ventillation bricks

[arl]

Just a quick question about ventillation bricks in a wall. How frequent should they be for a middle terrace house. we have quite a few at the front of the house but only one at the back. I presume this is because the back of the house is solid floors (apart from the dinning room) and dosnt need them?
I imagine that if they are only along one wall however that we wont get much airflow under the house. What do others do about this?
Im asking as we have damp on several walls in the house and this seems a good place to start.
Thanks

 

[Penners]

I seem to remember someone suggesting on this forum that ventilation bricks should be inserted at least every 3 metres along a wall to ventilate a suspended floor effectively.

You're right, of course, that if the ventilation bricks are only along one wall, this will preclude a cross-flow of air and rather reduce their efficacy.

However, if you have air bricks along the front wall of the house, even if you have only one in the back wall, you will still get some cross-flow effect, so long as there is a continuous underfloor cavity between the two.

 

[arl]

Thanks for that. seems we have enough then.

 

[Penners]

Thanks for that. seems we have enough then.

I take it from that comment that you're confident of there being unimpeded air flow between the front wall and back wall vents? No dwarf walls in the way?

 

[arl]

dwarf walls?

i have just noticed a small problem. the ventilation brick at the back of the house appears to be above the height of the internal floor so i imagine it wont be doing an awful lot of good. any ideas why it might be there? the internal floor dosnt appear to have been lowered. maybe the outside level was much lower and i might find some more lower down against what is now patio?

 

[Penners]

Dwarf walls are used to support the flooring joists for suspended floors, where there is no available structural wall. They are only high enough to support the joists, so are not visible from above the floor.

The vent above floor level could perhaps have been purely for ventilation of the room. If the room was/is the kitchen, could it have been an air supply to a range?

Yes, I should hunt lower down the wall for underfloor vent(s). If you haven't got any, I would urge you to consider installing some.

 

[arl]

Thanks Penners!
got the floor boards up last night and found "dwarf walls" but these have regular gaps in them so shouldnt impede air flow too much. However the footings of the wall dividing the two rooms only has the odd brick removed.
The area under the floor was damp but not wet, but did have a large amount of very slimey mushrooms and some good sized slugs! I am guessing this is probably a bit damper than it should be? A large number of the joists had been replaced so I think the damp may be a long standing issue.
So my next question is how deep do i need to excavate in order to insert ventilation bricks at the most effective position? Would the external soil level have been the same as the internal? (please excuse my complete lack of knowledge on victorian foundations) if not is there a standard difference ?

 

[Penners]

I'm not aware of any rule that says the air bricks must be any specific distance below the floor - just so long as they arebelow it.

As to the underfloor void, so long as it's deep enough for the joists not to be in contact with the soil, and for air to circulate under the joists, that should be sufficient.

If these criteria are satisfied, I shouldn't be too hasty to start digging out the sub-floor soil. You don't know how deep the foundations are, and it may not achieve much anyway. Much better to concentrate your efforts on ensuring that there are sufficient air bricks to give really good ventilation throughout.

 

[Gervase]

That doesn't sound excessively damp, particularly with the present weather conditions!
As Penners said, the main thing is to ensure that the joists don't make contact with the soil.
Provided you've got the ventilation sorted, you can even have puddles under there and not panic.

 

[worms]

I'm not aware of any rule that says the air bricks must be any specific distance below the floor - just so long as they arebelow it.

All my air bricks are above floor level! There is ony about 6 inches of clearance under the joists and I suspect that the water table might not be far below that at times. However when you open an inspection hole in the floorboards, there is a howling gale blows out into the room so the airflow obviously works OK. Joists are in good condition, except in one corner where there is high external ground level, so higher air bricks don't necessarily mean damp problems!

 

[Penners]

I suspect that the water table might not be far below that

Water table? In Ultima Thule? More like permafrost, I should have thought.

 

[arl]

I shouldn't be too hasty to start digging out the sub-floor soil.

oh no i meant excavate the external soil level. Im not about to start messing with the sub floor - not with the size of those slugs! They are man eaters.

 

[Lime]

What do the "large amount of very slimey mushrooms" look like?

 

[Penners]

What do the "large amount of very slimey mushrooms" look like?

More importantly, what do they taste like?

 

[arl]

They are white/cream with a bronzish colour towards the apex. They arnt really mushroom shaped more the sort of fungi you see on rotting trees. The shape seems quite variable but most look like very deflated balls, with sort of brain like ripples and folds. Thats a very bad description, i will try and get some piccies at the weekend.
Not sure you'd want to eat them though!

 

[ajbaker]

Sorry to piggy back on this topic, but I am currently considering the installation of an airbrick to ventilate the subfloor of my living room (only ground floor room with a suspended floor).

Pavement level outside is roughly the same as floor level, so will need to go down at an angle.

What is the cheapest and easiest way to achieve this?

I have seen some products that require two horizontal and one vertical shaft to be dug, then fitted with filters etc. etc. Does it really need to be so complicated? Would it be possible just to dig a diagonal shaft, install an airbrick outside and... something inside to prevent ingress of water?