A roof of handmade tiles is built in three stages: first, the roof slope is given the pitch required by the Spanish Building Code (CTE), which is 32 % for curved tiles laid without a waterproof membrane; then the tiles are laid from the eaves to the ridge with a good overlap—channel tiles concave side up and cover tiles straddling them—and, finally, the eaves, ridge, hips and valleys are fixed and finished. Handmade roof tiles are moulded by hand and fired at between 980 and 1,050 °C.
What is a handmade roof tile and how does it differ from a machine-made one?
A handmade roof tile is a piece of clay moulded by hand, one at a time, air-dried and fired in a kiln. A machine-made tile is extruded or pressed in series and comes out uniform in size and tone; a handmade tile varies by a few millimetres from one piece to the next and keeps the marks of its moulding.
That variation is not a defect: it is the hallmark of the product. Demosaica’s handmade roof tiles are made by hand, piece by piece, in five sizes, from about 9.5 × 7 cm to about 35.5 × 19.5 cm. The sizes are approximate and the tone may vary slightly, because they are made the way they always have been. The samples from our workshop are glazed in white, green and blue.
- Raw material: natural screened clay, as opposed to ground industrial blends with additives.
- Moulding: by hand, in a mould and over a convex former, as opposed to extrusion or mechanical pressing.
- Regularity: handmade tiles have to be sorted by size and set out with care.
- Where each fits: handmade tiles in restoration work, listed buildings, small roofs and wall copings; machine-made tiles on large roofs.
How are handmade clay roof tiles made?
They are made by screening the clay, mixing it with water into a plastic body, shaping it by hand over a curved mould, air-drying the piece and firing it in a kiln: the same principle as terracotta or zellige.
- Screening. Stones and roots are removed; in traditional tileworks, the earth from the clay pit could contain as much as 25 % stone. Whether the tile cracks as it dries depends on the clay’s plasticity.
- Mixing. Water is added in the pug mill—in the past the clay was trodden barefoot in a pool—until it is even and free of air pockets.
- Moulding. A clot of clay is pressed into a wooden mould and struck off by hand, and the piece is bent over a convex former. Old tiles still show the tile maker’s finger marks.
- Drying. In the shade, with the pieces not touching: about eight days in a traditional tileworks. Firing a damp piece is the quickest way to make it burst.
- Glazing (glazed tiles only). A coat of glaze that melts in the kiln and forms a glassy layer on the exposed face.
- Firing. At between 980 and 1,050 °C; including heating up and cooling down, the cycle takes around 45–52 hours. In the old wood-fired kilns, a batch took about six days to fire and another six to cool.
- Unloading the kiln. Cracked or poorly fired pieces are discarded—they sound dull when tapped—and the rest are packed on pallets.
The Provincial Council of Gipuzkoa preserves an account of the work of traditional tile makers. The same logic, applied to a glazed tile, lies behind the artisan process of making zellige.
What types of roof tile are there and how many do you need per square metre?
The most widely used types in Spain are the curved or Arabic tile, the mixed tile (channel and cover in a single piece), the flat tile (Marseille or Alicante type) and the flat interlocking tile. The number per m² ranges from about 9 for large mixed tiles to more than 30 for curved tiles, and the minimum pitch for each type is set by Table 2.10 of CTE DB-HS 1.
| Tile type | System | Usual size | Tiles per m² (channel + cover) | Minimum CTE pitch without membrane |
|---|---|---|---|---|
| Curved or Arabic | Separate channel + cover | 40–50 × 15–21 cm | 25–36 | 32 % |
| Mixed and single-channel flat | Single interlocking piece | 43–50 × 26–30 cm | 9–14 | 30 % |
| Marseille or Alicante flat | Side interlock | approx. 40 × 25 cm | 12–16 | 40 % |
| Flat interlocking | Interlock on all four sides | Varies by manufacturer | Varies by manufacturer | 50 % |
| Handmade clay (Demosaica) | Channel + cover | 5 sizes, from approx. 9.5 × 7 to 35.5 × 19.5 cm | Depends on tile and overlap | 32 % (laid like a curved tile) |
Sizes and tiles per m² are a guide only, taken from manufacturers’ data sheets. The pitches are those in Table 2.10 of CTE DB-HS 1 for roof slopes less than 6.5 m long, normal exposure and unfavourable climatic conditions, without a waterproofing layer; outside those conditions they are taken from the Spanish standards UNE 136020 or UNE 127100.
Be wary of the figures that get quoted: some sources give 9 tiles per m² for curved tiles and others more than 30, depending on whether they count only the channels or the covers as well. Here we count both. To work it out yourself, divide 100 cm by the distance between channel centres and 100 cm by the effective length (the tile length minus the overlap); multiply the two figures and double the result. With a 40 cm tile, a 10 cm overlap and 20 cm between centres, you get about 33 tiles per m². Add 5–10 % for cuts and breakages.
How do you tile a roof with handmade tiles, step by step?
You work from the bottom up: first the structure and pitch, then the deck, insulation and membrane, and finally the tiles from the eaves to the ridge. These are the steps, with the dimensions required by Basic Document HS 1 (protection against moisture) of the Spanish Building Code.
- Check the structure and pitch. Beams and purlins must carry the finished roof (curved tiles alone weigh around 45–50 kg/m²), and the roof slope needs a pitch of at least 32 %. Any less and the waterproof membrane is no longer optional.
- Prepare a continuous deck. Boarding, large hollow clay planks on dwarf brick walls, or sheets: clean, dry and even. Mark the eaves and ridge on it.
- Insulate, waterproof and ventilate. Insulation and, on top of it, a waterproof membrane; if it is bituminous, PVC or EPDM, the CTE requires it to be mechanically fixed on pitches above 15 %. Leave a ventilated cavity under the tiles: inlet at the eaves, outlet at the ridge, and between 3 and 30 cm² of openings per m² of roof.
- Set out the courses. Work out how many fit with the chosen overlap (7–15 cm for curved tiles, depending on pitch and exposure) and adjust it so that the last course reaches the ridge whole: the top tile is never cut.
- Start at the eaves. The first course is packed up so that it sits at the same pitch as the following ones, and the tiles overhang the eaves by at least 5 cm and at most half a tile. With handmade tiles, sort the pieces first and set the largest aside.
- Lay the channel tiles. Concave side up, with the wide end towards the eaves, working upwards and always lapping the upper tile over the lower one. In complete courses, not in columns.
- Lay the cover tiles. Concave side down, straddling the joint between two channels, with the wide end towards the ridge. Fix those at the eaves, along the verge and in the top course, and a proportion of the rest depending on pitch and wind.
- Finish the ridge, hips and valleys. Ridges and hips take special pieces that overlap the tiles on both slopes by at least 5 cm, and both these and the top course must be fixed. Valleys take a valley gutter or flashing: the tiles overhang it by 5 cm and those on the two slopes are kept 20 cm apart. Abutments with walls and chimneys are protected with a flashing that rises 25 cm above the roof covering.
- Gutter and inspection. The gutter needs a 1 % fall towards the outlet, and the tiles must overhang it by 5 cm. Go over the roof slope after the first heavy rain: that is when badly seated cover tiles show up.
Mortar, foam or dry-laid? How roof tiles are fixed
Today, curved tiles are almost always laid dry, and only the pieces that need it are fixed: eaves, verges, top course, ridge, hips and valleys, and some of the cover tiles. Bedding the whole roof in mortar is reserved for restorations and very exposed roof slopes.
- Dry-laid. Loose tiles on boarding or reed matting, fixed only at edges and junctions. A light, ventilated roof that is easy to repair tile by tile.
- Bedded in mortar. The channel tile sits on a pad of mortar and the cover tile on a raised strip of mortar. It stands up to wind and steep pitches, but it is heavier, ventilates less well and means breaking tiles to make repairs. Use masonry mortar, never neat cement: it cracks and stains the tile.
- With polyurethane foam. A bead under the channel and cover tiles: quick and light, but only with products approved for roof tiles, and with the eaves, top course and ridge also fixed.
- With hooks, clips or screws. Mechanical fixing to battens or boarding, the most secure option on long slopes, steep pitches and in areas with strong winds.
The CTE does not give a percentage: its section 2.4.3.6 requires a sufficient number of tiles to be fixed according to the pitch, the maximum height of the roof slope, the type of tile, the overlap and the building’s location. What it does always require is that the top course, the ridge and the hips are fixed.
Where are handmade roof tiles used besides roofs?
They are used to cap walls and boundary walls, to roof porches, gazebos and sheds, to finish off chimneys and small canopies over doors and windows, and as decorative pieces. Their range of small sizes and their glaze make them more versatile than a machine-made tile.
Wall coping is the most rewarding use: two rows laid channel-and-cover keep the rain off a brick or rubble-stone wall and give it a finish you see in Andalusia in courtyards and on the boundary walls of country estates. In a country house renovation, green-glazed tiles go well with exposed brick, lime and clay floors without tipping into pastiche.
Glazed roof tiles have a long tradition: they cover minarets, madrasas and fountains in Morocco, as we saw on our trip to Marrakech, and they appear in the crowning details of Seville’s Regionalist architecture, the same tradition as Sevillian tiles. They go well with a terracotta or fired-clay floor or with a dado of outdoor zellige.
The glaze vitrifies in the kiln and seals the exposed face, but the clay body is still porous on the back and edges: in our tests, our 15 × 5 cm terracotta had an average water absorption of 16.9 % and our glazed zellige 15.7 % (UNE-EN ISO 10545-3, in the full test reports). That is why, in areas with frost, it pays to treat exposed clay pieces with a water-repellent: water in the pores expands as it freezes and breaks the piece from within.
Common mistakes when tiling a roof
Hardly any leak comes from the tile itself; it comes from the way it is laid. The most common faults:
- Laying tiles at a lower pitch than the system allows, with no waterproof membrane underneath.
- Bedding every tile in cement mortar: a heavy, unventilated roof in which tiles have to be broken to replace a single one.
- Skimping on overlap: below 7 cm on curved tiles, the wind drives water under the cover tile.
- Starting without setting out: the courses come out crooked and the last one does not finish neatly at the ridge.
- Not packing up the first course at the eaves: it ends up at a lower pitch and leaks at the joint.
- Forgetting ventilation under the tiles: condensation, mould and wet insulation.
- Taking handmade tiles up onto the roof without sorting them by size.
- Walking on tiles already laid: work from boards and only step on the points of support.
Frequently asked questions about roofs with handmade tiles
How many Arabic (curved) tiles do you need per square metre?
Between 25 and 36 per m², counting channels and covers, depending on the length of the tile and the overlap. With a 40 cm tile and a 10 cm overlap you need about 33; with 45–50 cm tiles the figure drops to 25–30, and the roof will weigh around 45–50 kg/m² in tiles alone. With handmade tiles, measure the actual piece and add a 5–10 % allowance.
What minimum pitch does a curved-tile roof need?
CTE DB-HS 1 sets 32 % for curved tiles when the roof has no waterproofing layer, on roof slopes less than 6.5 m long and with normal exposure. For mixed and single-channel flat tiles, the minimum drops to 30 %. With a membrane under the tiles, lower pitches can be accepted following UNE 136020.
Can you build a tiled roof without mortar?
Yes, and it is the usual method. The tiles rest loose on the deck and are fixed with hooks, screws or foam only at the eaves, verges, top course, ridge, hips and valleys, plus some of the cover tiles if it is windy or the pitch is steep. The roof is lighter, better ventilated and easy to repair.
How are handmade roof tiles made?
From screened clay mixed with water, which is moulded by hand in a wooden mould and bent over a convex former. The piece is air-dried for several days, glazed if it is to be a glazed tile and fired at between 980 and 1,050 °C, in a cycle of about 45 to 52 hours. Every tile is different, because no two mouldings are the same.
Do glazed roof tiles need a water-repellent?
Not on the exposed face: the glaze vitrifies in the kiln and seals the surface. The clay body, however, is porous on the back and edges—our glazed zellige showed 15.7 % water absorption and our terracotta 16.9 %—so in climates with frost it pays to treat exposed clay pieces with a water-repellent.
Can old clay roof tiles be reused?
Yes, and it is common in restoration work. They are cleaned, any that are cracked, flaking or sound dull when tapped are discarded, and the rest are laid as cover tiles, which are the visible part, with new tiles as channels. That way the roof keeps its patina and the piece that carries the water is the new one.
If you are planning a roof, a wall coping or a porch with handmade tiles, take a look at the glazed handmade roof tiles in our catalogue and ask for samples; lead times, colours and minimum quantities can be checked with the workshop. You can also visit our showroom in Seville by appointment.
