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7 Types of Home Additions and How to Choose One

7 Types of Home Additions and How to Choose One

A home addition adds finished living space to an existing home. Sooner or later, an addition is a universal desire of most homeowners. Even homeowners who claim that their house is big enough may, from time to time, want a bigger kitchen, an extra bedroom, or a larger bathroom. Enter the home addition.

Home additions range from relatively low-cost attic or basement expansions to expensive and expansive full-size conventional additions that require excavation, footings, and additional siding and roofing. Garage conversions are considered additions since so much living area is added at once. An increasingly popular option is a secondary living structure detached from the main house: an ADU or DADU.

1.) Attic/Basement Conversion

Best for: Adding living space without changing the home footprint.

Although technically not an addition—it doesn’t expand the actual footprint of your home—converting existing unfinished space in a basement or attic can be one of the most cost-effective ways to add practical living space. And it is one of the few expansion projects that recoup its full investment through added real estate value.

But an attic or basement must meet certain structural qualifications to make it practical to turn them into code-approved living spaces. Ceiling height must be sufficient, and floor and ceiling structures must meet engineering requirements in order to support the structural loads of active living spaces.

A basement must be completely dry, and attics must be amendable to insulation and ventilation requirements mandated by the local building code. Attic conversions are practical only for homes with attics that are framed without roof trusses. Any converted spaces that include sleeping areas must have egress exits, which may mean adding special windows.

Nationally, the cost of finishing a full attic space averages about $40,000; basement finishing costs are usually about half that. But the costs can vary enormously depending on the size of the space and if structural alterations—such as new egress windows—are necessary.

2.) Conventional Full-Size House Addition
Best for: When much living space is required and property around the home is plentiful.

A conventional house addition is a multi-room structure that is built onto the side of a house and is permanently open to the main house. When well designed, a house addition blends into and creates an entirely different house. A house addition can have many types of areas: great room, dining room, family room, bathroom, guest bedroom, or primary bedroom. But it is rare for an addition to include a kitchen unless the addition is intended as an apartment suite.

Major additions have all of the issues and requirements that come with full house construction. They are subject to all of the same building codes and permit requirements, and they normally require extensive excavation, foundation work, and subcontractors who install wiring, plumbing, and HVAC service. When such additions are designed so that they have all the features needed for independent living, they are sometimes known as AADUs (attached accessory dwelling units).

This kind of project is considered a major addition, and nationally, costs an average of about $72,000, but it is easily possible to spend $150,000 or more if the addition is quite spacious or uses upper-end materials.

3.) Room Addition or Bump Out
Best for: Adding a single room to the home.

A room addition or bump out is a single-room structure built onto the side of a house. It is usually meant for a single function, such as a bedroom or bathroom. Sometimes it only expands the size of a single room in the existing house.

A room addition or house bump out is an addition scaled far down. It might be another 50 square feet added to your kitchen so that you can squeeze in a kitchen island. Or, you might cantilever a few more feet out into thin air to turn a cramped dining area into a comfortable place to eat and socialize. Room additions and bump outs often lay down a new roofline, employing a shed style or flat roof.

While these types of additions are less expensive than full-size, conventional additions, they are not cheap. They are still subject to building codes, permits, and inspectors. They require a foundation—an expensive project itself. So, it’s not unusual for a room addition to cost upwards of $50,000.

4.) Sunroom Addition
Best for: Adding protected recreational space but not living space.

A sunroom is an addition to the side of the house that is usually a supplemental living area. Sunrooms typically can be closed off from the main part of the house with doors.

Smaller than a full-size addition, sunrooms are most often made of pre-fabricated materials such as aluminum and thermal-resistant glass and assembled on-site. Sometimes, sunrooms are stick-built from lumber, concrete, and other materials used to build the house itself, resulting in a solidly built living area that visually matches the existing house.
Sunrooms are never used as permanent sleeping areas, and kitchens and bathrooms are never installed in sunrooms. Because sunrooms are not, by code, designed to be year-round permanent living structures, certain features are possible that are not possible when building a conventional addition.

For example, sunrooms can be built with oversized glass and other fenestration that is not possible with a conventional addition. Also, sunrooms are not required to have heating or air conditioning.

5.) Garage Conversion
Best for: Adding a sizable space for an affordable investment; in-law suites.

A garage conversion transforms a one- or two-vehicle-attached garage into a living space by adding flooring, replacing the garage door with a solid wall, and installing a ceiling. Usually, garage conversions become living rooms or bedrooms. Sometimes, garage conversions go full ADU (accessory dwelling unit) and become habitable living spaces, with bathrooms and kitchens. Such projects, known as AADUs (attached accessory dwelling units) are often done at the same time a new detached garage is built elsewhere on the property.

Converting a garage into a living space is a very tempting option since the basic structure of walls, foundation, subfloor, and the roof is already present. In addition, a number of the elements needed for living spaces such as electricity and a couple of windows are already in place—or partially so. Some garages already have drywall on the studs, leaving one less task to do.

6.) Tiny House or DADU (Detached Accessory Dwelling Unit)
Best for: Isolating new living space from the home; rental or in-law suites.

Whether you call it a backyard cottage, tiny house, guesthouse, carriage house, granny pod, or granny flat, an ADU or DADU (detached accessory dwelling unit) adds space to the house and property though it’s not physically attached to the home. DADUs add more space for families to live together or they can be rented out to help defray mortgage costs.
Because these are detached units with kitchen appliances, bathrooms, and sleeping/living spaces, a DADU must have its own plumbing, wiring, and HVAC service, rather than piggybacking on the utilities of the main house.

Thus, this is one of the most expensive types of addition, averaging at least $100,000. But in communities where zoning allows for such structures, a tiny house/DADU can become a valuable rental space.

7.) Second Story Addition
Best for: Homes that need much more finished living space, yet land is at a premium.

Second-story additions are major improvements to the home that can double the amount of living space, significantly improve the home’s resale value, and accomplish all of this without using any land.

A second-story addition is a major undertaking. The average cost of a second-story addition hovers around $175,000, while some second-story projects reach $600,000. Not only that but building a second-story addition is a serious lifestyle shift. Residents need to live elsewhere for months at a time since the construction is so pervasive throughout the home.3

But the rewards more than balance out the costs. Except for partial second-story additions, expect to double the amount of floor space. That 1,500-square-foot home expands to a generous 3,000 square feet. Not a single square foot of property is used, either. All of the work is built on top of the existing structure.

If you intend to hold onto the home for a long time, consider aging-in-place and mobility issues with second-story additions: How will you move between floors? Local zoning is another issue; your architect and contractor can assist with that.

How to Choose a Home Addition
No matter what the scale, creating a new living space in your home is a major project that requires careful planning and a hard look at your budget. Such a project can range from finishing off the unfinished attic, basement, or garage space at a cost of $20,000 or less, to major multi-room additions or a DADU (detached accessory dwelling unit) that can cost $100,000 or more.

While adding living space is a major investment, it can be a very logical approach if the need for more space is pressing and if the family budget allows for it. It is almost always more affordable, not to mention more convenient, to add on to an existing home rather than uproot your family to move to a new, more expensive residence. But give the project careful thought to make sure you are getting precisely what you need.

Will the Number of Residents Change?

A small bump-out may seem logical for today’s needs, but what about if your family expands? Or if aging parents need to come live with you? On the other hand, if you are anticipating an empty nest situation in the next few years, rather than a major multi-room addition, a smaller project that adds a luxury bath or home theater might be the better approach.

Will Your Financial Situation Change?
Young families on a budget may want to minimize the cost of their home improvement, but in a few years after careers advance, you may regret not investing in a more significant home addition. On the other hand, if you anticipate retiring in a few years, then now may not be the time to take on HELOC (home equity line of credit), home improvement loan, a second mortgage to pay for that major project.

Will the Home Addition Add to the Home Value?
Thoughtful, well-planned home additions can recoup a large percentage of their costs in added equity when you eventually sell the house. Such increased value is usually realized some years down the road—not immediately; major home additions are usually not a good idea if you plan to sell your home soon.
How Much Is the Funding Costing You?
If you will be borrowing money (many people do), keep an eye on interest rates. Do you have ready access to a low-interest loan, such as a home equity line of credit? Borrowing against your home’s equity usually provides the best interest rates because the lender’s loan is secured by your home and land.

Are current interest rates at a historically low point that makes it attractive to remortgage your home to include extra cash for your addition? If so, then it may be a good time to go ahead with that major project But during times of historically high interest rates, it may be better to choose a smaller addition that is more affordable.

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