Condensation is caused by the warmer moisture filled air coming into contact with a
considerably colder surface. This happens a lot with outdoor buildings as usually the
roof has no or little insulation and as the temperature outside drops it creates a cold
surface and the moisture in the air condensates on the surface.
The roof is not leaking and most the time you would not even notice it as it will
usually clear up within a few days of warmer weather. If however the roof has been
leaking it will add to the problem – you can usually tell the difference between a leak
and condensation as a leak will be concentrated in one spot and eventually drops onto the floor in the same position. Whereas condensation will usually bead over the whole
inside of the roof or on one side of an apex roof, any painted section will be
particularly prone to this as the painted surface will be colder than its surrounding
VENTILATION / CONDENSATION ISSUE
NEED A LITTLE ADVICE?
PRUNING : Prevent tree branches and bushes from rubbing against the shed felt, it takes surprisingly little time for a rubbing branch to cut through felt.
STORAGE : Do not store ladders, timber, bricks etc on the felt roof - this weakens the felt.
CLEANING : At least once a year brush any dead leaves, moss etc away as this accumulates adding extra weight and stress to the roof.
BIRDS : Try to prevent birds pecking at the felt (easier said than done - we know!). Birds can hear/sense the insects under the felt and will quickly ruin the protection usually along the ridge.
The cause of moisture in the air can be numerous reasons, including our own
breathing, but usually there is a cause which provides a source of water. A common classic is cut logs for fires; these contain a lot of moisture which is why log stores are roofed but have an open front to allow for evaporation. Potted plants, wet clothing, wet bikes, compost, loose coal, damp carpets the list is endless but the results are always the same as the garden building is normally closed up completely which stops any evaporation escaping.
THE REMEDY in all cases is to open up the building for some airflow to allow the moisture to escape; this can be done by leaving the door wedged open on a dry day or opening the windows slightly. Unfortunately, during winter when the outside air is damp as well it may take a while to clear. The alternative is to use a dehumidifier, it will shock you as to how much damp there is in a shed as you will be emptying the container quite often.
DON'T be tempted to put a heater in as you will only be warming up the trapped
moisture, but without ventilation you’ll not remove any of it.