What R-Value Actually Measures
R-value measures resistance to heat transfer — the higher, the better the insulation. But the numbers manufacturers print on garage doors are often calculated at the insulation core only, ignoring the steel skin, rails, and hinges. Real installed R-values are typically 30-40% lower than the sticker.
Common R-Value Tiers
R-0 (Uninsulated Steel)
Single-layer steel double-car door installed starts at $1,769 in DFW.
Fine for a detached garage with no HVAC. Rings like a drum, transmits every degree of outdoor temp. Fine for a detached garage with no HVAC.
R-6 (1 3/8-inch Polystyrene Foam)
Base-level insulation. Adds noticeable sound dampening. Real-world: 5-8°F difference vs. uninsulated on a 100°F day. Good for garages you park in but don't heat/cool.
R-12 (1 3/8-inch Polyurethane Foam)
The sweet spot for DFW. Polyurethane bonds to both steel skins (vs. polystyrene which just sits between them), so structural rigidity is dramatically better. Real-world: 10-15°F difference vs. uninsulated. Recommended if your garage shares a wall with living space, is climate-controlled, or is used as a workshop.
R-18 (2-inch Polyurethane Foam)
Premium tier. Diminishing returns unless your garage is fully finished-out living space or you have a bonus room directly above. Real-world savings vs. R-12: 1-2°F, ~$8-15/month HVAC. Costs $500-$850 more than R-12.
Where R-Value Doesn't Help
1. Weatherstrip gaps. A perfectly sealed R-18 door with a torn bottom seal loses more heat than an R-6 door with tight seals. Fix seals first. 2. Un-insulated jamb. If the wood frame around the door has no insulation behind it, R-value only affects part of the opening. 3. Attached garage with un-insulated walls. Your garage door is one of six surfaces — if walls and ceiling are un-insulated, the door is the smallest factor.
Real DFW Savings
For an attached, HVAC-adjacent garage in Dallas, upgrading from R-0 to R-12 typically saves $18-35/month in summer AC costs. That's ~$150-250/year, which pays back the insulated door upgrade ($350-550 vs. uninsulated) in 2-3 years. R-12 to R-18 typically doesn't pay back in a reasonable window.
Our Recommendation
For 90% of DFW homes: R-12 polyurethane. It's the biggest per-dollar comfort and utility-bill impact of any garage upgrade. Skip R-18 unless you have finished space directly above or beside the garage.