A coupling anchor is a metal anchor that ties together two beams lying in line with each other. The beams meet at a bearing — usually over a wall or a bressummer — and the coupling anchor turns those two loose ends into one continuous member.
What it does
In a floor spanning several bays, joists often do not run in one piece. Two shorter joists meet alongside or against each other on the same wall plate. Without a connection, those beam ends can move independently: the floor feels springy, and under load the joists can deflect sideways or work their way off the bearing.
A coupling anchor does three things at once:
- Takes tension — the beams can no longer pull apart.
- Lets the floor act as a diaphragm — coupled joists spread the load more evenly onto the wall.
- Restrains the wall — in versions that are also tied into the masonry, the anchor holds the wall plane against the floor.
Types
- Flat strap — a galvanised or stainless steel strap screwed over both beam ends. The simplest and most common form.
- Through rod with pattress plate — used in restoration of historic masonry: a rod through the wall, closed off on the outside with a wrought iron plate.
- Combined joist and coupling anchor — connects the beam ends and anchors them into the outer leaf at the same time.
Points to watch
- Screw, don’t nail. Coach screws or structural screws resist withdrawal; plain round nails barely do.
- Not into end grain. Screws in end grain have far lower withdrawal capacity. Always fix into the side or top face of the beam.
- Stainless in damp conditions. In a crawl space, a cavity or an external wall, galvanising is not enough — use stainless steel there.
- Leave historic wrought iron in place. Old anchors are often still fully functional and of historic value. Assess the corrosion before deciding to replace.
- Have it checked. A coupling anchor is a structural component. Increasing the floor loading calls for an engineer’s calculation, not a rule of thumb.
Related terms
- Anchor
- Joist anchor
- Floor joists
- Beam end
- Bearing
- Wall plate
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