Concrete Roof Tiles: Profiles, Prices and What to Order for Your Extension

Order the wrong profile and your roofer spends a day returning tiles instead of laying them. Order the right profile in the wrong quantity and you're three pallets short on a Friday afternoon, with scaffolding hired by the week and rain forecast for Monday. Concrete roof tiles are straightforward, but the differences between profiles, the interaction between pitch and headlap, and the fixing requirements under BS 5534 catch homeowners out every time. Get it right and your extension roof costs half what clay would. Get it wrong and you've paid for a delay that didn't need to happen.

What they are and what they're for

Concrete roof tiles are machine-made from sand, cement, and water, pressed into moulds and cured. They've been the default pitched-roof covering on UK housing estates since the 1960s. If your house was built between 1960 and 2000, there's a strong chance it has concrete tiles.

They're cheaper than clay, available in dozens of profiles and colours, and they last 50 to 60 years with no maintenance beyond the occasional replacement of a cracked tile. The trade-off is weight (large-format concrete interlocking tiles run around 44 kg/m2, which is heavier than clay interlocking tiles of the same profile) and aesthetics (they fade and weather over time where clay generally improves). Note: clay plain tiles at 71–90 kg/m2 are actually heavier than concrete interlocking tiles — the weight difference only holds when comparing like-for-like profiles. For an extension where you need to match an existing concrete-tiled roof, they're the only practical choice. Planning officers and building control both expect the new roof to match the original.

All concrete roof tiles sold in the UK must comply with BS EN 490:2011+A1:2017. That standard covers dimensional tolerance, freeze-thaw resistance, transverse breaking load, and water impermeability. Any tile from Marley, Redland (BMI), or Sandtoft (Wienerberger) will meet it. Tiles are also rated Class AA for fire performance under BS 476-3, which means they satisfy building regulations without any additional testing.

Types, profiles, and sizes

Concrete tiles come in three broad categories, and the differences matter because they affect how many tiles you need, how much your roof weighs, what pitch you can use them on, and what your roof ends up looking like.

Interlocking tiles are the most common. Each tile has a channel and rib system that overlaps with its neighbours, creating a watertight joint. They're large format (typically 420 x 330mm), fast to lay, and need around 10 tiles per square metre. This is what's on most post-1960s UK houses.

Plain tiles are smaller (265 x 165mm is standard) and overlap top-to-bottom by a much larger margin. They need roughly 60 tiles per square metre, which makes them significantly more expensive per m2 and slower to lay. They give a traditional, textured appearance that's closer to clay plain tiles. You'll find them on conservation area projects and period properties.

Large-format slates (concrete tiles made to look like natural slate) are flat-profiled and heavier, running 90 to 100 kg/m2. They're a budget alternative to natural slate but they don't fool anyone up close.

For most extension work, you're dealing with interlocking tiles. Here are the profiles you'll actually encounter:

Two things to notice. The Redland 49 is a smaller tile that needs 16 to 18 per square metre, nearly double the coverage of the large-format interlocking profiles. It's been a London and South East staple for over 50 years. And the Marley Mendip 12.5 goes down to 12.5 degrees, which is unusually low for a concrete tile, making it the go-to for shallow-pitched extension roofs where other profiles won't work.

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Through-colour vs surface-colour

This distinction catches people out years after installation. Through-coloured tiles have pigment mixed into the concrete before pressing. The colour runs all the way through. If a tile chips or fades, the underlying colour is the same.

Surface-coloured tiles have pigment applied to the face after moulding. They look identical when new but the coating wears off over time, exposing the grey concrete underneath. When you replace a damaged surface-coloured tile five years later with a new one, the colour mismatch is obvious because the surrounding tiles have faded while the replacement hasn't.

For extension work where you're matching existing tiles, this matters. If your house has 20-year-old surface-coloured tiles, a new tile of the same product will look different until it weathers in. Through-coloured tiles age more consistently.

Minimum pitch and headlap

Every tile profile has a minimum pitch (the angle of your roof slope, measured in degrees). Go below it and water backs up under the overlapping joint and into the roof space.

Pitch interacts with headlap (how much the upper tile overlaps the lower one). More headlap allows a lower pitch because water has further to travel uphill before reaching the joint. The standard headlap options are 75mm and 100mm.

For smooth-faced tiles, 75mm headlap typically requires a 22.5-degree pitch or steeper. Increase the headlap to 100mm and the minimum pitch drops to 17.5 degrees.

Granular-faced tiles (those with a textured or sandfaced finish) have higher minimum pitches than the same profile in a smooth finish. Sandtoft's Double Roman, for example, requires 17.5 degrees with a smooth finish but 30 degrees with a sandfaced finish. The rough surface holds water.

How to work with concrete tiles

You won't be laying these yourself (it's specialist work that requires scaffolding and experience), but understanding the process means you can tell if your roofer is doing it right.

Batten gauge

This is where most tiling mistakes start. The batten gauge is the spacing between the horizontal timber battens that the tiles hang from. It's determined by the tile's exposed length after accounting for the headlap, and it must be calculated from the ridge down to the eaves before a single batten goes up.

A roofer who starts nailing battens from the eaves upwards without calculating the gauge first will end up with an odd gap at the ridge that doesn't fit the tiles. The correct method: measure the rafter length, subtract the eaves overhang and ridge allowance, divide by the number of courses needed based on your tile's gauge. Then set battens from the top down, using a gauge rod (a piece of timber cut to the exact batten spacing) to keep every course consistent.

For large-format interlocking tiles with 75mm headlap, the typical gauge is around 345mm. At 100mm headlap, it drops to about 320mm. Your tile manufacturer's data sheet gives the exact figure.

Installation sequence

Tiles are laid right to left, bottom to top. The right-to-left direction means each tile's interlocking channel sits over the one below it on the left side, creating a continuous water channel that drains downhill. Working upward in columns minimises foot traffic on already-laid tiles.

The first course at the eaves should overhang the fascia board by approximately 50mm, directing water into the gutter. The eaves course uses either a shorter tile or an eaves tile specifically designed to sit at the correct angle on the tilting fillet.

Fixing requirements under BS 5534

BS 5534:2014+A2:2018 is the code of practice for slating and tiling, and it changed the rules substantially. Before 2014, many UK roofs were laid with tiles simply hooked over battens and nailed at intervals (every 5th row was common). Older roofs routinely had no nails at all. Some have lasted 60 years.

The current standard requires every single-lap interlocking tile to be mechanically fixed with at least one nail or clip. Perimeter tiles (the two tiles in from every edge) require two mechanical fixings. At pitches above 45 degrees, every tile needs a nail. Above 55 degrees, every tile needs a nail plus a tail clip.

The specific fixing pattern for your roof is determined by a site-specific wind load calculation that considers the roof's height, pitch, location, altitude, and surrounding terrain. Your roofer should be doing this calculation (or using the tile manufacturer's fixing guide, which provides lookup tables). If they tell you they're "just nailing every fifth row like we always do," they're not meeting current standards.

Membrane and battens

Tiles sit on 25 x 50mm treated timber battens, which sit on a breathable roof membrane draped over the rafters. The membrane must lap 150mm at horizontal joints and 100mm onto the next rafter at vertical joints. Maximum drape between rafters is 15mm per BS 8000-6, otherwise water pools in the sag instead of running down to the eaves.

Battens must be treated softwood (typically BS 5534 graded). Tile weight loading means they need to be properly supported. On a standard 600mm rafter spacing, 25 x 50mm is fine for most concrete tiles. Wider rafter spacing may need thicker battens.

How much do you need

Tile quantity

Start with the plan area of your roof (length x horizontal span). Then correct for pitch. A pitched roof has a larger surface area than its horizontal footprint. At 30 degrees, the correction factor is 1.15 (15% more area). At 45 degrees, it's 1.41 (41% more). At 22.5 degrees, it's 1.08.

Multiply the corrected area by the tiles-per-m2 figure for your chosen profile. For large-format interlocking tiles at 75mm headlap, that's typically 9.7 to 10 tiles per m2. For Redland 49s, it's around 17.

Add 10% wastage for a straightforward rectangular roof. Add 15% for a roof with valleys, hips, dormers, or other features that require more cutting.

Worked example: an extension roof measuring 6m long by 4m rafter length at 22.5 degrees. Plan area is 6 x 4 = 24m2. Pitch correction: 24 x 1.08 = 25.9m2. Using Marley Edgemere at 9.7 tiles/m2: 25.9 x 9.7 = 251 tiles. Plus 10% wastage: 276 tiles. Marley Edgemere ships in pallets of 240, so you need 2 pallets (480 tiles, giving you useful spares from the same batch).

Other materials

You'll also need roofing battens (linear metres = rafter length / batten gauge x roof length, plus 10%), breathable membrane (roof area plus overlaps), ridge tiles (one per 330mm of ridge, plus any hip tiles), and a dry ridge system for the ridge line. Lead flashing where the extension meets the existing house wall.

Cost and where to buy

Concrete tiles cost a fraction of clay. Budget interlocking tiles from lesser-known brands start around £7-£25 per tile. Mid-range tiles from Marley, Redland, or Sandtoft run £7 – £25 per tile depending on profile and finish. That translates to roughly £7 – £25 per square metre for materials alone, based on 10 tiles/m2 for large-format interlocking profiles.

For a typical 25m2 extension roof, materials (tiles, battens, membrane, ridge, fixings) come to roughly £500 – £900. Labour adds £500 – £900 depending on your area and access difficulty. Total for the tiled covering: £500 – £900. Scaffolding is separate.

Where to buy

Concrete roof tiles are a builders' merchant product. Travis Perkins and Jewson carry the main ranges from Marley, Redland, and Sandtoft with full pallet delivery. Online roofing specialists (Roofing Superstore, About Roofing, JJ Roofing Supplies) often undercut the big merchants by 10 to 15% on pallet orders.

Screwfix and Toolstation don't stock roof tiles. Don't look there.

Full pallets are much cheaper per tile than buying loose. A pallet of 192 Marley Modern tiles runs around £300 – £480 depending on the finish. Delivery is typically free above a threshold (often one pallet), but check lead times. Standard profiles ship within a week. Unusual colours or discontinued profiles take longer.

Matching existing tiles on your house

This is the single biggest practical challenge for extension roofing. Your 1980s Redland 49s in Rustic Red have been weathering for 40 years. New tiles of the same product will look noticeably different until they weather in, which takes two to five years.

Start by identifying what's on your roof now. Lift a tile from an inconspicuous spot (the roofer can do this) and check the back for a manufacturer stamp. It usually shows the brand, profile name, and sometimes a date. Measure the tile dimensions: 382 x 226mm is a Redland 49, 420 x 330mm is a large-format interlocking like Marley Modern or Edgemere.

If the profile is discontinued (Redland 52 is a common one), your options are reclamation yards (bring a sample tile), roofing merchants with old stock, or third-party replica tiles found through specialist suppliers. Buy more than you need because reclaimed tiles have higher breakage rates.

Alternatives

Clay roof tiles are the obvious alternative. Clay interlocking tiles are lighter than concrete interlocking tiles; they don't fade, and they look better with age. They cost roughly twice as much per tile (£0 – £0 for machine-made interlocking, more for handmade) and they're more fragile during handling. If you're building on a property with clay tiles, you need clay tiles. If you're choosing for a new-build extension where appearance is the priority and budget allows, clay is the better long-term material.

Natural slate costs roughly three times more than concrete and gives a completely different aesthetic. It's lighter per m2 than concrete interlocking tiles and lasts 75 to 100 years. Unless your existing roof is slate, this isn't usually relevant for extension matching.

Composite slates (fibre cement or recycled materials) are a modern alternative in the slate-look space. They're lighter than concrete, available in consistent colours, and cheaper than natural slate. They don't replicate a traditional concrete tile profile though, so they're not suitable for matching an existing concrete-tiled roof.

Where you'll need this

• Roof covering - the primary task where concrete tiles are specified, laid, and inspected as part of the pitched roof covering on an extension

Common mistakes

Ordering the wrong profile. "Concrete tiles" is not a specification. You need the exact profile name and colour. Your roofer should be matching these to your existing roof, but verify it yourself. Marley Modern and Marley Edgemere are both large-format interlocking tiles from the same manufacturer and they look different on a roof.

Ignoring the pitch limit. A low-pitched extension roof (below 22.5 degrees) rules out many common profiles. If your architect has drawn a 15-degree pitch, your tile options are limited to profiles like the Marley Mendip 12.5. A tile laid below its minimum pitch will leak.

Underestimating quantity. Homeowners who calculate tiles based on the plan area of their roof (length x width) without correcting for pitch end up short. A 30-degree pitch adds 15% to the tile count. A 45-degree pitch adds 41%. And then you need wastage on top.

Accepting galvanised nails. If your roofer fixes tiles with standard galvanised nails instead of stainless steel, those fixings will corrode within 20 to 30 years. The extra cost for stainless steel nails on an extension roof is under £30. The cost of re-fixing a roof because the nails have rusted through is thousands.

Panicking about efflorescence. White chalky patches on new concrete tiles are calcium hydroxide deposits that form when tiles get wet and dry slowly. It's cosmetic, it doesn't affect the tile's strength or waterproofing, and it weathers away naturally, typically within 6 to 12 months. Do not pressure wash it off. Pressure washing damages the tile surface and voids some manufacturer warranties.

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