Collar roofs

In some houses collar roofs can be found. The principle is not dissimilar to the closed couple roof but the horizontal tie is higher up the rafters. Houses with collar roofs often have rooms formed partly in the roof space, which results in a lower overall height and subsequent savings in walling materials. However, if the collar is too high it will not be effective and the rafters below the collar can still exert an excessive lateral thrust on the supporting walls. If the collar is kept fairly close to the rafter feet (not more than one-third of the roof height) and a good joint is formed between the rafters and collars by bolting or the use of fixing plates or carpentry joints, the roof should remain stable.