How it's drawn — and how it gets built.

Onni 606 is designed by IBI Group, the Toronto-based architecture and engineering firm. Midway through the project's permitting, IBI changed hands: the Dutch firm Arcadis agreed to acquire it in July 2022 and completed the deal on September 27, 2022.

Post-acquisition, IBI's buildings and placemaking teams were folded together with CallisonRTKL to form Arcadis' Architecture & Urbanism practice — so the firm credited on the drawings is now branded Arcadis IBI Group.

The project's own 2019 environmental filing describes the exterior as anticipated to be mainly glass — vision and spandrel — framed by metal mullions and accents, with some painted concrete bands along the podium. In plain terms: three predominantly glass towers rising from a more solid, banded base.

The towers stand about 600 feet above average finish grade atop a roughly 40-foot podium. Because that description is a developer-signed SEPA narrative from early design, the palette is indicative rather than final, and the built cladding may be refined through permitting.

Bellevue's land-use code (LUC 20.25A.060.A) normally requires a building to meet a “build-to line” at the back of the sidewalk, holding a continuous street wall. For 606 the city granted a departure along the 106th Ave NE frontage, letting the podiums of Tower 1 and Tower 3 take a curvilinear form pulled back from the sidewalk. Per the staff report, that pull-back accommodates a north pedestrian plaza, a mid-block driveway with an on-site vehicular turnaround (so pick-up and drop-off happen off-street rather than on 106th), and the roughly 15,000-square-foot Major Public Open Space at the south end — with the curved base reinforcing the city's vision of 106th Ave NE as a pedestrian-oriented “Entertainment Avenue.”

The same approval records the towers' geometry. Against a required 60-foot separation between towers above 80 feet, the design provides 65.7 feet between Towers 1 and 3, 92.5 feet between Towers 1 and 2, and 114.7 feet between Towers 2 and 3; the towers also exceed the 20-foot setback from the north and east interior property lines (Tower 3, for instance, at about 40 and 44 feet). Maximum lot coverage by above-grade structure is 64.6% (113,142 square feet), with the below-grade parking garage excluded from the coverage calculation.

The development is registered with the U.S. Green Building Council and is targeting a LEED Gold rating, split across two rating systems for its different uses — the office component under LEED v4 BD+C: Core & Shell and the residential portion under LEED for Homes (Multifamily).

Per the project's environmental file, all building systems are to meet the current Bellevue Energy Code, with electricity and natural gas as the primary energy sources for heating, cooling, hot water, cooking and lighting. Notably, a full reading of that filing's energy section turns up no reference to district energy, on-site solar or other renewables, cogeneration or thermal recovery — a useful negative finding given recurring speculation about district energy on the block, though it reflects the absence of any commitment in the 2019 checklist rather than proof none could appear in later design.

That said, the on-site “energy plant” in the permit record (relocated to Tower 1 in the 2024–25 refinement) appears to follow Onni's in-house “District Energy” model. As described on Onni's Seattle “Level” project, that model builds a central plant beneath a development to produce heating, cooling and domestic hot water, then distributes and recirculates it to each tower through a closed loop — capturing waste heat rejected from office cooling to pre-heat domestic hot water, so individual buildings need no boilers of their own. The office-plus-residential mix at 606 is exactly the pairing that mechanism is built to exploit — though Onni's published description is of its Seattle precedent, not of 606 specifically.

The Vancouver landscape architect LOCI designed roughly 48,000 square feet of outdoor plazas across several levels, anchored by a public plaza of about 17,000 square feet at the southwest corner featuring a splash park and public art. LOCI describes the open space as “destined to become the City's social heart.”

The three towers rise from a shared three-story podium — the element reporting describes as what “knits the towers together,” carrying the building lobbies, ground-floor retail and the childcare center at and near grade. The plazas are not all at street level: per the Seattle DJC, restaurants, a juice bar, the childcare center and other active uses face plazas that begin atop the podium around the fourth level and extend to the fifth floor, where the pools, bars and dog-walking area sit — so the amenity decks read as a continuous, multi-level open-space program stacked on the podium rather than isolated rooftop features.

Restaurants, a juice bar, bars, the childcare center, the two pools and a dog-walking area face the plaza network. LOCI coordinated its work with Balmori Associates, the lead designer of Bellevue's citywide Grand Connection greenway, so the master plan's design intent carries down to the block.

Along the Grand Connection itself, the project would redevelop and enlarge the existing Compass Plaza on the greenway's south side — extending it northeastward with new pathways, landscaping and hardscape, site furnishings and retail spill-out space. A retained red oak sits right on the Grand Connection / Compass Plaza boundary at the second level.

The approved design also keeps a piece of the block's public-art heritage: “Bellgate,” a 1985 abstract steel sculpture by artist Lee Kelly that stood at 106th Ave NE & NE 6th Street outside the former John Danz Theatre — one of the oldest works in Bellevue's public-art collection. Because the city holds no long-term easement on the land, the Bellevue Arts Commission has worked with the developer to relocate the piece so it stays publicly accessible, with interim storage during construction.

Design-review-era documentation itemized the commercial space as roughly 34,000 square feet of retail, a 22,000-square-foot food court and a 7,500-square-foot restaurant. The office-tower food court is intended to serve the general public via a new east–west midblock pedestrian connector along the north edge of the site. Later reporting cites about 38,000 square feet of retail/commercial overall, suggesting the program was consolidated during refinement. The divergence has a simple cause: the Seattle DJC cautioned that the ~38,000-sf figure is “squishy,” because what Bellevue classifies as “active use” can also include lobby areas — so a retail count can overstate true leasable storefront. Consistent with that, the current Bellevue Downtown Association profile lists 64,525 square feet of “active use” space across the podium frontages, a broader category than storefront retail alone.

At street level the superblock is reached by two driveways on 106th Ave NE plus one on NE 8th Street; the southern 106th Ave access is signalized. A third entry off 106th feeds a covered porte cochère serving the hotel and office lobbies.

Loading and waste are handled along a partially-covered, open-air service lane running down the east edge of the site — shared with the neighboring Symetra and Key Center buildings and reached from 106th Ave NE or by an extension from NE 8th Street, keeping service traffic off the public plazas.

That central access on 106th Ave NE will be controlled by a full new traffic signal, its west leg forming an offset four-way intersection with PACCAR's existing driveway across the street. Left turns are allowed into and out of both the project access and the PACCAR driveway; because of the offset geometry, the city will prohibit right-turn-on-red out of the PACCAR leg and may add further turn restrictions once final signal phasing is set. The two other accesses — a north driveway on 106th and one onto NE 8th Street, both shared with the development to the north — stay right-in/right-out only.

The city treats Onni 606 as a single phased, three-tower project rather than discrete phases: the towers rise in an overlapping sequence off a shared podium, topping out years apart. At design-review approval the schedule had staggered tower completions of roughly October 2027, February 2029 and April 2030.

Onni builds its projects itself — through its in-house Onni Contracting arm rather than a third-party general contractor; no outside GC has been announced for 606.

The hard part is the hole. The project's environmental file puts total excavation at about 356,853 cubic yards for the below-grade garage (originally designed as six levels, later refined to five). Groundwater sits 65–87 feet below grade, and the state warned that the dig will most likely reach the regional Advance outwash aquifer — so dewatering relies on sumps and pumps, complicated by PCE-contaminated groundwater that must be managed, with vapor-intrusion mitigation built into the towers. The geotechnical work, by Geopacific (2017), found pre-glacial outwash and glacial till with low liquefaction hazard.

Below that deep regional table, the geotechnical report also found perched water within the glacial till and pre-glacial outwash, typically at 30–40 feet, plus discontinuous seepage zones throughout the glaciated soils — and it is this shallow perched seepage, not the deep aquifer, that the excavation hits first and that the temporary sump-and-pump dewatering is sized to remove. The report also cautions that although none were struck in the borings, occasional boulders are frequently encountered in glacially consolidated soils and may be present — a known complication for shoring and mass excavation in Vashon glacial ground.

Downtown Bellevue sits inside the broader Seattle Fault zone — a roughly 43-mile (69 km) band of mostly blind, east–west reverse (thrust) faults the USGS has mapped through Bellevue, Newcastle, Sammamish and Fall City. It is the region's marquee shallow-earthquake hazard: a Lake Washington sediment record points to about seven magnitude-7-or-greater events in the last 3,500 years, and the most recent major rupture, around 923–924 CE, is estimated at magnitude 7 or larger. The surface-breaking strands run several miles south of the 606 block rather than under it.

That regional setting is why the project's own geotechnical work matters at the parcel scale. The Geopacific Geotechnical Investigation Report (November 2017, filed with the 2019 SEPA checklist) drilled borings across the site and concluded there are “no known mapped faults beneath the site; therefore, the potential for surface rupture at the site is considered low,” and that the potential for liquefaction is “considered to be low.” The named hazard here is regional shaking, not a fault trace through the foundations.

What works in a 600-foot tower's favor is the ground. Borings found dense-to-very-dense Vashon glacial deposits about 20–45 feet thick over very dense pre-glacial outwash — clean sand to sandy cobble and gravel, 20–65 feet thick — over hard pre-glacial alluvium running deeper than every boring. Stiff, glacially over-consolidated ground like this is among the better material to found a high-rise on, and is the physical reason both the liquefaction and surface-rupture ratings come back low — though it doesn't change the regional ground motion the structure must still resist. The SEPA narrative doesn't state the structural seismic parameters (site class or design category), which are set in the building-permit structural set rather than the environmental checklist.

The reason a 600-foot tower in Bellevue faces tougher seismic scrutiny than the checklist lets on is a 2019 code change: that year Bellevue adopted additional seismic requirements for buildings taller than 240 feet, which generally must use performance-based seismic design rather than prescriptive code alone — and all three towers sit far above that threshold. The change was driven by University of Washington earthquake research, the M9 Project, which found that the sedimentary basin beneath the Seattle–Bellevue area can amplify ground motion by a factor of two to five, much more than earlier estimates, an effect that falls disproportionately on tall buildings.

Onni 606's 2019 environmental filing treats fire and emergency response as routine — it anticipates no special emergency services beyond Bellevue's normal fire and medical response, framing the impact as incremental. What the filing doesn't spell out, because the building code does, is how much fire-protection machinery a 600-foot tower must carry: the approved site plan already labels a Fire Command Center off the office lobby, the code-required nerve center from which responders run a high-rise incident.

Because all three towers rise to roughly 600 feet, they clear the building code's highest tier of high-rise provisions. Bellevue reviews high-rises against its own High-Rise Checklist, built on the 2021 IBC/IFC: any building taller than 420 feet (other than residential R-2) must add an interior exit stairway beyond the normal minimum, and any building over 450 feet must feed its fire pumps from at least two water mains in different streets (IBC 403.3.2) — thresholds an apartment tower or mid-rise never reaches.

Layered on top are the systems every Bellevue high-rise needs: a fully sprinklered building with a secondary water source; combination standpipe/sprinkler risers; at least two fire-service access elevators where an occupied floor sits more than 120 feet above fire-department access; pressurized or smokeproof exit stairs above 75 feet; emergency standby power; and a Fire Command Center behind a two-hour barrier. Two items stand out locally: 800 MHz emergency-responder radio coverage that must be field-tested in the finished building (Bellevue City Code 23.11.510), and a Firefighter Air System — a pressurized air standpipe run up the main stairways so crews can refill air bottles without descending. These are code minimums for a tower this tall, not project-specific commitments; final systems are set in Bellevue's building- and fire-permit review.

Onni 606's three predominantly glass towers sit squarely within a recognized bird-collision risk profile: a tall, reflective glass cluster on a major migratory corridor. The project's 2019 SEPA checklist acknowledges it plainly, answering “yes” to whether the site is on a migration route — “The entire Puget Sound area is within the Pacific Flyway” — and listing songbirds, seagulls and pigeons observed on or near the block.

Despite that, the filing proposes no bird-safe glazing — and, more broadly, no aesthetic or glare mitigation beyond complying with the city's design guidelines through Administrative Design Review, none of it collision-specific. Detail on the façade's reflective characteristics and glazing was deferred to the building-permit stage, so whether any collision-deterrent treatment reaches the built curtain wall is unsettled in the public record. Because neither Washington nor Bellevue mandates bird-safe glazing, any such treatment here would be voluntary.

The conditions of approval do impose specific lighting and glazing rules — but their stated purposes are glare and visibility, not bird safety. Under design guideline UD-39 the lighting takes a “Dark Skies Compliant” approach that minimizes glare from the source, and conditions require all exterior lighting to carry cut-off shields preventing spill-over to adjacent sites, to be dimmable, with rooftop lighting tuned to “complement the Bellevue skyline at night.” A separate condition requires street-level storefront glazing on 106th Ave NE and the Grand Connection to be clear, non-tinted and non-reflective so the sidewalk can see into the active ground-floor uses. The recurring rationale is light pollution onto neighboring residential towers, skyline aesthetics and pedestrian transparency — none of it framed around collision deterrence. (Large expanses of clear glass at the base are themselves a recognized collision risk, so the transparency requirement is independent of, not a substitute for, any bird-safe treatment.)

On habitat, the commitments are modest and ground-level. The checklist's only proposed measure to preserve or enhance wildlife is the on-site landscaping, which it says “could provide limited habitat for urban wildlife” — the roughly 160 trees set within the Grand Connection greenway, along the 106th Ave NE frontage and in the plazas, using native and drought-tolerant species. It is framed as habitat enhancement but is not paired with any building-scale measure to reduce the collision hazard the glass towers introduce above it.