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A few years ago I had the opportunity for my mother-in-law to move in with my family in our NE Portland home. We didn’t have space in our home for her, and even if we did it seemed like giving her some privacy and personal space would make the situation better in the long run.
We decided to build a 200 square foot tiny home that would be largely self sufficient (with a bathroom and kitchenette), but that would rely on the main house for supplementary functions (storage, laundry, major cooking). When we started the permitting process the ADU System Development Charges (SDCs) were not waived as they currently are until
2013 2016 in Portland. Otherwise the costs are $12,000-27,000+, so we opted to create the building as a Detached Bedroom. This approach has pros and cons.
ADU vs DETACHED BEDROOM
The main difference between an ADU and a Detached Bedroom is that an ADU counts as additional density to the city, whereas a Detached Bedroom is considered an addition to the existing house. A Detached Bedroom cannot be rented out as a standalone apartment nor can it be built to function as one. The main way that the city draws this line is the presence of a full kitchen, as denoted by a sink and power for a range (220 electric outlet or gas). That said, this is a distinction that was made during my experiences with specific planners at specific times. City code is up for interpretation and I would strongly suggest taking any proposal in to the city and reviewing it with a planner early on in the process. In my project the sink is removed from the bathroom and serves double duty as a lavatory and a kitchenette sink. If you have two sinks in a Detached Bedroom I’ve heard that it is necessary to sign a covenant with the county that you will not rent it out. This configuration seemed to me the closest one could come to an ADU. No full kitchen and an inability to rent it out are two large marks against the Detached Bedroom, so why build one?
The biggest reason for me was cost. SDCs would have constituted 1/3 of the budget. It is inexplicable to me that you’d have to pay SDCs twice for an ADU and a 2 bedroom 1 bath house, but only once for a 5 bedroom 4 bath house. Another reason is design. There are strict regulations on the size, height, and placement of ADUs and how they relate to the main house. With a detached bedroom there are no regulations that wouldn’t apply to a normal house (size, height, lot coverage, etc). You could build a 3 story tower clad in purple sheet metal if you wanted, as long as it didn’t have a second kitchen in it (and met zoning code!). There are also provisions in the zoning code that the roof pitch, siding, windows, trim and eaves of an ADU need to match the existing house. These restrictions won’t affect many people but can be a problem if one wanted to pursue a modern or less conventional design.
The ultimate cost for the tiny house was around $27,000 or $135/sq. ft. I was initially aiming for $100/sq. ft. because it was a nice round number. However, building small is inherently more costly as you have all the utility connections, permit fees, windows, doors, fixtures, etc without the bedrooms and large living areas to spread out the expensive stuff. This was also despite a lot of cost savings, as I did all the design, drafting, interface with the city, also acted as the general contractor and did around half of the physical labor. For the other half I hired a handy friend, as well as subcontractors for the electrical, plumbing and tile setting. Windows were probably the largest splurge (Marvin Integrity fiberglass windows with wood interior) while areas cut back on were asphalt shingle roofing (instead of metal), electric heat (instead of gas), fiberglass batt insulation (instead of anything else).
A big focus of the design was the materials template. In a small space one has much more intimacy with all surfaces and objects, so making sure they are appealing is an even more important aspect of the design. We tried to use as much salvaged materials as possible and have as few painted drywall surfaces as possible. Instead, the majority of the walls are finished with American Clay and accented with wood and tile. The bathroom did end up being painted as was the exterior trim and some of the interior trim. Salvaged materials include the exterior siding, exterior doors, T&G fir flooring, cabinet doors, tile, interior wood trim and built-in furniture.
In the end the project took around 9 months and was done on weekends and during some Great Recession furloughs. It has been very successful as a way to accommodate a changing family while adding value to our home.
Schuyler Smith is an Architect and small living enthusiast in Portland, OR. He is the co-founder of Polyphon Architecture & Design LLC.