Encapsulation
Encapsulation means cleaning and coating the sheets with a sealing paint. It can extend the life of a sound roof by years and keeps fibres locked in. It does not fix leaks, and the roof still contains asbestos.
The cleaning step is the hard part. Wire brushing or pressure washing is not allowed for a householder to do safely, so the preparation is normally done by a trained contractor with the right controls.
Overroofing
Overroofing fits a new roof over the old one. It avoids disturbing the sheets while the new roof goes on, but the fixings pass through the old sheets, and the roof stays a problem for whoever removes it next. It also adds weight to old timbers.
When removal makes more sense
If the sheets are cracked, crumbling or leaking, or the garage is being sold, converted or demolished, removal is usually the better value. A cheap coating over a failing roof is money wasted.
If the roof is sound and you only want a few more years, encapsulation can make sense.
What to ask a contractor
Ask how the roof will be prepared, what the coating guarantee is, and what happens when the roof eventually needs to come off. A clear written answer separates serious firms from fast sprays.
Quick answers
How long does a sealing coat last?
Depending on the product and the roof condition, several years to a decade. It needs inspecting.
Is it legal to paint an asbestos roof myself?
There is no law against it for a householder, but cleaning the roof first releases fibres, so it is not advised.
Will a coated roof pass a survey?
It can, but the surveyor will still note the asbestos.