What is the minimum pitch for clay plain tiles?
Some types of single camber clay plain tile can be used on roof pitches as low as 30 degrees (depending on the manufacturer), however most can be used down to 35 degree pitches.
Minimum pitch for single camber clay plain tiles
Single camber clay plain tiles are curved along their width, which creates attractive, textured roofscapes, but also leaves slight gaps in the roof installation at the leading edge of the tiles. Wind-driven rain can cause water ingress at these points. Also, these gaps can affect the roof performance at low pitches, because the rate of water run-off is slower.
Marley Eternit’s Acme Single Camber and Hawkins clay plain tiles have been subjected to wind-driven rain testing to European standard prEN 15601 and can perform at a 30° pitch.
These single curved tiles are ideal for balancing the requirement for a premium clay roof with budget restrictions.
Minimum pitch for double camber clay plain tiles
Double-camber tiles are cambered along their width as well as their length, which can give a flatter angle at the top of the tile, when the tiles are laid at low pitches. This can lead to a rate of water run-off that is too slow to guarantee performance.
Marley Eternit’s Acme Double Camber clay plain tiles, as well as most other clay plain tiles on the market, are suitable for use at a minimum roof pitch of 35 degrees.
Why can other types of tile be used at lower roof pitches?
Some more modern types of roof tile can be used at lower roof pitches than plain tiles, such as pitches as low as 15 or even 12.5 degrees. These, such as Mendip concrete pantiles or Melodie clay pantiles, have profiled or interlocking shapes. The profiled shape quickly channels rainwater away from nail holes, edges and interlocks, improving the roof performance.
Additional design considerations
In 2014, BS 5534 was updated to include new wind loading calculations and stricter fixing recommendations that take into account more frequent high winds and driving rain.
BS 5534:2015+A1:2015, clause 5.5 provides general recommendations on the minimum pitch, head laps and side laps for roofs, for normal situations. More specific guidelines are provided for clay plain tile applications.
It is worth noting that generally, hipped or valley roofs should be designed with a higher pitch than regular mono- or duo-pitch roofs, because they are more vulnerable to water penetration. At the hips or valleys, the effective pitch of the hip/valley is reduced by 5-10°.
Clay plain tile accessories
A range of purpose-made valley tiles is offered to suit 30-50° roof pitches. These are suitable for a plan angle of 90° only and equal pitches either side of the valley.
Hip accessories include arris hip tiles, for use on hips with plan angle of 90° and equal pitches on adjacent roof slopes, and a maximum rafter pitch of 45°.
Third round hip tiles are available for dry fix systems, as well as for mortar security bedded hips, which are mortar bedded and mechanically fixed in line with BS 5534. They can be used at a maximum rafter pitch of 45°.
Granny bonnet hip tiles are used on hips in place of a ridge tile and provide a premium finish. They are used at pitches of 40° and 60°.
More information, including valley and hip design details, is available in Marley Eternit’s Clay Plain Tiles Guide.