What is a temporary diagonal brace (schranklat)?
A diagonal brace (Dutch: schranklat, also schrankhout, schoorlat or windlat) is a simple brace: a timber batten fixed at an angle to keep a structure square and stable. The Dutch word comes from the verb schranken: “to rack out of square”, like a timber roof, wall or cabinet that distorts into a parallelogram.
A diagonal brace is often fitted temporarily, for example to keep a timber window frame square while it is not yet fixed into the masonry, or to hold a post or column plumb while it is being set. There are also permanent diagonal braces: a batten nailed diagonally under a series of consecutive rafters to prevent the roof from racking.
Application
Temporary brace on window frames:
- First set the frame exactly square: measure both diagonals; if they are equal, the frame is square.
- Nail or screw a batten diagonally across the corner(s) on the inside, in a position where it does not hinder setting and anchoring.
- Leave the batten in place until the frame is anchored and the masonry or finishes around it are sufficiently rigid.
- Use small holes or screws in places that will be covered later, so that there is no visible damage to the frame.
On posts, columns and walls:
- Fit two braces at right angles to each other (for example front and side) and plumb the post with a spirit level before fixing the battens.
- Keep the braces in place until the concrete or anchorage has gained sufficient strength.
On roofs:
- A diagonal batten or wind brace under or along the rafters prevents the roof from racking in the longitudinal direction. For new build or major alterations, the stability of the roof must be assessed by a structural engineer; a batten is then no substitute for a designed wind bracing system.
Related Terms
- Brace or raking pile
- Braced and unbraced construction
- Roof structure
- Push-pull prop
- Propping
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