LAS VEGAS — Higher lumber costs, labor shortages and growing regulations are holding U.S. builders back as they try to ramp up construction to meet the huge demand for housing.

After starting about 850,000 single-family homes nationwide last year, builders around the country are forecast to construct almost 910,000 houses this year and increase production to 1 million homes by 2020, says Robert Dietz, chief economist of the National Association of Home Builders.

The rise in construction still won’t be enough, Dietz said at a meeting of the National Association of Real Estate Editors.

“We probably need about 1.2 million single-family starts,” Dietz said at a gathering this week in Las Vegas. “We continue to under build single-family housing.”

Higher materials costs are also hammering the industry.

A spike in lumber prices caused by the Trump administration’s tariffs on Canadian wood products is one of the biggest burdens on builders, Dietz said.

Lumber prices in the U.S. have risen 62 percent since January 2017, Dietz said.

“We get a third of the lumber we use in the U.S. from Canada,” he said. “A lumber tariff is very much a tax on homebuyers. It’s pushed up the price of a typical home by $9,000.”

Dietz said a lack of construction workers is also limiting homebuilding in many U.S. markets.

“Labor has been an issue of the industry for the last four or five years,” he said. “The job openings rate in the construction industry is now is actually higher than it was at the peak of the building boom,” even though builders are producing fewer houses than in the early 2000s. Almost 230,000 building sector jobs are unfilled, Dietz said.

Local building regulations and zoning requirements are also adding to higher new home prices and resulting in fewer starts.

Jim Boyd, a regional president with nationwide builder Toll Brothers, said longer production times caused by fewer workers and more local requirements are adding to construction costs.

“We are certainly experiencing a labor shortage — everywhere from California to Boise, Idaho, ” Boyd said. “What used to take six months to build now takes seven or eight months to build.