How do you match existing slates?

Slates are cut to named sizes, such as 500 by 300 mm, and the gauge of the roof, which is the distance between battens, is set by the slate length and the headlap. The headlap is how far each slate laps over the one two courses beneath it, and the figure depends on pitch and exposure. Cupa's guidance, for example, gives 115 mm for a 500 by 300 slate at 20 degrees, falling to 55 mm at 45 degrees and above. A replacement shorter than the original changes the way the courses lie, and a longer one will not sit flat against its neighbours. Width matters less, though a very narrow slate looks odd among broad ones and is more easily dislodged by wind.

Thickness matters just as much. Old slates are often thicker and more uneven than modern ones, and a thin replacement will tilt, rattle and shadow differently on the roof. We measure several slates, not one, since a roof laid over time may hold slates of more than one size. Our page on the weight of slate explains why thickness has structural consequences too.

Slate colour varies by quarry, from blue-grey to green-grey and darker, and it changes with age and wetting. Judge samples outdoors, dry and wet, in sunlight and in shade, because a slate that looks identical on a showroom bench can look off once it is on the roof. Texture counts as well: some slates are smooth and cleaved flat, and others have a rougher, more rippled face. A mix of surfaces shows as patches even when the colours agree.

Origin tells you more than appearance. Welsh slate and Spanish slate differ in colour, density and how they weather, which is the subject of our page on Welsh and Spanish slate. If the roof is old and nobody knows where the stone came from, a roofer who has handled similar roofs can often tell from the face and edges, and a supplier can offer samples to hold against it. Keep any spare slates from the loft or the garage, since they are the best evidence you have.

Reclaimed slate has been through decades of weather, so its colour, surface and edge already look right next to the old slates. It is also usually thicker than new, and the sizes tend to match older roofs, which were laid in set sizes of the period. Yards that deal in salvaged slate often hold batches sorted by size and colour, so it is possible to buy a small number for a repair.

The compromises are plain. Reclaimed slate is variable, some slates will be damaged or delaminating, and old nail holes may be in the wrong place for your gauge. You may need to pick through a pile or accept a few rejects, and a good yard will let you handle the slates before you buy. MyBuilder's slate guide, updated 21/08/2026, puts reclaimed slate at £110 to £150 per m² as a covering, between Spanish at £100 to £130 and Welsh at £140 to £180. For a repair of a few slates, the cost is the labour and access, not the slate.

If no reclaimed slate is available, new slate of the same origin and size is the next best choice. It will look darker or fresher at first, then weather towards the older slates over several winters, and the effect is greatest on a south slope in full sun. Sometimes we place the new slates on a rear slope or low on a hidden face and move sound old slates to the front, so the mismatch sits where it is least visible.

On a listed building, in a conservation area, or on any roof seen from the road, matching becomes a heritage matter as well as a visual one. Putting back the same slate in a repair seldom calls for planning permission, with listed status and an Article 4 direction as the two big exceptions, and the council's conservation officers can advise if you are unsure. If the substitute is heavier than the existing covering, the Planning Portal says approval is needed from building control where the new covering is 15 per cent or more heavier than the old. A handful of replacement slates will never come near that, but a mismatch in thickness across a whole slope could.

We take samples from a sound area, measure the slates, gauge and headlap, and photograph the slope so you can see the same detail we do. We also look at how the slates sit against the lead, because a replacement that fits the field of the roof may not fit at a valley, hip or abutment. The page on cracked slate deals with the repair itself.

The written quote names the slate we propose, says whether it is reclaimed or new, and gives the cost as a single total. For a larger job, see slate roof cost, or the main slate roofing page for the full service. We guarantee our workmanship for 10 years, in writing, and leave the roof and garden clear. If you can send a photo of the slope and a close-up of one slate, we can tell you what we would look for before the survey.