Why Important
This material is not suitable for Period Houses (built before 1960) and was usually used as a repair. They should be removed and the appropriate period roofing material used.
What to look for
Usually black tar-like rough material, which is softer than slate.
When to look
How to fix
Preferably it is best to replace completely, to reveal the full extent of the roof problems, the replacement bitumen roof is attempting to fix.
Avoiding creating problems
Only use fully qualified roofers to make repairs, as frequently poor patch repairs lead to significant water penetration and subsequent timber rot.