Parked my sdi up today after driving it in sunny conditions, got back to the car 4 hrs later and there is a 10" crack from the top of the screen drivers side towards the middle.

The car WAS perfect when I left it, I notice everything about my cars ...

The car was parked under a council cctv camera (broken, typical!), question is ... criminal damage or stress crack ?

Is there an obvious impact point that would suggest criminal damage? Like a slight spiderwebbing of the glass anywhere along the crack or is it just a long straight crack?

It's just a big crack that runs diagonally from the top right corner to the drivers' eye line.

I'm forensically aware and have looked for impact or cleaning marks on the glass ... no marks evident, and the crack is totally smooth on both sides of the glass. This is what makes me wonder if it's stress related.

Sounds like stress. I had this happen on a Corsa. Suddenly appeared at bottom of screen and spread to top as I watched. Weird experience. When the screen was replaced I saw that the bottom support was rusted, so guessed that the expansion of the rust plus a hot screen had suddenly become too much for the glass.

Funny that it hapened on a hot sunny day too ... oh cack!

happened to me too... was no obvious signs of chips or cracks when i parked at work, then i came to drive home and was a lovely big crack from the top diagonally to the mirror.

I assume it was weakened somewhere, then as the temp changed it gave way!

When its changed, make sure you check it thoughrily before signing! I checked the glass over, but I didn't notice the chunk of paint the guy took out when fitting it until several days after!

I went through three windscreens in 21/2 years in my Audi A3

Only one of them was because of a definite stone impact, as I heard it hit then the crack grew snake like from the top corner to the middle at the bottom (not much fun to watch in lane 3 on the motorway).

The other two were just like you. Car left in a sunny car park all day, and when I came back to it fresh crack.

The Audi was black and as such it did get very hot in the sun (hot enough to actually melt the rubber on the suction mount of the satnav), and I've wondered if this contributed to it.

They might tell you or not (only once on my three visits from autoglass), but the glue doesn't set straightaway, and takes a while to cure properly, and you can stress the glass by slamming the door too hard or going over nasty bumps while the glue cures.