On a terrace your roof is usually part of somebody else's. That raises two questions about matching and about the junction, and neither appears on a standard quotation unless you ask.
The cost variables for a tiled re-roof are the familiar ones: area and shape, the tile chosen, the condition of the timbers, access, and everything that goes with it. Those are at the end of this guide.
What comes first on Birkenhead's terraced stock are two questions a detached house never has to answer, and both of them are about the house next door.
On a terrace the roof usually reads as one continuous plane across several houses. Replace your section and the new covering sits directly against the old.
The difficulty is that after several decades the original tile range is almost certainly out of production. A close modern equivalent is the realistic aim, and it will not be identical — the colour, the profile and the surface will all differ slightly, and on adjoining roof planes that is visible.
There is no way round that except doing more of the terrace at once, which brings us to the saving nobody takes.
Where new covering meets old, water has to be kept out of the gap. This is a real detail, not a cosmetic one, and it is where a cheaply done terrace re-roof leaks in three years' time.
Done properly it is soakers interleaved with the courses, or a secret gutter arrangement. Done cheaply it is a bed of mortar, which cracks and lets water past. The cost difference is small; the difference in outcome is not.
Ask how a quotation proposes to handle it. It will not be mentioned otherwise, and a contractor who has thought about it will have a clear answer.
Where work involves cutting into, raising or rebuilding above a party wall — a chimney stack on the party line, for example — the Party Wall etc. Act 1996 may require you to serve notice on your neighbour. Straightforward re-covering up to the line normally does not, but the question is better asked at quotation stage than after the scaffold is up.
| Concrete interlocking | Clay interlocking | Plain tile | |
|---|---|---|---|
| Material cost | Lowest | Higher | Highest in clay |
| Units per m² | Fewest | Few | Many |
| Labour | Lowest | Low | Highest |
| Weight | Heaviest | Moderate | Moderate to heavy |
| Minimum pitch | Lowest | Low | High |
| Colour in 25 years | Weathers to grey | Holds | Holds in clay |
| On a Victorian terrace | Reads as modern | Better | Depends on the building |
Pitch. Every tile has a manufacturer's minimum below which it is not warranted, because below that angle wind-driven rain is pushed back up under the lap. Worth measuring on a rear outrigger, which frequently sits below the main slope.
Weight. Concrete tile is the heaviest common covering, and a great deal of Birkenhead's terraced stock was framed for slate. If your roof was originally slate and now carries tile, it has been carrying more than it was designed for — worth a proper look at the timbers during the strip.
On Victorian terraces it very often was, and it is usually possible to tell.
It matters because it tells you what the structure was sized for, and because a re-roof is the one moment when going back to slate is comparatively straightforward. Inside a conservation area it may also be the change a conservation officer would prefer to see.
Two separate systems. Planning: a like-for-like re-roof does not materially affect the external appearance of a building, so under section 55 of the Town and Country Planning Act 1990 it is not development at all and needs no permission. A visible change of covering can be a different matter, particularly inside a conservation area, where the test is applied more tightly.
Building regulations: where more than 50% of the roof's surface area is renewed, or the work forms part of a major renovation, regulation 23 of the Building Regulations 2010 requires the roof to be brought up to current thermal standards so far as that is technically, functionally and economically feasible — 0.16 W/(m²K) for a roof in an existing dwelling. A patch repair does not trigger it, and neither does a roof over unheated space such as a detached garage.
We will tell you what match is realistically achievable and how the party-line junction is being handled.
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