Read this before a fishscale roof is repaired or re-covered. It explains the pattern, the Northdown Road appraisal, how the slates are matched, and where like-for-like work stops and a planning question starts.
A fishscale roof is slated in a pattern, not in plain straight-edged rows. Each slate has a rounded lower edge, and when the courses overlap, the curves line up to look like the scales on a fish. The shape is purely decorative on the face of the roof, but it matters for repair, because a plain rectangular slate cannot stand in for a shaped one without changing how the whole slope looks.
Thanet's own conservation area appraisal for Northdown Road, in Cliftonville, records that some of the roofs there are covered with fishscale slates. It describes that conservation area, not every street in Thanet. If you have one, you already know it. The shaped tails are visible from the pavement.
This guide treats repair, matching and the rules in general terms. A fishscale roof is natural slate underneath its pattern, so everything on our slate roofing page applies as well, and the pages on slate roofs in a conservation area, listed building slate roofs and delaminating slates add detail.
What makes a roof fishscale
On a plain slate roof, every slate ends in a straight line along the bottom edge, which is called the tail. On a fishscale roof, the tail is cut to a curve. Slates are laid in courses, and each course sits slightly off-set from the one below it, so the rounded tails of one row fall in the gaps between the tails of the row beneath. The result is the overlapping scale pattern the roof is named for.
The pattern has three consequences for anyone working on the roof.
- A slate has to be the right shape as well as the right size. A square-tailed slate leaves a gap in the pattern where the curve should be.
- Slates are laid to a set width, so the courses line up. A slate of the wrong width breaks the alignment of the courses above it.
- The decoration is part of the roof's character. A fishscale roof that is re-covered in plain slate is a different-looking roof, even if the stone is the same.
Underneath the pattern, a fishscale roof is built like any other slate roof. Slates are nailed to battens, laid over underlay, and finished with a ridge, hips, verges and lead where the roof meets walls and chimneys. Nothing about the shape changes the need for sound battens, sound nails and sound lead.
Rounded tails show wear and damage clearly, since a chipped or lifted curve breaks the pattern and stands out from the street.
The Northdown Road appraisal
Thanet District Council's conservation area appraisal for Northdown Road names the covering. It describes the roofs in that conservation area as slated or tiled, with parapets often hiding them from the street, and it records that some roofs are covered with fishscale slates. That is the appraisal's description of an area, not a count of roofs.
Northdown Road is one of the Cliftonville conservation areas. Thanet's table gives its designation date as 20 October 2016, the same date as several others in Cliftonville. A separate Thanet appraisal, for the Cliftonville Clifftop conservation area, describes a mixed palette of roofing there, with red clay tile as well as natural slate, and mentions chimney stacks that have survived in numbers.
What the appraisals do not say matters as much as what they do. They do not say how many fishscale roofs there are, and they do not say a given street has them. Only a look at the roof itself settles which kind you have, and that is the first thing a survey does.
Two practical points follow from the parapet remark in the appraisal.
- A roof hidden behind a parapet may be seen only from above or from a neighbour's window, so the slating can be in worse condition than the street view suggests.
- The lead at the parapet gutter and the parapet flashings protect the slating behind them, and a failed lead detail lets water in behind slating that looks fine from the pavement.
Our survey records the slate type, the pattern and every parapet, valley and chimney, so the repair can be specified from what is actually there.
How fishscale slates fail
A fishscale roof fails in the ways any slate roof does, plus one or two that suit the shape. The common signs are the same as those on other pitched roofs, but they show differently in this pattern.
- Slipped slates. A corroded nail lets a slate drop, which leaves a gap in the scale pattern that is easy to see from the ground.
- Cracked or chipped tails. The rounded edge sticks out furthest on each slate, and it can break under a ladder, a falling branch or a footfall.
- Delamination. Slates that flake in layers lose their surface and their shape, which spoils the pattern and thins the slate at the nail hole.
- Failed lead. Flashings, soakers and parapet gutters that split let water in at the joints between the slating and the walls.
- Worn fixings. Nails that corrode through leave slates held by little more than their weight.
Rain is part of the picture. The Met Office climate station at Manston averages about 613 mm of rain a year, with 110.05 days of 1 mm or more, across 1991 to 2020. Those are figures for that station and not for any one street, but they show how often a roof here is rained on, and a roof with failing fixings meets every one of those days.
The shape shows its cost at the repair stage. A slipped slate on a plain roof can sometimes be replaced from a spare. On a fishscale roof, the replacement has to match the shape, and that is where a repair becomes a matching job.
Matching shaped slates on a repair
Matching is the heart of fishscale repair. A replacement has to look like the slates beside it and fit the pattern, and that depends on getting several things right at once. The table sets out what is measured.
| Feature | What to match | If it is wrong |
|---|---|---|
| Tail shape | The curve of the lower edge | A gap or a flat spot in the pattern |
| Width | The width of the original slates | Courses no longer line up |
| Length | The length, with the lap | The gauge is thrown out |
| Thickness | The thickness of the neighbours | A slate sits proud or lies flat |
| Colour | The weathered tone | A bright patch against old slates |
There are two broad ways to source a match. Sound slates can be salvaged from the same roof, for instance from a rear slope that is being repaired, and used on the visible side. Or new slates can be sourced in a shape and size to suit, which the roofer specifies from measurements and, ideally, a sample of the old slate.
A new slate sits visibly brighter than weathered ones at first. Placing new slates low on a slope or on a less-visible side lets them weather in. The match is taken from a sample of an original slate at the survey, where one can be spared, and not guessed from the street.
If many slates are failing, the matching question becomes a bigger one: whether to re-cover the slope in a matching pattern, and whether the old slates can be reused on the front.
Conservation areas and like for like
Repairing a fishscale roof with fishscale slates is like-for-like work, and like-for-like work is the easy case. Section 55 of the Town and Country Planning Act 1990 takes work out of "development" when it leaves a building's outside appearance materially unchanged. Thanet's conservation area page points the same way: in its words, like for like makes it less likely you will require planning permission.
The words to read carefully are "less likely". They are not "never". Replacing fishscale with plain slates changes the appearance of the roof, so it is not like for like, and the question of permission then arises. Within the same pattern, a replacement in a different material, such as man-made slate, is a judgement that the council is best placed to make.
Three checks apply to a fishscale roof, whatever the repair.
- Is the building listed? If so, works that affect its character need listed building consent under section 7 of the Planning (Listed Buildings and Conservation Areas) Act 1990.
- Is it in a conservation area? Class C permitted development still applies there, unless an Article 4 direction has taken it away.
- Does an Article 4 direction apply? Thanet District Council lists three of them, all in the Ramsgate area, and for Northdown Road the answer is to check with the council.
Class C is the permitted development class for alterations to a house roof. Our guide to planning permission for roof windows sets out its conditions. A flat has no permitted development rights at all.
Repair, or re-slate the slope
As with any slate roof, the choice is between mending what has failed and re-covering. A few slipped or cracked slates on an otherwise sound slope is a repair. Failing nails across a slope, or slates flaking across the slope, points to stripping and re-laying, with the sound slates saved for reuse.
Natural slate is long-lived. HomeBuilding puts Welsh slate at 100+ years of typical life, Spanish at 75 to 100 years, and reclaimed Welsh at 50 to 80 years. Those are ranges for typical roofs, never a promise, and slate itself can outlast the nails that hold it.
Fixings and cost
The fixing rules are the ones for any natural slate roof. BS 5534:2014+A2:2018 is the current standard, and it is not the law. Cupa, the slate maker, says it indicates a minimum pitch of 20 degrees for natural slate and rules out hook fixings below 25 degrees. A fishscale slope is measured at the survey, and the fixing method is chosen to suit.
As national guide figures, Checkatrade's June 2026 table gives natural slate repairs at £150 to £220 per m², up to 3 m² and excluding VAT. MyJobQuote, in October 2026, gives around £7,800 for a slate roof. Both come from national guides and neither is a price from us. Our written figure arrives once the survey is done.
If you have a fishscale roof with a slipped slate, a photo from the pavement is a good start. Send it, and the survey can begin from what is visible.
