Loft Conversion in Trussed Roofs
These roof structures are where the roof sections have been made in a factory as a
complete unit and brought onto site on a lorry. They are then craned or man handled into location. They are meant
to save on time of erecting the roof framing due to less labour involvement and also in material costs for when a
quantity of houses are built (say 4 or more).
These trussed roof structures are normally designed to span from wall to wall with no requirement for any of the
existing internal partitions to be load bearing. This gives the house designer far more scope on arranging the
internal layout of the first floor as the partitions 9usually studwork) can be located anywhere.
This means that the internal ties and struts of the truss form an intrinsic part of its structural support of
the entire roof from external wall to external wall. Most loft conversions require the ‘clearing out’ of any
internal bracing, ties or struts. Do this for a trussed roof and suddenly you have over spanned rafters and the new
floor joists are unlikely to be able to span more than 4.5M and take some of the roof loads.
This means that it can be quite normal to have extensive structural upgrading of the first floor with new beams
and posts simply to break the spare of the new floor joists. Some trussed roof houses are lucky and do in fact have
some first floor intermediate load bearing partitions that can be used for the new floor joists.
If your roof structure is of a pre-formed trussed rafter design, then by all means get an experienced house
extension designer or architect involved right from the start to do a structural feasibly study on just what needs
doing for its structural support but be prepared for the extra costs and be prepared to abort the scheme if it does
become too expensive.