On Tuesday, January 21, 2020 at 10:00:45 PM UTC, newshound wrote:
On 21/01/2020 19:20, wrote:
On Tuesday, 21 January 2020 15:03:15 UTC, Anna Bonaddio wrote:

I would be very grateful for some advice on this. We bought a house from a developer two years ago, the house included what we thought was a useful outhouse that could become a mancave at some point... simple construction, built with breeze blocks, but when we read up on the planning permission we realised it was a way of getting round planning permission for them as our car parking space is on top of it (there were protected trees in the way of the space that was on the original plans). I know it sounds eccentric that we park on top of it... that part of our garden is a storey below street level.

We've had constant damp patches ever since we moved in. The parking space is on a slope and we seem to get all the rain seeping into side of the outhouse that is at the lowest point. Everything in there is has mould on it and there is constant condensation inside the glass door. I have an electrician here today installing a fan, he has noticed there are two layers of the breeze blocks in the wall with a gap in between and he can see the bricks are damp in between the gap.

Next to our car parking space there is a narrow gutter leading to a drainpipe, that is also very narrow, but I can also see dark patches of damp and mould all over the ceiling of the outhouse (which is wooden struts supporting plywood and then whatever the builders put above that.

We did manage to get the developer to put some leading around the edge of the car parking paving, but it hasn't had any affect on the damp as far as I can see. Our neighbour shares the other half of this outhouse (he parks his car next to us) and he says there is no point in pursuing the developer, we just have to work out our own fixes.

If anyone has some advice I would be really grateful, I'm worried the outhouse will collapse under the weight of our cars as much as anything!

I can't help thinking there's just not enough info here. As a short term measure I'd plug a dehumidifier in. A fan I would not expect to keep on top of it or prevent further damage, and the damage from mould can be extensive and very expensive.

I'd suggest posting some pics of the outside so we can see what the relationship is between the outhouse & ground levels, slopes, water drainage etc. Maybe some pics showing construction details on the outhouse too. I'll admit to being surprised that, IIUC, you're parking your car on a plywood roof. Details might help, that might be a problem area in a couple of ways.


NT

+1.

Surely not on a plywood roof. That would be evident from inside. At the
least I would expect reinforced concrete beams, or perhaps a reinforced
concrete slab ideally supported on RSJs.

The roof is paving blocks above, and definitely wooden beams underneath. I've posted pictures below.