What is plumb?
Plumb means that a building element is exactly vertical, in line with the direction of gravity. The word comes from the plumb bob: a weight on a string that always hangs straight down (Latin plumbum, lead). A wall, post, frame or column that is not vertical is “out of plumb”. In Dutch the expression is te lood.
Its counterpart is level: exactly horizontal.
How to check whether something is plumb
- Spirit level with vertical vial: hold the level against the element; the bubble must sit between the lines. Flip the level once to check that the level itself is accurate.
- Plumb bob: hang the bob next to the element and measure the distance to the string at the top and bottom. Equal measurements mean plumb. Useful on tall walls and stairwells.
- Cross-line laser: projects a vertical line over the full height; ideal for setting several studs or frames in line.
Application
- Masonry: corners and ends are checked for plumb every few courses with a gauge rod or level.
- Frames and doors: a door frame that is out of plumb makes the door swing open or shut by itself.
- Stud walls: metal or timber studs must be plumb so boards can be fixed flat.
- Columns and piles: leaning reduces load-bearing capacity.
Common mistakes
- Measuring over too short a length: a short level on a long post hides a gradual lean. Use a long level or straightedge.
- Continuing to use a level with a damaged vial; check it regularly.
Related terms
- Plumb bob
- Plumb level
- Spirit level
- Decorative brickwork
- Window frame
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