Calculate ridge tiles, mortar, or dry-fix kits for your roof ridge
The ridge is the highest point of a pitched roof -- the horizontal line where the two sloping sides meet at the top. Ridge tiles cap this junction, providing a watertight seal while allowing the roof to breathe. Getting the right number of ridge tiles, along with the correct fixing materials, is essential for a weatherproof and compliant roof. In the UK, ridge tiles are available in three main profiles: half-round (the most common, with a smooth curved profile), angular (with a defined angle suited to steeper pitches), and universal (designed to fit a range of pitch angles). Standard ridge tiles are approximately 450mm long, and when laid with a mortar gap of about 12mm between each tile, you need roughly 2.2 tiles per metre of ridge length. The method of fixing ridge tiles has changed significantly in recent years. Traditional mortar bedding -- where each tile is set on a generous bed of sand-and-cement mortar -- was the standard approach for decades. However, mortar bedding has well-known problems: the mortar cracks over time due to thermal expansion and contraction, rain washes out the mortar joints, and high winds can lift unsecured tiles from a weakened mortar bed. This has led to a major shift towards dry-fix ridge systems. Dry-fix systems, now required by BS 8612 for all new-build properties in the UK, use mechanical fixings -- a continuous roll of ventilated membrane along the ridge, with each tile secured by stainless steel screws and clips. This provides superior wind resistance (tested to withstand wind speeds exceeding 100 mph), eliminates mortar maintenance, and ensures consistent ventilation along the ridge line. One dry-fix kit typically covers approximately 6 metres of ridge. This calculator determines the number of ridge tiles required (with waste allowance), the mortar or dry-fix kits needed depending on your chosen fixing method, and the two end caps required to finish the ridge neatly at each end.
To calculate ridge tile requirements: 1. Measure the ridge length in metres. This is the horizontal distance from one end of the ridge to the other. On a simple gable-ended roof, measure from gable to gable. On a hipped roof, the ridge is shorter than the building length as the hips reduce the ridge at each end. Use a tape measure along the ridge board if you have roof access, or measure the building below and subtract the hip returns. 2. Select the tile type. Half-round is the most popular choice and suits the majority of UK roof styles. Angular tiles are better suited to roofs with a pitch above 40 degrees. Universal tiles offer flexibility and are commonly used with dry-fix systems as they accommodate slight variations in pitch. 3. Select the fixing method. Dry-fix is recommended for all new installations and re-roofing projects. It is required by BS 8612 on new-build properties. Mortar bedding is still used for repairs and in conservation areas where a traditional appearance is required, though it is increasingly seen as outdated practice. 4. Adjust the waste allowance. A 10% allowance is standard for ridge tiles. Breakages during handling and installation are the main source of waste. If your ridge has junctions (where a hip meets the ridge), allow an extra tile at each junction point. 5. Review the results. The calculator shows tiles needed (with and without waste), mortar weight or dry-fix kits required, and the number of end caps. End caps are always 2 -- one for each end of the ridge.
The ridge tile calculation uses the ridge length and a standard tile spacing: Tiles needed = ridge length (m) x 2.2 tiles per metre, rounded up The 2.2 figure comes from a standard 450mm ridge tile with a 12mm mortar gap (or equivalent spacing with dry-fix clips), giving an effective tile pitch of approximately 462mm, or about 2.16 tiles per metre. The industry convention rounds this to 2.2 per metre to ensure sufficient tiles. For an 8-metre ridge: tiles needed = ceil(8 x 2.2) = ceil(17.6) = 18 tiles. Tiles with waste = tiles needed x (1 + waste percentage / 100), rounded up. With 10% waste: 18 x 1.10 = 19.8, rounded up to 20 tiles. For mortar bedding: mortar quantity = ridge length x 8 kg per metre. This accounts for the bed of mortar under each tile and the mortar filling at the joints. For an 8m ridge: 8 x 8 = 64 kg of mortar mix. A standard 20 kg bag of ridge tile mortar covers approximately 2.5 metres of ridge. For dry-fix systems: kits needed = ridge length / 6, rounded up. Each kit contains a ventilated roll, stainless steel screws, and fixing clips for approximately 6 metres. For an 8m ridge: ceil(8 / 6) = 2 kits. End caps = 2 (always). These close off the open ends of the ridge tile run and are essential for a weatherproof finish.
When ordering ridge tiles, ensure they match the main roof tile manufacturer and colour for a consistent appearance. Most major UK tile manufacturers (Marley, Redland, Russell, Forticrete) produce ridge tiles designed to complement their main tile ranges. For listed buildings or properties in conservation areas, you may need to use matching clay ridge tiles rather than concrete, and mortar bedding rather than dry-fix, to satisfy planning conditions. Always check with your local Building Control office if in doubt. Ridge tile work at height requires appropriate scaffolding and fall protection in accordance with the Work at Height Regulations 2005.