Sunrooms vs. Full-Room Additions

Six friends sitting around dinner table in naturally lit conservatory talking
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If you are seeking to add space to your home, one option is to hire a contractor to build a room addition that adds a bump-out or extension to the main footprint of the house. But it is also an option that can quickly alarm budget-conscious homeowners when the bids from general contractors come in. It is not at all uncommon for a custom-built addition to cost in excess of $100,000, and it is nearly impossible to get any custom addition of this type done for less than $50,000.

These prices quickly cause many people to look for alternatives to custom room additions. One very 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 about half of a traditional stick-built addition makes this a very attractive option for many people.

Definitions

To the novice, the various terms used for add-on living space can be confusing:

Stick-Built Addition

Stick-built is the shorthand term for any kind of structure that is built from scratch. In this case, it 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. These additions may have full basements beneath them 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 official square footage of the house. 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

The term 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 central heating/cooling service, although this is not a hard-and-fast rule. Many sunrooms now have electrical services, and they may have supplemental heating and cooling. 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 is a sunroom addition illustration
The Spruce / Alex Dos Diaz

Prefab vs. Custom-Built Sunrooms

Within the sunroom category, though there are two subcategories. 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.

More commonly, though, today's sunrooms are constructed from prefabricated kits that come with framework pieces of steel, aluminum, or fiberglass, along with the glass panels for the walls. Prefab sunroom additions are assembled in puzzle-like fashion, usually by qualified technicians. The fact that these are "kits" does not mean that assembly is an easy DIY project, although many homeowners have successfully assembled them. A prefab sunroom is designed and fabricated off-site then is shipped in pieces to your home packed in flat cartons. Assembly can be done by a homeowner, or more often by a contractor affiliated with the kit manufacturer.

Costs

Costs for sunrooms vary enormously. A recent survey showed that the average cost of a sunroom was $15,104, nationally, but that costs in excess of $75,000 are also possible for a large sunroom when a new slab-on-grade foundation was required.

Here are some typical costs for a 15-by-15-foot sunroom kit:

  • The starting price for wooden kit sunrooms built with standard materials is about $15,000.
  • Top-of-the-line aluminum and glass kit sunrooms can cost as much as $22,000.
  • Expect to pay $20,000 to $35,000 if you want the sunroom to be a four-season space, with finished walls and wiring and heating service.

Components

Since sunroom builders in recent years have been stepping up their game and rewriting some of the rules, these distinctions between stick-built additions and sunrooms are constantly changing and narrowing. For example, there was a time when most prefab sunrooms were not wired for electricity. Now, this is a viable option with most sunroom packages.

  • HVAC: 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: 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.
  • Provides 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 room addition adds more equity value to your home than does a supplemental sunroom.

Misconceptions

In their eagerness to add a sunroom, homeowners often make certain mistaken assumptions about sunrooms. Here are some corrections to common misconceptions:

  • Sunrooms do require building permits. In most communities, even the smallest sunroom kit or custom-built room will require a building permit in order to construct it.
  • Prefab sunrooms are 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.
  • 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 prefab sunroom kits can sometimes be assembled onto existing patio slabs or decks.

Prefab Sunroom Companies

Some reputable prefab sunroom manufacturers include the following:

  • 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.

Final Word

A sunroom is a fantastically 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 spaced 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.