Northampton has two roofing populations and assuming the wrong one is expensive.
The terraced quarter is largely slate on cut timbers, in long continuous runs with shared party details and valleys where rows meet. Those junctions are where water gets in, and a valley patched for twenty years will keep failing at the same point until the lead is renewed properly. Sealant delays the conversation rather than ending it.
Chimney stacks deserve particular mention on this stock. On a terrace the stacks are shared, exposed on all sides and usually still carrying original flaunching. Once the roof around a stack has been patched a few times the stack is generally next, and if scaffold is up for a re-cover, dealing with it then costs a fraction of bringing scaffold back in three years.
There is a specific Northampton case worth knowing. Where a terrace adjoins a former factory building, the roofs meet at a junction between two quite different structures of different heights, and those abutments were rarely detailed well. They are a common source of persistent leaks that get blamed on the wrong building.
The later housing is concrete tile on trussed rafters. 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. Re-covering triggers a Building Regulations requirement to look at insulation and we arrange that inspection. More on our roofing page.