Extension Ladder Overlap and True Working Height

Sections must overlap - 3 ft up to 36 ft nominal, 4 ft at 40 ft and longer - so a 24-ft ladder gives 21 ft of working length, and that length is the HYPOTENUSE at the 4:1 setup, putting the top support at 20.4 ft with the base 5.1 ft out. Subtract the 3-ft landing extension and the highest floor it serves is 17.4 ft. Three-section ladders lose overlap at two joints. Ladder angle gives the setup; this gives what you can actually reach.

overlap = 3 ft up to 36 ft nominal, 4 ft at 40 ft and longer; working length = nominal - overlap x (sections - 1); at a 4:1 setup the working length is the hypotenuse, so top support = L / sqrt(1 + 1/16) and base offset = height / 4; highest landing served = top support - 3 ft.

Extension-ladder section overlap and the 3-ft-above-a-landing rule as stated in the US Office of Congressional Workplace Rights extension-ladder fast facts, restating the OSHA/ANSI requirement, by name.

The OCWR fast-facts sheet is US-government public domain; OSHA 1910.23 and 1926.1053 are free at osha.gov.

Estimate. AHJ and licensed professional govern.

Field names used by the API: nominal_length_ft, sections, overlap_ft, working_length_ft, top_support_ft, base_offset_ft, max_landing_ft

• Overlap tiers 3 ft up to 36 ft nominal, 4 ft at 40 ft and longer; the 36-40 ft gap is taken conservatively as 4 ftOCWR extension-ladder fast facts (OSHA/ANSI requirement)
• 4:1 hypotenuse the working length is the ladder along the slope, so the height is L / sqrt(1 + 1/16)geometry of the 4:1 setup
• Landing extension at least 3 ft above the landing surfaceOCWR extension-ladder fast facts