I have a low pitched lean-to roof extension that is below the recommended roof pitch for our chosen tiles. Can I still lay the tiles?

Firstly its worth checking your options. If you have large format concrete tiles on your roof then you can find various profiled concrete tiles that go down to 15 degrees. Its always best to use a profiled tile rather than a flat tile, as the undulations in the tile help carry the water down the roof and keep it away from the interlocks, which can leak at low pitch. 

If you have plain tiles or slates on the main roof then it will not be advisable to use these on the extension as these traditional do not perform well at low pitch. One option would be to use an interlocking clay plain tile such as the Sandtoft 20/20, which can perform down to 15 degrees and can compliment both plain tiles or slates. Try to avoid low pitch large large format concrete tiles if you have traditional materials on the main roof  as these larger tiles can appear out of character, particularly on an extension where the roof area is smaller and closer to eye level.

It is possible to lay the tiles below their minimum roof pitch, however, your roof will be susceptible to water ingress between the tiles. In these circumstances the structure below the tiles or slates (sub roof) needs to be made fully watertight before the tiles are laid.