How to Build a Pitched Roof and Lay Roof Tiles

A pitched roof protects the house and gives it character. Building it properly means much more than simply laying roof tiles: the roof pitch, the structure and the waterproofing are what keep out leaks for decades. We'll talk you through the whole process, step by step.

Before you start: the roof pitch

The slope, or roof pitch, ensures that water runs off rather than pooling. With pantiles or interlocking tiles it is usually between 26% and 40%, depending on the region and rainfall: the steeper the pitch, the better the water runs off.

Materials and tools

Materials:

• Rafters or purlins (timber, concrete or metal)
• Roof battens and sheathing, or roofing underlay board
• Waterproofing membrane or Onduline
• Roof tiles and ridge tiles; mortar or fixing clips

Tools:

• Spirit level, string line and tape measure
• Drill, screws and saw
• Bricklaying trowel and float
• Safety equipment: always wear a safety harness when working at height!

Building the roof step by step

1. Set up the structure and the roof pitch

   Lay the purlins or rafters from the wall up to the ridge and give them the slope of the two roof planes. They must be levelled and well anchored.

2. Fit the substructure for the tiles

   Fix the roof battens, the sheathing or the board that will carry the tiles onto the purlins, leaving the overhangs free at the eaves and the sides.

3. Waterproof the roof

   Lay the membrane or Onduline from the bottom upwards, overlapping the sheets so that water can never get in through the joints. This is the step that keeps out leaks.

4. Mark out the rows of tiles

   Mark guide lines so the rows sit straight and with the correct overlap. Always start at the eaves, the lowest part of the roof.

5. Lay the tiles from the bottom upwards

   Each row overlaps the one below and each tile overlaps the one beside it. Fix them with mortar or clips depending on the type of tile and the roof pitch, and keep the rows aligned.

6. Finish the ridge and the edges

   Lay the ridge tiles (the top row) on a bed of mortar and neatly finish the eaves, the hips and the joints against walls or chimneys.

7. Check that it's watertight

   Make sure no loose pieces or gaps remain, especially at the ridge, the hips and around chimneys.

Professional tips

• Never go up onto a roof without safety measures: a safety harness and a fall-arrest line.
• Follow the overlap specified by the tile manufacturer.
• In windy areas, fix the tiles mechanically, not just with mortar.
• If you have any doubts about the structure or the load, consult a professional.

A well-built roof means decades without leaks. If you need to build or repair your roof, we're the specialists here in Calpe: Roof construction and repair · Request a quote.