Accessory Dwellings

A one-stop source about accessory dwelling units, multigenerational homes, laneway houses, ADUs, granny flats, in-law units…

Deborah Kelly’s ADU: Mossy Cobbles


Editor’s Note: This week’s ADU Case Study was written and contributed by Deborah Kelly, the owner of an ADU called Mossy Cobbles. Deborah worked with her son, Justin S. Kelly, who is an architect and engineer, to design the cottage for Deborah’s mother to occupy when she lived in Portland for half the year. It was constructed by the next door neighbor, Tony Kikes with hardscaping by another friend and neighbor, Steve Carruthers. The cottage is now available as a short-term rental and additional information can be found on Deborah’s website:


Kelly ADU

Quick Facts

  • Setting: suburban
  • Neighborhood: Garden Home, Portland, Oregon
  • Type: stand-alone detached unit (new construction)
  • Use: Short-term rental
  • Square Footage: 320
  • Year Built: 2006
  • Owners: Deborah Kelly
  • Designer: Deborah Kelly and her son, architect Justin S Kelly
  • Builder: Tony Kikes of Five K Construction

Kelly ADU Exterior

The cottage in our garden was planned as a place for my mother to stay for 6 months or so each year, visiting from California, and to be rented out the rest of the year to pay for itself. Though she was playing tennis twice a week at the time, after Dad passed away she only lived another 4 years, but was able to stay in the cottage enough to call it her own. After talking to a friend and reading some books on Bed & Breakfasts, the cottage was listed as a vacation rental. Like the rest of humanity, 97% of the guests have been interesting and fun to meet. It’s been a joy to operate the little business. The cottage has been listed with VRBO and HomeAway for 9 years, and we are considering Airbnb.


Kelly ADU in Trees

We live in Garden Home, a southwest neighborhood of Portland, next to the Fanno Creek Trail. The cottage is set back from the main house in a woodsy location, an 80-foot walk through the garden from the main house driveway, so you feel “elsewhere.”

Designed by my son, architect Justin Kelly and me, it was the most fun mother-son collaboration ever. The building has a very small footprint, but everything a person could ask for in a small apartment. The design places part of the bathroom and a storage area underneath the stairs. There is a hatch door on the first landing, and cabinets under the window seat to make use of those spaces for storage. The front loading washer and dryer are tucked under an ample peninsula that divides the kitchen and living room areas. The stairs to the loft make two 90 degree turns, and are an architectural feature in themselves. The open ceiling over the living area, and the multitude of windows, give the cottage an airy feeling that belies its small size.

The architect, who also made the topography map for the site, gave much thought to the orientation of the structure and windows to maximize views out toward the garden, creek, and woods. All the windows of the cottage look out onto greenery and trees.


Kelly ADU Window Wall

The wall of glass in the window seat makes it a dramatic part of the interior and a delightful spot to read, especially with lighted sconces at each end.There are windows rather than cabinets above the kitchen counters.

Mossy Cobbles was built in 2006 by my then-neighbor Tony Kikes of Five K Construction. It took longer than anticipated, with permits from the county and fire and utility services, required neighborhood mailings and a meeting, geological, biological and topographical surveys, and subcontractor delays, but in the end I couldn’t have been happier. The cottage was my dream home in miniature.


Kelly ADU Kitchen

The structure has a 16 x 20 footprint with a half loft for the bedroom. If the lot had been subdivided we could have made the cottage bigger, and included more storage and maybe a little wood stove. But I didn’t want to intrude on the slightly wild site with a bigger structure.


Kelly ADU Bedroom

The cottage has hydronic heating in the exposed aggregate floor. There is no blowing air, and this kind of heat feels cozy at a thermostat setting about 2 degrees lower than we’d otherwise use. It does take several hours to heat the cottage if the heat has been turned off all together. In the end it is cheaper to heat than it would have been otherwise. The hot water heater for potable water and ambient heat is under the building; Tony had to find one individual licensed for both types of installation to meet code. We looked at the idea of an on-demand hot water heater, the standard in many countries, but at the time there were too few people that knew how to service them and both Tony and I had heard some horror stories.


Kelly ADU Shower

The shower is has no door, but a curtain attached to the ceiling in order to accommodate a wheelchair if necessary. Since the floor is exposed aggregate the water hasn’t proved to be a problem.

Steve Carruthers, also a neighbor and friend, laid the hand hewn cobblestone patio. The patio is dry laid, with crushed granite between the stones to allow drainage, from roughly five tons of recycled Pearl District streets. (Before Portland streets, the stones, Belgian black basalt, were ballast in the holds of ships from Europe, waiting in the Columbia River to load timber from the Pacific Northwest.) Steve added massive basalt steps to and from the patio and alongside the cottage, so that the view from the main house kitchen window across the stones to the cottage is the best in the whole house.


Kelly ADU Porch

I wanted the cottage to have a timeless feel, with a nod to European mountain cabins. It has 3 foot eaves partly for the rain protection, but also for the sheltering effect that visually weighs down the building on the site. The shingle siding has the rustic look we wanted, and blended in well with Tony’s home just over the fence. My son is also an engineer, but he lives in the California Bay Area, and the county required an Oregon licensed engineer. Justin’s boss at the time is licensed in Oregon as well. So the foundation is up to California earthquake standards. The contractor was amazed at the amount of rebar designated, and added more concrete to make up for that. If there is a big earthquake and we’re still alive, we’ll have an optional place to live if the main house falls down!

The project was funded with a home equity line of credit, and will have paid for itself after a total of about 15 years. The vacation rental business will allow me to retire earlier than I would have otherwise.

If I had it to do again, I wouldn’t worry so much. Yes, it required a lot of persistence, but I couldn’t be happier with the building, and the vacation rental business is rewarding in many ways. We can schedule friends and family into the online calendar of availability whenever we want. Regarding space: there is no built-in closet in the loft, but a heavy metal curtain rod is used for hanging clothes. Though the cottage is too small for a couple of people who looked at it, everyone who has stayed has expressed satisfaction. In fact many people describe better sleep than usual!

We couldn’t be happier with the way the cottage has turned out, and wish to specially thank all of the following people, each one an artist:

  • Justin S. Kelly, AIA, Architect
  • Tony Kikes, Five K Construction
  • Steve Carruthers, Steven T. Carruthers Landscaping

About linamenard

Hi. My name is Lina Menard and I'm a small house dweller, designer, blogger, and builder. I'm currently collecting ADU Case Studies for Through my company Niche Consulting LLC, I help people design and build the home (and life) of their dreams! I also tell my stories about simple living in small spaces - like a travel trailer, a yurt, a backyard cottage, and tiny houses on wheels - at Niche News.
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