Last month, we looked at detailing
cathedral ceilings that are supported
by structures running lengthwise. This
month, we will consider the other
case, where the main structure spans
the width of the space.
Exposed Trusses
When the span is longer than it is
wide, trusses are in order. (In some
cases, trusses are also attractive in
short, wide spaces.) First, let's consider
trusses that are entirely visible within
the room. In this case, these trusses
carry purlins that run lengthwise in
the room and support the roof. Such
purlins have two problems.
First, when you set the purlins on
the trusses, do you set them vertically
– at an angle to the roof plane – or do
you set