Exploding Sunroofs – Fact or Fiction?

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Sunroofs and moonroofs do sometimes shatter without cause, and we have proof.

Exploding sunroofs are all the rage these days. Actually, it is technically a “moonroof” thing. Generally speaking, a sunroof is a metal panel that can tilt up or retract, and a moonroof is a tinted, tempered glass panel that can do that same trick. The ones that are “exploding” are the glass ones. A recent post by a CarTalk Community member on the topic drew respectful skepticism from the community members, many of whom felt it was nothing more than an urban myth. Based on our own experience, and research by Consumer Reports, we can say definitively, it is a real phenomenon, and on the increase.

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Our experience was like many who have had a moonroof shatter with no apparent cause. Driving on the highway, dry conditions, no bumps, and suddenly “POW!” Once the shock is over, one is left with glass in one’s hair, eyebrows, and lap. That image at the top of the page is the end result of a 2006 Honda Accord after its sunroof shattered on us. The shade was open when it happened, but we were able to get it closed and drive to a safe place to pick the glass from our face, hair, and clothes.

According to Consumer Reports research of National Highway Traffic Safety Administration data, moonroofs have exploded on over 200 models and 35 brands in the past 20 years. Luckily, nobody has died in an accident from this cause, that we know of. There have been a few dozen reports of injuries. In our own incident, we were unharmed.

Although the problem is widespread, it definitely happens with more frequency in some models. One example of a cluster of such problems was reported by a car service company that had five such moonroof failures in its fleet, all of which were 2014 Lincoln MKTs. Consumer Reports feels the Kia Sorento deserves scrutiny by regulators since it seems to have a high rate of failures.

Hyundai has been fighting a lawsuit brought by owners who say Hyundai is hiding a pattern of such failures on panoramic sunroofs. A similar case is underway, having been brought by owners of 2008 Nissans with moonroof failures. There are also Lexus and Volkswagen suits of this type. The problem spiked from 2012 through 2016 according to the data Consumer Reports compiled. Reports per year rose from about 40 to 50 per year to as many as 200.

Moonroofs are made from tempered glass which is pre-stressed for safety. The glass will break into small pieces when it breaks, helping to reduce injuries, versus the injuries that could result from large pieces of plate glass like you’d find in a window in your house. This type of safety glass can fail suddenly when a small defect is put under the right amount of stress.

So why not move to laminated glass which has a polyvinyl butyral (PVB) film sandwiched between two pieces of glass? Windshields have been made of this type of glass since the 1930s. The advantage is that the glass stays largely in place when it’s broken, and not shower the passengers with falling glass.

The disadvantage, though, is durability. Tempered glass is pretty tough stuff. It’s resistant to scratching, and it will stand up to a bit of torque before it shatters. That makes it the preferred material for anything that moves: side windows, moonroofs, removable panels, etc. Laminated glass is much more susceptible to scratching (as evidenced by what a set of worn wiper blades can do), and it will crack if torqued at all.

Polycarbonate glazing represents a solution to both durability and shatter-resistance. It also offers other significant benefits. It’s possible to form polycarbonate glazing into shapes designers never could with glass. It’s also much lighter than its glass counterpart.

The disadvantage right now, anyway, is that it’s much more expensive than glass. The only vehicles using polycarbonate glazing are high-end exotics like the Bugatti Veyron 16.4 Grand Sport, which features a panoramic sunroof constructed of Makrolon polycarbonate sheet.

For the moment, we’re living with tempered glass, and probably will be for the foreseeable future.

When the problem occurred on a vehicle we were driving, we photographed the car before we cleaned it. Looking for help with the repair costs, we first tried our Honda dealer. The car was still under its comprehensive warranty. Honda opted not to honor the damage as a defect. We then contacted our insurance company in our home state of Massachusetts. Our state has no deductible for glass claims unless a policyholder opts to waive that for a lower premium. In the end, our repair was delayed a few days as our dealership searched for the replacement parts. The insurer paid the cost of the dealership’s work to replace the moonroof. It has since gone another decade without any problems.

Image Note: Top of page image by John Goreham. Re-use with the written permission of BestRide or the author only.