Sources & formulas

Every calculator on BasementCalcs rests on established arithmetic and geometry plus stable building conventions. Unlike topics with a time dependency, "verification" here is mathematical: each formula is tested against known values and is therefore correct for good. Here are the technical foundations by area.

Geometry & quantities

• Count: piers or straps = ceil(length ÷ spacing).
• Wall area: perimeter × height (sq ft), for exterior membrane and sealer.
• Concrete / gravel volume: cubic yards = area (sq ft) × (thickness in ÷ 12) ÷ 27.
• Material quantity: area ÷ coverage × (1 + overlap/waste); round up to whole rolls/units.
• Units: 12 in = 1 ft; 9 sq ft = 1 sq yd; 27 cu ft = 1 cu yd.

Spacing, coverage & conventions (labeled planning bands)

• Pier spacing: ~6–8 ft — a licensed engineer sets the real count & load.
• Carbon-fiber strap spacing: ~4 ft (band 3–5 ft) for bowing walls.
• Vapor barrier: ~6–12 in seam overlap; roll coverage varies by mil — check the label.
• Drain-tile slope: ~1% (≈ 1 in per 8 ft), 3–4 in perforated pipe.

Cost, budget & finance

• Every cost tool uses the prices you enter ($/pier, $/linear ft, $/sq ft, $/cu yd, $/roll, $/gallon, per-unit, labor $/hour, APR) — no material price, labor rate, cost index or live loan rate is stored, so the site needs no maintenance.
• Contingency: total = subtotal × (1 + contingency%); typical band 10–20%.
• Cost per sq ft: $/sq ft = your total ÷ area (and area × $/sq ft back to a total).
• ROI: recoup% = your value protected ÷ your cost × 100 — illustrative only; home value protected is never guaranteed.
• Financing: standard amortization M = P·r ÷ (1 − (1+r)⁻ⁿ), r = APR ÷ 12 — illustrative, not a loan offer.

Permit rules, local code and material lead times vary by place and change over time — always confirm permits and code with your local building department, and have foundation movement assessed by a licensed structural or geotechnical engineer.