Question answered
Interlocking or plain tiles: which is better?
The short answer
Neither is better outright. Interlocking tiles are large, lock into each other and can go on shallower pitches, from about 12.5 to 25 degrees depending on the profile in Marley's range. Plain tiles are small and overlap course on course, so they need steeper roofs: 30 to 40 degrees for the clay ones and 35 degrees for concrete. Plain tiles give the traditional look, and interlocking tiles cover ground faster.
The two kinds of tile behave differently on a roof, so the better one depends on your pitch, your house and your budget. Here is how they compare, with no sales pitch for either.
How each one keeps water out
Plain tiles are little more than a hand-sized slab with a gentle camber. They shed water by lapping: each row hides the joints beneath it, and the bond is staggered so a tile always sits behind every gap. Because the tiles are small, a roof needs a great many of them, and each hangs on nibs over a batten with a nail in some courses.
An interlocking tile is larger and has a profile that locks into its neighbour along the side. Water runs down the channels and the lock stops it creeping sideways. Fewer tiles cover the same area, and each is fixed mechanically, because a single-lap tile has no neighbour lying over it to hold it down. That also means a roof of them goes on quickly, which is part of their appeal.
Both rest on battens over underlay, and both lean on that second layer and on sound fixings, which roof tile clips explains.
Pitch limits decide more than taste
This is where the choice is often made for you. Marley lists the minimum pitch for its concrete plain tile at 35 degrees. Its clay plain tiles range from 30 degrees for Hawkins and Acme Single Camber to 35 for Ashdowne and 40 for Canterbury. Its interlocking concrete tiles go lower, between 12.5 and 25 degrees depending on the profile, such as 17.5 for Edgemere and 22.5 for Double Roman. Always read the maker's own data sheet before ordering.
If a roof is shallow, plain tiles are off the table, and the choice narrows to an interlocking profile suited to that slope. If it is steep, as many Victorian roofs are, either will work.
The pitch itself depends on the frame underneath, which differs between older and newer houses, as set out in cut roof or trussed roof. A shallow pitch also leaves less room for error when wind drives rain up the slope.
Weight and what the roof frame can carry
Swapping one covering for another can add load. Approved Document A treats any rise in loading above 15% as significant. For the Planning Portal, a covering at least 15 per cent heavier than the old one needs building control approval. Where the frame cannot take it, strengthening follows.
This matters most when a light covering is replaced by a heavier one, or when a roof already shows movement, which is the subject of what roof spread is and how it is fixed. Before swapping coverings, the Planning Portal recommends having a structural engineer or surveyor assess the frame.
We do not guess at weights. The tile maker publishes the figure for every product, and the survey tells us what sort of timber frame is beneath before anything is ordered. Switching from plain to interlocking, or the reverse, is a decision the loft inspection should inform, never one made from the street.
Look, lifespan and upkeep
Plain clay tiles have a cambered, slightly irregular surface that suits older houses, and a conservation area is a good reason to keep it. Interlocking tiles give a flatter, more uniform finish. Modern profiles imitate plain tiles, but the shadow lines between courses differ.
On lifespan, Marley reports a minimum life of 60 years for clay tiles, established by the Building Research Establishment, and gives about 60 years for concrete, adding that this is no guarantee. MyBuilder puts clay replacement at 40 to 60 years and concrete at 30 to 50. Real life depends on exposure, workmanship and upkeep.
Moss, salt and frost shorten the life of either type. Damp lofts age a roof from beneath, too, which is why tile vents come into the conversation when a covering is chosen.
Cleaning moss from a roof is a job for a roofer with proper equipment, not a pressure washer in the wrong hands.
Where the money goes on a tiled re-cover
Cost follows the number of tiles laid and the work that surrounds them. Plain tiles take longer, because there are more of them and the fixing is finer. Interlocking tiles go on faster. Clay generally costs more than concrete as a material. Access, scaffold, roof shape, the count of hips and valleys and the condition of the battens all move the final total.
For a guide, Checkatrade's repair table, updated June 2026, puts concrete tile repair at £90 to £120 per m² and clay at £110 to £160, excluding VAT. Those are typical UK ranges for repair, not re-roof prices.
A full re-roof is looked at in pitched roof cost. Our price is put in writing after the survey and covers the whole job. Whoever quotes you, ask if VAT and scaffold are inside it. Other tiled-roof work is gathered on the pitched roofing page.
Choosing a tile: further questions
Can plain tiles be swapped for interlocking ones on one roof?
Often, but not without checks. The pitch must suit the new profile, the battens will be re-gauged, and the change in weight has to be set against the 15 per cent threshold. In a conservation area or on a listed building the look matters to the council, so ask the Adur & Worthing planning team first.
Do interlocking tiles last as long as clay ones?
Published lifespans for both sit in a similar band of decades, with clay often given the higher figure. In practice, how well the roof is fixed, ventilated and maintained matters more than the label, so a well-kept concrete roof can outlast a neglected clay one.
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