Mother-in-law houses could get size boost

Increasing the allowed size of accessory dwelling units, commonly called mother-in-law houses, could be one way Bainbridge Island handles affordable housing and density concerns.

The city’s current code says mother-in-law units cannot be larger than 800 square feet.

Local architect Jeb Thornburg told the council that is a “reasonably sized” single person or couple’s home, although a 900-square-feet mother-in-law unit could have two bedrooms and be more family friendly or allow for live-in caregivers.

Thornburg said there could be “significant market demand, significant market value” by increasing the threshold.

Poulsbo also has an 800 square-feet limit for mother-in-law units with the stipulation that they can be bigger if the unit is located on the ground floor or a basement.

The county allows 900 square-feet or 50 percent of the primary residence’s square footage, whichever is smaller.

Port Orchard has the same restrictions as the county, while Bremerton allows for the largest mother-in-law units at 1,000 square feet or 60 percent of the primary residence’s square footage, whichever is smaller. Bremerton also has a minimum of 300 square feet.

The city of Bainbridge Island has permitted 280 mother-in-law units since 1992, although others could have been permitted by the county or built without permits, said Kathy Cook, City Planning and Community Development director.

The council did not take any action with plans to discuss the increase at another meeting.

One thought on “Mother-in-law houses could get size boost

  1. As an architect, I strongly support a change to the current 800 square foot limit on ADUs on Bainbridge Island. The current limit is an arbitrary number, not based on good space planning, and not allowing for the extra room needed for units that allow aging in place. My experience has been that a decent-sized second bedroom is not possible in 800 square feet. Giving architects and homeowners the flexibility to build an ADU up to 900 square feet (or more) will lead to an increase in the number of affordable housing units and greater housing diversity on the island. Aligning with the county standards seems like a great place to start!

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