Home Addition Second Story ADU Design Lake Forest Park
A 1950s mid-century home on the north shore of Lake Washington — expanded upward for a master suite with views, and outward with an ADU designed as a complete, self-contained home.
Lake Forest Park sits on the north shore of Lake Washington. The homes here were built mid-century, and many have good bones — sight lines, site placement, proportions that work. This one had all of that.
The clients bought it knowing they wanted to expand it, not replace it. The goal was a second-story master suite connected to the original structure and an ADU substantial enough to function independently.
Designed to Extend Without Overwriting
The second-story addition was positioned specifically to capture Lake Washington views from the master suite. Window placement was intentional — large openings that frame the water without overexposing the interior to western light. The en-suite bathroom and walk-in closet complete the suite.
The ADU is designed as a complete home, not a guest unit. Three bedrooms, a separated office, and three bathrooms mean it can house extended family, guests, or tenants without functional compromise. The program was taken seriously from the first planning stage.
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Adding a second story to a mid-century structure is not straightforward. The original roofline, the proportions, the way the home reads from the street — all of those have to be respected or the addition looks like an afterthought. Feasibility studies and zoning analysis were required before a single design decision was made.
The ADU had real program requirements: three bedrooms, an office, three bathrooms. Fitting that into a secondary structure while maintaining functional separation from the main house demanded careful planning across the full site.
“The main house kept its character. The addition captured views the original owners never had. The ADU created options the property never had before.”
Our Design Approach
How We Planned the Expansion
Materials across both additions reference the mid-century language of the original home without copying it directly. The palette is cohesive from the street and through the interior — the addition reads as considered rather than borrowed from a different aesthetic entirely.
The ADU separation was handled at the site planning level. Circulation, entry points, and outdoor space allocation were all planned to give the ADU genuine independence while maintaining the cohesion of the overall property. It functions as a rental, extended family housing, or guest accommodation without feeling like any of those uses was an afterthought.
Permit facilitation was part of the scope. Zoning compliance for the ADU program — three bedrooms, office, three bathrooms — required navigation of Lake Forest Park’s land use policies from the outset. Getting the permit process right at the start meant no redesigns mid-project.
Location
Lake Forest Park, Washington
Original Structure
1950s mid-century home
Addition
Second-story master suite with Lake Washington views
The key is reading the original structure carefully before making any addition decisions. Mid-century homes have specific proportional relationships — roofline height, window-to-wall ratios, the way the facade meets the ground — and any addition that ignores those relationships will read as an afterthought from the street. The second-story addition at Lake Forest Park was designed to work within the proportional logic of the original rather than impose a different scale on top of it. Materials were chosen to reference the mid-century language without copying it, which keeps the addition from looking like a pastiche or a foreign object.
A genuine ADU has to meet program requirements that a guest unit does not. Three bedrooms, three bathrooms, and an office that functions as a real workspace — those aren’t amenities, they’re functional requirements for long-term occupancy. Site planning determined the entry, circulation, and outdoor space allocation independently of the main house, so the ADU has its own sense of arrival and privacy. The result is a unit that works for extended family, long-term rental tenants, or guests without the occupants feeling like they’re in a secondary space.
Yes — and this is often one of the most compelling reasons to add a second story to a single-story home on a lot with view potential. At ground level, neighboring structures, landscaping, and grade changes frequently obstruct sightlines that exist at height. The second-story master suite at Lake Forest Park was positioned and oriented specifically to capture Lake Washington views through large window openings. Window placement was also calibrated to frame the water without overexposing the interior to western light — the view and the thermal performance were addressed together.
Permit facilitation for a project of this scope involves zoning analysis, setback compliance, height limit verification, and ADU-specific land use requirements that vary by jurisdiction. Lake Forest Park’s policies around ADU bedrooms, parking, and separate utility connections all had to be confirmed before the design was finalized. Getting these requirements into the design from the outset — rather than discovering compliance issues after drawings are complete — prevents mid-project redesigns that cost time and money. Permit facilitation is part of our scope because it’s not optional: the project doesn’t get built without it.
A well-designed ADU adds functional flexibility and long-term property value. For the Lake Forest Park clients, the ADU can serve extended family use now and transition to rental use later — or the reverse. The three-bedroom program makes it competitive as a rental in the Lake Forest Park market. The key design consideration for rental flexibility is independence: separate entry, adequate storage, laundry, and no shared spaces that would create friction between occupants of the main house and the ADU. All of those were addressed at the planning stage rather than retrofitted after the fact.
Your home should stop you. Every time you walk in.
The work in this portfolio is the standard we hold ourselves to on every project — not just the celebrated ones. We take on a limited number of engagements each year, which means the projects we commit to receive our full attention from the first conversation through the final installation.
If you’re considering a renovation, a new build, or a full redesign, tell us about your home. We’ll tell you honestly whether we’re the right fit — and what working together would look like.
