Garage door R-value: what the numbers mean and which one to buy

R-value tells you how well insulation resists heat moving through it. Clopay puts it simply: the higher the R-value is, the better the garage door keeps your space warm in the winter and cool in the summer.

Your garage door is a big panel between your garage and the outdoors, so the number on it is worth understanding before you buy.

Not sure what is letting in drafts or water? Start with our page on a garage door that lets in drafts or water.

R-0 to R-20: what the range covers

The spread is wide. A single-skin steel garage door has no insulation, while a door with foam between the skins has some. Clopay describes the R-0 to R-2 range of a non-insulated door, and says standard polystyrene doors typically fall between R-6 and R-9.

At the top end, Clopay's own Intellicore doors have R-values ranging from R-6.3 up to R-20.4 depending on the door model, thickness, and panel style. On Clopay's insulation page, its Canyon Ridge Carriage House door with 5-layer polyurethane is listed at R-20.4, and its Modern Steel line runs from R-6.3 to R-18.4.

Ask for the rated R-value of the exact model you are quoted, not the range for the whole line.

Polyurethane vs polystyrene

Clopay compares two foams and says polyurethane doors offer higher R-values than polystyrene doors.

Polyurethane is a foam that manufacturers inject into the garage door, filling every gap, and it creates a dense, strong layer between the door panels. Clopay's other guide adds that the polyurethane foam bonds directly to the steel.

Polystyrene is more common in rigid panels that fit between a garage door's layers, and it is typically the more budget-friendly insulation option. Polyurethane usually adds more to the price.

Why the joints matter: R-value vs U-factor

A sectional door is constructed from horizontal panels connected by hinges. Those joints, and the guides along the sides, are part of the door too.

Clopay draws the line this way: R-value looks at individual materials or sections of the door, while U-factor takes in every component, joints and guides included. With U-factor, lower is better. A lower U-factor means the whole door insulates better and uses less energy. If a maker gives you both numbers, the U-factor is the one that counts the joints and guides.

Seals are part of the picture

Foam inside the panel can't stop air that slips around the edges. Clopay recommends installing high-quality perimeter weatherstripping and durable bottom seals alongside the insulation.

The bottom seal wears out first: Clopay says most seals need replacing every two to three years, depending on climate and use, and Amarr says around two years or more with proper maintenance.

The fix at the floor is a threshold seal bonded to the concrete; our weather seal guide covers the types.

How to choose an R-value for your garage

Clopay's guidance comes down to where the garage is and how cold it gets:

• Attached garage, or a cold climate: an R-value between 10 and 13 is best.
• More extreme climates: aim for an R-value of 15 or higher.
• Detached garage, or a more temperate zone: a moderate R-value between 6 and 10 may suffice.

What you can check yourself

You can look at your own door. Close it and check the bottom seal: it should sit flat against the floor with no daylight showing under it. Check the side seals the same way.

What the rating can't tell you is how a given door holds up at its joints and seals after years of use. That is a question for a technician who has worked on that product line. If you'd like a professional evaluation of whether your current door's insulation and seals are performing as rated, Garage Door Pro Services (our affiliated installer) offers inspections that cover both thermal performance and seal condition.