Underfloor ventilation

[oldbutnotdead]

Morning all.
Situation- replacing suspended timber floor, walls are solid full brick (9 inch)
Problem- external ground level is well above internal floor level (about 250mm), I can't risk just removing external ground because the foundations are rather shallow.
Problem 2- there isn't much of a cavity so I can't fit those natty telescopic air bricks- or not without taking out great chunks of wall and putting a lot of slips back in. Plus the brickwork isn't in brilliant condition.
Problem 3- existing airbricks are at the level of the wallplate (and too low in the outside wall)- even if I put gaps in the wallplate, the insulation (required) will obstruct them.
My thought- acquire a core drill and put 40mm or 50mm holes through the wall at about 60 degree angle (so outside the hole is about 100mm above ground, inside the hole is below wall plate and above oversite). Think I'd need 1 hole every 500mm to get acceptable airflow (40mm hole gives area of about 1200 sq mm so 2 per metre would give me 2400 sq mm, if I do 50mm that comes to about 3800 sq mm/metre)
Any thoughts? In particular building regs and that little note about 'any pipework used for ventilation must be minimum 110mm diameter'
Cheers

 

[theprinceofdarkness]

Sounds OK, but I would use 60mm holes so you can use soffit vents to tidy up the outside of the holes. I still have a problem though with the steep angle, just to make it look nice, perhaps a combination, say 60mm straight in, then at some point drill your 60 degree hole downwards. This will make the front surface of the vent flush. if you use a 50mm hole what are you going to do on the surface - vent?
Frank

 

[oldbutnotdead]

I'm not happy about the steep continuous angle either but I can't drill up from inside (clay is only 180 below the underside of the joists, hole centre inside will be about 90 below joists thus 90 above clay) and I'd have to knock lumps out of the outside wall to drill down from the wall centre (that isn't very clear but I do understand what you're saying).

I'm sort of hoping that my cover plan (cut tube flush at the angle so the hole presents externally as an oval then fix some sort of louvred vent thing - something like Toolstation 84919) will prevent rainwater and wind driven splash from entering the tubes. And bonus with them being straight (not level I know) is there'll be less resistance to airflow- the ground is quite damp so the more air movement I can get under the floor the better!

Ta for thoughts, keep them coming!

 

[oldbutnotdead]

Ahhhhhhhh, inspiration has struck! Combination scheme;
Remove one brick from outside skin
Start drilling diagonal down hole centre about 70mm in to outer skin in the left hand corner of the hole, penetrate through to inside at correct height (hopefully)
Repeat on right hand corner of hole
Stick 2 x 50mm tubes through the hole, trim so the cut end is vertical
Insert plastic airbrick (only 60mm deep) into outside wall, point up and make good
Or that's the theory anyway.