Image of the day: Why do North American construction costs increase with density?

Regulatory requirements for mid-rise buildings

From a recent report on single-stair buildings, published by the Pew Charitable Trusts:

The United States and Canada have a particular construction cost problem not seen in many of their peers abroad: As building typologies grow denser, per-square-foot costs rise. These cost dynamics favor the construction of suburban housing types, such as single-family houses and low-rise apartment complexes, in the United States and Canada, while mid- and high-rise rental and condominium buildings are largely priced as luxury products.

In much of the world, costs stay roughly the same as developers move from single-family houses to low-rise apartment buildings to mid-rise apartment buildings (four to six stories tall). That is true because economies of scale (for example, a single roof, foundation, or lobby serves more floors and housing units) and diseconomies of scale (for example, apartment buildings often include elevators, while single-family houses can just have stairs) roughly balance each other out.

The stark rise in cost according to density seen in Canada and the U.S. but not abroad hints that the diseconomies of scale in these countries’ housing construction are not inherent qualities of construction, but rather have a regulatory origin. In fact, building codes in the United States draw a number of hard and expensive lines between low- and high-density forms of development that are not found abroad.

Specifically:

There are density- and height-related cost differences between the U.S. and Canada and other countries because of regulations related to structural materials; mechanical, electrical, and plumbing systems; and fire protection systems.

Certain building heights trigger a change in structural materials: For example, U.S. codes require a transition from light wood-frame construction to concrete and steel above a certain height (typically six stories, but it depends on the jurisdiction), creating a shift in materials not found abroad.

U.S. and Canadian codes also impose many unique requirements in mechanical, electrical, and plumbing systems as building density rises. The U.S. and Canada, for example, require so-called active fire protection measures like sprinklers more than other countries, with nearly every city and state requiring sprinklers even in small new multifamily developments with as few as three units. For single-family homes, townhomes, and duplexes, however, 48 states have fully or partially removed sprinkler requirements through legislation or code adoption. Outside the U.S. and Canada, sprinklers are typically required only in high-rises.

Elevator cabin sizes in Canada and the U.S. must also be larger, at lower heights, than those in Europe, Asia, and Oceania, and must comply with a different set of technical standards. Similar differences can be found throughout U.S. and Canadian building codes, affecting almost every system in a building.

Some of the most stringent aspects of multifamily building codes in the U.S. and Canada involve egress. Both countries require a second staircase at some of the lowest heights in the world, even for relatively small apartment buildings. These stairs must be enclosed in a shaft protected by a door, whereas in many high-income European countries, a stairway can be open to apartment landings for low- and mid-rise buildings. Where two stairs must be provided, in most U.S. jurisdictions they must now be located on opposite sides of the building.