Until those systems and other protections are in place, “it’s really like a lumber yard of two-by-sixes in the air,” said William M. McLaughlin , the executive vice president of development at AvalonBay Communities, which owns about 85,000 apartments across the country.

The first 54 units of a wood-frame townhouse development under construction in West Oakland, Calif., caught fire in October. Called the Ice House, the 124-unit project was being built by City Ventures, a developer with 22 projects under construction throughout the state.

Security personnel monitoring 24-hour on-site cameras called the Fire Department shortly after the fire started, but all six of the buildings under construction went up in flames, said Phil Kerr , the developer’s chief executive of homebuilding. The cause was determined to be arson.

Financially, City Ventures was fine. The company was well capitalized and had a revolving construction loan led by Wells Fargo and an insurer “who stepped up right away,” Mr. Kerr said. Losses were around $15 million.

The more pressing need was helping buyers; sales of about 50 units were scheduled to close in less than two months. City Ventures offered to maintain those contracts at the early pricing levels, which were $650,000 to $750,000. The company also offered to switch buyers to the other half of the project, now scheduled to be finished before the half under demolition. Buyers who needed to move in right away were offered a 10 percent discount on another City Ventures project less than a mile away.

About 30 of the 50 buyers stuck with their contracts, Mr. Kerr said.

“Our sales and construction team spent a lot of time working one on one with buyers to answer their questions,” he said. “Everybody was emotionally affected, but they turned that very quickly into: ‘This is a challenge. Let’s hit it head on.’”