Where should I install new air bricks?

[thias]

In the process of renovating our house. We found a number of rotten joists in all downstairs rooms, including the hallway.

As well as replacing the joists, that run front to back, we need to install some air bricks (it currently has none) but there's already an extension across the rear of the house which has a solid floor so can't easily duct vents through there to provide full front to back ventilation.

All internal walls are solid so cross ventilation is also a problem if we go for side to side ventilation. Unless we fit air bricks to the internal walls too?

What's the best way to proceed?

 

[JohnD]

We found a number of rotten joists in all downstairs rooms, including the hallway.

have you found the water leak yet?

how old is the house, and who blocked the airbricks?

 

[thias]

The property was built around 1880. It has no existing air bricks. There's no obvious signs of any leak, the soil its self is bone dry, at the minute, so we believe it's been caused by a mix of the soil moisture content increasing in winter (where the joists are resting on the soil!) and the lack of ventilation over the last 140+ years more than anything else.

 

[Mr Chibs]

Sounds a bit like my place was, I ended up with a couple of air vents for approx 4m of wall in each room. Some where there already, and I've added a couple more.

I've got them on most walls, so when there is a breeze from any direction they will do their job.
Being an old house, I too had solid walls, some double skin, some single.
You can still knock a brick out and install a vent, even half a brick, so you can connect all rooms together... within reason.

 

[thias]

Lifted one of the problematic floors this morning. Started to look into where I could install some airbricks to realise the joists were actually sitting at ground level, so there's no room beneath the joists outside to install any airbricks!

What are my options? Lower the outside ground level? Raise the inside floor level? Any other ideas?

I'm beginning to see why a builder I spoke with said to pour a solid floor instead...

 

[JohnD]

either periscope vents, or reduce the level outside.

It is very common for paving and flowerbeds to be raised against a house wall, leading to damp.

In some cases you can use a redundant chimney as an exit point for air to rise up from under the floor.

 

[Mr Chibs]

Poured floors and Wet ufh

 

[thias]

Poured floors and Wet ufh

Builder's coming around this week to discuss exactly that. We were already digging out the sub floor to allow for better ventilation so we now have the required depth to do it.

My biggest concern with pouring a floor has always been forcing any moisture up along the DPM and into the walls.

 

[Mr Chibs]

I suppose the theory is that the lime mortar will wick any moisture away your house may be lime based due to the age.

 

[JohnD]

if there are any pipes under the floor, renew them before laying the new floor.

it will be a hundred times harder afterwards.

 

[thias]

if there are any pipes under the floor, renew them before laying the new floor.

it will be a hundred times harder afterwards.

All heating pipes will be getting pulled out, we'll stick UFH in above the insulation/below the screed. The house is being rewired anyway so the sparky will drop the new cable down from above instead of it running under the ground floor.

The water mains pipe does come into the house through the dining room (we think this was the original kitchen). It looks to be copper so it's been replaced at some point but we could probably do with shifting that before we pour the slab.