Garage Door R-Value Explained: What the Numbers Really Mean for Canadian Homeowners

R-18, R-12, R-9, R-6: What Are You Actually Paying For?

Walk through any garage door showroom in Ontario and you will see the same number plastered across the brochures: R-value. One model says R-9. The next says R-16. The premium one says R-18 or higher. The natural assumption is that bigger is better, the way more horsepower is better in a truck, and that doubling the number doubles the insulation.

That assumption is mostly right, but the picture is more complicated than the showroom card admits. Two doors with the same printed R-value can perform very differently in a London winter. Two doors with very different printed R-values can perform almost the same. And the industry's main trade body, the Door & Access Systems Manufacturers Association (DASMA), explicitly cautions buyers against using R-value alone to compare doors. As DASMA puts it in Technical Data Sheet #163, R-value is "of limited usefulness" because it describes the centre of one section of the door, not the door you actually install.

This guide is the plain-English version of that data sheet. What R-value measures, what U-factor measures, how the two differ, what the numbers really mean for heat loss, and what an honest insulated garage door is worth to a Canadian homeowner. No marketing fluff, just the verified physics and the practical buying advice that comes out of it.

What R-Value Actually Measures

R-value is a measure of thermal resistance. It tells you how strongly a material resists heat flow. The higher the R-value, the harder it is for heat to push through. The units are technical: hour-square-foot-degree-Fahrenheit per Btu, or (h·ft²·°F)/Btu in shorthand. You can ignore the units. The practical takeaway is that R-value is a relative score.

The score is calculated, not measured. For a garage door section, DASMA uses this formula:

For an insulated steel door, the air film component is fixed at about 0.85 (calculated by ASHRAE for a still interior and a 15 mph wind on the exterior). The steel skins contribute almost nothing on their own. Virtually all of the R-value comes from the foam insulation in the middle of the sandwich. That is why two doors with the same foam thickness and the same foam type tend to land at the same R-value, regardless of brand.

Where the R-Value Number Gets Misleading

Here is the part the showroom card does not mention. DASMA's TDS 163 makes the point bluntly: the calculated R-value applies only to the centre of one section of the door. It ignores the seams between sections. It ignores the steel stiles at the ends. It ignores the weatherseal compression around the perimeter. It ignores the small thermal bridges where the rollers and hinges attach. In an installed door, every one of these areas leaks heat faster than the foam in the middle.

The result is that a real garage door installed in a real opening performs worse, sometimes significantly worse, than the calculated R-value would suggest. The honest number is what DASMA calls the U-factor.

U-Factor: The Number That Actually Describes an Installed Door

U-factor is the opposite of R-value in one sense: lower is better. It measures thermal transmittance, how much heat actually moves through a complete door system. And critically, U-factor is tested, not calculated. Under the ANSI/DASMA 105 test standard, a manufacturer ships a complete door to an accredited lab, the lab installs it in a sealed thermal chamber, and the lab measures how much energy it takes to keep one side warm while the other side is cold. The result accounts for every seam, every joint, every weatherseal, and every piece of hardware on the door.

Because U-factor is measured on a complete door, it is the metric DASMA, ASHRAE, and most building codes prefer. The trade-off is that it is more expensive to obtain (the test costs thousands of dollars per door model), so not every manufacturer publishes it for every model. The big residential brands that participate in the DASMA Thermal Performance Verification Program, which include Amarr, Clopay, Garaga, Wayne Dalton, Haas, and others, do publish verified U-factors on their high-end insulated doors. If you are shopping seriously and the dealer can show you a verified U-factor, take it over a calculated R-value every time.

Why Two "R-9" Doors Can Perform Differently

Two factors swing the real-world insulation of a door more than the R-value sticker:

1. Construction Type: Sandwich vs. Single-Skin

An insulated steel door comes in two main constructions. A single-skin door has one steel face on the outside and a foam insulation panel slid into a U-channel behind it. A sandwich door, sometimes called a three-layer door, has steel on both faces with foam permanently bonded between them. In a sandwich door, the foam is part of the structural panel; in a single-skin door, the foam is loose backing.

Sandwich doors do not just feel sturdier, they perform measurably better. The bonded steel-foam-steel structure creates a thermal break between the interior and exterior skins, the foam stays in continuous contact with both faces, and the panel itself is stiffer (so it flexes less, which means the weatherseals stay sealed). Two doors can be rated R-9, but if one is single-skin and one is sandwich, the sandwich door will deliver noticeably better real-world performance in a cold London winter.

2. Insulation Type: Polystyrene vs. Polyurethane

Two foams dominate the residential market: polystyrene (the white styrofoam-like material, also abbreviated EPS) and polyurethane (a tan, fine-celled foam that is sprayed in as a liquid and expands to fill the cavity). Polyurethane has roughly twice the insulating value per inch of thickness, so a door with 1-3/8 inches of polyurethane can hit R-12 to R-16, while the same thickness of polystyrene tops out around R-6 to R-9.

Polyurethane also bonds to the steel, which makes it the foam of choice in sandwich-construction doors. Polystyrene panels are usually loose-fit, which works well in lower-end single-skin doors but loses some efficiency at the panel edges and the sliding joints.

3. Thickness

Everything else equal, a thicker section holds more foam. The most common Canadian residential garage doors come in 1-3/8 inch and 1-3/4 inch (44 mm) thicknesses. A few premium models go to 2 inches (51 mm) or beyond. Thicker is always more insulating, but the gains are not linear because the air films and skins stay constant. Going from 1-3/8" polyurethane to 1-3/4" polyurethane is a meaningful upgrade in cold-climate performance, while going from 1-3/4" to 2" is more incremental.

Typical R-Values by Door Construction

The table below summarizes the R-value ranges you will see on residential doors sold in Canada. These are calculated R-values per DASMA's published formula, so they reflect the section centre, not the assembled door. Treat them as relative comparisons, not absolute performance numbers.

What R-Value Do You Actually Need?

The honest answer depends on what is on the other side of the door. The right number for an unheated detached garage is different from the right number for an attached garage that shares a wall with the living room.

Unheated Detached Garage

If the garage is not connected to the house and you do not heat it, the door is essentially an exterior shed door. The interior will track outdoor temperature within a few degrees regardless of door R-value. R-6 to R-9 is plenty. The bigger payoff in this case is from a non-insulated door's tendency to dent, condense, and rust; even a budget insulated door solves those problems.

Attached Garage, Unheated

This is the most common situation in London Ontario. The garage shares a wall (and often a ceiling) with the heated portion of the house, so heat loss through the garage matters even when the garage itself is unheated. R-12 to R-16 is the practical sweet spot. Going from R-6 to R-12 produces a noticeably warmer garage and a noticeably warmer wall on the inside of the house. Going from R-12 to R-18 produces a smaller but still meaningful improvement.

Attached Garage, Heated or Workshop

If you actively heat the garage (workshop, home gym, finished space), every Btu lost through the door is a Btu you are paying to replace. R-16 to R-18 is the right starting point. R-18 and above is worth the upgrade if you keep the space at room temperature year-round. At those levels, the door's insulation is comparable to a 2x4 stud wall with batt insulation, which is a good benchmark for a finished room.

Net-Zero or Passive House Builds

For homeowners building to passive house or net-zero standards, R-18 is usually the minimum and many specifiers move to R-24 or higher with custom or commercial-grade doors. At that level you are also paying attention to the door perimeter weatherseal, the air tightness of the section joints, and the thermal break detail at the bottom rail. Natural Resources Canada's guidance on what makes an energy-efficient home is the broader context for these decisions.

R-Value Is Only Part of the Heat-Loss Picture

A garage door can have an excellent R-value and still leak heat like a screen if the rest of the system is neglected. The two biggest non-insulation losses are:

• Air infiltration through bad weatherseals. The bottom seal, the side seals, and the top seal together cover a perimeter of about 32 to 40 feet on a typical double door. Any gap in that perimeter is a direct path for cold outside air to push into the garage. A door with R-18 and a 3/8-inch bottom gap will feel colder than a door with R-12 and a tight seal. We cover this side of the equation in our garage door seal guide.
• Conduction through the panel joints, stiles, and hardware. These are the elements that R-value calculation ignores but U-factor testing captures. On a single-skin door, the stiles are usually a thermal bridge of steel running from outside to inside. On a sandwich door, that bridge is partially broken by the foam.

The practical implication: a sandwich-construction door with a tight perimeter seal and intact section joints will outperform a higher-R-value single-skin door with worn-out weatherstripping every time. If you are upgrading an older door, ask the dealer about both the R-value and the seal system, not just the foam.

Energy Star and the Canadian Picture

Garage doors are not currently part of the Energy Star Canada program in the way windows, exterior doors, and appliances are. Energy Star certifies windows and doors that face the exterior of the heated envelope, and the program treats the garage door as part of an unheated buffer space in most house designs. That said, the standards that govern Canadian residential garage doors, including DASMA TDS 159 on foam plastics for Canadian applications, push manufacturers toward higher-quality insulation by default.

The practical Canadian buying advice is to look for a verified DASMA Thermal Performance Verification Program label on the door (or in the product literature). That label tells you the U-factor was tested by an independent lab, not just calculated.

Real-World Performance: What an Insulated Door Means in Comfort and Cost

For homeowners with an attached garage, the practical difference between a non-insulated door and a well-insulated one shows up in three places:

• Interior temperature on cold days. A non-insulated door at -20°C outside leaves the inside of the door at roughly -10°C to -15°C. An R-12 to R-16 door at the same outside temperature stays around -2°C to +2°C on the inside face. That is the difference between a garage that frosts the windshield overnight and one that does not.
• Wall surfaces in the house. The shared wall between an attached garage and the house is usually insulated to R-12 or R-20 in older builds and R-22 to R-24 in newer ones. If the garage door is non-insulated, that shared wall sees the full outdoor temperature on the garage side, and the interior wall feels noticeably colder. A well-insulated door warms the entire envelope.
• Heating cost. For an actively heated garage, the door is one of the largest single sources of heat loss. We work through a realistic London cost analysis in our energy savings calculator article. The short version: in a heated double garage, an insulation upgrade often pays back the door's price difference in 7 to 10 years, with the comfort improvement starting immediately.

Quick Buyer's Checklist

When you are looking at a quote, walk through these questions:

• Is the door single-skin or sandwich (three-layer) construction? Sandwich is the better choice for any attached or heated garage.
• What foam is used: polystyrene or polyurethane? Polyurethane offers roughly twice the R-value per inch.
• What is the section thickness? 1-3/8" is mainstream; 1-3/4" is the typical cold-climate upgrade.
• Is the published R-value calculated or is there a tested U-factor? The U-factor is more reliable.
• Is the door listed in the DASMA Thermal Performance Verification Program?
• What does the perimeter seal system include (bottom, sides, top, between sections)?
• Is the insulation continuous through the section, or are there cold spots at the stiles?
• For older buyers using existing doors: are the existing weatherseals worn? A seal replacement can be a higher-value upgrade than buying a higher-R-value door.
• Is the use case unheated/detached, attached/unheated, or heated? Match the R-value to the situation.
• If you are insulating an existing door instead of buying new, our DIY insulation kits article walks through what works.

Frequently Asked Questions

If I add a DIY insulation kit, does my door now have an R-value?

Sort of. A foam-board retrofit kit adds insulation thickness behind your existing door panels, which raises the calculated R-value of the section. The combined R-value depends on the foam used and the install quality, and is generally in the R-8 to R-10 range. The kit will not match a factory-built sandwich polyurethane door, because retrofit kits do not bond to the steel face the way factory polyurethane does, and they do nothing for the perimeter seals or the panel joints. They are still worth it as a budget upgrade for an unheated attached garage, and we get into the trade-offs in our DIY insulation kits guide.

Does insulation make a garage door heavier?

Yes, but not dramatically. A 16-foot double sandwich polyurethane door at 1-3/4" weighs roughly 30 to 50 lb more than the equivalent single-skin polystyrene door. The springs are sized to match the door weight, so the door is balanced as installed and the opener does not work harder. The weight just means the door has more body when you handle it.

Will a higher R-value door soundproof my garage?

It will help, especially against high-frequency noise (lawn equipment, traffic). Foam insulation is moderately good at absorbing airborne sound. But the door is still a relatively thin, flexible barrier compared to the wall around it, so do not expect studio-grade isolation. The bigger sound benefits in most homes come from a quieter opener (belt-drive or jackshaft) and good weatherstripping.

Does R-value degrade over time?

Polystyrene foam is essentially permanent and does not lose R-value with age. Polyurethane foam can lose a small amount of R-value over the first few years as the blowing agents in the foam diffuse out and are replaced by air, a process called thermal drift. Modern polyurethane formulations are designed to minimize this, and the long-term aged R-value is what manufacturers typically publish. After the initial settling period, the R-value is stable for the life of the door.

What about the windows in my garage door, do they hurt the R-value?

Yes, but not as much as you might think. Modern garage-door window inserts use double-pane insulated glass, which is roughly R-2 per pane (R-4 to R-5 combined with the frame). A panel of windows is lower-R than the surrounding insulated steel, but the difference is small in proportion to the whole door. If the rest of the door is well insulated and well sealed, a band of windows across the top section costs you only a few percent of the door's average R-value. We go into the trade-offs in our windows guide.

Is R-value the same in Canada and the United States?

The R-value formula is the same on both sides of the border because the imperial units originate in ASHRAE's American Society of Heating, Refrigerating and Air-Conditioning Engineers standards, which are followed by both countries. You will sometimes see Canadian sources publish RSI values (the metric equivalent, R per square metre per watt). To convert, divide an imperial R-value by 5.68 to get RSI. For garage doors, North American manufacturers consistently use the imperial R-value scale.

How does R-value relate to my insulation in walls, attic, and basement?

For context, modern Ontario building code calls for roughly R-22 to R-24 in above-grade walls, R-50 to R-60 in attics, and R-12 to R-20 in basement walls, depending on the climate zone and home age. A garage door rated R-12 to R-16 is meaningfully lower than the surrounding wall (because of the seams and the construction), but it is in the ballpark of older insulation standards and is more than enough for an attached garage that does not need to be at room temperature. For deeper context, Natural Resources Canada's "Keeping the Heat In" guide is the authoritative reference for Canadian home insulation.

The Honest Summary

R-value is a useful starting point, not a final answer. Higher is better, all else equal, but all else is rarely equal. A door's real-world performance depends on the construction (sandwich vs. single-skin), the foam type (polyurethane vs. polystyrene), the thickness, the seal system, and the quality of the installation. The most reliable performance number is a verified U-factor from a DASMA-recognized lab, not a calculated R-value on a brochure.

For most southern Ontario homeowners with an attached garage, the practical answer is a sandwich-construction polyurethane door in the R-12 to R-16 range. For an actively heated garage or a finished space, step up to R-16 to R-18. Buying higher than that pays off only if the rest of the building envelope is at the same level, and the budget for a high-R-value door is usually better spent on tight weatherseals, a well-balanced spring system, and proper installation rather than chasing R-20-plus numbers.

If anything in the showroom does not add up (an R-value that seems too high for the construction, a U-factor that is not available, a seal system that is not specified), ask. A reputable dealer will be able to show you the data sheet for the model you are buying, including the verified U-factor if it is published. That five-minute conversation is what tells you whether the marketing matches the engineering.