Sunroom Addition Basics For Your Home

Brick and stone cottage style home with sunroom, patio and landscaped backyard, Quebec, Canada
Perry Mastrovito / Getty Images

If you want more space in your home, the usual course is to hire a contractor to build a full-size addition or a room addition that adds a bump-out or extension to the main footprint of the house.

But that stick-built option is also one that can quickly alarm budget-conscious homeowners when the bids from general contractors come in. A custom-built addition, at the least, will cost in excess of $100,000, with most additions costing several times that amount.

A popular alternative is a sunroom—a space that bridges indoor and outdoor spaces with a comfortable supplemental living area. The fact that a sunroom usually costs far less than a traditional stick-built addition makes this a very attractive option.

What a Sunroom Is

A sunroom is usually defined as a recreational space bridging indoor and outdoor living areas, usually with a considerable amount of wall space dedicated to glass—often as much as 80-percent.

Building codes generally do not require a sunroom to have electricity or heating/cooling service, although this may not be the case in every municipality. Many sunrooms now have electrical services, and they may have supplemental heating and cooling. 

According to the International Energy Conservation Code (IECC), any conditioned living space cannot have more than 40-percent of the wall space given over to glass windows.

Sunrooms often are built on floating concrete slabs with shallow perimeter foundations, somewhat like those used for a garage; full basements beneath sunrooms are rare.

What a Stick-Built Addition Is

Stick-built is the shorthand term for any kind of structure that is built from scratch.

In this case, stick-built refers to house additions, room additions, and other bump-outs that are constructed from wood, concrete, glass, house sheathing, and shingles—nearly every component that is used when building a home.

Stick-built additions may have full basements in regions where that is the norm. A true room addition must have full electrical service and HVAC service. This type of room addition adds to the square footage of the house and is recorded by your local tax assessor.

what is a sunroom addition illustration

The Spruce / Alex Dos Diaz

Prefab vs. Custom-Built Sunrooms

Within the sunroom category, there are two categories: prefabricated or custom-built. Prefabricated sunrooms are more the norm and tend to be a bit less expensive, but it won't adapt to your home. Custom-built sunrooms definitely adapt to your house and property yet cost more than prefabricated units.

Prefabricated Sunrooms

Today's sunrooms are most commonly constructed from prefabricated kits that come with framework pieces of steel, aluminum, or fiberglass, along with glass panels for the walls. 

Prefab sunroom additions are assembled in a puzzle-like fashion, usually by qualified technicians. The fact that these are kits does not mean that assembly is an easy DIY project, although experienced homeowners have successfully assembled them.

A prefab sunroom is designed and fabricated off-site. It is then shipped by common freight carrier in pieces packed in flat cartons.

Assembly can be done by a homeowner or more often by a contractor affiliated with the kit manufacturer.

Custom-Built Sunrooms

Sunrooms can be custom-built by a local general contractor who will design and build the sunroom to your specifications.

Such sunrooms have traditional stud-and-truss framing and shingle roofs, but the walls are predominantly glass, formed by patio doors or full-length windows. Because sunroom construction isn't all that common, look for a contractor who specializes in sunrooms or at least one who has significant experience with sunrooms.

Sunroom Costs

Costs for sunrooms vary enormously. A small sunroom may cost around $8,000, and owner-built sunrooms can cost even less. A large sunroom with a new slab-on-grade foundation may cost more than $80,000.

For a 15-by-15-foot sunroom kit, example costs:

  • The starting price for wooden kit sunrooms built with standard materials is about $17,000.
  • Top-of-the-line aluminum and glass kit sunrooms can cost as much as $24,000.
  • Expect to pay $24,000 to $38,000 if you want the sunroom to be a four-season space, with finished walls and wiring and heating service.

With sunroom kits, you do need to supply the labor, plus peripheral materials. For a fully finished four-season sunroom, budget between $25,000 and $80,000 for the project.

Sunroom Considerations

Heating and Cooling

Sunrooms are not required to have central heating and cooling (HVAC). Custom-built sunrooms usually have at least heating, often in the form of electric baseboards or fan-driven heaters. True room additions, on the other hand, must have the same central HVAC service as the rest of the house.

Electrical Service

Sunrooms are not required to be wired for electricity, though they increasingly are, especially when they are custom built. Even prefab sunroom kits may have provisions for adding electrical service. 

Stick-built room additions, on the other hand, are required to follow the same code requirements for electrical service as the rest of the house—which is one of the reasons they are more expensive than sunrooms.

Construction Costs Vs. Resale

On the whole, sunrooms have a lower construction cost per square foot than regular room additions built by general contractors and subcontractors. Square footage costs for sunrooms are usually about half that of room additions.

Yet, if you're trying to maximize the overall value of your property, it might be worth spending more for a site-built full addition. Initial costs will be higher but the eventual resale value will also be higher.

Type of Supplemental Space

The main purpose of a sunroom is to provide supplemental space with generous natural light for reading, growing plants, housing a spa, etc. This is an important real estate distinction because supplemental space is viewed differently from the essential living space that is provided by a true room addition.

In short, a true addition or room addition adds more equity value to your home than does a supplemental sunroom.

  • Do sunrooms require building permits?

    Sunrooms do require building permits. In most communities, even the smallest sunroom kit or custom-built room needs a building permit. Electricity needs to be permitted, too.

  • Are prefab sunrooms cheaper than custom-built sunrooms?

    Prefab sunrooms are often, but not always, cheaper than custom-built sunrooms. There are many different add-ons you can specify for a prefab kit, and a top-of-the-line sunroom kit with all possible options can approach the cost of a room addition. What tends to give the impression of prefab units being cheaper is that they are sold as materials only. When a prefab company quotes you a price, they are quoting the price of the sunroom kit only.

  • Do sunrooms need foundations?

    Your sunrooms might need a foundation. Foundation requirements are as varied as the localities where these codes apply. Generally, you will need a proper building foundation for your site-built sunroom, although some lightweight prefab sunroom kits can sometimes be assembled onto existing patio slabs or decks.

  • Can you grow plants in a sunroom?

    A sunroom isn't exactly the same as a greenhouse. A greenhouse is built specifically for growing plants, so it will have a hardscaped floor with built-in drainage to accommodate spills. It will also be positioned at just the right place in your yard for growing plants. A sunroom will have more sun than in any other part of the house, if only because of the increased fenestration. But it won't necessarily be on the side of the house that gets the most sun (unless you specify so).

Prefab Sunroom Companies

  • TEMO Sunrooms: Beginning in 1967 with founder Nino Vitale, TEMO has been making sunrooms, screen rooms, and patio covers ever since. Now located in Clinton Township, Michigan, TEMO has expanded to basements/additions and pergolas. TEMO sunrooms are installed in one to two days.
  • Patio Enclosures: Based in Macedonia, Ohio, Patio Enclosures has been making sunrooms since 1966. In addition, the company makes solariums, screen rooms, sunroom blinds and shades, and sunroom furniture.
  • Florian: Based in Georgetown, South Carolina, Florian makes a variety of upper-end sunroom kits, along with greenhouses and conservatories.
  • Colorado Sunroom and Window: Based in Denver, Colorado, Colorado Sunroom and Windows makes sunroom kits in a variety of styles, and quotes prices based on your specifications.

Should You Buy a Sunroom?

A sunroom is a tempting alternative to a conventional, full-sized addition. On average, these light-bathed spaces are cheaper than stick-built additions, and since fewer subcontractors are involved, sunrooms go up quickly.

Although the space added by a sunroom is defined as supplemental space—not the essential living space offered by room addition—for many homeowners, a sunroom is a perfect choice.

Unless very well-built, many sunrooms don't add much to the home's resale value. Some buyers may even view the sunroom as a deficit.

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  1. How does COMcheck calculate percentage of glazing? US Department of Energy.