Trench Shoring Reference
How OSHA 1926 Subpart P App C / App D actually works — the framework of the timber and aluminum hydraulic tables, their spacing rules, and their hard limits. The full tables live in the appendices (public domain) and on manufacturer tabulated data; this chart is the map. The competent person selects and verifies on site; state plans can be stricter.
The two shoring families
| Aspect | Aluminum hydraulic (App D) | Timber (App C) |
|---|---|---|
| Table structure | D-1.1 (Type A, vertical shores), D-1.2 (Type B, vertical shores), D-1.3 (Type B, waler systems), D-1.4 (Type C, waler systems only) | Two sets by lumber strength — mixed oak (C-1.x) and Douglas fir (C-2.x) — each with a table per soil type |
| Depth bands | Up to 8 ft / 8–12 / 12–15 / 15–20 ft; over 20 ft → manufacturer or RPE tabulated data | 5–10 ft / 10–15 / 15–20 ft; over 20 ft → RPE route |
| Key spacing rule | Hydraulic cylinders: 4 ft on center vertically, in every table | Type A, 5–10 ft deep, trench to 6 ft wide (oak): 4×4 cross braces at 4 ft vertical × 6 ft horizontal, 2×6 uprights at 6 ft, no wales |
| Cylinders / members | 2-inch cylinders (18,000 lb minimum) for narrower configs; 3-inch (30,000 lb) as width and depth grow | Cross-brace, wale, and upright sizes per table cell |
| Sheeting | Type A: none required · Type B: plywood in some configs · Type C: ALWAYS sheeted (waler systems only) | Uprights per table (tight sheeting in weaker soil) |
| Legal status | Both appendices are Option 1 under 652(c)(1) — usable as-is, no engineer required within their limits | Both appendices are Option 1 under 652(c)(1) — usable as-is, no engineer required within their limits |
Reading a shoring table without hurting anyone
Every cell assumes its inputs: the soil type (from the classification), the depth band, the width band, and the surcharge limits in the notes — exceed any one and the cell no longer applies. The minimum-three-shores rule and the Type C always-sheeted rule are the two most-missed footnotes. Shields are the other path entirely — a box protects the crew inside rather than holding the trench open — and get their own rules on the trench box chart.
Common questions
How far apart do hydraulic shores go?
Vertically: 4 ft on center, in every Appendix D table. Horizontally: per the table — 8 ft for Type A at ordinary depths, tightening as the trench deepens and the soil weakens, down around 5–6 ft for Type B vertical shores at 15–20 ft. Type C never gets vertical shores at all: waler systems with full sheeting only.
Can you use the OSHA shoring tables without an engineer?
Yes — that is their whole point. Appendices C and D are Option 1 under 1926.652(c): within their limits (Types A/B/C soil per Appendix A, depths to 20 ft, the listed widths and surcharge assumptions) a competent person deploys them as-is. Outside any limit, you move to manufacturer tabulated data or an engineered design.
How deep do the shoring tables go?
20 feet — both appendices. A circulating claim says the hydraulic tables reach 25 ft; they do not. Past 20 ft the appendix rows literally read "refer to 652(c)(2) and (c)(3)" — manufacturer or engineer-approved tabulated data, or an engineered design. See the deep excavation rules.
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