The fire that destroyed a historic building in Old Town Clovis early Monday probably burned for several hours before it was discovered and an alarm system probably would have saved the structure, officials said Thursday.

Fire Capt. Ryan Brubaker also said a fire sprinkler system would have gone a long way in limiting damage. Fire officials toured the devastated building on Fifth Street near Pollasky Avenue on Thursday and offered advice on preventing future fires in the popular downtown area.

Officials estimated that the two-alarm blaze caused about $1.5 million in damage to the structure and another $500,000 in damage to property in the building that housed Country Rose Antiques & Accents. Because the building was made of non-reinforced masonry, it will probably have to be demolished.

The fire also caused smoke and water damage to Clovis Antique Mall next door, but firefighters were able to prevent the blaze from spreading to that business. Fire prevention officer Andy Isolano noted that firefighters only broke one item when they entered that building to contain the blaze.

Officials are still investigating the fire's cause but Brubaker said fighting a blaze in the old building filled with antiques created special challenges for firefighters. He said there was a great deal of combustible material in confined aisles. That forced firefighters to take a "defensive posture," meaning they could not enter the building and could only battle the blaze from outside.

Officials said the fire probably smoldered for a long time before passersby spotted flames from the building. The fire probably started in the attic area; the roof was ready to collapse and send a heavy air conditioning unit crashing down by the time firefighters arrived.

Deputy Fire Marshal Gary Sawhill said older buildings such as the razed structure often have few electrical outlets, tempting occupants to use extension cords, which greatly increase the chance of a fire -- especially when they are placed under rugs and tied in knots. Often items are stored near appliances such as water heaters, creating another risk.

Officials on hand Thursday advised business owners to not block exits with merchandise and to keep fire extinguishers handy. Officials estimated that it would probably have cost about $30,000 to install a sprinkler system in the destroyed building, but the system would bring down insurance premiums and add value to the property.

Owners of Country Rose are still trying to determine what they will do with the property, Clovis Fire spokesman Chad Fitzgerald said. But Larry Gamble, who owns nearby properties in Old Town, was hopeful the neighborhood would remain intact without the 1920s-era building.

"It's a terrible loss, but there is an attitude of resilience (in Old Town)," he said. "We'll come back. I'm sure the rebuilding process will be consistent with the Old Town look."

The reporter can be reached at (559) 441-6339, jguy@fresnobee.com or @jimguy27 on Twitter.