Leaving aside the problems with asbestos disposal. What would be the best material to replace the (properly disposed of) corrugated asbestos cement roof? Corrugated bitumen sheets seem ok for sheds but they seem a little flimsy for a garage roof.
Modern materials aren't durable, are they? Onduline is about 15 years if looked after (kept cleanish and moss etc. removed - not much else that one can do), steel only a bit longer. The roof on my shed is asbestos cement, has had a lot of moss, is only about
7 - 8 deg. slope and is ~60 yo. Yes, it has a few cracks but it doesn't leak. Trouble is, although I'd like to replace it before it cracks in a critical place, there seems to be nothing that would be easy to use. There is only 1 support in 3m at a low angle and anything new would require at least 3 or a full deck - and even a deck needs more support. I'll leave it until a tuit lands in the garden.
I've never had this problem - possibly because it's about 20' high, and even with a few people in there there's never enough moisture / volume ratio to cause trouble,.
Care with installation is important, particularly on shallow pitched roofing. Rain can *bounce* under the sheet laps. Steadmans will recommend using a butyl strip seal and stitcher screws along the laps.
... you only need to plan on replacing it once. (In 2008, government staticians reckoned that a 64 year old man in 2011 would have a life expectancy of 22.3 years - so the odds of not making 25 years is only slightly less than 50/50)
It's 3m long, same as the shed next to that was done with Corruline, so 2m sheets give a good overlap - about 90cm - and should be enough to stop water getting blown back up the slope.
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