Sunroom Addition Cost 2026: 3-Season vs 4-Season

Quick answer

Angi’s sunroom guide (updated October 29, 2026) puts the national average for a new sunroom addition at about $47,000. Most projects run $22,000 to $75,000, or roughly $150 to $300 per square foot, and large custom rooms reach about $120,000.

The biggest price split is between three-season and four-season rooms:

Three-season room: $10,000–$40,000 (Angi), or $8,000–$50,000 at $80–$230 per square foot (HomeGuide).
Four-season room: $25,000–$120,000 (Angi), or $20,000–$80,000 at $200–$400 per square foot (HomeGuide; guide dated August 22, 2025).

Enclosing a porch, deck or patio you already have can cost less, but only if that base can carry a room.

Sunroom cost at a glance

Type	Angi (2026)	HomeGuide
Three-season room	$10,000–$40,000	$8,000–$50,000; custom $80–$230/sq ft
Four-season room	$25,000–$120,000	$20,000–$80,000; custom $200–$400/sq ft
Prefabricated sunroom	$6,000–$40,000	$5,000–$50,000 (kits $20–$150/sq ft)
Solarium	$30,000–$75,000	$30,000–$100,000
Conservatory	$6,000–$80,000	$50,000–$150,000
Typical new addition	$22,000–$75,000 (average $47,000); $150–$300/sq ft	$100–$350/sq ft

The two publishers define categories differently. HomeGuide’s conservatory is a high-end glass-roofed four-season room, while Angi’s range also includes lighter structures. Compare the room you actually want, not the label.

Three-season vs. four-season: what you are paying for

Angi describes the difference this way:

Three-season room: walls with large windows, a finished floor and a roof, often with electricity. It is not insulated and has no heating or cooling, so its use depends on the weather.
Four-season room: insulated and equipped with heating and cooling, so it can be used year-round. Many have knee walls to make room for ducts and wiring.

HomeGuide notes that most three-season rooms do not have electrical connections, though some prefab units include them. In practice, a four-season room is closer to a glass-heavy home addition than to a porch.

Decision guidance:

If you mainly want a bug-free, sheltered space for spring through fall, a three-season room or a deck with a screened roof may meet the need for far less.
If you want a home office or family room used in January, plan, permit and budget for a conditioned room from the start.
Converting later costs extra: HomeGuide lists $3,000–$20,000 to convert a three-season room to four-season.

Code and energy rules worth knowing

These references are from the 2021 International Residential Code (IRC), published by the International Code Council. Its Chapter 11 contains the residential energy provisions of the 2021 International Energy Conservation Code (IECC). Your jurisdiction may use another edition or local amendments.

Definition (R202): a sunroom is a one-story structure attached to a dwelling with glazing over 40 percent of the gross area of its exterior walls and roof.
Structural categories (R301.2.1.1.1): sunrooms must comply with the AAMA/NPEA/NSA 2100 standard. The construction documents must identify one of five categories:
- Categories I–III: thermally isolated, nonhabitable and unconditioned. They range from screened or plastic-film openings to glazed openings with extra air and water resistance.
- Category IV: thermally isolated, with its own heating or cooling control or system, and described as nonhabitable and conditioned.
- Category V: heated or cooled and open to the main structure.
Which category you declare shapes the design, so decide how you will use the room before the drawings are made.
Insulation (N1102.2.12 / R402.2.12): sunrooms that enclose conditioned space must meet the code’s insulation requirements. There is an exception for thermally isolated sunrooms: ceiling insulation of R-19 in climate zones 0–4 and R-24 in zones 5–8, and walls of R-13. The wall separating the sunroom from the house must still meet the full envelope requirements.
Glazing (N1102.3.5 / R402.3.5): sunrooms enclosing conditioned space must meet the fenestration rules. Thermally isolated ones in climate zones 2–8 may use windows with a U-factor up to 0.45 and skylights up to 0.70.

Thermal isolation usually means keeping doors or windows between the sunroom and the house, rather than opening the sunroom up to it. It also means not heating or cooling the sunroom with the main house system. Removing that separation later can turn the room into a fully regulated part of the house.

Cost by component

Item	Published range	Source
Site preparation	$500–$5,600; excavation $1,300–$4,600 extra	Angi
Foundation	$500–$6,000 (Angi); $1,000–$6,000 or $5–$15/sq ft (HomeGuide)	Angi, HomeGuide
Foundation by type, per sq ft	Slab $5–$10; pier and beam $7–$11; crawl space $7–$14; new deck $15–$30	HomeGuide
Windows	$300–$2,000 each (Angi). Per window: single-pane $290–$460, double-pane $450–$1,000, triple-pane $600–$1,300 (HomeGuide)	Angi, HomeGuide
Doors	Sliding glass $700–$2,400 (HomeGuide); patio door $1,300–$11,000 (Angi)	HomeGuide, Angi
Roof	$500–$7,000 (asphalt $500–$1,000; glass $3,000–$7,000)	HomeGuide
Insulation (four-season)	$500–$1,500 (Angi); $300–$1,500 or $1–$4/sq ft (HomeGuide)	Angi, HomeGuide
Electrical wiring	$250–$600+ for an average sunroom; panel upgrade $850–$1,700	HomeGuide
Heating and cooling	$2,300–$20,500 (Angi); ductless mini-split $2,000–$6,000 (HomeGuide)	Angi, HomeGuide
Flooring	$1,500–$4,300 (Angi); $2–$15/sq ft (HomeGuide)	Angi, HomeGuide
Permits	$250–$1,500 (Angi); $200–$500 (HomeGuide)	Angi, HomeGuide

Angi says labor typically makes up 40% to 60% of the total. Related guides: mini-split cost, sliding patio door cost, skylight cost and electrician cost.

New addition vs. enclosing an existing porch or patio

These are different projects. Get quotes for the one you actually have.

New sunroom addition: a new foundation, floor, walls, roof and tie-in to the house. It needs a full building permit and will likely be reviewed for setbacks, structure and, if conditioned, energy compliance.
Enclosing an existing porch, deck or patio: reuses the base and sometimes the roof. HomeGuide prices this at:
- a deck or patio into a sunroom: $8,000–$30,000;
- a screened porch into a three-season room: $4,000–$10,000;
- a screened porch into a four-season room: $10,000–$20,000.
Angi gives $41,500–$46,000 for converting a porch to a sunroom, which is less than its $47,000 new-build average mainly because you skip the foundation.

The two publishers’ porch figures differ widely, likely because they assume different scopes. Treat the Angi figure as closer to a full four-season conversion.

The catch is structural. HomeGuide notes that an existing base may need reinforcing to carry the added weight. A deck built for people and furniture was not necessarily designed for glass walls, a roof load and, in some areas, snow. A patio slab poured without footings may not be suitable as a foundation.

Before you assume a conversion is cheaper, have a contractor or engineer confirm what is under the surface. Our concrete patio cost guide covers slab pricing if you need to start over.

Worked example: a 12 × 14 ft sunroom

Angi gives 12 × 14 ft (168 sq ft) as the average sunroom size. This hypothetical example compares per-square-foot totals with a sum of published line items. It is not a quote.

Per-square-foot totals

Three-season, custom (HomeGuide): 168 × $80 = $13,440; 168 × $230 = $38,640 → $13,440–$38,640
Four-season, custom (HomeGuide): 168 × $200 = $33,600; 168 × $400 = $67,200 → $33,600–$67,200
Any type (Angi, $150–$300/sq ft): 168 × $150 = $25,200; 168 × $300 = $50,400 → $25,200–$50,400

As a cross-check, Angi’s own 14 × 14 row (196 sq ft) is $29,400–$58,800, which equals 196 × $150 and 196 × $300.

Four-season line items (HomeGuide)

Slab: 168 × $5–$10 = $840–$1,680
Insulation: 168 × $1–$4 = $168–$672
Asphalt roof: $500–$1,000
Ten double-pane windows: 10 × $450–$1,000 = $4,500–$10,000
Sliding glass door: $700–$2,400
Wiring: $250–$600
Mini-split: $2,000–$6,000
Flooring: 168 × $2–$15 = $336–$2,520
Cleanup: $300–$700
Permit: $200–$500

Low end: 840 + 168 + 500 + 4,500 + 700 + 250 + 2,000 + 336 + 300 + 200 = $9,794. High end: 1,680 + 672 + 1,000 + 10,000 + 2,400 + 600 + 6,000 + 2,520 + 700 + 500 = $26,072.

The line items alone fall well short of the $33,600–$67,200 per-square-foot range. That gap is the point of the exercise. HomeGuide’s component list does not include framing of the walls and roof structure, tying into the house, or general contractor labor and overhead, and Angi says labor alone is 40%–60% of a sunroom budget. If a quote looks like a sum of windows, a door and a mini-split, ask what structural and labor work is missing. Budget from the per-square-foot range, then add site work (excavation $1,300–$4,600 per Angi) and contingency with our project budget calculator.

Choosing between a sunroom and other ways to add space

A four-season room priced at $200–$400 per square foot can cost as much as converting existing space. Compare it with an attic conversion or a garage conversion if you mainly need floor area.
Separate living quarters for a relative or a tenant are an ADU question, not a sunroom one. See our ADU construction cost guide.
Glass-heavy rooms gain and lose heat quickly. Glazing performance (U-factor) and how the room is heated and cooled affect comfort and running costs as much as the purchase price. Ask for the window U-factor in writing.

FAQ

How much does a sunroom cost in 2026?

Angi reports an average of about $47,000 for a new addition, with most projects between $22,000 and $75,000.

Is a four-season sunroom worth the extra cost?

It is if you will use the room in winter or summer extremes. Four-season rooms need insulation, better glazing and their own heating and cooling, which is why HomeGuide prices them at $200–$400 per square foot versus $80–$230 for three-season rooms.

Do I need a permit for a sunroom?

Angi says a building permit is required for any sunroom addition. Enclosing a porch typically needs one as well. Confirm with your local building department.

Can I put a sunroom on my existing deck or patio?

Often, but only if the structure can carry the load. HomeGuide notes that an existing base may need reinforcing. Get it checked before you design anything.

Can I heat a sunroom from my main HVAC system?

That depends on the code category and on whether the room is thermally isolated. Connecting it to the house system or removing the separating doors can bring full energy-code requirements into play. Discuss this with your designer and building department.

Bottom line

Decide first how many months a year you will use the room. That one choice drives insulation, glazing, heating and cooling, electrical work and code category. Verify what your existing base can support, budget from per-square-foot totals rather than a short list of parts, and compare itemized local bids.

Reviewed by the Home Cost Desk editorial team on November 3, 2026. Prices are national planning ranges from dated sources; local rules and quotes govern.

Sunroom Addition Cost 2026: Three-Season vs. Four-Season and Porch Conversions