossflow, I would not rule out ducting air through the kitchen so that a vent can be provided at the rear of the building.

It is quite common for such ventilation pipes to be put below the concrete floors of kitchens in new houses or below extensions precisely for the purpose of providing crossflow to a timber floor in an adjacent room (it is a Building Regulation requirement in fact).

I am not suggesting that you dig up the floor of the kitchen to lay a ventilation pipe, though that could be an option if you were retiling the kitchen floor. If there are kitchen units running along the side wall of the kitchen then I cannot see any reason why a ventilation pipe cannot run in the void between the bottom of kitchen units and the concrete floor. Even a couple of smallish pipes say 50mm or 60mm diameter will provide quite a bit of ventilation if a crossflow is created.

PS. The pipe/s will have to rise within the thickness of the wall between the living room and the kitchen, so there will have to be a bit of work done to chase out the wall there, but it can be done from the living room side without much disturbance to the kitchen side

mlotito

Thanks all. Sounds like putting everything back as it was is the best solution.
I was concerned the floor might be drafty without the carpet, but as there's no ventilation to the outside anyway, it'll probably be fine!