An ashlar piece is a short vertical post in a roof structure that stands on the ceiling or floor joist and is tenoned at its head into the rafter or roof beam. In Dutch roof carpentry the member is called a kreupele stijl and belongs above all to the improved Dutch truss.
Why it is there
In a simple roof, the load comes down onto the wall plate — and that load has a horizontal component pushing the walls outwards. This is the classic problem of spread: walls that after decades visibly lean outwards at the eaves.
The ashlar piece solves it by rerouting the load path. It carries much of the roof load down into the floor structure — onto the ceiling joists and so onto the floor beams — instead of onto the wall plate. The wall is pushed outwards far less.
How the foot is held
The post itself would tend to slide outwards at its base. That is prevented in two ways:
- With a sole plate. A sole piece under the foot spreads the load over several joists rather than one, and holds the post in place.
- By notching the post into the joist. The post is given a tooth that bears directly into and against the joist, so the horizontal component is taken there.
The post is often also tied to the wall plate with a short block or a bracket piece.
In alteration and repair
- Never cut an ashlar piece out to gain space in the loft. It is precisely the member that resists spread; remove it and the roof puts its load back onto the wall plate.
- Check the foot. Rot in the base of the post or in the sole plate, or a sagging joist underneath, defeats the whole arrangement. Always look at this during a survey.
- In a loft conversion the post is usually built into a knee wall. That is fine, as long as the post and its foot connection stay intact.
Related terms
- Wall plate
- Roof truss
- Sole plate
- Brace
- Knee wall
- Spread
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