The pros and cons of building an annex, as opposed to a home addition
Putting new space under the same roof as the rest of your house isn't always the best or the only option. Building an annex might be a simpler or more effective way to get the kind of flexibility you're after. Some annexes are freestanding; others are semidetached, linked to the house by a deck, terrace, bridge, or other covered passageway. Examples of structures that commonly function as annexes include garages, sheds, garden pavilions, and self-contained living quarters. An annex may occupy a portion of the structure, such as the attic space above a garage or the indoor half of a garden pavilion, or it may include the entire structure.
One of the chief advantages of an annex is privacy. In a household where solitude is a rare commodity, creating an oasis away from the house may be the only way to ensure real peace and quiet when you need it. The degree of separation offered by annexes makes them particularly suitable for spaces that call for extra privacy, such as guest quarters, a home office, or an apartment for live-in relatives.
Annexes are also good options for spaces that need extra noise buffering, such as a teen lounge, a kids' playroom, or a room for playing musical instruments. Another advantage is minimal—or no—alteration of your home's existing roofscape, exterior walls, room layout, or supply of natural light and views. Because a home annex is mostly or totally freestanding, it won't require changing your home's roof pitch, giving up windows, or rerouting household traffic. All you may need to change is the shape of your deck or terrace or the location of plants, shrubs, or paths in your landscape.
The design of a freestanding or semidetached structure needn't be as conventional as a fully attached structure because it's more a part of the landscape than of the house proper. Therefore, a home annex offers an opportunity to escape the relative formality of "regular" shelter and indulge in a bit of architectural whimsy by incorporating visually playful elements such as picturesque window shapes, lattice screens, or arbor-style roof structures. Some annexes even function primarily as at-home getaways—spaces tucked away in the backyard or perched beside a pool or patio that capture the feel of someplace more remote, like a cabin in the woods.
One disadvantage of a home annex is that you have to extend utility lines beyond the house to provide the new space with basic services such as heating, cooling, electricity, and running water. This can be costly, but the added convenience—or lack of other options—might be worth it.
Another obstacle to consider when building a home annex is the set of codes that regulates the design and location in residential areas, especially when used as a separate living unit. In many communities, separate units aren't allowed in areas zoned as single-family residential, so you may need to apply for a variance if you include a kitchen and a bathroom in your annex. But an annex can offset these drawbacks by freeing up part of the main house and multiplying space.