Lake Oswego allows one ADU up to 800 sq ft on most single-family lots, with no parking requirement and a possible waiver of system development charges. Serden Group handles feasibility, the pre-application conference, design, permits and construction.
Whether an ADU is allowed in Lake Oswego is usually settled — outside the R-W waterfront zone, it is. The real questions are where it fits around protected trees and slopes, how it connects to utilities, and whether the SDC waiver makes sense for how you plan to use it. We answer those first.
Detached units, attached units, above-garage builds and basement or garage conversions. Feasibility, engineered plans, the city’s pre-application conference, permits, site work, construction and final inspection under one contract.
A standalone unit in the back or side yard on its own foundation — kitchen, full bath, bedroom, and its own entry and address.
Built off the existing house on a new footing line, with a separate exterior door and a code-compliant separation wall.
Converting space you already own — insulation, egress, ceiling height, a new kitchen and bath, and a legal second address.
A second story over an attached or detached garage, with the foundation and shear capacity verified before design starts.
We confirm your zone allows an ADU, map setbacks, trees and slope, check utility connections, and outline whether the SDC waiver fits your plans.
Plans and structural drawings, the required pre-application conference with the city, then the building permit through e-Permitting.
Tree protection and erosion control inspected first, then foundation, framing, utilities, finishes and final inspection.
Lake Oswego homeowners choose Serden Group because one team takes the ADU from feasibility through permits and construction — no juggling designers and builders, and a unit built to last in the Pacific Northwest.
Great experience working with this company. They were professional, responsive, and the quality of their work was solid. They even took the time to treat me to lunch and go over the project details, which I appreciated. Would recommend.
The SERDEN Group did a complete remodel of our two upstairs bathrooms. Every step of the way Dennis, and his team, were communicative, kind, timely, and productive. They worked diligently, caring about the impact of having workers in your home. Everyone was friendly and attended to our creative ideas for the bathrooms. In the end we have two amazing new bathrooms. Our family is grateful for SERDEN and are wonderfully reminded daily of their excellent work. Thank you!
I recently hired Serden Group for a full kitchen and bathroom remodel, and I couldn't be happier with the results! From start to finish, the team was professional, reliable, and detail-oriented. The quality of their work is outstanding — everything from the tile installation to the cabinetry and finishes looks beautiful and well-crafted. They completed the project on time and within budget, which is rare to find these days. I highly recommend Serden Group to anyone looking for top-quality remodeling work. They truly exceeded my expectations!
I had a very pleasant experience with SERDEN GROUP company. They remodeled my bathroom, and I am completely satisfied with the result. Fast and high-quality work. Denis answered all of my questions, suggested great solutions for the renovation, and delivered everything he promised. I 100% recommend them.
Had the pleasure to work with this team on a project for one of their clients. They followed through with every request from start to finish and we can proudly say that, they really put their best foot forward with all their work. Our team would love to continue to work together for future jobs!
Local Knowledge · Lake Oswego, OR
The rules below come from the City of Lake Oswego’s ADU guidance and Oregon law. We confirm each one for your lot during feasibility.
In Lake Oswego, OR, one ADU up to 800 sq ft is allowed on a lot with a detached single-family home in every residential zone except R-W (Residential-Waterfront); conversions of existing house space may add 200 sq ft. No parking is required. A pre-application conference is required before the building permit, and system development charges can be waived if you record an agreement not to use the unit as a short-term rental. Detached ADUs typically cost $220,000–$380,000 in 2026.
The core limits are simple.
State law limits what can be required.
SDCs can add significant cost, and Lake Oswego offers a waiver.
Most of the cost variation comes from the site.
| Scope | Typical cost | Timeline |
|---|---|---|
| Basement or garage conversion | $90K–$210K | 4–6 months build |
| Detached one bedroom | $220K–$380K | 6–9 months build |
| Two bedroom or complex site | $380K+ | 8–12 months build |
| Feasibility, pre-app and permits | Varies by site | 3–5 months |
Lake Oswego requires a pre-application conference before it issues an ADU building permit. Conferences are usually held on Thursday afternoons about two weeks after you apply. The permit is then filed through the state e-Permitting portal, and the ADU must meet the Oregon Residential Specialty Code.
Before issuing the permit, the city inspects tree protection and erosion control. Homeowners cannot do the electrical work themselves; our licensed trade partners pull those permits.
From First Addition and Old Town to Lake Grove, Westlake, Palisades and Mountain Park — plus West Linn, Dunthorpe and Tualatin. We check each lot for zoning, trees and utilities before design. Our Lake Oswego office is at 333 S State St, Lake Oswego, OR 97034 — design consultations by appointment.
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Questions? Call (360) 836-7775
Three tiers cover most ADUs we build. Each includes design, engineering, permits, construction and finishes. System development charges are listed separately, since Lake Oswego may waive them.
Ranges are planning figures, not quotes. Your fixed price follows feasibility, a site visit and a written scope.
Both sides of the lake, from 1920s First Addition cottages to 1980s Westlake and Mountain Park homes.
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Everything Serden Group builds in Lake Oswego, the same service in nearby cities, and the planning guides clients read before they start.
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