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Duplex Detached Accessory Dwelling Units for Berkeley Property Investor

2 bed | 1 bath | 578 sq. ft.
Local property investor Harmol came to Cottage hoping to build multiple ADUs on an existing multifamily lot located near the Berkeley Marina. Harmol's main priorities were to increase the property's rental income potential and raise the equity value, while also adding to the city's low housing stock. Cottage stepped in from the very beginning to check off all those boxes.
My whole ADU strategy went hand-in-hand with Cottage."
“My whole ADU strategy went hand-in-hand with Cottage," Harmol explained. "Cottage was really good at walking me through city guidelines—what’s feasible and not feasible—and Cottage didn’t oversell me on anything.”
The Cottage Design team designed two units, each at 578 square feet and including 2 bedrooms and 1 bathroom, to be attached back-to-back to maximize livable space while minimizing project costs.
Because many renters in Berkeley are students, having a duplex ADU that felt inviting and communal was another important consideration for the project from the very beginning. This was reflected in the mirrored unit design. Cottage was able to put together the preliminary design for Harmol to review and give feedback on with a quick turnaround time, while providing our ADU expertise to value engineer the design as much as possible, which saves Harmol on construction costs.
“My ADU all comes down to speed of execution and efficiency," Harmol said. "That has all been there with Cottage.”
While modular ADU or prefab ADU companies are limited to having separate units that require setbacks between ADUs and are less cost efficient, Cottage took a different approach from the start. Our team laid out a duplex floor plan with a shared plumbing wall (highlighted with the blue line below) and a mirrored design that minimized the number of ridge walls (dotted red lines below).
With this plan, Cottage was able to significantly reduce framing, plumbing, roofing, and foundation costs for the ADU, with the savings passed directly to the homeowner. These design details fulfilled the property owner's desire for two space-efficient, cost-efficient, and maintenance-efficient rental accessory dwelling units.
“If I had gone with a different provider and they had said, 'These are the five model units we offer, either they do work or they don't,' those kinds of things are annoying to me," Harmol told us. "If my ADU provider starts telling me I can’t build an ADU because the driveway is 9.8 feet wide and the ADU needs 10 feet to get to the backyard, that doesn’t work well. You need to come in as the problem solver, and not someone who is adding problems to make my investment tougher to close, and that is the deal breaker for most other ADU providers.”
Building a rental ADU or even two rental accessory dwelling units like this design does not mean you need to sacrifice on quality. The front door of each unit opens to a spacious open floor plan kitchen and living room space, and each rental ADU unit has plenty of room for a full-sized couch, table, and TV area. A kitchen skylight placed close to the entryway hallway and closet lets in additional light to make this Cottage feel like home, rental ADU or otherwise.
Other finish choices, such as those in the bathrooms, can increase the rental income potential and value of the property. The property owner decided to invest in an upgraded bathroom space for both units, with features such as wall to ceiling tile, a zero threshold walk-in shower, and high shower windows for great air flow and ample natural light. These custom options were important to Harmol from the start, and Cottage was able to meet his needs for the custom, site-built ADUs.
"The fact that Cottage can tailor the ADU to each person’s preference, each lot, and each home - that is crucial," Harmol said. "That’s where Cottage brings value.”
Are you interested in adding rental income while significantly increasing your property value and cash flow with one or more ADUs? Contact us today using the link below for a Free, No-obligation Consultation & Estimate with one of our ADU experts!

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