What is a lateral restraint strap?
A lateral restraint strap is a flat metal strap that ties a masonry wall to the floor or roof structure, and where the joists run parallel to the wall it is fixed across several joists. It stops the wall from bowing or leaning outwards. In Dutch the traditional version is called a strijkbalkanker: a heavy flat iron strip starting at the joist alongside the wall and running at right angles across the joists. Dutch sources translate it as strap anchor.
A wall that carries joist ends is held in place by the joists themselves. A wall parallel to the joists has no such connection; only the first joist runs alongside it, usually with a small gap. The strap links that wall to the stiff floor, which acts as a horizontal plate.
Recognising it
Look for a flat steel strap with a turned-down end hooked into or fixed to the wall, running across the tops or undersides of the joists and nailed or screwed down. Short solid blocks between the joists usually sit under the strap.
In practice
- Span several joists. UK guidance under Approved Document A describes horizontal straps fixed across at least three joists, with solid noggings between the joists and packing between the wall and the first joist.
- Space them properly. The same guidance commonly gives 30 x 5 mm galvanised or stainless steel straps at a maximum of 2 m centres. Check the current Approved Document or your structural engineer for your situation.
- Keep the strap tight to the wall. A loose strap only starts working after the wall has already moved.
- Inspect old straps and anchors. In older buildings check for corrosion and loose fixings when floors are opened up.
Common mistake: removing straps during floor renovation and not refitting them. The wall then stands free of the floor.
Related terms
- Beam anchor
- Gable end
- Common joist
- Beam layer
- Ring beam
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