If your garage bakes every summer and freezes on the odd January morning, you are not imagining it — a bare garage door does almost nothing to slow the weather. Insulation is the fix, and it does more than temperature: it makes the door quieter, sturdier, and easier on the AC. Here is the whole picture.
Start with R-value
R-value measures how well the door resists heat moving through it — higher is better. A single-layer steel door is roughly R-0. A polystyrene (foam-board) door lands around R-6 to R-9. A polyurethane-injected door hits about R-12 to R-18, and that is the tier that actually matters in North Texas. Here is how to pick the right R-value for your garage.
Polyurethane vs. polystyrene
Both add insulation, but polyurethane is denser, bonds to the door, and delivers a quieter, stiffer panel with a higher R-value. Polystyrene is cheaper and helps a little. For our climate we almost always steer folks toward poly. See our full comparison of the best garage door insulation.
Is it worth it?
For an attached garage — or one with a room above it — yes, insulation is usually worth it. It reduces the heat load your AC fights and kills the draft. For a detached, unconditioned garage the case is weaker, though many neighbors still add it for the quieter door. We break down exactly when it pays off here.
Buy insulated, or insulate what you have?
If you are replacing the door, choosing insulated from the factory is the better value — it seals properly and costs only a little more. If you are keeping your door, a DIY kit helps as a stopgap. Here is how to insulate a garage door yourself, step by step.
What it costs
On a new door, stepping up to insulated usually adds only a few hundred dollars over a bare single-layer — and it is the tier most DFW homeowners land on anyway. Build yours in our door designer for an instant installed ballpark, or see full ranges on the cost guide.
R-value vs. U-factor: which one measures a door
For garage doors, R-value and U-factor are not the same thing, and the difference matters. A door’s advertised R-value is calculated at the center of one section, not measured across the whole door. U-factor is the measured, whole-door number that building codes use — and for U-factor, lower is better.
- R-value on a garage door is a calculation of one section’s center; DASMA says that method ‘should not be used for garage door assemblies.’ DASMA TDS-163
- U-factor is the whole-door measurement (ANSI/DASMA 105) that captures joints, seals and hardware — and lower is better. DASMA TDS-163 Amarr
- For garage doors, R-value ≠ 1/U-factor. They are not reciprocals. DASMA TDS-163
- Clopay’s polyurethane Intellicore doors range from about R-6.3 to R-20.4 depending on the line. Clopay
- ENERGY STAR does not certify garage doors at all — it covers windows, entry doors and skylights, rated by U-factor. An ‘ENERGY STAR-rated garage door’ claim is incorrect. ENERGY STAR
| R-value | U-factor | |
|---|---|---|
| What it measures | Center of one door section (calculated) | The whole installed door (measured) |
| Test method | Component calculation | ANSI/DASMA 105 |
| Used by building codes | No (not for assemblies) | Yes |
| Better when… | Higher | Lower |
“U-factor provides the highest degree of confidence when evaluating and comparing the thermal performance of garage door assemblies.”
In Texas heat, an attached garage’s door is part of your home’s thermal envelope. DOE guidance focuses on air-sealing and insulating between an unconditioned garage and the living space, and defers R-value targets to the IECC climate-zone tables rather than a single garage-door number. U.S. DOE
Sources: DASMA TDS-163 · Amarr · Clopay · ENERGY STAR · U.S. DOE
Key takeaways
- R-value measures heat resistance — higher is better; poly doors (R-12 to R-18) are the tier that matters in Texas.
- Polyurethane beats polystyrene for heat, noise, and durability.
- Insulation is usually worth it for attached garages or rooms above the garage.
- On a new door, insulated adds only a few hundred dollars — and it's the common choice anyway.
- Keeping your door? A DIY kit or a fresh weather seal are cheaper stopgaps.