Energy-efficient windows in the Texas climate.
Most window efficiency advice online is written for cold climates, where the goal is keeping heat in. Austin has the opposite problem for most of the year, and that flips which number on the label you should be reading.
Read SHGC first, U-factor second
Every window carries an NFRC label with two numbers that matter here:
- U-factor: how quickly heat conducts through the assembly. Lower is better. This is the headline number in cold climates.
- SHGC (solar heat gain coefficient): the fraction of the sun's radiant energy that gets through the glass. Lower is better. This is the headline number in ours.
Austin is IECC Climate Zone 2A: hot and humid, cooling-dominated. Your air conditioning runs far more hours than your heating does, so the dominant load is solar gain coming through glass, which is SHGC, not U-factor. A window with an excellent U-factor and a mediocre SHGC is optimized for Minnesota.
The ENERGY STAR Southern-zone criteria are U-factor ≤0.40 and SHGC ≤0.25, which matches the 2021 IECC baseline for Climate Zone 2A. Treat those as the floor, not the target, and confirm the current requirement with the City of Austin for your specific project.
Specify by elevation, not by house
The single most common miss we see is one glazing package ordered for every window in the building. The four faces of a house have genuinely different problems:
- West: the hardest elevation in Austin. Low afternoon sun drives straight into the glass during the hottest part of the day, and overhangs barely help because the sun is coming in at a shallow angle. This is where the lowest SHGC earns its money.
- South: high sun for long hours, but at a steep enough angle that a decent overhang genuinely shades it. Low SHGC still worth having.
- East: morning gain. Less punishing than west because the house has not yet soaked up the day's heat.
- North: little direct sun. You can afford a higher-visible-transmittance package here and get better daylight without the heat penalty.
Specifying per elevation costs nothing extra in engineering and makes a difference you can feel in the rooms.
What the frame contributes
Less than the glass, but not nothing. Raw aluminum conducts heat readily, which is why a thermally broken frame, with a polyamide barrier separating the inside and outside halves, is not optional in this climate. Every aluminum window we supply is thermally broken; select configurations reach a U-factor as low as 0.22 depending on the glazing package, comfortably inside the Southern-zone criteria. The aluminum vs vinyl comparison covers this in more detail.
Where the money actually goes furthest
- Fix air leakage first. A window that does not seal properly makes its label numbers irrelevant. This is why installation quality outranks product specification.
- Buy SHGC on the west and south. The best return per dollar in this climate, and you will notice it in August.
- Buy U-factor everywhere, but do not pay a premium chasing the last fraction of it here.
- Buy triple glazing for noise, not for the energy bill.
What we would not claim
We are not going to give you a payback period. Savings depend on your existing windows, the house's insulation and air sealing, your thermostat habits and your utility rate, and anyone who produces a precise figure without knowing all four is making it up. New windows in Austin reliably improve comfort, noise and afternoon usability of west-facing rooms. Treat the energy saving as a genuine bonus rather than the business case.
Questions homeowners and builders ask us
What is the difference between U-factor and SHGC?
U-factor measures how fast heat conducts through the whole window assembly. Lower is better, and it is what matters most in cold climates where you are trying to keep heat in. SHGC, the solar heat gain coefficient, measures how much of the sun's radiant energy passes through the glass. Also lower is better, and in a cooling-dominated climate like Austin's it is the number that changes how your house actually feels.
What are the ENERGY STAR numbers for Texas?
Austin sits in the ENERGY STAR Southern climate zone, where the criteria for residential windows are a U-factor of 0.40 or lower and an SHGC of 0.25 or lower. The 2021 IECC baseline for Climate Zone 2A is the same pair of numbers. Confirm the current requirement for your project with the City of Austin before you order, because codes are revised, and the version in force is the one that governs.
Should I get triple glazing in Texas?
Usually not for energy reasons alone. Triple glazing mainly buys U-factor, and U-factor is the less important of the two numbers here. The money generally does more work spent on a better low-e coating and a lower SHGC. Where triple glazing does earn its cost in Austin is noise: near a busy road, a flight path or a commercial frontage, the acoustic difference is immediately noticeable.
Does window film do the same job?
Film lowers solar heat gain on glass you already own, so it is a reasonable stopgap. It does nothing for a failed seal, a rotten sill, a drafty frame or a window that no longer opens, and it can void some glass warranties. If the windows are otherwise sound, film is a sensible cheap fix. If they are not, it is money spent on the wrong problem.
Specify the right glass for each elevation
Send us the floor plan or just tell us which way the house faces. Glazing packages are specified per elevation, because the west side of your house has a different problem from the north side.