ABSTRACT
Chapter 5 on Roof Structures explains the advantages of modern trussed rafters, one of which is the ability to span large distances without any intermediate support. This effectively means that modern houses do not require any form of internal loadbearing walls on the upper floor when this type of roof construction is used. Consider the two diagrams below. The example on the left shows a cross-section through a typical house built in the early part of the 20th century. An internal loadbearing wall is often required to support the first floor and part of the roof structure. The wall is often off-centre as rooms may be of different sizes. In the second example, which is typical of most construction since the 1960s, the loadbearing wall is only supporting the first-floor joists and will, therefore, sometimes be built on a thickening in the slab rather than a traditional foundation.
