What is a wind brace?
A wind brace is a diagonal beam, board or metal strap that stiffens a structure against the horizontal forces of wind. A rectangular frame of posts and rails can rack sideways, like a cupboard without a back panel. Adding a diagonal creates triangles, and a triangle cannot change shape without one member getting longer or shorter.
Where are wind braces used?
- In roofs: between trusses or rafters and purlins or ridge, diagonally in the roof plane or along the length of the roof. This stops the roof racking over like dominoes when wind pushes on a gable.
- In timber frame and half-timbered walls: diagonally in walls where sheathing does not already provide stiffness.
- In sheds, canopies and carports: as short knee braces between post and beam, or as a diagonal across a whole bay.
Types
- Timber: a board or beam fixed with bolts, screws or carpentry joints to each member it crosses.
- Steel: thin galvanised bracing straps run diagonally across rafters or trusses and securely anchored at the ends.
- Sheet materials: in modern construction, roof or wall sheathing in plywood or OSB often does the bracing job (diaphragm action), provided it is properly nailed or screwed.
Common mistakes
- Removing it during alterations: when adding a dormer, rooflight or opening up a loft, braces or parts of the sheathing are sometimes removed. Always have a structural engineer decide how stability will be maintained.
- Weak connections: a brace only works if its ends can transfer the force. One nail at each end is rarely enough.
- One direction only: a single brace mainly works in tension or compression. A cross or braces in both directions provide stability against wind from either side.
- Slack straps: steel bracing straps must be tight; slack straps only start working once the structure has already deformed.
Related terms
- Brace
- Corner brace
- Foot brace
- Saltire cross brace
- Braced and unbraced
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