Four things to consider when deciding to build a basement apartment

[DC Accessory Apartments Forum]

I chatted with Ileana Schinder, an experienced architect working on basement apartments in DC. She offered some helpful advice for any homeowner considering converting their basement into a separate living unit. – Cheryl Cort

What is your scope and timeline? – those are the first questions Ileana always asks a prospective basement apartment builder when determining the feasibility of the project.

According to Ileana, in DC, the cost to build a complete basement apartment starts at $100,000. When creating a living unit where there wasn’t one, “$100k may not be enough,” she explained. “The apartment will require all new plumbing, mechanical, etc.” The cost of creating a new basement apartment will always cost less than it would to buy the same square footage in living space in the same area, she said.

To understand the cost versus return on creating the basement apartment, Ileana suggests a homeowner think about the worth of the house pre-basement apartment, add the cost of the construction and then compare it to the final value of the house with the rentable basement. Like all investments, it takes money to create a return. She joked that basement apartments sound like a safer investment than bitcoins, and a better bet than the stock market.

When considering investing in a basement apartment, she said there are four main drivers of cost:

1. Ceiling height: The building code requires 7 feet of clearance. If you are short of 7 feet, there's a cost associated with digging down. If you dig far down, you might need to reinforce the building -- called underpinning. If you have to dig more that 6 inches, you will likely need underpinning and that can be expensive ($5,000-10,000 or more). If height is less than 6 inches too low, you might not need underpinning. Underpinning requires a lot concrete and time added to the schedule. More time + more concrete = more money.
2. Location of utilities (mechanical and electrical): Consider where the existing mechanical system and electrical panel are located. For two or more dwellings in a rowhouse, the building code requires that shared utilities cannot be inside any one unit. They must be either in a common space, or divided per unit. There's a cost associated with this, and some factors to keep in mind: 
• An electrical panel located in the front or back of rowhouse basement will be easier to access. If it’s in the middle basement, it will need to be moved (costs could be $5,000-$6,000)
• A new hot water heater costs about $1,000, but adding a second unit means relocating the existing hot water heater. Installation with piping can cost $3,000. 
• The boiler for the owner’s unit would need to be moved to the main floor, which could cost up to $5,000.
• If the unit uses forced air for air conditioning, you would need separate ductwork for each unit.
• More utility modifications might be needed, which will cost extra.
• Note: less utility separation is required for a single family detached house subject to the International Residential Code (IRC), but a rowhouse must comply with complete separation under the International Building Code (IBC). Any renovations on an existing house would be follow the International Existing Building Code (IEBC) rules.
  
3. Alterations needed for the existing building: Are the alterations minimal or will they reduce the quality of your living space? Would your home feel less spacious? Would they reduce the value of the house, or enhance it? Would you need to void an internal staircase? Modify your front door? What do you lose, gain, and what’s the cost? 
4. Access during construction: Needless to say, a space that is hard to access will have cost implications. Excavation costs are among the most significant to consider for tight spots, such as the difference between having alley versus no alley access. In her experience, Ileana has seen all kinds of excavations. One Georgetown house excavated via hand buckets... through a window! Most basement excavations, however, have at least access through a door. Some can even use mechanical equipment to remove the dirt. 

So how much is enough? “If there’s no excavating and no major utilities moved, $100,000 is enough,” she notes. But remember, every case is different.

Ileana also highlights some questions to consider in determining if your investment is worthwhile: How will the owner use the apartment today? Who will it be used 20 years from now? Will your property generate income from a renter or be occupied by an aging parent? With aging parents, you might also consider accessibility. For example, she says, stairs may not be an issue for a young renter but, if you plan for a grandparent to live there, will access via stairs be a problem?

Costs and challenges of converting a basement into living space sound a little intimidating, but remember the upside -- in most circumstances, it’s likely to be one of the best investments you can make. Building out a separate living unit might also be the perfect solution to keeping a family member close -- but not too close.

To get in touch with Ileana, contact her at:

Ileana Schinder, Architect, AIA, LEED AP BD+C, Certified Passive House Consultant
E. i...@ileanaschinder.com, T. 202-431-6760, W. www.ileanaschinder.com

Are you an architect who has tips for would-be accessory or basement apartment builders? Get in touch and let us know.