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Sunroom cost = floor area × price per square foot for the type. Three-season rooms run about $80–$230 per sq ft and four-season rooms about $200–$400 (HomeGuide, 2026). Worked example: a 12 × 12 ft sunroom is 144 sq ft, so a mid-range three-season room costs about $18,648–$25,992 and a mid-range four-season room about $38,304–$48,096.
With these inputs:
| Result | Value |
|---|---|
| Estimated sunroom cost | $18,648 – $25,992 |
| Room area | 144 sq ft |
| Price per sq ft at this level | $130 – $181 |
| Full published range | $11,520 – $33,120 |
| Same room as a four-season room | $38,304 – $48,096 |
| Formula | 144 sq ft × $130–$181 |
Building on an existing deck or slab saves the foundation only if it can carry the walls and roof: have a builder or engineer check the footings and joists. A four-season room counts as living space, so expect a permit, energy-code glazing and HVAC.
A sunroom is priced by the square foot, and the type decides the rate: a three-season room (glass or screen panels, no heating or cooling) runs about $80–$230 per sq ft, and a four-season room (insulated, double-glazed, heated and cooled) about $200–$400. Enter the room size and how basic or premium the build is to see the likely range, the full published range and what the same room costs as the other type.
About $80–$230 per sq ft for a three-season room and $200–$400 per sq ft for a four-season room (HomeGuide, 2026). A 12 × 12 ft (144 sq ft) room is roughly $11,520–$33,120 as a three-season room and $28,800–$57,600 as a four-season room.
A three-season room has glass or screen panels but little or no insulation and no heating or cooling, so it is comfortable from spring to autumn. A four-season room is insulated, double-glazed and heated and cooled, so it can be used all year and is treated as part of the house for permits and energy code.
A mid-range three-season 12 × 12 room is about $18,648–$25,992; a mid-range four-season room about $38,304–$48,096. Basic kits on an existing slab sit at the bottom of the range.
It can be, because you skip most of the foundation, but only if the deck's footings, beams and joists can carry walls, glass and a roof. Many decks can't without new footings; have them checked before you order a kit.
A four-season room that is heated and cooled usually counts as living space and adds more value than a three-season room. Check local comparable sales before you spend for resale.
Yes, usually by a wide margin, because screens cost far less than glass and there is no HVAC. Price one with the screened porch cost calculator.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.