In September, the Seattle City Council made significant amendments to Mayor Bruce Harrell’s proposed update to the City’s Comprehensive Plan, which included a series of height and density bonuses for a new development type known as stacked flats.
These bonuses could pave the way for the construction of 12-unit multiplex apartments in areas that were previously limited to single-family homes, thereby transforming the city’s former single-family zones.
Officially rebranded as “Neighborhood Residential” (NR) zones in 2023, these areas account for approximately three-quarters of Seattle’s residential land.
While the council opted against making major changes to the mayor’s proposed growth map, the revised NR zoning regulations could hold significant implications, especially if builders successfully implement and replicate the stacked multiplex model across these formerly exclusive single-family lots.
As proposed by Mayor Harrell, the rules would permit three-story stacked flats covering less than half the lot area, or four stories on 60% of the lot area if affordable homes were integrated into the project.
Housing advocates expressed concerns that the constrained capacity and various existing barriers would deter developers from pursuing stacked flats, likely pushing them towards lower-density townhomes.
Matt Hutchins, principal at CAST Architecture and a member of the Seattle Planning Commission, has long been a proponent of stacked flats.
He challenged the stringent restrictions associated with Neighborhood Residential zones, coining the concept of the “Seattle Sixplex” during the protracted growth plan discussions.
Hutchins stated, “We’ve only done half of the Comprehensive Plan, in reality, only really addressing neighborhood residential.
People were much more keyed into Neighborhood Centers, because those are going to be even larger jumps.
But neighborhood residential is going to be fundamentally, fundamentally changed, and for the better.”
The final vote on the plan is still pending, with no specific date set, and could potentially occur as late as Christmas.
Currently, the Council has shifted its focus toward budget deliberations.
Despite the anticipated dominance of townhome developments in Seattle’s formerly single-family zones, with four-unit townhomes now permissible on nearly every lot throughout the city due to a state mandate, Hutchins remains optimistic.
He believes that if developers can effectively navigate the new incentives, the alternative pathway may yield promising results, envisioning a scenario he dubbed the “Tangletown 12.”
Hutchins speculated, “We’re talking about like maybe 5% of the townhouse projects become stacked flat projects.
There are still significant headwinds that are going to drive people into the safe harbor of four townhouses.
However, there are now avenues for more ambitious developers who want to take advantage of these [stacked flat] incentives.”
A standard 5,000 square foot single-family lot could allow for a four-story, 12,000 square foot structure, providing an opportunity for six 2,000 square foot units, given sufficient tree preservation.
However, most builders are likely to favor townhomes, which offer a more established market and immediate financial returns.
Stacked flats, in contrast, involve the complexities and risks of renting, making them less appealing to many developers.
In a bid to encourage more ambitious development, the Seattle City Council passed a variety of amendments aimed at eliminating city-imposed density limits and establishing incentive bonuses for stacked flats.
Councilmember Bob Kettle’s amendments 90 and 70 increased the permissible ‘floor area ratio’ (FAR) limits, the maximum unit count, and coverage for stacked housing units.
These changes allow buildings on all NR lots to expand in size by 33%, adjusting the FAR cap from 1.2 in the mayor’s initiative to 1.6.
With additional incentives, the FAR could escalate to 2.0, representing a 67% increase over the mayor’s original zoning proposal and a 43% uplift from his stacked incentive zoning.
Additionally, Councilmember Alexis Mercedes Rinck’s Amendment 85 adopted Washington’s new parking reform measure two years ahead of schedule, lifting parking mandates for new homes under 1,200 square feet, child care centers, affordable housing, and businesses smaller than 3,000 square feet or those included in mixed-use structures.
Further amendments introduced density bonuses for various housing types.
Amendment 78, led by Councilmember Joy Hollingsworth, offers bonuses for developments located near schools that allocate at least a quarter of their units to three-bedroom apartments or bigger.
Amendment 79 exempts Type A accessible units from all density limits barring height restrictions.
Additional amendments provide density incentives to projects that either conserve or plant trees.
Kettle’s Amendment 94 grants a one-story height bonus (up to four floors), eliminates parking requirements, and waives ‘amenity prerequisites’ for any development retaining a tree with a diameter of 24 inches or larger or planting sufficient trees to cover at least 10% of the lot’s area at maturity.
Amendment 91 further increases allowed density by nearly 50% if a development retains either a heritage tree, two trees exceeding 24 inches in diameter, or meets certain ‘green factor’ standards through adequate foliage planting or establishing a ‘green roof,’ among other requirements.
As a result, the stacked flat initiatives cumulatively provide a level of density that surpasses the city’s Lowrise 1 (LR1) zones and slightly outpaces Lowrise 2 (LR2) zones.
Existing zoning regulations confine LR zoning to designated urban centers, with only a few areas being grandfathered in.
The next stages of the One Seattle plan could potentially raise LR1 and LR2 zones sufficiently to alter this dynamic, though such modifications appear to exceed the current scope of planned updates, which do accommodate slight Midrise zoning increases.
Hutchins anticipates that lots favorably positioned to retain trees will particularly attract stacked flat developers.
He elaborated, “If you happen to have a corner lot with a large tree on a corner that’s in an undevelopable setback, and it’s located kind of like right on your periphery, then you’d be able to leverage those additional lot coverage and height without really having any impact on the footprint or design of the building.”
Ideal sites include corner lots, those with alleys, or places where parking isn’t obligatory in neighborhoods where market conditions also don’t demand parking for market viability.
Ron Davis, who advocated for statewide parking reform on behalf of Sightline Institute, underscored the importance of the state-mandated parking reforms accelerated by Rinck’s successful Amendment 85.
Davis, who narrowly lost a bid for Seattle City Council in 2019, noted that accommodating off-street parking on small lots can pose considerable challenges, especially when efforts are made to protect and enhance the tree canopy.
“The work we did through the parking bill last year removes parking as a binding constraint on almost every project,” Davis remarked.
“The bill makes it so you can’t require parking for 1,200 square feet or less, and that’s basically all multifamily and backyard cottages, right? And some townhomes.”
The Washington State Legislature has shown interest in reforming state building codes, which would allow for the construction of fourplexes under residential codes instead of the more stringent and costly commercial standards applied to most apartment buildings.
This change could significantly benefit fourplex builders, although Hutchins noted its limited relevance for larger multiplexes like 12-plexes.
He explained, “If you’re building a 12-unit building, it doesn’t matter; you’re already into SPC [commercial code], regardless.
There’s another sweet spot around when street and infrastructure improvements are required.”
Such upgrades, usually mandated by the Seattle Department of Transportation or Seattle Public Utilities, can inflate costs to a level that overwhelms the budget for smaller, middle housing projects.
Building housing comes with its complexities, particularly when stepping outside conventional development norms prevalent in the city.
Nevertheless, Seattle’s set of stacked flat incentives could motivate some forward-thinking builders to explore more innovative development avenues.
While housing advocates express excitement over these potential changes, there remains a desire for more robust measures.
Davis concluded, “I love the stacked flat bonus.
I’d like to see that kind of FAR everywhere, with substantial bonuses above that, around schools and parks for things like family housing.
There’s just a lot we’re not doing yet, but it’s a step, I guess, in the right direction.
It’s just a real, real small step, and a lot less than what the community was really clear they wanted.”
Nick Sattele contributed to this article.
image source from:theurbanist