Every number here is a working estimate to check with your building authority. Whoever prints this page takes responsibility for what is in it.
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The 100 mm (3 15/16 in) sphere test
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One gap between pickets was left 4 1/4 in wide among gaps that all look alike, and the stair and the gap under the bottom rail need testing too.
Every number here is a working estimate. Check it with your building authority.Turn JavaScript on to work the lesson. The drawing shows how it starts.
The rule this lesson teaches
No opening may pass a 100 mm (3 15/16 in) sphere, on the level or on the stair; 3 7/8 in clear is the usual working number in wood.