A Calgary man says the sunroof of his brand new BMW suddenly shattered and he is now on the hook for repairs.

The sunroof on Tom Irwin's 2012 BMW X1 is fixed now, but several months ago he says it spontaneously exploded.

"Just a very loud bang that happened out of the blue,” said Irwin.

The dealer told Irwin to expect to pay the $4000 dollar repair bill even though the car had fewer than 5,000 kilometers on it.

"The immediate reaction was bring it in so we can look at it however it's glass and it's not covered under warranty. That's without even looking at the vehicle,” said Irwin.

No matter what Irwin said, the dealer and BMW Canada maintained that a rock or some other object broke the glass.

CTV Calgary Consumer Specialist Lea Williams-Doherty received a similar complaint last year from a Calgary man about his 2011 BMW 328i.

The complainant in that case told Lea that BMW refused to repair his sunroof too and stated that a rock must have shattered his glass as well.

Lea contacted BMW Canada to ask if there could be a defect in the vehicles that causes some sunroofs to spontaneously shatter and BMW told her no.

The company says that because the sunroofs sit within their own housing, they are not part of a vehicle's structure and therefore not subject to pressures exerted on the vehicle.

BMW said that the only explanation is that an object hit the tempered glass from the outside.

When Lea told the company that the owners were certain that nothing fell on their vehicles, BMW said it could have been a delayed reaction.

They say a rock may have chipped the surface of the tempered glass without the owner knowing.

Lea checked with a glass expert at the University of Calgary to see if tempered glass could be chipped and not shatter.

“Tempered glass doesn't, in my experience, typically get pitted the same as a windshield or normal plate glass. So a delayed shatter is unlikely? It’s very unlikely, yes,” said Mark Toonen.

BMW says Alberta has the highest number of these incidents in Canada because of the pea gravel we use here in winter during road sanding.