West Elevation Glass Specification

One House, Four Different Problems

A house has four elevations and they do not share a climate. The north glass sits in ambient light all day. The east glass gets a couple of hours of low morning sun while the air is still cool. The south glass takes a high overhead angle that a normal eave shades for most of the summer. The west glass takes direct low angle sun from mid afternoon until sunset, in the hottest part of a Riverside day, at an angle no eave can block.

Most quotes ignore all of that and price one glass package for the whole house. That is either overspending on three walls or underspending on one.

The Number That Decides It

Solar Heat Gain Coefficient is on every NFRC label, expressed between zero and one, and it is the fraction of incoming solar energy that ends up as heat inside the room. It accounts for what passes straight through the glass and what the assembly absorbs and then re radiates inward.

Rough figures worth carrying around:

• Clear dual pane, no coating: around 0.70.
• Standard single silver low E: around 0.38 to 0.45.
• Spectrally selective double or triple silver low E: around 0.20 to 0.25.

That is a difference of roughly two thirds of the afternoon load on the same opening. Nothing else in a window quote moves comfort that far.

Where the Coating Goes

The four glass surfaces in a dual pane unit are numbered from outside in. Surface one is the weather face, surface two is the inside face of the outer pane, surface three is the outer face of the inner pane, surface four is the room face.

For a hot climate the solar control coating belongs on surface two, so it reflects the energy before it enters the cavity. Put the same coating on surface three and it behaves as a heat retention layer, which is exactly what a heating dominated climate wants and exactly wrong here. This is a genuine specification detail and it is worth asking about, because it is not something you can see once the unit is glazed.

Daylight Is Not the Price You Pay

The usual worry is that heat control means a dark or tinted room. Tinted glass does work that way. A spectrally selective coating does not, because it is engineered to pass the visible band while rejecting the near infrared.

The check is on the same label. Visible transmittance, VT, is the fraction of daylight that gets through. Divide VT by SHGC and you get the light to solar gain ratio. Above one means the coating is being selective rather than simply darkening everything. A good west wall product will land above that comfortably while still holding SHGC near a quarter.

What We Record on the Visit

For each opening: compass orientation, glazed area, eave or overhang depth, existing exterior shade including trees and neighbouring structures, the frame material and condition, and whether the room is one people actually complain about.

That last one matters. A west facing window in a garage is not worth the upgrade. A west facing slider onto a living room where the family stops sitting after three in the afternoon is the whole reason to do the job.

The Honest Version of the Advice

If the opening already sits under a deep covered patio, the sun never reaches the glass and the premium coating changes very little. If the room is on the west side but the real complaint is a hot ceiling, the attic is the leak and new glass will disappoint you. If the house is on the market in a month, spend on the visible frames rather than on a coefficient nobody will read.

We would rather specify two windows correctly than eleven windows generically.

Call (951) 974-8968.