I am currently going through the process of finalising an order for double glazed thermal break windows for a new owner build. We are looking to take advantage of a north orientation at the rear and have the eave overhang designed to give full shading between November & February. We have smaller amounts of windows on the east & west but as we have views to the west do want some windows that will need to have glazing with a lower solar heat gain. Various suppliers have raised concerns about cracking of glass caused by differential expansion when some parts of the glass are in shade and some parts are in sun. While this appears to be a bigger problem with tinted and lower SHGC types of glass it appears it could also be a problem with our north facing glass on sunny winters days when the air temp is low but the days are clear and sunny. As a result at the moment for the north windows we are looking at clear toughened glass for the outer pane and clear laminated with low e (face 3) for the inner pane (Most of these windows are full height or in wet areas so we need "safety glass" for the inner). For the East & West windows we are looking at the external pane including an ITO interlayer which cuts the SHG but is not tinted. I am uncertain whether we should have the low e on face 2 or face 3 for the west windows.
The south windows shouldn't have any thermal cracking issues so maybe we will have laminated glass as the outer pane for security reasons but still low e on face 3.
Has anybody experienced this thermal cracking problem or is it something that is just becoming an issue as more sophisticated types of glass become available and statutory requirements mean more people are installing upgraded glazing??
With the costs associated with this standard of windows it would be disappointing to end up with cracking windows.
Also while various gases such as Argon give improved U values it would appear gas loss over time would negate this effect. Does anybody have any idea of how long the benefit would last??
Over to the experts
Stephen.