Hillside ADU Design Process: Next Steps, Refining a Design and Layout

In our last post, we discussed the process of translating the needs of the client, the existing site conditions, and the local regulations into a set of three designs/schemes for a 1,000-square-foot detached ADU on a hillside.

Once the client chose to go with the first scheme, we shifted our focus to the interior layout and generated some floor plans that showed the many options for laying out the rooms in the space. We also started to look at the shape and style of the roof as we turned the scheme into a more realistic design that would comply with the city and state regulations.

Here are the layouts we explored in depth.

The options

The first layout (Option A) placed the bedrooms, each with its own bathroom, on the sides of the house. This allowed a wider great room. The second option (Option B) took a more privacy-oriented approach and placed the bedrooms and baths at the back of the house, creating a longer great room. This was preferable because the living and kitchen spaces would have greater exposure to the epic San Francisco Bay view. Both were good options for laying out the ADU.

Option A

The first option was wider, which helped us keep the depth to a minimum. This was a big factor since we had to stay under the height limit while minimizing expensive excavation. We shifted the main door to the side to serve both the main home’s driveway and a potential new driveway at the bottom of the lot.

The layout affords space for a bench and bathroom near the entrance and opens up as you enter the great room. The wall of windows and sliding glass doors on the view side takes advantage of natural light and helps make the space feel bigger. The ADU's great room is flanked by a wall of kitchen and storage cabinets with natural wood fronts.

The bedrooms both feature picture windows for morning and evening views of the San Francisco Bay. The restrooms are in the back of the house, where windows and views are less important.

Option B

The second option was a different approach to the space, shifting the bedrooms and bathrooms, which won't necessarily get as much use as the great room, into the back of the ADU. This opens up the full width of the ADU on the front for windows and doors to a wrap-around deck. By having a wider great room, we could line up the kitchen island, dining table, and living room all in a row rather than having them feel like they were on top of each other. The efficiency of the layout helps consolidate many of the plumbing and fixtures to the center of the house rather than spreading them out across the ADU.

Getting the biggest ADU with a height limit

One of the biggest issues the project ran into as we developed schemes was limiting how much costly excavation and sitework we would need to do while keeping under the height limit. The style of the house was starting to take on a mid-century modern feel, and it was assumed that a single sloped shed roof would open up towards the view. However, this became a costly design option.

We developed a comparison looking at both gable and shed roof options. A shed roof is the cheapest and easiest to build, but it forces us to dig more. We looked at a shed roof sloped up towards the existing house with clerestory windows for natural light, but the client was concerned about privacy for the ADU. The gable option made our living and great room spaces taller and would ultimately bring in more daylight because we could lift the ceiling up to the height limit.

The comparison below framed out the discussion between the wider Option A compared with the deeper Option B. The client ultimately chose to go with Option A with a gable roof A (not shown in the comparison image), which means we will only have to dig in the very back, where our foundation will go. We will highlight the structural design for this hillside ADU in a future process post.

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