Repairs: roofs and rainwater goods

New buildings with pre-trussed frames should incorporate perforated galvanised steel down leg straps to secure the wall plate and help resist plate rotating, and to prevent wind suction exerting excess pull on it. This is an area where it is difficult to effect a repair unless the building owner is prepared to accept plaster being chased out within the top floor to fix the straps to the inner face of the wall (always assuming a masonry wall of course).

When carrying out new work, ensure that the straps are actually fixed – often they are there, but not secured.

Solution

Down leg straps can easily be fixed onto the gable wall, and across the 2 frame assemblies, in each end of a conventionally gabled roof in accordance with the installation recommendations (as illustrated). This provides a degree of improvement, but a fully specified wall plate strap down has to be optimal.

Rafters viewed from beneath

COST SEQUENCE - Retro-fitting bracing to pre-trussed roofs

1. Cut through timber 100mm by 12.5mm section nominal into sufficient lengths to pass into the roof space. Allow for battening to the underside of the rafters.
2. Double screw all fixing positions on chevron 'V'. Ensure that any overlaps between boards are taken across a mimimum of 2 rafter sets.
3. Run horizontal/lateral braces across the underside of rafters or internal chord positions. Again allow for doubling up fixings across rafter positions/over laps to make up board lengths. Double screw all fixings to roof timbers.
4. Ensure that lateral braces (one for each roof slope) terminate within 10mm or less of internal face of gable walls to take up any racking and prevent slack within the braces.
5. Fix galvanised 38mm by 4mm section steel down leg straps passed across minimum 2 rafter sets at each gable end. Screw fix to underside face of rafters and allow for minimum of 2 screw fixings plugged to internal face of gable wall. Allow for 1 down leg fixing per roof slope/gable wall abutment.
6. Pricing assumes a typical roof plan section size of 7m in each direction and typical roof pitch of 35 degrees.

Retro-fitting bracing to pre-trussed roofs - COST £900

Small works pricing

Since the original price estimating in 2008 the economic turmoil of the last few years has caused some disparities in pricing - if you are reviewing these figures in the London area they may look laughable - if you are located in Hull they might still look a bit expensive. Please treat them with caution and of course always consider obtaining more than one quote against which to test prices. Reference to the BCIS or a small works pricing book such as Spons or Laxton's will help assess costs and the hourly labour rates upon which they are based.