I have a double garage with a sloping 'big 6' corrugated asbestos roof which is about 30+ years old. The roof joists are getting very wet in places. At first I thought it must be due to rainwater getting in through one or two of the holes through with the 6" galvanised roofing nails were driven. However, after carefully sealing any possible such leaks, the wetness continues. Yesterday (which was a cold but rain-free day), I went into the garage and inspected the roof, just after nightfall, and I discovered that almost the whole underside of the roof had a lot of condensation on it. Since the roof is gently sloping, that condensation runs along the enderide of each corrugation ridge, until it meets a joist. That is where the water gets into the wood. One weird thing I noticed is that some sheets of the asbestos seem more prone to condensation than others.
Are there any tricks I can employ to stop the condensation?
If not, does anyone know of any way to divert the water away from the joists? I thought of gluing a short length of string to the underside of each ridge, just upward of each joist, so that the water drips down the string and into the garage... but it's not a very satisfactory solution, because I have a lot of perishable stuff stored in the garage.
Can anyone offer any suggestions?