Laying and Installation of Clay/Concrete Tile Roofing

Clay tiles are made from fired clay. Laid correctly, they last for decades and keep their colour for a long time. Glazed versions have a smoother surface, so rain runs off faster and moss finds it harder to take hold. Manufacturers also make lightweight clay tiles for older or weaker roof structures.

Concrete tiles are very accurate in size, so they go down quickly and in neat, regular rows. They are strong but usually heavier, so the roof timbers must carry their weight comfortably. Flat profiles with simple lines are a popular choice for modern houses.

When choosing, compare three things:

• The weight of the tiles and whether the roof structure can carry it (on a renovation it is wise to have a structural engineer check the timbers)
• The minimum roof pitch the manufacturer states for that tile
• The appearance and how the roof will fit in with neighbouring houses

Some people consider standing seam metal roofing instead. It is lighter and copes with lower pitches, but it is noisier in the rain and looks quite different from a traditional tiled roof.

Tiles are only the top layer of the roof. If something underneath is wrong, even high quality tiles will not save it. Before tiling starts, these layers should be in place:

• The roof structure, meaning the load-bearing timbers, treated against insects, fungi and moisture
• A secondary waterproof layer, usually a breathable roofing membrane, which catches any rain blown under the tiles and carries it down to the gutter
• Counter battens, which create a ventilated gap between the membrane and the tiles
• Tiling battens spaced according to the technical data sheet for the specific tile
• For a habitable loft, insulation between the rafters and a vapour control layer on the room side

Why does batten spacing matter so much? Every tile model has a precise gauge. Even a few millimetres out and the tiles will not interlock properly, gaps appear and the roof starts to leak. The spacing is always measured to the manufacturer's figures, never by eye.

Ventilation is just as important. Air moving under the tiles from the eaves up to the ridge carries moisture away. If the ventilated gap is missing or too shallow, moisture condenses, the timbers get damp and the insulation works less well.

Standard interlocking tiles are usually laid on roofs with a pitch above roughly 22°. For lower pitches there are special tile models and solutions with an extra waterproof layer and seals. The exact limit is always set by the manufacturer of the specific tile.

A good roofer does not start with tiles but with a tape measure. The whole roof is set out so that there are as few cuts as possible and the rows line up at the edges and at the ridge.

1. Measure the roof and set out the number of rows and columns of tiles.
2. Fit the gutter brackets and gutters before the tiles.
3. Lay the first row at the eaves, which sets the line for the whole roof.
4. Lay the tiles from the bottom up, with each row correctly bonded to the one below.
5. Secure the tiles with clips, especially at the edges, near the ridge and in exposed spots, following the manufacturer's instructions.
6. Finish the details: verges, valleys, and the ridge with ridge tiles and a ventilated ridge roll.
7. Flash around the chimney, roof windows and other penetrations.
8. Check that everything is watertight and clear off-cuts and cutting dust from the roof.

The metalwork around chimneys, roof windows and valleys is where roofs leak most often. That is why it helps when the tinsmith works alongside the roofer and they solve the details together, rather than fixing them afterwards.

This is work at height. It belongs in the hands of an experienced team with scaffolding or other fall protection. Laying a tiled roof yourself is not recommended.

The simplest case is a large, plain gable roof with nothing passing through it. The roofer lays whole tiles in regular rows and there is little extra work. These things make the job longer and more expensive:

• A complex roof with dormers, hips and valleys where a lot of cutting is needed
• Several chimneys, roof windows or other penetrations
• A steep roof or poor access, for example a narrow street with no room for scaffolding
• A low pitch that needs extra sealing
• On a renovation, stripping and removing the old roof covering and any repairs to the timbers

If you are replacing the roof covering on an existing house, check with your local building authority first whether you need permission or have to notify them. Rules differ from place to place and often depend on whether the appearance, the material or the load-bearing structure changes. In conservation areas and on listed buildings there are usually stricter requirements. In a block of flats, decisions about the roof are made with the building management or the owners' association.

Repairing a leaking roof is an unpleasant and costly job. Most problems can be avoided if the tiles are laid properly the first time. These mistakes come up again and again in practice:

• Missing or too shallow counter battens, so the roof cannot breathe and the timbers get damp
• Inaccurate batten spacing, so the tiles do not sit properly
• Tiles laid on a lower pitch than the manufacturer allows, without extra sealing
• Weak or missing fixings on edge and ridge tiles, which the wind then lifts off
• Poorly flashed chimneys, windows or valleys
• Tiling in rain or frost, when the membrane and seals do not bond as they should

Sensible ordering also helps. Tiles are usually ordered with a margin of roughly 5 to 10 per cent for cuts and breakages. Buying more of the same batch later can be difficult, because the shade varies slightly between production runs.

When you take over the work, look at the roof from outside and from the loft. Check in particular:

• The rows of tiles are straight and the tiles interlock evenly
• Edge, ridge and exposed tiles are fixed with clips
• The ridge is closed with ridge tiles and ventilation at the eaves and ridge is not blocked
• Flashings around the chimney, windows and valleys are tight and shed water in the right direction
• The gutters fall correctly and water drains into the downpipes
• There are no damp patches or damaged membrane visible from the loft
• No off-cuts or debris are left on the roof or in the gutters
• You have received the tile data sheets and the documents needed for the warranty

It is worth looking into the loft again after the first heavy rain. Any small problem will then show up while the work is still under warranty.