This garage fire in Oshkosh was caused by varnishing towels left in a garbage can inside the garage.
Many people may not be aware that varnishing rags are at risk for spontaneous combustion. This is because things like varnishes, linseed oil, some wood stains and exterior deck sealers etc., do not dry through evaporation of water like most things. They dry through the process of oxidation and the process of oxidation produces heat. Proper handling of staining materials is essential to prevent fires.
For this restoration we ended up tearing down the old garage and building a completely new one.