NASCLA Site Construction: how to study it
Site Construction is 15 of the 115 scored questions on the NASCLA Commercial General Building exam, about 13%. That makes it the third-largest area and more than twice the size of any single trade area after it. It is also one of the most numeric: trench rules, slopes, volumes and grades all come down to arithmetic you can practice.
Check anything you rely on against your own licensed code book and the edition your AHJ enforces.
What the bulletin says, and what it leaves out
PSI's Candidate Information Bulletin (updated 7 Jul 2026) gives the area name and its count of 15, with no topic list. The topics below are our reading of the area name and the reference list.
Topics to cover
- Excavation safety. When a protective system is needed, the kinds of protection, ways out of a trench, spoil setback, inspections and finding utilities before digging. Subpart P of 29 CFR 1926 holds these.
- Soil types and slopes. Stable rock, Type A, Type B and Type C, and the maximum allowable slope for each.
- Earthwork quantities. Cubic yards, bank, loose and compacted volumes, swell and shrinkage, and average end area.
- Utilities and pipe. Bedding, haunching and backfill, laying gravity pipe to grade, compaction in lifts and dewatering.
- Stormwater. The stormwater pollution prevention plan (SWPPP), erosion control versus sediment control, and inspections and records.
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Books to open first
Our suggestion from the titles. NASCLA publishes no mapping.
- 29 CFR 1926, Subpart P and its appendices on soil classification and sloping.
- Pipe and Excavation Contracting: trenching, pipe and excavation estimating.
- The EPA guide Developing Your Stormwater Pollution Prevention Plan, free from the EPA.
- Principles and Practices of Commercial Construction: general site work.
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The OSHA numbers to know
Each value was read in the eCFR text current to 4 Nov 2026. The wording here is ours.
| Situation | Rule | Section |
|---|---|---|
| When protection is needed | A protective system unless the excavation is entirely in stable rock, or is under 5 ft deep and a competent person sees no sign of a possible cave-in | 1926.652(a)(1) |
| Way out of a trench | Stairway, ladder, ramp or other safe exit in trenches 4 ft or deeper, with no more than 25 ft of sideways travel to reach it | 1926.651(c)(2) |
| Spoil and equipment | At least 2 ft back from the edge, or held by retaining devices | 1926.651(j)(2) |
| Inspections | Daily by a competent person before work, as needed during the shift, and after every rainstorm or other event that raises the hazard | 1926.651(k)(1) |
| Slope with no soil classification | No steeper than 1 1/2 horizontal to 1 vertical (34 degrees from horizontal) | 1926.652(b)(1) |
| Simple slopes 20 ft deep or less | Type A 3/4 : 1, Type B 1 : 1, Type C 1 1/2 : 1 | Subpart P, Appendix B |
The first number in a slope is horizontal. A 1 1/2 : 1 slope is flatter than 1 : 1.
Worked examples
All numbers are invented. Each is worked two ways.
Top width of a sloped trench. A trench in Type C soil is 6 ft deep with a 3 ft wide bottom, sloped on both sides. Each side runs out 6 x 1.5 = 9 ft. Top width = 9 + 3 + 9 = 21 ft. Check: 3 + 2 x (6 x 1.5) = 21.
Haul volume. A trench is 150 ft long, 4 ft wide and 5 ft deep. Bank volume = 150 x 4 x 5 = 3,000 cubic feet, and 3,000 / 27 = 111.11 bank cubic yards. With 20% swell, the loose volume is 111.11 x 1.2 = 133.33 cubic yards. In 12 cubic yard trucks that is 133.33 / 12 = 11.1, so 12 loads. Check: 27 x 111.11 = 3,000 (to rounding), and 11 loads would carry only 132 cubic yards.
Pipe grade. A gravity line falls 1% over 320 ft. Drop = 320 x 0.01 = 3.2 ft. With an upstream invert at elevation 104.75, the downstream invert is 104.75 minus 3.20 = 101.55. Check: 3.2 / 320 = 0.01.
Common mix-ups
- Erosion control versus sediment control. Erosion control keeps soil in place: seeding, mulch, blankets, limiting bare ground. Sediment control catches soil that has already moved: silt fence, inlet protection, sediment basins.
- Feet versus inches. A 6 in. layer is 0.5 ft. Convert before you multiply, and divide by 27 last.
- The 5 ft rule is not a free pass. Under 5 ft still needs a competent person's look, and stable rock is the only blanket exception.
- Bank, loose and compacted are different volumes of the same soil. Read which one the question gives and which it asks for.
How to practice
Learn the Subpart P numbers until you can write the table above from memory, then tab the section and its appendices so you can confirm them fast. Work volume and grade problems with your exam calculator. Read the EPA guide's plan sections once end to end; it is free to download. The NASCLA study guide pairs Site Construction with Concrete in one week; see the Concrete guide and the full list of OSHA topics.
Practice it
Work earthwork volumes with the free cut and fill calculator. Erosion and sediment control is covered in SWPPP basics for builders, and ground that differs from the contract documents in differing site conditions.
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Sources
Show the list
- PSI Candidate Information Bulletin 1458, content outline and reference list, updated 7 Jul 2026. Retrieved 5 Nov 2026.
- 29 CFR 1926 Subpart P, Excavations, OSHA. Values checked against the eCFR text current to 4 Nov 2026.
- Developing Your Stormwater Pollution Prevention Plan: A Guide for Construction Sites, U.S. EPA, 2007, document 833R06004. The bulletin says it is free from the EPA as a download or a printed copy; search the document number to find it.
Facts come from the sources listed above. If something has changed, tell us and we will correct it within 2 business days.
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