A foundation levelling course is the topmost course of a masonry foundation, laid dead level so the superstructure can start from one true datum all around the building. In Dutch it is called the *paslaag* — literally the “fitting course”, because everything is made to fit in this course.
Why this course decides the rest
A foundation is rarely built perfectly flat. The trench rises and falls, and the lowest courses are usually laid rough. This course absorbs all of it:
- Absorbing height differences — thicker or thinner bed joints and, where needed, cut units bring the course to a single level.
- One datum all round — the whole building starts from the same height, so the gauge works out equally in every wall.
- Checking setting out — on this course the final external dimensions and the diagonals are checked one last time before the superstructure begins.
How to build it
- Establish the highest point of the foundation first, with a level or laser, and work upward from there.
- Keep bed joint thickness within sensible limits. A bed joint of roughly 10 to 15 mm is normal; deal with bigger differences by adding a course or cutting units rather than by laying one very thick joint.
- Place the damp-proof course on or immediately below this course, so rising damp cannot reach the superstructure.
- Once laid, mark the gauge on a storey rod, so every wall gets the same course spacing.
How it differs from the first course of the wall
This levelling course still belongs to the foundation and is its last course. The first course of the superstructure sits directly on top of it. Both exist to get the work level and true, but they are not the same course.
Related terms
- Foundation
- Gauge
- Bed joint
- Damp-proof course
- Setting out
- Superstructure
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