Shed was put up in 2011 but this year it has started getting really bad mould on the inside of the roof. The building itself is standard shed airtight, ie gaps all over the place and the felt is the stuff that came on it, is in a good visible state but always felt quite thin. Any thoughts on what is causing it? Every now and then I use a fan heater in there if I’m fiddling with bikes but beyond that its just left. If the felt on the roof is letting water through and getting the boards underneath damp, then would that be enough to cause the mould?

I’m thinking of putting a new layer of felt over the top of the existing layer to try and help further waterproof the roof or do I need to take the existing off, cover it whilst the boards dry out and then do a new layer on the roof? Never had mould in a shed before so somewhat baffled.

I’m currently having the same problem. Black mould no less forming on the wall corners and edges.

Mine has gone a bit like that this year. It’s never done it before. I was thinking it’s just the weather. there so much moisture everywhere.

I suspect there’s water evaporating off the floor/walls and condensing on the colder roof. Is one wall in sunshine during part of the day when the roof is in shade?

I’d put some fence treatment on the roof and then add some sort of insulation.

If it has power then maybe a de-humidifier (not a condensor type)?

I suspect the problem is lack of ventilation combined with a very wet year, causing damp to linger. Either improve ventilation of reduce the amount of damp in there.

I had a terrible mould problem in the shed at my old house as it was built like a lean-to so all the ground moisture was getting into it and no amount of ventalation holes or waterproofing paint solved it. Fixed it completely by installing a solar vent in the roof similar to the below which although doesn’t have a battery it draws enough air through the day to get rid of the mould. You can get them online or a boat chandlers

http://www.firststopsolar.co.uk/gm712-solar-ventilator-19-p.asp

Glad i’m not alone then, similar to the above i had no problem last year.

Wwaswas – yes, the back side of the roof which doesn’t get the sun is much worse than the other side. It does have power in the shed so will maybe look at that option. Will get some treatment for the roof (presume you mean inside and out although i need it to stop rainging for the latter 🙄 ) and will also source some of those polystyrene panels to go in the roof joists to help insulate.

That solar ventilator looks good as well.

Thanks so far.

I had the same in my shed. As I havent got power in the shed I made a solar powered ventilation system using a 12v computer fan and a timer. It has a solar regulator to control the charge to the battery and a seperate timer that turns the fan on for a couple of hours in the morning. The shed has been completely damp free since I installed it 2 months ago.
If you have power in the shed already it is even easier. You need a fan, cowled grill for the wall and a power supply. Shouldnt cost more than £15.

My (brick) shed has been terrible for it this year. I even had white fluffy mould growing on my saddle when I left it in there a bit damp. Never had that before!