🇺🇸 United States · Construction cost guide · Updated 2026
How much does it cost to build a granny flat in the United States?
Building a granny flat in the United States typically costs $63,000 to $117,000 in construction cost — roughly $1,400–$2,600 per square metre over 45 m² of floor area. That excludes land, professional fees and statutory charges.
The United States is a high-cost construction market by global standards — it is the baseline our construction cost index is measured against (index 100). This page prices a granny flat — self-contained one-bedroom annexe with kitchenette and shower room — at 45 m² of gross floor area, then breaks the cost down element by element so you can see where the money actually goes. Costs are quoted in USD for comparability; the local currency in the United States is USD ($), and a bill of quantities generated from your own drawings is priced in USD using the CSI MasterFormat divisions standard.
What is being priced
The figures on this page price a granny flat in United States at 45 m² of gross floor area over 1 storey, specified as self-contained one-bedroom annexe with kitchenette and shower room. Construction cost only — land, professional fees, statutory charges, utility connections and loose furniture are all excluded, and together commonly add another 15–30%.
Cost by specification level
| Specification | Construction cost (USD) |
|---|---|
| Basic / low-cost finish | $45,360 – $84,240 |
| Standard finish | $63,000 – $117,000 |
| Premium finish | $91,350 – $169,650 |
Where the money goes
Elemental split of construction cost for a granny flat of this type. Percentages are concept-stage cost-planning proportions; the ranges below apply them to the totals above.
| Element | Share | Cost (USD) |
|---|---|---|
Substructure & foundations Excavation, strip footings, hardcore, blinding, DPC and ground slab. | 15% | $9,450 – $17,550 |
Walling & superstructure Masonry, lintels, ring beam and any suspended floor. | 22% | $13,860 – $25,740 |
Roofing Trusses or rafters, covering, ceilings, fascia and rainwater goods. | 14% | $8,820 – $16,380 |
Internal finishes Plaster, screed, floor and wall tiling, ceilings and painting. | 18% | $11,340 – $21,060 |
Joinery & fittings Doors, windows, cupboards, worktops and ironmongery. | 9% | $5,670 – $10,530 |
Services (plumbing & electrical) Wiring, distribution board, fittings, water reticulation, sanitaryware and drainage. | 14% | $8,820 – $16,380 |
External works & preliminaries Site setup, supervision, paths, boundary works and connections. | 8% | $5,040 – $9,360 |
Get the real number for your own plans
A benchmark tells you the ballpark. Upload your dimensioned drawings and get an itemised, source-cited bill of quantities priced in USD ($), measured to the CSI MasterFormat divisions standard United States professionals use.
Price my United States projectBuilding granny flats in United States — frequently asked
How much does it cost to build a granny flat in the United States?
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Building a granny flat in the United States typically costs $63,000 to $117,000 in construction cost — roughly $1,400–$2,600 per square metre over 45 m² of floor area. That excludes land, professional fees and statutory charges. At a basic specification the same building lands nearer $45,360–$84,240; at a premium specification, $91,350–$169,650.
What is the cost per square metre in the United States?
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About $1,400–$2,600 per m² for this building type at a standard finish. Per-m² rates rise with storey height (frame, cores and cranage) and with specification, and fall on simple single-storey plans.
What is the biggest cost item?
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Walling & superstructure — about 22% of construction cost, or $13,860–$25,740 on this build. Masonry, lintels, ring beam and any suspended floor.
Does this include land, fees and furniture?
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No. These are construction costs only — materials, labour, plant and site preliminaries. Land, statutory approvals, professional fees, connections, landscaping and loose furniture are all additional, and together commonly add 15–30% on top.
How do I get an accurate figure for my own plans in the United States?
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Benchmarks give you the ballpark; a measured bill of quantities gives you the number. Upload your dimensioned floor plans to Enormous Buildings and get an itemised, source-cited BoQ in USD in the CSI MasterFormat divisions format that the United States quantity surveyors and lenders expect — free to preview.
Why do build costs vary so much between countries?
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Three things dominate: labour cost, how much of the material basket is imported, and the code requirements the building must satisfy. The United States sits at index 100 against the United States at 100, which is why the figures above differ from what you'd see quoted for the same building elsewhere.