Home Addition Cost Calculator

Room addition and bump-out costs per square foot — foundation, envelope and mechanical work included, because an addition is a small house.

Your project

Finish level

Estimated total cost

$115,000 – $184,000

400 sq ft · Mid-range · National average

$288 – $460 per sq ft

Materials
$42,000 – $67,200
Labour
$50,000 – $80,000
Permits & fees
$8,000 – $12,800
Contingency (15%)
$15,000 – $24,000
Typical timeline
12–32 weeks of active work
Recouped at resaleAbout 55% of a mid-range spend
$82,225
  • National average pricing. Pick your region to adjust for local labour rates.
  • This is a planning range, not a quote. Get three itemised bids and compare the scope line by line — the cheapest bid is usually the one that left something out.

What the estimate includes

  • Foundation or slab
  • Framing, roofing, siding and windows
  • Insulation, drywall, flooring and paint
  • Electrical, HVAC extension and lighting
  • Architectural drawings and permits

What it does not include

  • Kitchen or bathroom fit-out inside the addition
  • Upgrading the existing furnace or panel to carry the new load
  • Site work, tree removal or utility relocation
  • Variance applications where setbacks are tight

What actually moves the price

  • An addition is a small house: foundation, roof, envelope and mechanicals all over again. That is why per-square-foot costs beat almost every interior remodel.
  • Second-storey additions cost more than ground-level ones because the existing structure and foundation must be verified — and often reinforced — to carry the load.
  • Tying the new roof into the old one, and matching siding and windows on a house that no longer sells those products, is where the visible cost of a cheap addition shows up.

How these estimates are built

  • Base costs are typical 2025–2026 US pricing per square foot at each finish level, drawn from national remodelling cost surveys and contractor bid data.
  • Your region multiplies that base — coastal metros run 30–40% above the national average and rural markets 15–20% below, almost entirely on labour rates.
  • The contingency is added on top of the base range rather than taken out of it, because that is how the money actually behaves on a job site.
  • The materials, labour and permit split shows how the mid-point of the range typically divides. It is a way to read a bid, not a second estimate.
  • Resale recoup figures follow national cost-versus-value patterns. No renovation returns more than it costs — treat the figure as a partial rebate on something you are buying for yourself.

Frequently asked questions

How much does a room addition cost?

$150–$250 per square foot for a simple bump-out, $250–$400 for a typical room addition, and $400–$700+ for an upscale or second-storey addition. A 400 sq ft addition is therefore roughly $60,000 to $280,000 depending on tier and region.

Is an addition cheaper than moving?

Often, once you count agent commission, closing costs, moving expenses and a new mortgage rate. The case against is that additions recoup only about 55% at resale, so it is a decision about how long you will stay, not about the resale maths.

How long does a home addition take?

Three to eight months of construction, plus one to three months beforehand for design, engineering and permits. The permit stage is the one people underestimate — it is also the one you cannot speed up.

Before you commit the budget, see it finished

Upload a photo and generate photorealistic versions of the finished space in any style. It is far cheaper to change your mind here than after the cabinets arrive.

Visualise the finished space

Material calculators for this project

Concrete CalculatorCubic yards for a slab, footing or column — and the honest bag count, so you know when to stop bagging and call a truck.Drywall CalculatorSheet count for walls and ceiling, plus the screws, joint compound and tape that always get forgotten on the first trip.Roofing CalculatorRoof area, squares and shingle bundles from your footprint and pitch — plus underlayment, ridge cap and a replacement cost range.

Related projects

Whole-House RenovationGut renovation and whole-house remodel costs by square footage, finish level and region — the number to know before you buy the fixer-upper.Basement FinishingWhat it costs to turn an unfinished basement into living space — including the egress, moisture and ceiling-height issues that decide the budget.Deck BuildDeck costs by size, material and region — pressure-treated through composite, including footings, railing and stairs.