Calculate hip tiles, irons, and fixings for hipped roof construction
A hipped roof -- where all four sides slope downwards from the ridge to the eaves -- is one of the most common roof shapes on UK houses, particularly on detached and semi-detached properties built from the 1930s onwards. The hip is the external angle where two sloping roof surfaces meet, running diagonally from the ridge to the eaves corner. Each hip requires special tiles to cap the junction and provide a watertight seal, just as ridge tiles cap the top of the roof. Hip tiles are available in several profiles to match different roof tile types. Bonnet hip tiles are the traditional choice for clay and concrete tile roofs, wrapping smoothly around the hip with a curved profile. Angular hip tiles provide a sharper, more defined profile suited to modern roof designs or steeper pitches. Universal hip tiles are designed to accommodate a range of tile profiles and roof pitches, making them a popular choice with dry-fix hip systems. A standard hipped roof has four hips -- one at each corner of the building. However, the number of hips can vary: an L-shaped house might have six or more hips, while a simple hipped extension might have just two. The length of each hip rafter depends on the roof pitch and the span of the building. Hip tiles are spaced at approximately 2.2 tiles per metre (the same spacing as ridge tiles), with each tile measuring approximately 450mm and a gap of about 12mm between tiles. Like ridge tiles, hip tiles have undergone a significant shift from traditional mortar bedding to modern dry-fix systems. BS 8612 now requires mechanical fixing for hip tiles on all new-build properties in the UK, and dry-fix is strongly recommended for re-roofing projects. Dry-fix hip systems include a continuous ventilated roll that follows the hip line, with each tile secured by stainless steel screws and clips. One kit typically covers approximately 6 metres of hip length. Hip irons are galvanised steel brackets fitted at the foot (bottom) of each hip rafter. They support the lowest hip tile and prevent the entire run of hip tiles from sliding downward under gravity and wind pressure. One hip iron is required per hip.
To calculate hip tile requirements: 1. Measure the hip rafter length in metres. This is the distance from the ridge (top) to the eaves (bottom) along one hip. If you cannot access the roof, you can estimate the hip length using the roof pitch and building dimensions. For a standard 35-degree pitch with a 4-metre horizontal span from the corner to the ridge, the hip rafter is approximately 5.6 metres long. If all hips are the same length, measure just one. 2. Enter the number of hips. A standard hipped roof has 4 hips. Count each diagonal hip on your roof. An L-shaped building might have 6 hips, while a simple hipped extension off the back of a house has 2 hips. Do not count ridge lines or valleys -- only the external diagonal angles. 3. Select the tile type. Bonnet hip tiles are the most common choice in the UK and suit most clay and concrete tile roofs. Angular hip tiles give a contemporary appearance. Universal hip tiles work with a range of tile profiles and are particularly popular with dry-fix installations. 4. Select the fixing method. Dry-fix is recommended for all new installations. Mortar bedding is still used for repairs or where planning conditions require a traditional finish. 5. Adjust the waste allowance. A 10% waste allowance is standard for hip tiles. Breakages are more likely than with ridge tiles because hip tiles are more difficult to handle and install at an angle. 6. Review the results showing total hip length, tiles required (with waste), hip irons, and mortar or dry-fix kit quantities.
The hip tile calculation follows the same spacing as ridge tiles: Total hip length = hip rafter length (m) x number of hips For a hipped roof with 4 hips of 4 metres each: total hip length = 4 x 4 = 16 metres. Tiles needed = total hip length x 2.2, rounded up. For 16 metres: ceil(16 x 2.2) = ceil(35.2) = 36 tiles. Tiles with waste = tiles needed x (1 + waste percentage / 100), rounded up. With 10% waste: ceil(36 x 1.1) = ceil(39.6) = 40 tiles. Hip irons = number of hips. One iron per hip, fitted at the foot of each hip rafter. For a standard 4-hip roof: 4 hip irons. For mortar bedding: mortar quantity = total hip length x 8 kg per metre. For 16m: ceil(16 x 8) = 128 kg. For dry-fix systems: kits needed = total hip length / 6, rounded up. Each kit covers approximately 6 metres. For 16m: ceil(16 / 6) = 3 kits. The 2.2 tiles per metre figure is an industry standard based on 450mm tiles with approximately 12mm spacing. This is the same rate used for ridge tiles, as hip tiles are typically the same size and shape, just installed at a diagonal angle rather than horizontally along the ridge.
When installing hip tiles, the hip rafter must be straight and true before tiling begins, as any bow or twist will be visible in the finished hip line. On older UK properties, the hip rafter may need straightening or replacing before new hip tiles can be installed. The cut tiles (plain tiles or interlocking tiles that meet the hip line) should be cut to leave a clean, even line with consistent spacing. These cut tiles generate the most waste on a hipped roof -- the main roof tile calculator should include a higher waste allowance (15-20%) to account for hip and valley cuts. Always install hip tiles from the bottom up, starting with the hip iron and first tile, working towards the ridge. The junction where the hip meets the ridge requires careful detailing -- a three-way mitre cut or a purpose-made hip-to-ridge junction piece.