DIY Doctor UK DIY Forums

I have self built a wooden building, it 30 feet by 8 feet. I have divided it into 2 sections. 2/3 of the building I use as a shed, workshop and growing area. The other 1/3 is partitioned internally with a through door and used as a den/summerhouse. At this far end the doors have yet to be built and I have blue sheeting and a fabric mat hanging in the opening. This is working in so far as it keeps the rain out (well almost). It does feel damp in this section.

I am getting a large amount of water dripping from the ceiling at the opposite end of the building. I've worked out that this is condensation collecting, freezing overnight in the frost and then melting and dripping down onto the shelves.

I want to know is this because it's unfinished, and therefore letting a lot of damp air, or because I incorporated corrugated plastic sheets and plywood/felt roof coverings.

7 feet of the sheds 30foot length is roofed with corrugated plastic and I have continued the rest of the roof in ply and felt covering. I then built large shelfs under the roof and used kitchen worktop to create workbench under the roof. In spring I use the shelves effectively as a greenhouse to bring on seedlings and having the clear roof allows plenty of light to work.

It works really well however I wonder if this is also the source of my condensation problems in winter. The condensation drips onto the workbench at the point the plastic roof sheet is fixed by battens. I have inspected all the sheet fixing screws and am sure they are fixed and the plastic bushes acting as a waterproof barrier.

I have yet to finish the project. At the opposite end of the structure I have 2 blue plastic sheets covering the opening where I intend to install double wood french doors.

I realise this is letting in damp air and aid condensation. I really want to understand that this is the sole reason and not due to my roof design.

The damp problem comes from water dripping off the underneath of the plastic sheets. The roof sheet do not appear to be damp on the underside next to the plastic and further along the building.

I wonder if the action of the sun not he roof increases the problem of damp which I'm sure is evident from not having finished the building yet. Also, if the pure design of it is going to continue to cause issues.

Your supposition is correct.

You have condensation, from warm wet air meeting a cold smooth surface.

About 200 times a year, warm wet air arrives, meets the cold ground and shows as dew or frost.

You get the same thing on your car left outside overnight.

Because of the way the shed is at present, open to the sky, the water vapour in the air is moving into the shed and freezing or condensing onto the cold surface.

Where you have a complete building, the frost/dew stays on the outside.

The key thing is, that water vapour like heat, always moves from hot to cold.

As the ground is cold, the water in/on the ground stays where it is.

It is only the water vapour in the air that does this.