Estimating rehab costs: from napkin bands to line-item job costing
Three levels of renovation math — the 60-second per-foot bands, the room-by-room walk-through method, and the full line-item scope of work — plus the contingency discipline and the ten costs everyone forgets.
How do you estimate renovation costs? At three levels of precision, each matched to a decision: napkin bands ($/sqft by renovation tier — enough to screen a deal in sixty seconds), the walk-through method (room-by-room and system-by-system pricing during a showing — enough to make an offer), and the line-item scope of work (quantity-times-price job costing — the document your contractor bids against and your lender draws against). Beginners lose money by using level one where level three was owed; professionals move through all three on every deal, each level tightening the last. The estimate is half of your offer math — ARV is the other half — and unlike ARV, this number you can actually control.
Level 1: the napkin bands
For screening a lead in the driveway, per-square-foot bands do honest work — calibrated to your market (coastal metros run 1.5–2×; these are mid-market figures):
Level 2: the walk-through method
Offer-grade estimating prices the house as five systems plus rooms, because that's how renovation dollars actually cluster. The big five first — they're binary and large: roof ($8–15k asphalt replacement; read the ceiling stains), HVAC ($6–12k full replacement; check the data plate's age), electrical ($8–15k for a rewire/panel; knob-and-tube or a fuse box decides it), plumbing ($5–15k repipe; galvanized supply lines decide it), foundation (the walk-away conversation — get a structural opinion before contracting anything with stair-step cracks). Then the money rooms: kitchen ($12–25k mid-grade full redo), baths ($6–12k each full), and per-room cosmetics ($2.5–4k a room covers paint, flooring, doors, hardware, lighting). Add exterior (siding, windows at $400–700 each installed, landscaping), then the forgotten ten (below), then contingency. A disciplined investor walks a house with this checklist in 30 minutes and lands within 15% of final cost — which, run through MAO math, is offer-grade.
Level 3: the scope of work — real job costing
Under contract, the estimate becomes a scope of work: every line item with location, specification, quantity, material allowance, and labor — "Kitchen: 14 LF shaker cabinets (allowance $210/LF installed); 32 sqft quartz ($68/sqft installed); GE slate appliance package ($3,400)…" — organized by trade and sequenced by construction order (demo → structural → rough mechanicals → insulation/drywall → finishes → punch). This document is the entire management system in embryo: contractors bid against it (three bids on the same scope is the only real price discovery — vague scopes produce unbiddable bids and infinite change orders), the draw schedule pays against its completed sections, allowances cap the selections that blow budgets (every "we'll pick the tile later" is an unpriced liability), and variance tracking against it is how you learn — your actual-vs-estimate file across five projects is the most valuable proprietary data a renovator owns. Software (FlipperForce-class tools, or a rigorous spreadsheet) helps; the discipline is the asset. Two closing rules from the job-site graduates: walk the house with your contractor before finalizing any budget you'll be held to — their eyes on-site beat your checklist — and never let the contingency migrate into the scope; it's insurance against the wall you haven't opened, and pre-1950 houses always have one.
Frequently asked questions
+How much does it cost to renovate a house per square foot?
Mid-market bands: cosmetic renovations run $15–30/sqft, moderate (kitchen, baths, some systems) $30–60, heavy renovation $60–100, and full guts $100+. Coastal metros run 1.5–2× those figures. Per-foot bands are screening math — offers require pricing the big five systems and money rooms individually, since two systems and a kitchen routinely carry 70% of a budget.
+How do I estimate rehab costs during a walk-through?
Price the big five systems first (roof, HVAC, electrical, plumbing, foundation — each large, binary, and checkable in minutes), then kitchens ($12–25k) and baths ($6–12k), then per-room cosmetics at $2.5–4k a room, then exterior items, permits and dumpsters, and 10–20% contingency. The method lands within ~15% in 30 minutes, which is offer-grade through the 70% rule.
+What is a scope of work in flipping?
The line-item construction document: every task with location, specification, quantity, material allowance, and labor cost, organized by trade in build order. It's what contractors bid against (three bids on one scope = real price discovery), what draw schedules pay against, and what change orders amend in writing. Vague scopes are where flip budgets go to die.
+How much contingency should a renovation budget include?
As a budgeted line, not a hope: 10% on cosmetic scopes, 15% on moderate ones, 20%+ on gut renovations and anything pre-1950 — because opened walls answer questions inspections can't ask. Expect to spend most of it; the projects that 'come in under budget' usually just had honest contingencies. Never let it migrate into scope upgrades mid-project.
+What renovation costs do beginners forget?
The unglamorous ten: permits and re-inspection fees, dumpsters (plural), utilities during the rehab, builder's-risk insurance, lawn/snow during the hold, materials price drift between estimate and order, delivery fees, the punch list (the last 2% that takes 10% of the money), staging, and the carrying costs that accrue while all of the above runs long. Together they're routinely $5–10k the napkin never saw.
The other half of the offer: determining ARV and the 70% rule. Executing the budget: hiring and managing contractors. The full strategy map: house flipping.