Introducing CAST’s Infill Housing Toolkit: We put together recent, current, and future projects to showcase strategies and case studies for abundant housing infill development.
Site Typologies
Constrained Lots
Typical Infill Lots
Large, Assembled Lots
Design Features
Single Stair
Stacked Flats
Low-Energy Design
Low-Carbon Building
Diverse Unit Mix
Open Space
ECHO, a 10-unit apartment building in the Eastlake neighborhood of Seattle, is now a Design Certified PHIUS (Passive House Institute US) Core 2021 project.
This apartment building will replaces a single-family structure in this residential urban village, adding missing-middle housing. It utilizes the stacked flats concept which pushes the bounds of the single-family envelope but maintains an urbanism-friendly street frontage.
The two homes on the ground floor are both fully accessible. And, the top two units have high ceilings with lofted sleeping areas.
High-performance design elements include: thermal control, airtightness and moisture control, balanced ventilation, and high-performance glazing.
TEAM
Developer: West Crescent Advisors, LLC, Nancy Melton
Architect: CAST
Passive House Institute US: @passivehouseinstituteus
Builder: Carrig Construction @carrig_construction
Project Consultant: Woodworth Construction Management LLC, Lydia Anne, @woodworth_built
Civil Engineer: Davido Consulting Group, Inc. @dcgengr
Structural Engineer: Harriott Valentine Engineers @harriottvalentine
Mechanical Engineer: Ecotope @ecotope_inc
Envelope Consultant: B.E.E Consulting, LLC
Electrical Engineer: TFWB Engineers, Inc
Windows: Alpen Windows – Passive House Certified
Landscape Architect: @karenkiestlandscapearchitects
Arborist: Moss Studio
Geotechnical Engineer: PanGEO, Inc.
Surveyor: Terrane @terranesurveying
Third party verifier: Balderston Associates
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.
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
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.
Seattle Architect pursues passive house certification with missing-middle housing on Lake Union
Echo on Eastlake apartments is pursuing Passive House certification, with early design and feasibility studies complete on the new 10-unit apartment building in Seattle’s Lake Union neighborhood.
This building will replace an existing single-family structure in this residential urban village, adding missing-middle housing. It utilizes the stacked flats concept which pushes the bounds of the single-family envelope but maintains an urbanism-friendly street frontage. There is one central stair and no shared walls. And, the two homes on the ground floor are both fully accessible.
Six-to-twelve-plexes offer a superior urban experience, more housing units, more housing variety, and at least some fully accessible housing units. They also may preserve more tree canopy, increase open space, and optimize daylight compared to townhomes.
More to come in the months ahead.
TEAM
Developer: West Crescent Advisors, LLC
Owner’s Representative: Woodworth Construction Management LLC @woodworth_built
Architect: CAST architecture
Builder: Carrig Construction
Civil Engineer: Davido Consulting Group
Landscape Architect: Karen Keist Landscape Architects
Arborist: Moss Studio
Geotechnical Engineer: Pangeo, Inc.
Surveyor: Terrane
Structural Engineer: Harriott Valentine Engineers
Envelope Consultant: B.E.E Consulting
Seattle Architect CAST partners with The BLOCK Project
CAST has partnered with The BLOCK Project which builds fully equipped, healthy homes for people experiencing homelessness.
We are excited to have just permitted our second BLOCK Project home!
BLOCK Homes are permitted and placed in homeowners' backyards throughout Seattle. This model gives residents a place to call home and our communities an opportunity to make a real difference in supporting our unhoused neighbors and addressing the issue of homelessness together.
Their mission: To inspire deliberate relationship building and community engagement as a pathway to ending homelessness.
www.the-block-project.org
@facinghomelessness
Port Gamble S’Klallam Tribe’s Hatchery & Beach Shelter Construction Progress
Kingston, Washington
The new building will house office and utility space for the @portgamblesklallams salmon hatchery program and a separate open-air structure used by the Tribe’s commercial fishing operations.
Salmon hatchery operations require a constant flow of clean streamwater. The project includes a new earthen dam and water intake structure in the adjacent ravine that provides reliable flow at a constant pressure. Downstream, equipment housed within the building filters the water and regulates its oxygen content before supplying it to the indoor incubation tanks and outdoor fish runs.
Salmon fishing is central to the Port Gamble S’Klallam Tribe’s traditional identity and its contemporary outlook. This project seeks to recognize 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.
Learn more about the Port Gamble S’Klallam Tribe.
TEAM
Architect: CAST architecture
Contractor: www.paccivil.com
Geo-tech: Robinson Noble
Structural: SSF
MEP: Glumac
Civil: Cannon
Landscape Architect: Pacific Landscape Architecture
Archeologist: Willamette Cultural Resources
Survey: AES Consultants
Intake System Engineer: Kleinschmidt Group
Specifications: Applied Building Information
Windows: @jeldwenusa www.dahlglass.com
See more about the Hatchery project here.
Jansen Court missing-middle housing in the Capitol Hill neighborhood of Seattle.
Seattle architect designs missing-middle housing
Jansen Court Apartments is a Built Green 4-Star 10-unit studio apartment building on the back of a 30’ parcel in Capitol Hill, preserving a turn-of-the-century house in the front yard.
With a single stair, this 4-story apartment building was quite the puzzle -- the complexity of regulations are magnified on a small project. Each level is different, with a basement, typical story, vaulted story, and unit with roof access. They're small, 400-600 SF, but nicely livable spaces.
And, it’s in Capitol Hill with a pretty street and bustling neighborhood. Walk Score: 92!
CAST is closely associated with efforts to improve housing affordability through increasing the “missing middle” moderate density infill within existing neighborhoods.
Photo credit: @lensit.studio
A Seattle Detached Accessory Dwelling Unit
Sustainable living in a tiny home
CAST is featured in Porch’s round-up: Everything About Tiny Living: Tips From the Experts
We are rethinking space and home. CAST believes tiny homes, accessory dwelling units (ADUs), and backyard cottages are inherently sustainable building options, as well as sensible answers to the housing crisis. Tiny homes require fewer materials to build, create less waste, and use less energy to power, heat, and cool when compared to traditional single-family houses.
In addition, people who live in tiny houses will own fewer possessions and spend less overall. Downsizing will influence lifestyle in many ways—streamlining possessions, becoming more mobile, and building financial security—which leads to a lower carbon footprint. Typically, as one moves into a tiny home, other segments of life change positively as well including overall consumption of goods, services, and even food. And this, in turn, reduces the impact on the environment. Specifically, with carbon footprint in mind, the factor that will have the most impact is the size of the home.
Good design matters. Our backyard cottages are designed to be energy efficient, low cost, and built for privacy within their context. Daylighting is important in every home and especially in small spaces. Effective storage is essential. Layering and overlapping are key to designing successful small spaces while using different materials will create well-defined areas. Plan to maximize every square foot in common living areas and integrate outdoor space. Covering outdoor space makes it feel like an extension of the home, without having to heat or cool it.
Density and more efficient land use are critical to addressing our housing crisis, climate change, and persistent inequities in access to housing. Modest infill houses like tiny homes, ADUs, and backyard cottages are a key strategy to empower citizens to provide new housing, build generational wealth, and leverage taxpayers’ investment in infrastructure, transit, schools, and parks. Plus, these homes could create an affordable housing inventory.
Photo, above: Cindy Apple Photography
Photo, below: Benjamin Drummond Photography
A functional and sustainable tiny home in Washington’s Methow Valley
See more of this tiny home on our website.