ventilation to suspended wooden garage floor

[heathen44]

I have a pitched roof garage at the bottom of my garden, (asbestos roof). I have use of half of the garage, next door has the other half. We have both had the doors blocked up, due to security, and put a single door in one garden wall. The garage foundation is only three bricks deep to ground level. I am getting wet patches on the inside of the garage, just above the bricks, and in one corner at ground level. This dries out when the door and windows are open. I have boarded the walls, and spent some time draught proofing the garage, to make it usable as a games room. I may have overdone it, and prevented the walls from being able to breathe. To install a wooden floor, I need some ventilation under the floor. I cannot afford to raise the floor above the 3 brick foundation level, due to head space, so air bricks are a bit tricky. Can I put air bricks in the bottom row of bricks, ie at ground level? Can I simply try to drill holes through the bricks, from the inside, or is this just a ridiculous idea? Can I also drill holes through the wall blocks, at a higher level, to ventilate the roof area? Please help. Thank you.

 

[ajrobb]

The damp patches sound like condensation. You can either improve ventilation and keep the space mostly unheated or install insulation with vapour proof layer. Instead of a suspended floor, you could avoid air bricks and lay a damp proof layer, rigid insulation and board over the top. Have a look at Celotex garage conversions, the PDF download looks useful.

 

[heathen44]

Thanks very much for that. Food for thought, and certainly will save me some hard graft. Do you think any kind of self levelling screed would be a good idea, to level the floor, or would this be counter-productive? I would probably need to put a thick screed down, which would defeat the object and raise the floor too much (?) If no screed, any good idea about how to best level the floor? All the best.
Steve

 

[ajrobb]

It is normal to put just sand under insulation when you are insulating a solid floor. I don't know if you'd get away with it under a timber floor. Maybe a weak mortar under the damp proof layer. I guess it depends on how much slope you have.

 

[heathen44]

Great idea, thanks very much. Sand or weak mortar to level the lowest points, then damp proof membrane, insulation and board! Thanks again.
Steve

 

[ajrobb]

I think you need to use T&G chipboard on top of insulation. I'd go as thick as pos (22mm) and glue the joints. Don't forget to stagger the joints by at least 600mm. This protects the insulation from concentrated loads. Your choice of flooring on top of that. It's not going to be the greatest floor but there are plenty just like it.