Slate roofing
Slate repairs, re-slating and matching
Slate outlives almost everything else on a building. Most slate roofs that look finished are not: what has failed is the nail, the batten or the underlay, and the slate itself is perfectly serviceable.
Types of slate
| Type | Character | Notes |
|---|---|---|
| Welsh | Fine-grained, splits thin, consistent blue-grey to purple | The traditional covering on much of London’s Victorian stock. Reclaimed Welsh slate is sought after and priced accordingly |
| Spanish | Widely available in a range of grades | Grade varies a great deal. The important question on any Spanish slate is the grade and the pyrite content, not the country |
| Brazilian | Even colour, flat, dimensionally consistent | Often used where a uniform modern appearance is wanted |
| Composite / synthetic | Engineered slate substitutes | Lighter, cheaper to lay, and useful where the structure will not take natural slate. Not accepted everywhere — check before specifying on a period property |
How a slate roof goes back together
Step 1: Strip and sort
Slates are taken off and sorted. Sound ones are set aside for reuse; broken and delaminated ones are put out.
Step 2: Membrane and battens
A breathable underlay and new treated battens, gauged to the slate size and the pitch. This is what has usually failed rather than the slate.
Step 3: Slating
Laid to the correct headlap for the pitch and exposure, nailed twice, with the courses set out so the perpendicular joints break properly.
Step 4: Lead and finishing
Flashings, valleys and abutments dressed in milled lead, then ridges, verges and hips finished.
Nail sickness, and why a roof fails before the slate does
A slate roof usually ends its life because the fixings corrode rather than because the slate wears out. Slates begin to slip in ones and twos, then in patches, and each slipped slate exposes the one below. That is nail sickness, and it is the point at which patch repairs stop being economic — you are paying repeatedly for a process that will continue across the whole roof.
The judgement is how far along that process a roof is. A handful of slips in twenty years is maintenance. A dozen in two winters, with more visible from the ground, is a roof telling you what is coming.
The other common finding is delamination: slates splitting into layers along their bedding planes, usually visible as flaking at the tail. That is the slate itself failing, and it is not repairable.
Slate roofs we have worked on
Case studies are published here as jobs finish, with photographs taken on site before, during and after the work.
Slate questions
Can you match my existing slate?
Usually. Matching means size, thickness, colour and texture, and for a partial repair it usually means reclaimed slate rather than new. On a front elevation the match matters; at the back it may not be worth the premium, and that is your decision to make with the prices in front of you.
How long does a slate roof last?
Natural slate as a material is measured in generations rather than decades — many London roofs are on their original slate with newer battens and fixings underneath. What determines the life of the roof as a whole is the fixings, the battens and the underlay, which are all replaceable.
My property is listed. Does that change things?
Yes. Listed buildings and conservation areas usually require like-for-like materials and can require consent before work starts, including for repairs that would be permitted elsewhere. Establish that with the local authority first; it changes both the specification and the timescale.
Will my roof structure take natural slate?
If it is on there now, yes. It becomes a question when a roof is being changed from a lighter covering to slate, or where the structure has been altered — for example after a loft conversion. That is a structural question and should be answered by someone qualified to answer it before the slate is ordered.
Not sure what your roof needs?
An inspection ends with a written report and photographs, whether or not you go ahead with the work.
Inspection fee: £99.00.