Looking after a shed so it lasts

Timber outdoors is fine wet and fine dry, and rots where it is repeatedly both while unable to dry out. That is why the failures cluster where water sits rather than where it lands: the bottom of cladding, the ends of bearers, the joints between horizontal members, and anywhere the ground is close enough to splash.

The second cause is movement. A base that settles unevenly racks the frame, and a racked frame stops the door closing — which is usually the first symptom anybody notices, and is a structural message rather than a hinge problem.

Felt is the covering most sheds arrive with and the one with the shortest life. It fails at the edges and the ridge first, then splits, and by the time water is visibly coming in the boards beneath have usually been wet for a season.

The decision worth taking early is whether to replace like for like or to upgrade. Re-covering a roof on an empty shed is an afternoon; re-covering one on a shed full of tools and a bench, after the boards have gone soft, is a different job entirely. That asymmetry is why a better covering is worth paying for once rather than repeatedly.

• Check the edges and the ridge each autumn — Lifting, cracking and exposed nail heads are where it starts. Wind gets under a lifted edge and takes the rest.
• Clear what has landed on it — Leaves and moss hold water against the covering permanently, which is the condition it is least able to survive. Overhanging branches are the underlying cause and cutting them back is the real fix.
• Look inside after heavy rain — Dark patches on the underside of the boards and rust marks around nails locate a leak far more precisely than looking at the roof does.

• Keep soil, gravel and planting off the cladding — Anything piled against a wall holds water against it and bridges whatever gap the base provided. This is the commonest self-inflicted shed failure and it is entirely undone by moving a border.
• Look at the bearers and the ends of the boards — End grain absorbs water far faster than a face does. Soft timber at the bottom of a corner board is the beginning of the same problem that eventually reaches the frame.
• Treat when the timber tells you, not on a schedule — Water no longer beading, colour gone silver-grey, and a dry chalky surface are the signals. Treating a damp shed or one in the wrong season seals moisture in, which is worse than being late.
• Watch the base for settlement — A door that has started to bind, a gap opening at a corner, or a floor with a bounce in it are all the base rather than the shed. Fixing the shed without fixing the base means doing it again.

A sealed shed with no ventilation is a condensation box. Warm damp air meets a cold roof overnight, water forms on the underside, and it drips onto whatever is below — which is why tools rust in a shed that has never leaked. Ventilation is the fix and it feels counter-intuitive, because the instinct is to seal everything.

The related point is that insulating a shed without a vapour control layer on the warm side moves the condensation from a surface you can see to a cavity you cannot. That is a build decision rather than a maintenance one, and it is the reason the wall section on the shed building page is worth reading before insulating rather than after.