Daventry’s roofing work divides the same way the town does, and the estate side of it is the larger share.
The housing built from the 1960s onward is concrete tile on trussed rafters, laid in quantity and to a consistent standard. That makes diagnosis fairly quick. The usual failures on this stock are at the details rather than in the field of the roof: verges, ridges, flashings at abutments and the junctions where a later extension met an older roof and nobody thought hard about the flashing.
In the older core there is slate on cut timbers, with valleys and abutments that need lead renewed properly rather than patched again. A valley that has been sealed for twenty years will keep failing in the same place until it is done correctly.
The weight point matters when re-covering. A roof built for concrete tile will generally take slate, but a roof built for slate cannot always take concrete tile, because concrete is heavier. If somebody offers to re-cover an old slate roof in concrete without examining the structure first, get a second opinion.
Re-covering is where Building Regulations become involved, because replacing a substantial part of a covering triggers a requirement to look at insulation, and we arrange that inspection and see it through to sign off. In the conservation area the covering material is not a free choice. More on our roofing page.