Improperly discarded floor finishing products and sawdust spontaneously combusted behind a home in Billerica, Mass., on May 16, causing the garage’s roof to collapse, according to Billerica Wicked Local.

The products from floor refinishing, including rags and sawdust, were left in trash bags behind the home, Billerica Deputy Fire Chief Thomas Ferraro told Wicked Local.

The floor had been refinished the day before to prepare the home for a sale. Specifics on the types of finishing products used were not available.