Matching roof tiles when the original is unavailable

When the original roof tile is no longer made, the way to match a roof is to match its profile and texture first and its colour second. A concrete interlocking tile in roughly the right shade next to a clay plain tile roof reads as a different building, because the shadow lines, the lap and the unit size are all wrong. Get the profile right and a slight difference in colour weathers out within a few seasons.

That matters whether or not an application is needed. Permitted development under Class A of Part 1 of Schedule 2 to the Town and Country Planning (General Permitted Development) (England) Order 2015 carries a condition that the materials used in any exterior work must be of similar appearance to those used in the existing house. A visibly mismatched roof is a breach of that condition, not merely an aesthetic misjudgement.

Why tile profile matters more than colour

A roof covering has three characteristics the eye reads from the street: the size of the unit, the depth of shadow between courses, and the surface texture. Colour comes fourth.

Plain tiles are small, laid double lap, and give a fine grain with a dense pattern of horizontal shadow lines. Interlocking tiles are much larger, laid single lap, and produce long continuous shadow lines with a visible roll or flat pan. Pantiles give a strong S-curve. Slate gives flat, thin courses with crisp edges and almost no relief.

Put any two of those next to each other and the difference is obvious at 30m, whatever the colour. That is why a case officer looking at a photograph of a rear extension will comment on an interlocking tile against plain tiles and say nothing about a plain tile two shades lighter than the original.

Clay plain tiles against concrete interlocking

The practical choice on most Victorian and Edwardian houses is between clay plain tiles and a concrete interlocking tile that costs considerably less and lays faster.

Two technical points limit the substitution. Plain tiles need a steep pitch, generally around 35 degrees as a minimum for standard double lap work, while interlocking tiles are designed to work at much shallower pitches. So a shallow single storey rear extension roof cannot take plain tiles at all without a different detail.

The second is weight and batten spacing, which is a structural question rather than a planning one but drives the design. A plain tile roof is heavier per square metre than most interlocking roofs, and on an extension tied into an existing structure that difference has to be accounted for.

Where the main house has plain tiles and the extension roof pitch is too shallow for them, the honest answers are to raise the pitch, to use a different covering that is clearly of its own kind such as standing seam metal or a single ply membrane on a flat roof, or to accept a sympathetic substitute and explain the reasoning. What rarely succeeds is a concrete tile pretending to be a plain tile.

Reclaiming tiles from the original slope

The best match for an old roof is the old roof. Where an extension removes part of an existing slope, or where a rear outrigger is being raised, strip and set aside the sound tiles and relay them on the elevation that matters most.

The method is straightforward. Strip carefully, sort into sound, reusable and broken, use the reclaimed tiles on the most visible slope, and cover the less visible slope with new tiles of matching profile. On a terrace this usually means reclaimed tiles to the front or to whichever slope is seen from the street, and new tiles to the rear.

Expect losses. Hand-stripping a clay plain tile roof laid a century ago typically yields a usable proportion well short of the whole, and old nibs break. Order the new tiles knowing that, and keep a small stock for repairs.

Reclaimed tiles bought in rather than salvaged from the house carry two risks worth stating: inconsistent frost resistance in tiles of unknown age, and provenance. Ask where they came from.

Verge, ridge and valley details

Details give away a roof faster than tiles do. Three are worth specifying rather than leaving to the roofer.

The verge, where the roof meets the gable, was traditionally bedded in mortar with an undercloak, sometimes with a tile-and-a-half course. A plastic dry verge system on a Victorian terrace is immediately visible and frequently the subject of a condition requiring removal. If a dry system is used for durability, choose one with a low profile in a dark colour.

The ridge changes the silhouette. Half-round ridge tiles sit differently from angular or hogback ridges, and swapping one for the other on part of a roof is noticeable along a whole street. Match what is there.

Valleys are where plain tile roofs show their quality. A swept or laced valley is the traditional detail on clay plain tiles and is expensive. A lead-lined open valley is simpler and acceptable in most settings. A GRP valley trough on a prominent front roof slope will be commented on.

Slate: natural, Spanish and fibre cement

Slate roofs are easier to match in profile and harder to match in character. Natural slate varies in colour, thickness and surface between quarries, and the difference between a Welsh slate and an imported slate of the same nominal size is visible in texture and in how the roof ages.

Three practical points. Match the size as well as the material, because slate sizes vary and a change in course height alters the proportions of the whole slope. Fibre cement slates are flat, uniform and thinner at the edge, and read as a modern material at close range, which makes them a reasonable choice on a rear extension and a poor one on a street elevation in a conservation area. And on a listed building, slate substitution is a matter for listed building consent in its own right, supported by a Heritage Statement describing the existing covering and the effect of the change.

Where a different tile is acceptable

There are situations where matching is the wrong objective. A clearly contemporary extension with a flat roof, a zinc or standing seam covering, or a glazed roof, is not trying to match and should not pretend to. Officers generally accept a frank difference more readily than a poor imitation.

The cases where a different covering is usually accepted:

• Rear single storey extensions not visible from the street.
• Flat or shallow-pitched roofs where the original covering is technically unsuitable.
• A designed contrast on a contemporary addition, explained in the Design and Access Statement rather than left for the officer to interpret.
• Roofs behind a parapet where the covering is not visible at all.

The cases where it is usually refused are front roof slopes, roofs in a conservation area visible from a public vantage point, and anything on a listed building. Where an Article 4 direction applies, the permitted development route may not be available either, and replacing windows where an Article 4 direction applies explains how those directions work.

An illustrative example

A 1900s terrace has a rear outrigger being raised to create a larger bathroom, with the main roof in clay plain tiles. The original tile pattern is no longer manufactured. The builder strips the outrigger slope, salvages enough sound tiles to cover the new rear slope facing the garden, and uses a current clay plain tile of the same nominal size on the small side slope that is not visible from the lane. The verge is mortar bedded with a tile-and-a-half course to match the existing. This example is illustrative and not a specification for any particular house.

Discharging the roofing materials condition

Where permission has been granted with a condition requiring materials to be approved, make the submission easy to approve. Councils discharge these quickly when the evidence is specific.

What works:

1. The manufacturer, product name and reference for each covering, with the nominal size.
2. A photograph of the proposed tile alongside the existing roof, taken in daylight, not a product brochure image.
3. A note of which slopes receive reclaimed tiles and which receive new.
4. The verge, ridge and valley details named, with a sketch where the detail is unusual.
5. Where a sample panel is offered, say where it will be built and invite inspection.

Submit before the roof goes on. A condition discharged retrospectively after a mismatched roof is complete leaves the council with a choice between accepting something it refused and asking for the roof to be redone, and neither conversation goes well. The same discipline applies to wall finishes, as the materials condition on render and cladding sets out.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it, and remember that a Lawful Development Certificate is the only formal way to confirm that works are lawful.

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