Solutions for ‘Dark Spaces’ in Office-to-Residential Conversions

Architect Charles Bloszies shares his research on potential uses for these residual, unlit spaces.

Headshot of Charles Bloszies

The economic goal is finding uses for dark spaces that have value, according to Charles Bloszies. Photograph by Lori Fuller, courtesy of the Office of Charles F. Bloszies

As the new way of working and its consequences sink deeper into everyone’s reality, office-to-residential conversions are increasingly a hot topic. Yet these projects come with a varied array of obstacles.

Converting an office building to a completely different use such as residential, is not an easy process. Challenges vary from zoning issues, managing the lack of natural light, to having to set up completely new plumbing and HVAC systems. Could finding new uses for residual, dark spaces—deprived of natural light and ventilation—enable landlords and investors to convert more underperforming buildings?

Multi-Housing News talked to architect Charles Bloszies, who together with his team has come up with a series of ideas to make use of the unlit spaces that remain in the core of buildings after placing the residential units. In San Francisco, where his studio is based, these spaces can range between 12 and 19 percent of the available floor area, so finding viable fixes to maximize the potential of this space is vital to an adaptive reuse project’s success. 

What are the biggest challenges in office-to-residential conversions from an architectural perspective?

Bloszies: Size of the floorplate and typical office layouts restrict access to natural light and air, plus many office buildings are ‘landlocked’ with limited street or public frontages. Older office buildings addressed the light and air—mostly air—issues prior to the advent of air conditioning with narrow floorplan depths, light wells, L-, E- and U-shaped plans, with high ceilings. These are more suitable for conversion to residential uses than modern office buildings ushered in around 1950. 

Possible dark space uses in office-to-residential conversions

Possible dark space uses in office-to-residential conversions. Image courtesy of The Office of Charles F. Bloszies

Large floorplates result in core space unsuitable for residential use—we call these dark spaces. Office layouts typically gang restrooms, elevator and utility shafts in one location, in the center or on the side of the floorplate. Residential units each have at least one bathroom, so the entire plumbing system needs to be reconfigured and so do the heating, air conditioning and ventilation systems.

In seismic zones, a change in occupancy from office to residential triggers earthquake upgrades, equating to expensive heavy construction throughout the structure.

Have these dark spaces been a decisive factor in repurposing office buildings?

Bloszies: All buildings contain spaces that do not require natural light, including fire stairs and the items mentioned earlier, but office buildings typically have more than residential buildings need. Elevators are the best example—office building elevator demand is much higher, so some elevator shafts may be available in conversion projects for other, dark uses.

What uses would be suitable for making these spaces work in a new, residential setting?

Bloszies: The economic goal is finding uses for dark spaces that have value. Some cities, like New York for example, allow office use in residential buildings—an extra room or two in a unit not needing natural light and air. San Francisco planning codes do not allow office use in residential buildings, specifically banning most live-work plans. This restriction will most likely—and should—change, given the post-pandemic trend for working from home.

Other options are storage and shared amenity spaces. On lower levels and especially on the ground floor, certain retail uses, such as a grocery store, could survive—another societal issue for cities driven by online retail. Gyms and entertainment venues could work, too.

San Francisco invented the ‘parklet’: conversion of parking spaces into other uses, while ground-floor restaurants already spill out onto the sidewalk. Planners encourage the development of multi-use residential buildings which engage the street and contribute to a livable city, so these trends will be supported by almost everybody.

Proposal for the conversion of a four-story office building to residential use. Image courtesy of The Office of Charles F. Bloszies

We have been exploring some unusual and even odd-ball dark space uses. Surplus elevator shafts can be used for utility risers and exhaust ducts for ground-floor restaurants. The shafts can provide passive cooling by drawing cool air upwards—stack effect. Wind turbines could be placed in these shafts to generate energy around-the-clock. Hydroponic, vertical farms are another idea, which could supply produce to a ground-floor restaurant.

San Francisco is a proving ground for autonomous vehicles—another controversial issue—and right now driverless cars are commonly seen on the streets. One dark space use is a parking garage for these cars, which can drive themselves into the nooks and crannies of most column grids, a kind of autonomous car dispensary. Critics of ride sharing complain about traffic snarls caused by Uber and Lyft drivers waiting for their next fares—the autonomous car dispensary would address this problem.

Is there unusable dark space—too large, too difficult to access, etc.?

Bloszies: Not really, given the ideas outlined earlier. Finding tenants to lease these dark spaces is another story, but we are optimistic.

Would the dark spaces models that you created work in other markets, such as Manhattan for example?

Bloszies: Absolutely, especially in cities where zoning regulations allow more flexibility. Public review and regulations, however, are important and this is one reason San Francisco is such a great city, despite developer and architect frustrations with the public process. But as downtown cores are hollowed out, we are confident creative policy initiatives will be rolled out.

Possible dark space uses in office-to-residential conversions

Possible dark space uses in office-to-residential conversions. Image courtesy of The Office of Charles F. Bloszies

At the moment, are San Francisco’s zoning laws permissive of office-to-residential conversions and does the city offer incentives for such projects?

Bloszies: Not yet, but there is a lot of public talk in the news. Most incentives are aimed at affordable and workforce housing, but policy makers are considering relaxing some of the regulations concerning uses, like live-work.

Do larger floorplates allow for larger residential units, hence leading to higher-end apartments?

Bloszies: Yes. Design of larger units is much, much easier, although the unit depths are generally limited to 25-35 feet. However, in California, the need is for affordable and workforce housing, not high-end units, so policy and incentives are aimed towards these goals.

In San Francisco, the work-at-home model resulted in a portion of the high-income tech workforce leaving the city for less expensive housing, so demand for more expensive units may have waned a little. This trend is starting to reverse as these folks are returning to their cultural roots.

Do you have any office-to-residential conversions in your portfolio and if so, could you share a few notes on them?

Bloszies: Yes, but they were mostly the result of serendipitous circumstances. In 2006, we designed a conversion of a dilapidated office building into to a Ritz-Carlton Club—125 fractional ownership and condominium units. The original owner was unaware the building had been over-clad in the 1960s, hiding the first skyscraper on the West Coast that was built in the 1890s for the San Francisco Chronicle newspaper. We removed the cladding, faithfully restored the exterior and added 10 stories, for a total of 24.

Until the Hearst Building in New York was completed, the project was the largest vertical addition to a historic building in the world. In this case, the owner capitalized on buried architectural treasure only historians knew existed.

As part of the Ritz-Carlton project, we converted another nearby office building to residential use, including 30 residential units to satisfy San Francisco’s affordable housing requirement mandated for market-rate residential projects.

What other feasible uses are there for unused office space and what are your predictions for the future of office conversions?

Bloszies: All kinds, pretty much determined by building configuration and location. In San Francisco, there is talk about an urban college campus. Politicians, developers and owners are concerned about the future of the office building stock. They realize the city created a kind of tech monoculture, much like Napa Valley developed too many vineyards and a single societal or agricultural event can have a profound effect.

Right now there is very little activity on this front in San Francisco, despite the residential needs and record-high office vacancy rates. Brokers and land use attorneys we talk to are telling us there are four factors driving this sluggishness: high cost of real estate, high construction costs, market for high-ROI residential and the San Francisco approval process. All of these factors are moving in directions that will make office to residential conversions more economically feasible, but we’re not quite there.

Once the movers and shakers return from summer vacations, I think we will start to see some serious activity as owners and developers explore alternatives to office use almost everyone agrees will not return to pre-pandemic levels. We are looking forward to providing creative ideas to foster this activity here in our beloved city and elsewhere.

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