The assessed value of all Bay Area property soared to $1.72 trillion in 2018-19, up 7.8 percent from last year despite wildfires that destroyed thousands of homes and businesses in Sonoma and Napa counties.

This year’s growth in assessment rolls beat last year’s 7.4 percent increase, thanks to a strong economy, fast-rising property prices and frenetic construction. Growing companies such as Apple, Tesla, Facebook and Salesforce were top contributors to the rolls in their respective counties.

The roll is the assessed value of all real and personal property in a county as of Jan. 1 each year. It’s the amount subject to property tax, which averages 1.2 percent in California, including voter-approved local taxes. County assessors generally have until the following July 1 to complete and report the roll for their county.

The vast majority of the roll is real or “secured” property — residential, commercial and industrial land and buildings. Personal property, despite its name, is primarily business equipment such as computers, office furniture and machinery, along with boats and aircraft. This is also known as unsecured property.

The assessed value is not the same as market value, which can be far higher. Under Proposition 13, real property is assessed at market value only when it changes ownership (with some exceptions). In between, it can only go up by an inflation rate capped at 2 percent a year, plus the value of major improvements or additions.

Personal property is reassessed every year, but after the first year, its assessed value typically falls as it depreciates.

The main things that add to a county’s roll are the inflation rate (2 percent this year), new construction, property changing hands at higher prices and new equipment. Most assessors said all four contributed to their gains this year, although some counties reaped outsize gains from expanding companies.

In Santa Clara County, Apple added $1.5 billion to the roll. Most of that came from ongoing construction at its spaceship headquarters, Apple Park, and the purchase of existing office buildings and business property. The campus (excluding equipment) is now assessed at $3.5 billion, but that includes land purchased several years ago and now subject to Prop. 13 limit, said David Ginsborg, the county’s deputy assessor.

Santa Clara County’s total roll grew by $33 billion, or 7.3 percent, to $483.2 billion, largest in the Bay Area.

San Francisco posted the largest percentage increase — 10.8 percent, same as last year. Its roll grew by $25 billion to $256.2 billion. The city’s most valuable building is now Salesforce Tower at 415 Mission St. It’s assessed this year at $1.34 billion, up from $561 million last year, according to an assessor’s office report.

Alameda County added about $968 million to the assessed value of Tesla’s land, plant and equipment, bringing the total to about $2.6 billion. Tesla CEO Elon Musk’s goal “was to produce 5,000 (Model 3) cars a week. He expanded greatly to meet that goal,” said Brian Hitomi, Alameda County’s chief deputy assessor.

San Mateo County’s roll grew 8 percent to $222.5 billion. Its single largest contributor was Facebook, which added about $700 million in taxable value at its Menlo Park headquarters and other locations.

Contra Costa County’s roll grew by 6 percent to $204.3 billion. The biggest single contributor to that growth was Chevron’s Richmond refinery, which was assessed this year at $3.3 billion, up $300 million from last year, Assessor Gus Kramer said.

Sonoma County has requested a 40-day extension to complete its roll, which was complicated by the loss of roughly 5,000 properties, mostly homes. Because the fires started in October, four months into the fiscal year, the assessed value of fire-ravaged properties will be reduced for the last nine months of the year.

A property’s land and buildings are assessed separately. Homes that were destroyed will have their building value reduced to zero and their land value reduced by about one-third, said Greg Walsh, Sonoma County’s chief deputy assessor.

“As homes get rebuilt, if they build back to the same size and condition, we will generally reinstate their pre-fire Prop. 13 assessment,” Walsh said.

If fire victims, instead of rebuilding, buy a new home in the same county, they can transfer their same pre-fire assessment to the new home, as long as they pay no more than 120 percent of what their old home was worth just before the fire. If they pay more than 120 percent — say 140 percent — the additional 20 percent will be added to their pre-fire assessment. Different rules apply if they buy a home in a different county.

Sonoma County has estimated that the fires will wipe about $1.8 billion off its roll this year. It expects that the roll will come in about 2.5 percent ahead of last year, instead of 4.6 percent.

Napa County’s roll rose to $39.3 billion, up $1.85 billion or 4.9 percent. The increase “might have been approximately 2 percent greater except for the $500 million loss in assessed value because of the October 2017 fires,” Napa County Assessor John Tuteur said in a press release.

Kathleen Pender is a San Francisco Chronicle columnist. Email: kpender@sfchronicle.com Twitter: @kathpender