Civil Engineering Reference
In-Depth Information
better conversion value in terms of usable floor space. It is also unlikely that major struc-
tural problems will be encountered when attempting to convert a lean-to or monopitch
roof unless, of course, it is constructed using trussed rafters. Simple lean-to roofs are often
constructed using rafters supported off the wall plate at the higher level and lower level
and with a single purlin between (see Fig. 8.9). Furthermore, unlike converting the main
roof, the lean-to has one major advantage in that a separate access staircase is unlikely to
have to be created. It is often quite simple to form a doorway into the new attic through
the wall of the existing property from the first or second floor level (see Fig. 8.10).
The lean-to loft conversion will best work where tall rooms exist on the first floor, thus
giving a good usable headroom in the attic. These tall rooms are often found in houses of
the eighteenth and nineteenth centuries (see Fig. 8.11).
Bolted or TDA Truss Roofs
This type of roof has been described earlier and reference can be made to Fig. 4.4. Clearly
the truss is a major component in such a roof construction and is not easily replaced if re-
moved to provide a clear roof void for conversion. The only real solution is to provide
purlins to support the rafters and ceiling joists, taking full account of the fact that the new
attic floor will also have to be supported by some form of purlin as it is unlikely with this
type of roof that there will be any supporting partition wall below.
To break the length of span of these purlins, it may be necessary to extend up a structural
wall from the ground floor through the existing ceiling, the other supports for
