Second dwellings on lots zoned for single-family housing are generally forbidden in the Washington area, but “accessory structures” such as home offices, exercise studios and workshops are allowed if owners meet local government zoning and building rules.
Reworking an existing shed, garage or other outbuilding has one big advantage: Its use and location are grandfathered from any later, more restrictive zoning laws. This can make getting a permit for renovation much easier, said Glenn MacCullough, an architect in Arlington County.
You may also be able to salvage and recycle some of the materials, and you can use the structure as a life-size model in conceiving design ideas, said Jeffery Poss, an architect in Urbana, Ill. “Whether it’s drawing on it or cutting holes in it, it’s much more direct than working with a computer program or something like that.”
The cons? Older buildings may need major rebuilding because of rot, termite damage or original structural inferiority. Their concrete-slab floors may also need repairing.
Entirely new structures have their bonuses as well: You can position them in the most appropriate and sensitive areas of the lot.
What drives up costs? The framing is the economical part, but well-made, stylish and energy-efficient doors and windows are expensive. “The closer you keep to using off-the-shelf items, the more you can manage costs,” said Poss, who also teaches at the University of Illinois.
Basic electric service from the house will power lights, outlets and certain heating devices. But air conditioning typically requires a beefed-up electrical feed to a subpanel, which in turn is dependent on the house having enough extra capacity to serve it, MacCullough said.
Plumbing adds another level of expense and hassle, and a bathroom, beyond its own expense, would require a tie-in to the home’s sewer system. “Anytime you’re dealing with utilities or plumbing, it’s going to drive up the cost,” Poss said.
Difficult site access adds its own challenges to a contractor reliant on heavy equipment, and the farther the satellite from its mothership, the greater the plumbing and electricity costs.
“It can get expensive very quickly,” Poss said.