We work with property owners across the Seattle and Eastside area and duplex conversions keep coming up in conversations lately. The math on paper looks compelling. Two units on the same lot, same property taxes, potentially 30 to 70 percent more gross rental income than a single-family rental on the same property. But we also know the upfront costs are real. Design fees, permits, structural work, separate utilities, two kitchens, two bathrooms. In Seattle that typically runs anywhere from $150,000 to well over $400,000 depending on the scope and condition of the home. Most owners we talk to are looking at payback periods somewhere between 8 and 15 years when everything is modeled honestly. What we find is that the owners who do it well go in with a realistic pro forma, not a best-case one. Vacancy allowances, maintenance reserves, the full picture.

Curious if anyone here has been through a conversion and whether the numbers played out the way you expected. What did you wish you had modeled differently before starting? We put together a full breakdown of the costs, timelines, and what makes a property a strong candidate here.

Has anyone actually run the numbers on converting a single-family rental into a duplex in Seattle?