Rex says
Money math without the spreadsheet headache. Plug in your numbers and I'll show you exactly where the dollars land.
Try a scenario
Click to load — tweak from there.Inputs
Applies a regional labor-and-bid multiplier to the whole job.
Result
All-in cost to build up
$321,540
Construction cost
$310,340
Temporary housing
$11,200
Cost per new square foot
$402
Contingency reserve
$47,340
Low end of band
$279,740
High end of band
$401,925
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How to use this
- 1Enter new second-story area (sq ft).
- 2Enter build rate for the new floor ($/sq ft).
- 3Enter region — Applies a regional labor-and-bid multiplier to the whole job..
- 4Enter foundation and framing reinforcement ($).
- 5Enter tear-off and new roof ($).
- 6Enter staircase and downstairs rework ($).
- 7Enter hvac capacity and new ducting ($).
- 8Enter months living elsewhere (months).
- 9Enter temporary housing cost ($/mo).
- 10Enter contingency (%).
- 11Read your all-in cost to build up on the right — it updates as you type.
- 12Hit Share to keep the scenario or send it to someone.
About this calculator
Adding a second story looks efficient because you reuse the lot and the foundation, and then three costs nobody budgets for show up: the existing structure usually needs reinforcement, the entire roof comes off and is rebuilt, and the family has to live somewhere for three to six months. Skip those and you will be short by a third. This calculator prices the new floor per square foot with a regional index, then adds foundation and framing reinforcement, a full re-roof of the new footprint, a staircase and the floor area it steals downstairs, HVAC capacity, and temporary housing at a monthly rate. Worked assumption for the defaults: an 800 sq ft second story at $240/sq ft, $30,000 of reinforcement, $18,000 re-roof, $14,000 stair, $9,000 HVAC, four months of housing at $2,800 — about $322,000 nationally, and closer to $430,000 in a top-tier metro.
Worked example
Using the values the calculator loads with:
Inputs
- New second-story area: 800 sq ft
- Build rate for the new floor: 240 $/sq ft
- Region: US national average — 1.00×
- Foundation and framing reinforcement: 30000 $
- Tear-off and new roof: 18000 $
- Staircase and downstairs rework: 14000 $
- HVAC capacity and new ducting: 9000 $
- Months living elsewhere: 4 months
- Temporary housing cost: 2800 $/mo
- Contingency: 18 %
Results
- All-in cost to build up: $321,540
- Construction cost: $310,340
- Temporary housing: $11,200
- Cost per new square foot: $402
- Contingency reserve: $47,340
- Low end of band: $279,740
- High end of band: $401,925
What each field means
Inputs
- New second-story area (sq ft)
- The new second-story area used in the calculation, measured in sq ft. Starts at 800 sq ft so you have a working example on load. Accepted range: 200–4000 sq ft.
- Build rate for the new floor ($/sq ft)
- The build rate for the new floor used in the calculation, measured in $/sq ft. Starts at 240 $/sq ft so you have a working example on load. Accepted range: 120–700 $/sq ft.
- Region
- Applies a regional labor-and-bid multiplier to the whole job.
- Foundation and framing reinforcement ($)
- The foundation and framing reinforcement used in the calculation, measured in $. Starts at 30000 $ so you have a working example on load. Accepted range: 0–200000 $.
- Tear-off and new roof ($)
- The tear-off and new roof used in the calculation, measured in $. Starts at 18000 $ so you have a working example on load. Accepted range: 0–120000 $.
- Staircase and downstairs rework ($)
- The staircase and downstairs rework used in the calculation, measured in $. Starts at 14000 $ so you have a working example on load. Accepted range: 0–90000 $.
- HVAC capacity and new ducting ($)
- The hvac capacity and new ducting used in the calculation, measured in $. Starts at 9000 $ so you have a working example on load. Accepted range: 0–60000 $.
- Months living elsewhere (months)
- The months living elsewhere used in the calculation, measured in months. Starts at 4 months so you have a working example on load. Accepted range: 0–18 months.
- Temporary housing cost ($/mo)
- The temporary housing cost used in the calculation, measured in $/mo. Starts at 2800 $/mo so you have a working example on load. Accepted range: 0–20000 $/mo.
- Contingency (%)
- The contingency used in the calculation, measured in %. Starts at 18 % so you have a working example on load. Accepted range: 0–35 %.
Results
- All-in cost to build up
- Returned as a money amount in US dollars and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Construction cost
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Temporary housing
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Cost per new square foot
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Contingency reserve
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Low end of band
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- High end of band
- Returned as a money amount in US dollars. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
Does every house need reinforcement to build up?
Not every one, but assume it until an engineer says otherwise. Older footings, undersized first-floor walls and long spans are the usual triggers, and the structural report costs a fraction of the surprise.
Can I stay in the house during the work?
During roof-off framing, no. Most families move out for the framing and dry-in phase and return for finishes, which is why the tool prices months rather than the whole schedule.
Where does the regional multiplier come from?
It is a job-level index against a US national average of 1.00, built from the spread contractors quote between low-cost rural markets and the highest-cost coastal metros. Materials vary less than labor, but bids move together, so one index tracks real quotes better than splitting them. Swap in your own multiplier by picking the tier closest to two bids you already have.
Why does the tool add a contingency?
Because renovation scopes change once walls are open. On finished-space work 10–15% is normal; on anything touching foundations, sewer lines, or 1970s-and-older wiring, 20% is the honest number. If your contingency is never spent, you finished under budget — that is the point.
Accuracy and limitations
- Results are estimates before tax, fees, and inflation unless an input explicitly covers them.
- Rates are treated as fixed for the whole period — variable-rate products will drift from this projection.
- This is educational maths, not financial advice. Check anything contractual with the lender or your accountant.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Cost to Add a Second Story Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/cost-to-add-a-second-story-calculator
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/cost-to-add-a-second-story-calculator" target="_blank" rel="noopener">Cost to Add a Second Story Calculator — RevenueLab</a> (2026).</p>
Source: [Cost to Add a Second Story Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/cost-to-add-a-second-story-calculator) (2026).