Project planning

Equipment project planning

Right-sizing equipment before you rent saves money and rework. These are the field-tested rules of thumb for sizing excavators, lifts, generators and compaction — plus the buy-vs-rent math and the certification you'll need.

Sizing rules of thumb

Excavator sizing

Max dig depth should exceed required depth by ≥ 6 in.
Mini < 7 t (tight/finished sites) · standard 7–45 t (most commercial) · large > 45 t.
Residential foundations run ~8–10 ft deep; drainage trenches ~3–6 ft.

Aerial / boom lift

Working height ≈ platform height + ~6 ft (operator reach).
Telescopic horizontal outreach ≈ platform height − ~9 ft.
Max outreach is at mid-height, not full height — read the ROM chart.

Generator sizing

Add 10–20% headroom above load; run at 50–80% load.
Motor start surge: 1-phase 3–5× running amps; 3-phase DOL ~7×.
kW = kVA × 0.8 (100 kW ≈ 125 kVA).

Soil compaction

Loose lift: granular 8–12 in · cohesive 4–6 in (~4× max aggregate).
~4–8 passes with a 10-ton vibratory roller; most density in first ~5 passes.
Iowa DOT Type A: ≥ one rolling per inch of lift depth.

Buy vs rent: the 60% rule

If a machine is used more than ~60% of the time (about 12–14 days/month, ~150 working days/year), buying usually beats renting on lifecycle cost. Below ~40%, renting clearly wins; 40–65% is the "run-the-numbers" zone. Remember that hidden ownership costs — depreciation, insurance, maintenance, storage — add roughly 20–30% per year on top of purchase price. Use our rent-vs-buy calculator to check your case.

Rental logistics & timing

Reserve popular machines early — availability tightens when construction backlogs rise. Plan delivery windows and consolidate deliveries to cut transport fees ($75–$200 each way). Book weekly or monthly rates rather than stacking day rates for anything over a few days.

Certification & safety

Under OSHA 29 CFR 1926.453/.454, employers must train and authorise every aerial- and scissor-lift operator (fall protection, load limits, inspections) before use. OSHA doesn't "certify" operators, but industry certifications are commonly valid for three years and often required on commercial sites.

FAQ

How do I size an excavator for my dig?

Pick a machine whose maximum dig depth exceeds your required depth by at least 6 inches. Mini excavators (under 7 t) suit tight or finished sites, standard 7–45 t machines cover most commercial work, and large machines above 45 t are for heavy earthmoving.

What working height boom lift do I need?

Working height equals platform height plus about 6 feet of operator reach — so for 40 ft of working height, choose a 34 ft platform. Horizontal outreach on a telescopic boom is roughly platform height minus ~9 ft, and maximum outreach occurs at mid-height, so always check the range-of-motion chart.

How do I size a generator?

Total your running load, add 10–20% headroom, and round up. Aim to run the generator at 50–80% load. Account for motor starting surge: single-phase induction motors draw 3–5× running amps to start, three-phase direct-on-line about 7×. Convert with kW = kVA × 0.8.

How thick should compaction lifts be?

Spread granular soils in 8–12 inch loose lifts and cohesive soils in 4–6 inch lifts, roughly four times the maximum aggregate size. Expect about 4–8 passes with a 10-ton vibratory roller, with most density gained in the first ~5 passes.

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Sources

Figures are drawn from the sources above and were accurate at the time of writing; market data and rates change — treat ranges as indicative and verify current figures for decisions.