To estimate repair costs, walk the property system by system — roof, HVAC, electrical, plumbing, kitchen, baths, flooring, paint, windows, and exterior. Price each line item at local material and labor rates, then add a 10-15% contingency. A line-item estimate beats any per-square-foot rule of thumb because it forces you to account for the big-ticket systems that actually blow budgets. The number you build this way is the number you can defend to a lender, a partner, or an end buyer.
Why Per-Square-Foot Rules of Thumb Fail
"Budget $30 a foot" feels efficient, but it hides the only thing that matters: what this specific house needs. A light cosmetic refresh can come in under $20 a square foot, while a full gut with new systems can clear $75. A single number averages away the roof, the panel, and the HVAC — the items most likely to wreck your margin. Use per-square-foot figures only as a sanity check on a number you built from line items, never as the estimate itself.
The Line-Item Method: Walk the Systems
Go through the property in a fixed order so nothing gets skipped. For each system, note whether it needs nothing, a repair, or a full replacement, and attach a real local price:
- Structure and exterior: roof, foundation, siding, windows, landscaping.
- Systems: HVAC, electrical panel and wiring, plumbing and water heater.
- Interior: kitchen, bathrooms, flooring, drywall, interior paint, doors and trim.
This is the same category structure a strong analysis tool uses — Appraize's repair estimator breaks every estimate into these line items with material and labor priced to your market, which is the discipline you are reproducing by hand here.
The Big-Ticket Items That Blow Budgets
Five systems cause most blown rehabs because they are easy to under-scope on a quick walk and expensive to fix: roof, foundation, HVAC, electrical, and plumbing. Price these specifically every time. A roof that looks "fine" from the street can be three layers deep and need a full tear-off; a panel that works can still be a fire hazard that no buyer's inspector will pass. Never fold these into a general allowance.
Add a Contingency — and Know Why
Add 10-15% on top of your line-item total, and 15-20% on older homes or full guts where opening walls will reveal surprises. The contingency is not padding. It is the budget for what you could not see on the walk-through — the rotted subfloor under the vinyl, the knob-and-tube behind the plaster. Investors who skip it are not running leaner; they are just absorbing those costs out of profit.
Worked Example: A 1,500 Square-Foot Rehab
A cosmetic-plus-systems renovation, line-itemed at local rates:
- Roof, full replacement: $9,000
- HVAC, replace: $7,500
- Electrical, panel and updates: $4,000
- Plumbing repairs and water heater: $3,500
- Kitchen, mid-grade: $14,000
- Two bathrooms at $6,000 each: $12,000
- Flooring, luxury vinyl plank across 1,500 sq ft: $7,500
- Interior paint: $4,000
- Windows, ten units at $450: $4,500
- Exterior paint and landscaping: $4,500
- Permits and miscellaneous: $3,000
The line-item subtotal is $73,500. Add a 15% contingency of about $11,000 and your rehab budget is roughly $84,500 — about $56 per square foot. A $30-per-foot rule of thumb would have told you $45,000, missing nearly $40,000 of real cost, most of it in the roof, HVAC, and electrical you cannot see in a drive-by.
Calibrate to Your Local Market
Labor and material costs swing widely by metro. A $12,000 kitchen in one market is a $20,000 kitchen in another, and flooring crews charge very different rates city to city. National averages will mislead you. Build a short price list for your own market from the contractors you actually use, and update it as you close deals.
Bottom Line
Walk the systems, price every line, protect the number with a real contingency, and calibrate to where you invest. That discipline turns repair estimating from a guess into a number you can stand behind. Appraize generates a full line-item repair estimate by category, calibrated to local labor and material costs, as part of every analysis — so you can pressure-test your own walk-through number in seconds. Your first 3 analyses are free.
