The short answer
Usually yes, if three things line up: size, thickness and colour. A new slate must share the length and width of its neighbours, or the courses will not overlap as they should. Colour is harder, because old slates have weathered for years. On a slope seen from the street, salvaged slate in the right tone often gives the closest match.
A well-matched slate vanishes into the roof. A poorly matched one is the first thing you see from the road.
Size comes first
Slates are cut to a length and a width, and a whole roof is laid to those measurements. If a replacement is shorter than the slates around it, the overlap between courses, called the headlap, shrinks, and wind-driven rain can reach the batten behind. If it is wider, it will not drop into its gap without trimming, and a trimmed edge is a weaker edge.
How do I find out what size my slates are?
Measure one that has come down, or ask us to take a sample at the survey. We record length and width in millimetres, and how much of each slate shows, which roofers call the exposure. Old roofs are not always laid in the metric sizes sold today, so a close fit may mean cutting a larger slate down to suit. Our guide to roof slate sizes explains how size and slope work together.
Never order by guesswork from the ground. A slate that looks about right from the lawn can be a few millimetres out, and a few millimetres is enough to spoil a course.
Thickness decides how it sits
Thickness is the measurement that gets forgotten. A slate much thicker than its neighbours sits proud, props up the slate above it and leaves a slot where the wind gets in. A thinner one sits hollow and can crack under a roofer's boot or a ladder foot.
Does a thicker slate last longer?
Not by thickness alone. Slate from different quarries and different seams varies in strength, so thickness is only one clue, and a thin slate of good stone can outlast a thick one that splits along its grain. For matching, what counts is that the new slate lies flat on the course below and tucks cleanly under the course above. We test that on your roof with a trial slate before a batch is ordered. The detail is set out in our answer on slate thickness.
Where a roof has been mended before, a mixture of thicknesses may already be in place. The survey notes which slopes are consistent enough to match and which are a patchwork that needs a different plan. Edges tell the story: a slate that rocks under a thumb, or shows a dark gap along one side, is usually the wrong thickness for its slot, and the courses around it need a look as well.
Colour and weathering
Colour is where matches go wrong most often. Natural slate comes in greys, blue-greys and greens, and two slates from different quarries can look quite unlike each other in daylight. An old roof has also weathered, so even stone from the same quarry looks darker and cleaner than the old stock for a good while.
Will new slates stand out next to old ones?
They can, particularly on a front slope in raking light. The remedy is to put them where the eye does not go. Salvaged slates in the right tone suit the visible slope, and the new ones go to a rear slope or a porch. New slate weathers closer to the rest in time, though how far it gets depends on the stone, and some stones keep a bright edge for years. Wet slate also looks darker than dry, so judge a sample on a dry day. If the shade matters to you, tell us before an order goes in, and we will hold sample slates against your own roof in daylight, because shade changes between a merchant's yard and a sunny gable. A sample seen in the right light saves a poor choice later.
Salvaged slate and protected buildings
The best source is often your own roof, and it costs nothing to look. While a slope is stripped, sound slates from a hidden rear slope or an outbuilding can move to the front, and replacements are fitted out of sight. Merchants of reclaimed slate sell by size, so a measured sample helps them find you a fit. Slates lifted from an old Somerset roof often come in a spread of sizes, and a good merchant sorts them into batches that suit a run of courses.
Does a listed or protected roof change the choice?
On a protected building the match is more than neatness. Class C under permitted development normally allows a re-roof of a house in the same material, yet a listed house needs listed building consent as well when the work touches its character. Inside a conservation area, ask Somerset Council's planning team before the material changes, and keep a record of what was on the roof beforehand. A sample slate and a few photographs of the slopes make the conversation with the planning team quicker. Our slate roofing page covers the wider job, and a photo of the slope lets us plan the measuring visit.
More on matching slates
Is reclaimed slate cheaper than new?
That depends on the size you need and how many of that size a supplier holds. Scarce sizes cost more and common ones cost less. Whatever mix of reclaimed and new slate your roof calls for, you receive a single written total once we have surveyed the slopes.
Can fibre cement slates be mixed with natural slate?
They can share a roof, but they weather differently, and the join usually shows as a change of texture and colour. For a repair on a natural slate roof we use natural slate. Our answer on natural versus fibre cement slate explains the differences in more detail.
The full picture: Slate roofing in Taunton ยท More short answers