Most modern roofs are built with trussed rafters. These are a series of timber trusses which are normally spaced at around 600mm centres. They generally span between the outside walls of the building with no internal support being provided. If normal trusses have been used (ie not attic trusses) then the roof space will be full of bracing timbers.

The most common alteration for this type of roof is when a loft conversion is planned. It is possible to strengthen the roof to allow the bracing timbers to be removed so that the space can be used. However, the alterations need to be properly designed and built. If this type of alteration is not done properly it will lead to all sorts of difficulties later on. At best it will be picked up by a Surveyor when you eventually sell the house. At worst it will lead to excessive deflection or the collapse of the roof.

Our basic design is for a ridged trussed rafter roof. If your roof is complicated with hips and valleys then please get in touch and we will provide you with a custom quote.

The price for our structural calculations for alterations to a trussed rafter includes carrying out a detailed structural analysis of the existing truss. Our structural design also includes preparing the calculations for the necessary strengthening work.

We need the following information to design this type of alteration:

The span of the trussed rafters

The length of the building (at right angles to the trusses)

The type of roof covering (eg slate or concrete tiles)

Design information

All design work is carried out in accordance with BS5268 (The structural use of timber).

The calculations provided will be suitable for Building Regulation approval.