Concrete prefab garage has had a new flat roof, replacing corrugated cement board. That used to suffer badly from internal condensation in winter and I'd hoped the recent replacement ply decking+EPDM would fix it.
In the recent few months it has started to get black mould and feels damp to touch - all over, so sure it isn't a leak. Everything else in the garage remains dry except the deck, one 25l water barrel and one 28lb metal weight (both of which have a lot of thermal mass).
Three questions, as I guess both the symptom and cause need sorting (and I'll be armed with the correct info when talking to the roofer)...
i) For the mould - I assume I need to deal with it asap to stop the deck being damaged? Some kind of fungicide wash and let the garage air thoroughly?
ii) To then protect the deck from rotting in future, is there a preferred treatment?
I've used Cuprinol on other outside wood in the past - and it states it is suitable for interior wood at risk of condensation. However, is it also worth using one of the anti condensation paints on top?
These seem to have mixed reviews and are expensive. If there is still condensation and it no longer soaks into the wood, then it’ll drip internally (as used to happen with concrete sheets). I suppose that is better than a rotting deck!
iii) The 18ft x 12ft detached garage is not airtight and cannot realistically be made so. I think that rules out: seal+insulate+possible heater/dehumidifer, so instead I need to increase ventilation?
Up-and-over door has one inch gap across the top already. No other doors/windows. Drilling into prefab concrete seems like a bad idea
There is no soffit at the far end, just fascia. Sides have 1 inch and 2 inch soffits respectively.
I could just chuck in a floor fan to move the air around and hope that that is sufficient to replenish with colder outside air. Not convinced though.
I was also thinking of adding vent holes to the soffits. We live in a windy area so that might be okay, but:
- it might not clear the air between the joists without an additional fan (soffits are parallel to the joists)
- would some intake or extractor fan likely to make any difference?
I’ve already sealed the concrete pad and overlaid with duramat pvc floor tiles. That might have made it worse but is much nicer.
In the recent few months it has started to get black mould and feels damp to touch - all over, so sure it isn't a leak. Everything else in the garage remains dry except the deck, one 25l water barrel and one 28lb metal weight (both of which have a lot of thermal mass).
Three questions, as I guess both the symptom and cause need sorting (and I'll be armed with the correct info when talking to the roofer)...
i) For the mould - I assume I need to deal with it asap to stop the deck being damaged? Some kind of fungicide wash and let the garage air thoroughly?
ii) To then protect the deck from rotting in future, is there a preferred treatment?
I've used Cuprinol on other outside wood in the past - and it states it is suitable for interior wood at risk of condensation. However, is it also worth using one of the anti condensation paints on top?
These seem to have mixed reviews and are expensive. If there is still condensation and it no longer soaks into the wood, then it’ll drip internally (as used to happen with concrete sheets). I suppose that is better than a rotting deck!
iii) The 18ft x 12ft detached garage is not airtight and cannot realistically be made so. I think that rules out: seal+insulate+possible heater/dehumidifer, so instead I need to increase ventilation?
Up-and-over door has one inch gap across the top already. No other doors/windows. Drilling into prefab concrete seems like a bad idea
There is no soffit at the far end, just fascia. Sides have 1 inch and 2 inch soffits respectively.
I could just chuck in a floor fan to move the air around and hope that that is sufficient to replenish with colder outside air. Not convinced though.
I was also thinking of adding vent holes to the soffits. We live in a windy area so that might be okay, but:
- it might not clear the air between the joists without an additional fan (soffits are parallel to the joists)
- would some intake or extractor fan likely to make any difference?
I’ve already sealed the concrete pad and overlaid with duramat pvc floor tiles. That might have made it worse but is much nicer.
