What your drawings should specify - and what loose tolerance costs on site.
Drawings often leave tolerance vague, written as “to standard” or “as required”. The result is a frame that arrives out of plumb with no agreed measure of acceptability.
Specify overall column verticality (typically within 5–10 mm over the height), column spacing at the base, rafter alignment, and bolt-hole positions. State whether members are measured before or after galvanising, and whether site welding or bolting is the default.
A frame that is 20 mm out over 12 metres is usually acceptable. A frame that is 50 mm out means the cladding does not fit, the doors do not line up, and steel must be heated and shifted on site. Most of these problems start with tolerance not being discussed before cutting.
Column verticality is typically specified within 5–10 mm over the height. Bolt-hole positions are usually held within 1–2 mm, and base-plate level is checked before fabrication. State these in the drawings so the workshop and the site crew work to the same numbers.
We run a fabrication check on every structural drawing before cutting steel, and raise any unrealistic tolerance or un-weldable connection before fabrication.
Many out-of-tolerance frames are caused by slabs out of level. We verify slab levels before fabricating, and design base plates that can be shim-packed rather than forcing the column to match the slab.