Masonry walls should benefit from some form of lateral restraint to restrict movement of the separating or gable walls.
It is important to get this detail right first time round as remedial or post construction installation rarely provides the necessary fixity.
Here are some handy tips to follow to ensure you get it right first time and avoid unwanted bowing walls!
Separating walls, at roof level, fall into 3 main categories:
- Where rafters are level or within 300mm vertically on each side of the wall
In this case packing the rafters either side of the wall tight to the masonry on both sides will be satisfactory. If straps are used, these should be no more than 2m apart for dwellings up to 3 storeys and no more than 1.25m apart for dwellings over 3 storeys. Straps should also be in line on each side of the walls and fixed across at least three rafters.
2. Separating walls with rafters greater than 300mm apart vertically on each side of the wall should be provided with restraint straps.
3. Separating walls with horizontal staggers between two dwellings should be provided with restraint straps.
Lateral restraint to gable walls should be provided at rafter level at all times. Restraints are only required at ceiling level where the height from the top floor level and ½ the roof height is 16 times, plus 10mm, the thickness of the wall that is being restrained.
Lateral restraint straps should:
1. Be galvanised with a minimum cross-section of 30mm x 5mm
2. Hooked over a solid block – screw fixing to face of blocks Is not acceptable.
3. Have noggins between rafters/joists with packing between the wall and first member.
4. Straps should span a minimum of three rafters/joists with at least one fixing in the third member.
5. Alternatively, fix straps to the longitudinal bracing, provided straps are at centres not exceeding 2m.
See diagram below.
By Olivia Catterall