Repairs: roofs and rainwater goods

Older pitched roofs may have a half-brick skin to the gable triangle, even though the wall beneath the roof or ceiling joist level is of cavity masonry construction.

Solution

Double check this: if you are putting in new purlins you will need to raise an inner skin of brickwork at least sufficient for the purlin to rest on.

A full cavity thickness is desirable because a half-brick gable may be susceptible to wind load or suction, particularly if the pointing is of any age. Many such walls failed in the storm of 1987, and a stitch in time would have offered considerable reinforcement to many of these.