What is a slof?
A slof (also balkslof or slofstuk) is a Dutch carpentry term for a short timber laid across several floor joists to spread the load from a short post or brace over those joists. There is no exact English equivalent. The nearest terms are sole plate (a timber under the foot of a post or raking shore that distributes its load) and spreader.
Its role in the Dutch roof truss
The slof is typical of the improved Dutch truss (verbeterd Hollands spant). In this roof, a short post called a kreupele stijl stands on the attic floor and carries part of the roof load down into the floor structure instead of onto the wall plate. That reduces the outward thrust on the external walls. The slof always runs at right angles to the joists, so the post bears on two or more joists instead of one, and it stops the foot of the post from sliding outwards. Under a brace it can act as a sole plate.
In everyday Dutch, a concrete ground beam is also often called a funderingsslof (foundation slof). That is a different component altogether: see foundation beam.
Application
When converting or surveying an older Dutch-style roof:
- Find the foot of every post. Does it stand on a cross timber spanning several joists, or directly on a single joist?
- Check for rot. Eaves areas are often damp. Probe the timber; soft wood means the load is no longer being spread.
- Look for deflection. A joist sagging under the bearing point points to overloading or decay.
- Do not remove it to get a flat attic floor. Without it, the full load lands on one joist and the post foot can slide.
- Involve a structural engineer before replacing a slof or post. The roof will need temporary propping.
Related terms
- Dutch truss
- Common joist
- Timber brace
- Wall plate
- Knee wall
- Foundation beam
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