Between a portal frame's column and its rafter sits a small, unglamorous member: the knee brace. And along the eave, the eave strut quietly connects the roof to the wall. Both are small, both are essential, and both are frequently misunderstood by buyers.
1. Knee braces: the transfer of load
The knee brace connects the column to the rafter at an angle, stiffening the corner. Without it, the frame corner can deform too much, and the column base and roof connections carry unexpected bending. A knee brace transfers horizontal force (from wind or crane loads) into the frame, protecting the connection and keeping the building square.
2. Eave struts: joining roof and wall
At the eave, the top of the wall meets the bottom of the roof. The eave strut is the horizontal member that connects the rafter to the wall girt, carrying wind pressure from the wall into the roof frame and supporting the fascia and gutter line. It also gives the cladding a straight, solid fixing line at the building's most visible junction.
3. Where you find them
Knee braces: at frame corners, usually as angles, channels or flat plates.
Eave struts: along the full length of each eave, usually cold-formed C or Z sections.
4. Why they should not be "value-engineered" away
Removing knee braces to save a few kilos of steel can force bigger columns and connections elsewhere - often costing more and reducing safety. Skipping eave struts makes the wall top unstable and the cladding flutter. These members are engineering decisions, not optional extras.
In short: knee braces and eave struts are small members with critical jobs - load transfer at frame corners and a stable junction between roof and wall. A responsible designer includes them, and buyers should confirm they are in the design and the shipment.
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