Why have the ridge tiles on my new house come off? Is the mortar too weak?

Experience has proved that the correct mix of mortar (ie 1:3 cement:aggregate) is more than adequate to resist the highest winds ever likely to occur in the UK. However, where there is movement within a roof structure, particularly where the roof passes over masonry walls, the mortar bed can crack, leaving the ridge tile vulnerable to wind uplift. In new buildings in particular, where timbers etc are drying out and shrinking, differential movement can be a problem. For this reason, the current British Standard for slating and tiling, BS 5534, recommends that where differential movement can take place, such as at gables and abutments, ridges should be mechanically fixed as well as bedded.