A through-runner is a beam, joist or element that spans in one unbroken piece across two or more supports. The term is used in carpentry and masonry to describe parts that are explicitly not jointed or stopped at an intermediate support.
Structural significance
A through-runner behaves differently from a simply supported beam:
- Continuous beam — distributes loads across multiple spans
- Stiffer behaviour — less deflection than a jointed solution
- Negative moment — tension at the top over the intermediate support
- Less material needed — design is more efficient under uniform loading
In timber construction especially, a through-runner is preferred wherever stock length permits. A continuous purlin is stiffer and steadier than the same purlin in separate pieces.
Applications
Through-runners appear in many places:
- Purlins — running continuously across multiple rafters
- Floor joists — over several internal walls or main beams
- Course in masonry — a continuous bond course or string course
- Skirting and trim — a continuous skirting board without joints at corners
- Sheet piling — continuous waling on the pile profile
Examples
Timber
A continuous floor joist over an internal wall is stronger than two joists meeting on that wall. The through-runner spreads the load and stiffens the structure.
Masonry
In a façade, a continuous bond course or drip course is often used as a transition between floors, running uninterrupted across the whole façade.
Trim
In panel doors, the vertical stile is sometimes called a through-runner: it runs from bottom to top while horizontal rails butt against it.
Points to consider
- Top reinforcement or strengthening — over the intermediate support
- Forming — long through-runners can be hard to transport and place
- Load transfer — ensure sound bearing at every support
Related terms
- Beam
- Purlin
- Joist
- Continuous support
- Course
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