ADUs 101 and the Future of Seattle Housing | A Conversation with Matt Hutchins

Chris Walter, @ChrisWPhoto, talked with Matt Hutchins about the significance of Accessory Dwelling Units (ADUs).

At CAST architecture, we have been focused on ADUs for more than a decade. They're fun to design, perfectly fit a niche for new housing in established neighborhoods, and provide many benefits for owners and residents.

https://www.youtube.com/watch?v=PJaLht9v5Yw

CAST’s Cedar Cottage is a City of Seattle Pre-approved DADU. Our vision is to adapt the high-design cottage, simplify it, and make it accessible.

See more at www.castcottages.com

“Part of the reason we love backyard cottages is just the opportunity. If you have a home with a possibility for a second house – it could be whatever you want it to be – a studio, a place for grandma, a rental, and having that flexibility is huge. We have people who have it as an Airbnb, or a long-term rental, as a place for their kids and then their retirement home. This flexibility is fantastic. It opens up so many opportunities in this great city.”         -- Matt Hutchins, AIA, Certified Passive House Designer

Backyard cottages = Flexibility and Opportunity

RiversMeet Winthrop Proposed Mixed-use building

ON THE BOARDS - METHOW VALLEY’S RIVERSMeet WINTHROP proposed MIXED-USE BUILDING

RiversMeet, a proposed mixed-use project in the town of Winthrop in Washington’s Methow Valley, is positioned to become the upvalley entrance to “old downtown.” The site is a challenging set of narrow parcels overlooking the confluence of the Methow and Chewuch Rivers.

CAST’s client, Peter Goldman, as part of his development proposal, intends to request the town make zoning changes to allow for long-term rentals in the commercial district. RiversMeet is envisioned as a template for how buildings can work within Winthrop's westernization code while striving for high levels of sustainability and providing more inclusive housing options.

The program will provide two 2-bedroom residential units overlooking the river, with approximately 1,870 SF of pedestrian-level retail space. The second floor incorporates 1,870 SF of office space. The second floor incorporates 1,870 SF of office space, continuing the client’s tradition of renting below market rate to community non-profit businesses.

Team
Client: Peter Goldman and Martha Kongsgaard
Architect: CAST architecture
Builder: North Star Construction Company  www.Northstarbuilds.Com
Civil & Structural: DCG   www.dcgengr.com   
Electrical: TFWB   tf-wb.com
Environmental:  Grette  www.gretteassociates.com  
Geotech: Geoengineers  www.geoengineers.com/ 
Mechanical: Ecotope   www.ecotope.com 
Survey: Tackman   www.tackmansurveying.com

Give Middle Housing a shot!

Matt Hutchins’ comprehensive discussion, at Medium, of the Washington state Model Code for Middle Housing and how we can have it produce more housing in line with HB1110.

In HB 1110, the State Legislature read the will of the people and demanded that we tackle the housing crisis more proactively by allowing Middle Housing in most cities and towns. Washington State Department of Commerce has created a basic zoning template that supersedes local code if town planners balk at updating their own code to comply. The draft version of that Middle Housing Model Code is out for comment (comment here by December 6th!). I have analyzed the real world implications of how it would regulate new housing and how we can tweak it to better support the creation of townhouses, flats, and infill development.

Here are my recommendations:

1. Allow Middle Housing to be larger than single family houses: more lot coverage, smaller setbacks, and make them taller.

Diagram of current allowable single-family building sizes in 6 cities to illustrate that the Model Code’s Floor Area Ratio system is actually more restrictive.

It seems like an obvious point that the bulk of a building or buildings for up to 2, 4 or 6 households might be larger than one with just a single household, but a close look at some of the cities governed by this new legislation reveals that the draft code is MORE restrictive than current codes. It would effectively be a downzone in structure size in order to house more people. That isn’t a good trade, and for all the proof that Middle Housing has wide ranging benefits, we should have a code that supports it.

Middle housing is not just a bridge between the densities of single-family neighborhoods and denser areas, it is also a incremental increase in size between those building types.

 

2. Measure lot coverage, not FAR

There is a policy conversation about two methods for measuring building size: 1) lot coverage X height vs. 2) lot size X Floor Area Ratio. The draft code uses FAR for Tier 1 and 2 cities (the larger cities and the municipalities around them), and Lot Coverage for Tier 3 cities (smaller cities).

In the six Tier 1/Tier 2 cities I picked to analyze, five use lot coverage not FAR. The model code should follow suite. It is easy to implement, understand and compare apples to apples to existing codes.

Diagram of small cities buildable footprint illustrates how extra flexibility in lot coverage will translate to new housing for those communities.

Meanwhile Tier 3 cities, the code uses lot coverage to provide flexibility for how to develop successful infill housing, because lot coverage isn’t the critical threshold, the market is. I think this part of the Model Code will be actually be good for many smaller jurisdictions that are struggling with housing cost and access.

 

3. Set thresholds by looking at what can be feasibly built, not what might be politically expedient.

Illustration of all the new building types and whether they would be viable under the draft Model Code for typical lot sizes.

There is often a disconnect between how planners see development standards and how developers implement them. But ground truthing the code, when it is a draft, to understand the inevitable determinative impacts on the housing types that will get built, is the key to making the good development we want to see also the easiest to build.

Using a typical 5000 sf parcel zoned under the new code for 4 units, applying the FAR, we can build 4000sf. It becomes immediately apparent that many of the housing types we’re hoping for will never materialize and other types are going to yield less that then maximum number of units. Of the six types, I would expect the only feasible project is three townhomes. It is unlikely we’d generate very many 1000sf townhouses, 1200 sf triplex units or courtyard apartment buildings under the added cost of the IBC compliance.

The FAR needs to be up between 1 and 1.2 before we’d see the fourth townhome, or an apartment building.

 

4. Lean into making the most efficient and affordable housing form (small apartment buildings) the default infill Middle Housing type.

Our Spokane Six on the left works today, but wouldn’t be viable under the draft Model Code. This illustration shows that it would need to be 21% smaller.

Small apartment buildings have significant headwinds when it comes to financing, construction and operation. They also are the greenest, most efficient, context friendly and often least expensive forms of housing. They are also the best for preserving usable open space and landscape for large trees. They are the lowest common denominator building block for tackling the housing crisis. If the code works for those, then the other forms, like ownership townhouses, will work too.

When we tested our recent Spokane Grand sixplex, using the new Model Code, we discovered that we’d have to reduce the size by 21%, loose one of the porches, and downgrade the units from family friendly two bedrooms to one bedrooms. The pro forma for the development fell apart. If it can’t work in Spokane, with low land cost, reasonable construction cost, steadily climbing rents, there is very little chance these buildings would be viable in Puget Sound or other Tier 1 and 2 cities.

Without zoning incentives to build apartments, the market will continue to underproduce less expensive rental housing, even if we see some new ownership townhomes.

 

5. Reduce parking minimums.

Parking is always the cart that drives the horse. We have a housing problem not a parking problem.

So much has already be said and written about the high price of parking mandates, so I’m going to appeal to pure geometry.

On residential lots, designing for parking is step 1, before you even start to conceive of a building. For a sixplex on an alley, where parking is required, one space per unit arranged along the alley would require a lot width 56' feet minimum, which is wider than most urban lots. In order to provide the parking, much of the back yard is overtaken with pavement, more than 1/3rd of the site, lessening the quality of life for residents, creating stormwater issues and additional costs.

Without an alley, it is always worse; more than half of our typical lot is parking or driveway.

 

6. Regulating aesthetics on small neighborhood buildings is unnecessary micromanagement.

Strike this section. Or don’t. It is really so milquetoast that compliance isn’t an issue, but there will be lots of overlap/conflict with local codes that do regulate these simple aesthetics. Most townhouses are less that 20 feet wide — does a building’s design need to change every time there is a door? It is so fussy. In the interest of less bureaucracy, we should stamp out regulatory creep preemptively.


A Model Code that works.

The State’s Model Code is an opportunity to create a baseline for Middle Housing but it has to work. And this draft code would be so much more effective if it wasn’t second guessing its own mandate.

A final Model Code based on incremental increases of size over current single family structures, lot coverage not FAR, without parking minimums and design prescriptions, which allows builders the flexibility the make the homes people need, is the right direction forward for a statewide standard.

Sedge Cottage

New sedge backyard cottage: 3 bedroom DADU

At 997 net square feet, the Sedge Cottage is a highly livable footprint that provides well-daylit space for living, necessary storage, flexibility on many sites, and two covered outdoor porch spaces. Within its compact form, the design features three bedrooms and two baths, a galley kitchen with a peninsula and plenty of storage. It features a bedroom and 3/4 bath on the main level that works well for an aging parent, as a guest room or work-from-home office. Standard, wood-frame construction, vented shed roof, slab-on-grade foundation, the careful placement of windows, and a simple exterior allow for low-cost construction without sacrificing durability, function, or style.

The design is under the height limit and can fit on the smallest lots, around trees, or on sloped lots, with space for adjacent parking if desired. The outdoor covered area is perfect for a BBQ and the cottage can be oriented toward the principal residence for multi-generational living around a courtyard. The front porch clearly marks the entry of the accessory dwelling.

The design targets 4-Star Built Green, with details for reduced air infiltration, energy-efficient heating, cooling, and water heating systems, passive solar heat gain in window/shading in summer, low-VOC finishes, no fossil fuel appliances, and all LED lighting.

See more at CASTcottages.com

Sitka Cottage

New Sitka Cottage: 3-bedroom DADU

At 1,000 net square feet, the Sitka Cottage features three bedrooms and two baths upstairs, an open living room and kitchen, storage, and an additional powder room tucked away on the first floor.  It fits flexibly on many sites with a walk-out terrace off the living room/kitchen. The three bedrooms upstairs are reasonably sized and work well for a family. Standard, wood-frame construction, vented shed roof, slab-on-grade foundation, careful placement of windows, and a simple exterior allow for low-cost construction without sacrificing durability, function, or style.

The design is under the height limit and can fit on standard to small lots, around trees, or on sloped lots, with space for adjacent parking if desired. The cottage can be oriented toward the principal residence for multi-generational living around a courtyard. The front door is on the corner and can be placed on either the short or long side of the design, depending on site orientation.

The design targets 4-Star Built Green, with details for reduced air infiltration, energy-efficient heating, cooling and water heating systems, passive solar heat gain in window/shading in summer, low-VOC finishes, no fossil fuel appliances, and all LED lighting.

See more at CASTcottages.com

CLT Berm House in Mazama, Washington

Cross-Laminated Timber Berm House in Washington's Methow Valley

The Berm House is a private residence that doubles as the common house and gathering space for a 19 house mixed-income community in Washington’s Methow Valley. The house is set into the landscape, with a panoramic view of the farmland down valley, but hidden from the road by a berm that ramps up onto and across the roof. 

The south-facing building orientation optimizes winter solar exposure coupled with large overhangs to protect from snowfall and the intense summer sun. The home is post and beam structure with a cross-laminated timber (CLT) roof prefabricated in northeastern Washington. The design incorporates Passive House principles including managing seasonal heat gain from solar exposure, advanced air sealing, and mechanical ventilation. Thermal bridges are minimized by wrapping the house in continuous external insulation, including structural EPS under the foundation, isolating the home from outdoor temperature swings. The earthen roof adds thermal mass, wildfire protection, and a promontory to take in the down valley vista.

The great room portion of the house was designed for friends and neighbors to gather, share meals, and be a social center for the community. Off the great room, a five-foot wide hall leads to three guest suites and the primary suite. The uncomplicated and efficient floor plan shows a clear division between the private and public spaces. The mechanical room, pantry, storage, guest bath, and laundry spaces are arranged along the berm side of the house’s section.

The material palette is predominately warm woods. The CLT ceiling and glulam posts and beams were manufactured nearby, and a coffee table and kitchen bar were crafted locally from a fir tree felled on the property. The exterior employs the Japanese shou sugi ban preservation technique. The boulders throughout the site and as part of the berm were pulled from the site and placed by the owner. 

Team
Owner: Lee Whittaker
Methow Housing Trust
Architect: CAST architecture
Contractor: Methow Valley Builders 
CLT: Vaagen Timbers
Concrete subcontractor: JR’s Five Star Concrete
Geotechnical Engineering: GeoEngineers

See more here.


New Missing-Middle Housing - Hawthorne Hills Three

Hawthorne Hills Three:
Single-family residence, ADU & DADU

This project renovates an existing home and adds an attached accessory dwelling unit (AADU), and a detached accessory dwelling unit (DADU) to thoughtfully develop this single-family home into three rental units in the desirable Hawthorne Hills neighborhood of Seattle. It brings forward a model of urban density, providing much needed ‘missing middle’ housing. The exterior of the two buildings is unified in onyx-grey fiber cement siding with cedar accent areas. The home is 4-Star BuiltGreen certified.

The main home, with three bedrooms at 1,150SF, is renovated for modern living. The kitchen features three skylights that maximize natural light and brighten the core of the home. The original warm oak floors were refinished and unify the spaces.

The 410SF AADU takes advantage of the original house’s slightly set back position on the lot to build a new unit to the front and side setback.  The entry opens to the bright kitchen and living space. Within the compact footprint, a hallway through the utility room leads to the bathroom and a separate bedroom.

The backyard cottage is a 1000SF two-story home. Situated on the lot for privacy, a private walkway leads to the front door. The DADU boasts three bedrooms with vaulted ceilings on the top floor. Downstairs, a generous great room and kitchen with expansive glass doors open to the patio and private backyard. The efficient, open plan and bonus storage add to the versatility of the home.

See more here.

TEAM
Builder: Cadre  General Contractors
Civil: Davido Consulting Group/Watershed
Survey: Terrane
Structural Engineer: Owen Gould
GeoTechnical: Cobalt GeoSciences
Andersen Windows & Doors

Photography: Peter Bohler

The Port Gamble S'Klallam Tribe's new Hatchery & Beach Shelter

New tribal Hatchery & Beach Shelter

At the beach at Point Julia on land occupied by the tribe since time immemorial, the Port Gamble S’Klallam Tribe’s Hatchery and Beach Shelter combines pragmatic uses with symbolic content. Salmon fishing is central to the Port Gamble S’Klallam Tribe’s traditional identity and its contemporary outlook. The new 1,800 SF two-story building accommodates both office and utility space for the Port Gamble S’Klallam Tribe’s salmon hatchery program, along with a separate open-air structure used by the Tribe’s commercial fishing operations. This project recognizes the cultural importance of both the place—a focal point of their history—and the program, while providing solutions to allow these activities to flourish in the 21st century.

The lower level of the Hatchery houses a garage, maintenance shop, and egg-incubation room with equipment that is both durable and moveable. The upper floor contains offices, water-quality testing, and filtration equipment. The conference room on the southwest corner can be entered separately, accessible to the wider community.

The new hatchery forms a gateway to the beach from the landward side, and the beach shelter is the Tribe’s front door on the sea. It will provide a work area for fishermen who pull their boats onto the beach and will also provide recreation space for the community. On the beach between the two structures, the native landscape is being restored, along with traditional edible and medicinal plants, and salt-tolerant erosion control plantings.

hatchery, exterior, PNW design

See more here.

TEAM
Owner: Port Gamble S’Klallam Tribe
Architecture: CAST architecture
Photography: Lara Swimmer
Contractor:  Pacific Civil & Infrastructure
Geo-tech: Robinson Noble
Structural: Swenson Say Faget
MEP: Glumac
Civil: Cannon
Landscape Architect: Pacific Landscape Architecture
Windows: Jeld-Wen  
Archeologist: Willamette Cultural Resources
Survey: AES Consultants
Intake System Engineer: Kleinschmidt Group
Specifications: Applied Building Information
Art/light installation: S’Klallam artist Jimmy Price
Conference table / Entry bench: Craig Kohring

The Urbanist - STATE MODEL CODE FOR MIDDLE HOUSING IS MISSING ENOUGH HOUSING

STATE MODEL CODE FOR MIDDLE HOUSING IS MISSING ENOUGH HOUSING

BY MATT HUTCHINS (GUEST CONTRIBUTOR)

See full article and graphics here: https://www.theurbanist.org/2023/07/10/state-model-code-for-middle-housing-is-missing-enough-housing/

Commerce recently had a consultant create a form-based code, but the draft fails to advance housing abundance.

Now that Washington State’s Middle Housing bill (HB1110) has been signed into law, the next question is what implementation will look like — what kind of housing and where. The Department of Commerce has published a request for consultants to draft a model code that 1) will help jurisdictions write their own compliant middle housing code or 2) will supersede local zoning if they fail to implement their own in advance of the deadline (six months after their comprehensive planning update).

While we don’t know what cities and towns are thinking, we do have a picture of how Commerce is approaching the middle housing code. Last fall, Commerce hired a consultant to “inform about and assist local governments with middle housing policies, regulations, and programs.” 

In May, a focus group of planners, developers, and architects previewed a draft ‘Toolkit’ that illustrates four strategies that local governments could overlay on their residential zoning to allow new denser housing types within existing detached single family neighborhoods. The foundation of this toolkit is a form-based code meant to create ‘objective’ standards for middle housing that can be applied widely.

The issue is that the toolkit, rather than solving for affordability, feasibility, and the lowest carbon footprint, is primarily focused on crafting development guidelines that will keep new infill development the size of average houses and thus minimize the outcry from vocal neighbors. While this might be an easier to swallow approach for Washington cities and towns, it doesn’t scale up to address the deeper issues that HB 1110 was passed to address: the massive shortfall of new places for people to live. 

While Commerce’s original intent was to come up with instructive materials broadly applicable to most local governments, the effort lags behind what more progressive jurisdictions are already doing. But when we dig into the details, the toolkit suggests real reductions in development capacity: smaller footprints, bigger setbacks, and lower roof heights than are currently allowed in many Puget Sound cities. At its very worst, it will give slow-growth municipalities the option to select a new zoning overlay that is more prescriptive and restrictive, thus spoiling any chance that any new middle housing will be built.

Let’s go through the proposed new toolkit and look at some of the underlying flaws. 

  • They state, “This toolkit does not provide standards for buildings taller than three stories.” For three of the four overlays in the Toolkit, buildings are conceived as two and a half stories with a height bonus for hip and gable roofs –  less that most of Washington cities’ least dense residential zones today. Rather than proposing an actual incremental increase, it ignores the status quo as a starting point. If you want a single pitch ‘shed’ roof, the 22-foot height limit is actually less than what we allow for a backyard cottage in Seattle today.

  • Parking is mandated throughout the toolkit, a reversal for many jurisdictions that are moving away from required off street parking. Indeed one of the strengths of HB 1110 is releasing parking restrictions for new housing.

  • Most overlay zones top out at four units per parcel, equivalent to Seattle’s second least dense zone, Residential Small Lot. Much of the ‘middle’ housing that is missing is between a house-sized triplex and the ‘5 over 1’ medium-sized apartment building. While this toolkit focuses on redundant standards for housing types we already allow, like townhouses and triplexes, it is silent on helping planners visualize appropriately-scaled urban buildings that might have between six to twenty units.

  • Townhomes today, for better or worse, are the least expensive middle housing alternative available in the market, and the toolkit hamstrings their development with provisions that limit the number per building and the building length. The most successful rowhouse style homes on corner lots wouldn’t comply.

  • The toolkit increases barriers for sites with multiple buildings on a single site, which would render many currently popular types of middle housing, such as detached townhouses, cottage clusters in Residential Small Lot zoning, and arguably even detached accessory dwelling units nearly impossible to build on compact urban lots.  

  • The toolkit does not provide flexibility for sites that might want to preserve existing housing and build more. It assumes parcels are cleared rather than provide provisions for new buildings in the backyard, lot splitting, or additions that add units.

  • While much of today’s urban design discourse is centered around neighborhoods where goods and services are accessible within a 15-minute walk or roll, the toolkit doesn’t have any provisions for mixed uses like daycares, commercial suites or corner stores.

  • Finally, as one gets into the details of each overlay, it is chock full of reductions: larger setbacks, less lot coverage, less height, larger minimum lot areas, prescriptive design standards – each taking a bite out of the viability of future housing. When we compared a fourplex we’re currently designing in Spokane against the toolkit, we’d need to reduce the footprint by 32%, lose the front and back porches, and downgrade the 2-bedroom units to 1-bedrooms.  

  • Unlocking the residential potential of urban land is critical if we’re going to provide the more than 1.1 million homes Washington State projects we’ll need over the next 20 years, and that means reintroducing multi-family housing types that exclusionary zoning has regulated out of existence.

    With this upcoming model code, we can take a good hard look at how new infill development is built, but we first have to move past the idea that middle housing is house-sized buildings carved into more apartments, or cottage clusters. Overall, the toolkit’s conceptual limitations and prescriptive ‘objective standards’ don’t reflect the real conditions of Washington neighborhoods.  

    A more serious effort would worry less about what neighbors might think and center our goals of housing abundance and climate action leading with middle housing types that work all the way up to four- and five-story mid-sized buildings in keeping with the best practices of urban planning around the world. Washington needs a flexible model code that supports the big picture goals of abundant housing.