Recently soldered plumbing pipes may have caused wooden studs to become too hot, resulting in a fire last week that destroyed an apartment building under construction, Lawrence fire officials said Friday.

But that is only a theory. The official cause of last Saturday’s fire at Chase Court Apartments, 1942 Stewart Ave., will be listed as undetermined, said Mark Bradford, deputy chief with Lawrence-Douglas County Fire & Medical.

Investigators ruled out arson or any other suspicious cause, Bradford said.

“No further investigation is planned,” he said.

Once the flames started, they quickly enveloped the three-story apartment building, sending up flames and smoke that could be seen for miles.

The fire originated in the southeast second-floor apartment of the destroyed building, fire investigators determined. The fire spread rapidly after it started because Sheetrock had not been installed on any of the walls or ceilings and the attic was open.

Construction workers had been in the building that morning working with open flame equipment to solder plumbing pipes, Bradford said.

“They left about noon and didn’t plan on coming back,” he said.

It isn’t unusual for soldered pipes to cause a wooden stud to get too hot, Bradford said. If construction workers are aware of it, they can pour water on the hot spot.

The fire was reported to 911 at 1:21 p.m. Saturday. The first fire units arrived at 1:24 p.m., Bradford said. The fire was brought under control in about 45 minutes.

Two other buildings adjacent to the main fire were damaged. One of them was occupied, but no one was hurt. Total damage was listed at $600,000.