The conversion of office buildings to residential is a lasting and growing byproduct of the COVID-19 pandemic, which catapulted remote working to the forefront and made it a continuing trend. Plumbing and fire protection will be central to the conversions, with plumbing the big beneficiary.

Fundamental to these conversions is a national office vacancy rate that reached a nearly 30-year-high of 17.1% in the third quarter of 2022, according to CBRE, which adds that “A surplus of available office space will continue to weigh on fundamentals for the foreseeable future.”

As a result, apartment conversions from office buildings are at an all-time high in the United States, according to a December 2022 report by RentCafé, having made way for 11,000 apartments in just the last two years – with another 77,000 apartments currently undergoing conversion. The top 10 cities with the most converted apartments from offices in 2020-2021, according to RentCafé, are in eight states and the District of Columbia and stretch from coast to coast: Washington, DC (#1), Chicago, IL (2), Philadelphia, PA (3), Los Angeles, CA (4), Alexandria, VA (5), Nashville, TN (6), Union, NJ (7), Baltimore, MD (8), Hyattsville, MD (9), and Dallas, TX (10).

In New York City, Mayor Eric Adams recently unveiled the recommendations of a city-led task force to facilitate the conversion of underused office space into new housing for New Yorkers. The recommendations would apply to 136 million square feet of office space — roughly the amount of office space in the entire city of Philadelphia — and could create housing for up to 40,000 New Yorkers in midtown Manhattan and other business districts.

This growing nationwide pattern of converting office buildings to residential will be influenced in the future primarily by economic factors, based on our experience as consulting engineers advising many of New York City’s largest property owners. The engineering is clearly doable.

The first consideration for a property owner will be the prospect of renting the office space for its intended purpose. If that prospect is good enough, there will be no incentive to bear the cost of conversion to residential, which would presumably have a lower rental value as well. That means that the steel-and-glass office towers of midtown Manhattan and other major commercial districts in the nation will likely remain just that.

The potential for conversion, therefore, lies primarily in older, masonry-clad, mid-sized buildings. Those buildings typically have smaller footprints that are more conducive to conversion — and thus less distance from elevator banks and other core services to much-prized access to windows.

If the economics make sense, then conversion can take place from an engineering perspective. There may be opportunities to reuse some of the existing infrastructure — beyond the core structure itself — depending on the current layout. There should be enough existing electrical power, for instance, except for the demands of electric kitchens, which are now the way to go, given current restrictions on the use of natural gas.

Residential infrastructure is quite different, however, from office infrastructure, and that is where the plumbing becomes crucial. Since office buildings typically have a centralized plumbing system and residential buildings have a distributed one, an entirely new plumbing system is likely needed in any conversion, depending on the layout of the building.

The existing piping system is also likely not salvageable, depending on past use. Ultrasonic tools that test the remaining thickness of piping can estimate how much longer it can be used.

The need for bathrooms and kitchens is vastly greater in residential buildings than in office buildings. As a result, residential buildings typically need centralized hot water systems — in contrast to the localized, point-of-view, water heating common in office buildings. The ventilation needed for bathroom and kitchen exhausts is also quite different in the two building types.

When new hot-water systems are needed, consideration should be given to the latest energy-efficient technology, specifically heat pumps. They can generate hot water three times as efficiently as traditional water heaters and can reduce carbon emissions in the process. This is important, as the hot-water system will go from being a small part of the energy use in an office building to a large part in a residential one.

When it comes to fire protection, there is more potential for reuse of components of existing systems. The vertical infrastructure servicing fire protection is typically located in the fire stairs in both building types, and the sprinkler system may well be reusable. In addition, fire safety requirements are often more stringent for office buildings than for residential ones.

The choice between cooking with gas or electricity can affect fire protection needs as well as carbon emissions. Natural gas can also raise air quality issues, and regulations may make reusing gas piping systems more difficult.

The conversion of office buildings to residential is an important and growing trend in American cities. Designers and implementers of plumbing and fire protection systems will be vital to realizing those conversions and to achieving the revitalized downtowns that will result.