Sunroom cost = floor area × price per sq ft for the type; a 12 x 12 ft four-season sunroom (144 sq ft) costs about $35,000 at US-average prices, roughly $243 per sq ft, with a range of $21,000 to $49,500. A three-season 12 x 12 is about $23,000, and a prefab kit about $10,700.
How much does a 12x12 sunroom cost?
It depends on what kind of room it is. All figures below are for 144 sq ft with a new foundation, permits and a 10% contingency, at US-average prices:
| Type | Typical | Range |
|---|---|---|
| Three-season, unheated | $23,000 | $13,100 to $33,500 |
| Four-season, insulated and heated | $35,000 | $21,000 to $49,500 |
| Prefab kit, installed | $10,700 | $8,300 to $13,700 |
How the sunroom cost is calculated
Fixr's sunroom guide (November 2022) prices a four-season addition at $130 to $300 per sq ft, a three-season room at $80 to $200 and a prefabricated sunroom at $50 to $75. Bob Vila (May 2024) reports a national average of $47,000 and a range of $20,800 to $72,600, with four-season rooms at $25,000 to $80,000, three-season at $10,000 to $40,000 and prefab kits at $5,000 to $30,000. Fixr's shares of a $55,000 sunroom split the total into lines: foundation 8%, heating and cooling 6%, electrical and utilities 4%, and the rest for frame, roof, glass and finishes. A three-season room is not conditioned, so it has no heating line.
Cost = area × price per sq ft for the type, split into foundation, frame, HVAC and electrical + permits + 10% contingency
Worked example: 12 x 12 ft four-season sunroom
| Line | Typical |
|---|---|
| Foundation | $2,500 |
| Frame, roof, glass and finishes | $25,500 |
| Heating and cooling | $1,850 |
| Electrical | $1,250 |
| Permits | $800 |
| Contingency, 10% | $3,100 |
| Total | $35,000 (range $21,000 to $49,500) |
Fixr's own table gives 120 sq ft (12 x 10 ft) at $15,600 to $36,000, which is $130 to $300 per sq ft; scaled to 144 sq ft that is $18,700 to $43,200, and the calculator adds permits and contingency on top. If a patio or slab already exists, turn off "New foundation" to drop $2,500 and the contingency on it: $32,000.
Cost by size
| Size | Area | Four-season, typical |
|---|---|---|
| 10 x 10 ft | 100 sq ft | $24,500 |
| 12 x 12 ft | 144 sq ft | $35,000 |
| 12 x 16 ft | 192 sq ft | $46,000 |
| 12 x 20 ft | 240 sq ft | $57,500 |
Fixr's custom-built 12 x 20 ft sunroom is $31,200 to $72,000; the calculator's range for the same room without permit and contingency is exactly that.
Three-season or four-season?
A three-season room has screens or single glazing and is not heated, so it is cooler to build but only usable in mild weather. A four-season room has insulated walls and roof, double-pane low-E glass and a heating and cooling source. Bob Vila's ductless mini-split range is $2,000 to $14,500 for the heating and cooling; size it with the mini-split size calculator. Glass is a large lever: Fixr lists single pane at $3 to $8 per sq ft, double pane at $10 to $20 and triple pane at $12 to $22.
What raises the price
- Glass. Windows are $3,500 to $15,000 and doors $1,000 to $8,000 of a sunroom (Bob Vila).
- Foundation. Foundation is $1,000 to $6,000 (Bob Vila); a deck that cannot carry the room needs new footings.
- Heating and cooling. Four-season rooms need it; three-season rooms do not.
- Age of the data. Fixr's sunroom prices date from 2022, the oldest source used here, so treat them as a floor.
Permits
A sunroom is an addition. A screened three-season room on an existing deck may go under a lighter permit, but a heated four-season room needs a full permit, energy-code windows and a proper foundation. Fixr puts permits at $400 to $600 and Bob Vila at $400 to $1,800.
What to work out next
Size the concrete slab, the framing and the roofing. If the window count is your main cost driver see the window replacement cost calculator, and for other kinds of additions the home addition cost calculator. All estimates are in the project costs hub.
These are dated estimates from published national data adjusted for your state, not a quote.