The main floor of William and Yuki French's addition is a flexible, family-room space that can be used as an apartment with a small kitchenette. The cumaru-clad outdoor deck, which connects to the main house, also includes a hot tub.  Photo 4 of 6 in Budget Breakdown: A Seattle Couple Expand Into a Backyard Addition For $413K

Budget Breakdown: A Seattle Couple Expand Into a Backyard Addition For $413K

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The main floor of William and Yuki French's addition is a flexible, family-room space that can be used as an apartment with a small kitchenette. The cumaru-clad outdoor deck, which connects to the main house, also includes a hot tub.