Stand on any street in north Hampshire and look up. Some roofs show a fine, textured grain of small tiles, each course overlapping the next like scales. Others show broad, flat or gently ribbed tiles that make bold parallel lines down the slope. The first is a plain tile roof. The second is interlocking. The two do the same job and are laid in very different ways, and the difference shapes how a roof looks, how fast it goes up, what it costs and how it can be repaired. This guide explains both, so you can recognise what you have and choose between them with open eyes.
What a plain tile is
A plain tile is a small, slightly curved rectangle, with a standard size of 265 mm by 165 mm. Historically made from clay, they are now also made in concrete. Two small nibs on the back hook over the battens, and two holes take nails. Plain tiles are laid in a "double lap", which means each point of the roof is covered by at least two layers of tile, because the tail of one course covers the joint between tiles two courses below. The camber, a slight curve along the length, helps water run to the centre and clear of the joint.
Because they are small, plain tiles take many hundreds to cover a house, and each needs placing individually. That is why plain tile roofs have the fine texture that suits older houses, and why they cost more to lay.
What an interlocking tile is
An interlocking tile is much larger, commonly covering the area of several plain tiles, and has a profile along its sides that locks into its neighbour. That side lock is the key: it forms a channel that keeps water moving downslope, so the tile does not depend on a double lap. Interlocking tiles are laid in a "single lap", where each tile overlaps only the course below. The most common are made of concrete in profiles introduced from the middle of the last century, which is why they dominate the estates of the 1960s onward. Interlocking clay tiles also exist and are used where the clay look is wanted.
Because each tile covers a large area and clicks into the next, a roofer can lay a slope quickly and with fewer fixings per square metre. That is the main reason interlocking tiles became the standard for volume housing.
Appearance and character
This is often the deciding point. A plain tile roof has a soft, uneven, handmade look, with variation in colour from tile to tile and a pleasing texture across the slope. On a period house, a Victorian terrace or a village cottage, it is the covering the building was designed for. Many conservation areas expect it, and a roof in an area of character or on a listed building may need consent to change it. Check with your council's conservation officer before changing the look of a roof in those settings.
An interlocking tile has a bolder, flatter, more regular appearance, with clear straight lines. On a 1970s or 1980s house, it is the covering that belongs, and replacing it with plain tiles can look out of place. Some interlocking clay tiles are made to imitate the plain tile look, but the profile and the line of the joints usually give them away.
Pitch and exposure
Plain tiles rely on overlap and gravity, so they need a steeper roof. A typical plain tile roof is pitched at around 35 degrees or more, and a low-slope roof will not suit them. Interlocking tiles can be laid at lower pitches because the side lock stops water crossing between tiles, with many profiles rated down to around 22.5 degrees and a few lower. The exact minimum for any tile is the manufacturer's figure, and our guide to minimum roof pitch for tiles explains how to find it.
That matters when you are covering an extension. A shallow lean-to will often rule out plain tiles and point to an interlocking profile rated for the angle. On a steep roof you have a free choice.
Weight and structure
Which is heavier depends on the exact products, and you cannot judge it by holding a single tile. The correct comparison is the finished weight of the covering per square metre, as published by the manufacturer, including the battens. Plain tiles use a double lap and so carry more material per square metre than their size suggests. Large concrete interlocking tiles are heavy individually and heavy overall. Clay plain tiles are often lighter per square metre than concrete, but not always.
The practical point is the one that matters in Building Regulations: a covering that tips the scales 15% or more past the old one brings building control into it, and the structure may need checking. When changing from one format to another, that comparison is worth making before the order is placed. Our answer on how heavy concrete and clay roof tiles are and the guide to concrete versus clay both help.
Eaves, ridge, hips and edges
The two formats also differ in how they finish at the edges, and the details are where a roof tends to age. Plain tiles use special pieces to finish: tile-and-a-half and half-round pieces at the verge, and short eaves tiles at the bottom course. Interlocking tiles use matching verge tiles, eaves clips and dry-fit systems that suit their profile. Plain tile roofs commonly end at the verge with an undercloak course and a mortar pointing, while interlocking roofs are more likely to take a dry verge system.
Hips and ridges differ too. A hip on a plain tile roof is often dressed with bonnet hip tiles or lead soakers (small pieces of lead that go under each course), which suits the fine texture. Interlocking roofs take hip and ridge tiles of a matching profile. Both formats now expect those parts to be mechanically fixed, as the tiling standard sets out. Our guide to hip tiles, hip irons and dry hip systems explains the options, and the page on dry verge systems shows how a verge is finished without mortar.
Cost and laying time
Plain tiles cost more to lay because there are more of them and each is placed with care. A given area takes a roofer noticeably longer in plain tile than in interlocking, and the labour is where much of the difference sits. The tiles themselves, particularly clay and hand-made, can also cost more. Interlocking concrete is the economical option for a plain roof with simple shapes.
Any figure you read online is a national average, so treat it as a rough guide. Typical UK ranges reported by one cost guide put a re-roof in concrete tiles on a three-bedroom semi at £6,500 to £10,500, and the spread rises when the covering is clay or hand-made, or the roof has dormers, hips and valleys. The price of your roof comes from the survey and sits in a fixed written quote.
| Feature | Plain tile | Interlocking tile |
|---|---|---|
| Size | Small, 265 mm by 165 mm standard | Large, covering the area of several plain tiles |
| Laying | Double lap, each tile placed individually | Single lap with side lock |
| Typical minimum pitch | Around 35 degrees | Commonly around 22.5 degrees, some lower |
| Look | Fine texture, suits period buildings | Bold lines, suits postwar estates |
| Labour | Slower, so dearer | Quicker, so cheaper |
| Single-tile repair | Easy to lift and replace | Need care around the side lock |
Repairs and maintenance
Plain tiles are forgiving. A single cracked tile can be lifted by sliding a trowel or a tile lifter under the courses above, and a new one slid in and hooked on its nibs. Because there are many tiles, small repairs spread across a roof are common, and a patchy look can result if the replacements do not match. Our answer on replacing a single roof tile covers the method and the pitfalls.
Interlocking tiles are harder to replace in a single piece because the side locks tie neighbouring tiles together, and a broken tile often has to be removed with care or cut out. The big tiles also make a broken one visible from the ground. On the plus side, there are fewer joints and fewer fixings to fail. Whichever you have, the repairs that matter most are on the fixings, the ridge and the valleys. Our guide to nail sickness and the feature on roof valleys are good places to look.
Matching and mixing
Questions about matching come up on almost every tiled job, and they come up for a reason: a roof is read as a whole from the street, and a patch of different tile draws the eye straight to it.
You cannot mix plain and interlocking tiles on one slope and expect a good result. The laps, the gauge and the thickness do not agree, and the join shows. On an extension, builders sometimes use a clearly different tile on the new roof. That works when the two roofs are separate planes. When a new section runs onto an old one, the sensible approach is to match the existing tile as closely as possible. Our page on matching new tiles to an old roof covers the practical options, including reclaimed tiles.
Which one should you choose?
Match the house. If the building is old, built for plain tiles, or in a protected area, keep to plain tiles and accept the cost. If it is a postwar house roofed in interlocking tiles, a like-for-like replacement is usually the better value and the better look. For a low-pitched extension, the pitch will probably decide it for you. For a tight budget on a simple roof, interlocking is the economical path.
We help you decide on the roof itself. At the survey we measure the pitch, photograph the existing covering, check the fixings and the battens, and note any constraints from the building's setting. The report names the tile we would use and why, with a fixed written quote behind it. The work is guaranteed in writing for ten years, and the site is cleared when we finish. See our pitched roofing in Basingstoke page for the rest of the service.
