The roof void in a typical terraced house is illustrated in Fig. 3.1; the distance between the party or compartment walls, i.e. those dividing the houses, is often relatively small and there are frequently load bearing internal walls to be found on the ground floor, supporting the first floor joists. As can be seen from the figure, by removing the 'collars' a useful room void would be achieved. The collar is, of course, there to tie the rafters together by stiffening the purlins and bracing the rafters. If the collar is removed some alternative restraint must be found. If room height is adequate, extra collars could be fitted to act as attic ceiling joists and to lighten the load on the purlins; an additional ridge purlin can be fitted, supported on steel shoes built into the party wall. It should be noted at this point that in some terraces no party wall will be found as has been stated earlier, and if this is the case then one must be constructed using methods adequate to provide both fire and sound performance to the adjoining properties.
Was this article helpful?