EHH week 32: exterior sun shades

This house presented a challenge for solar design.  Since the site has a great view of the lake and mountains to the west, we oriented the house north-south such that most rooms have a west facing window to enjoy the view.  There is only one small window facing south in the entire house.


Paradoxically, the only solar heat we could get through the windows would come from the west in summer afternoons, just when we don’t want it.  So instead of letting the sun in, we need to keep it out.  In a superinsulated house like this one, that is especially important to avoid overheating.


We selected low solar heat gain coefficient (SHGC) glass for the windows.  A special coating blocks 79% of the sun’s heat without affecting the clarity of the view.  For the hottest summer days, we also installed exterior sunshades.  Unlike interior blinds, the exterior shades stop the sun before it passes through the glass and becomes internal heat. 


The shades are controlled by a hand held remote so the homeowners can lower them when the sun is strong.  They are made of PVC fabric in an open weave, so they allow a partial view out, even when they are covering the window glass.  Aluminum guides along the sides keep them in place if it is windy.


It is important to note that we are not restricting the sun’s daylight, just the solar heat.  The windows have a visible transmittance (VT) of 57%, so they let in plenty of daylight.