Interesting issue that came up with exposed EPS (Neopor) in a relatively mild climate. Within 8 months of UV exposure from fall through spring (low UV intensity), the product melted:



The theory was that the suns UV hitting the glass created hot spots and degraded the foam quicker in the area on the window sill. EPS begins to melts at around 175F and this was possibly attainable with the sun at the correct angle to the glass. Sort of a "magnifying glass" effect. Either way, exposed EPS and even polyurethane to the suns UV is not a good thing.

Double pane windows that are partially evacuated tend to have slightly concave glass. This does indeed act like a magnifying glass, and there are cases of vinyl siding being damaged by the intense heat- sometimes even on neighboring houses. My windows are Low E and are quite reflective. I've noticed that on chilly mornings, the reflection on the ground will thaw the frozen ground much faster than the surrounding area.

Have you brought this to the attention of the manufacturer/supplier? If so, what's their response?

Some EPS specs say "6 months maximum" for UV exposure. I'd be conservative and use 3 months as the limit.

Yes, 8 months is too long for that. Could this be an argument for "Outtie" windows?

Posted By NFC on 14 Apr 2015 01:11 PM
Yes, 8 months is too long for that. Could this be an argument for "Outtie" windows?

The only argument here is waiting too long to cover and protect the foam. 8 months is 5 months too long.