R-value describes a door section. U-factor describes the whole door. R-value is the calculated thermal resistance of one section: the core, the steel skins and the thin layer of still air that clings to each face. U-factor comes from testing a complete assembly to ANSI/DASMA 105, with its section joints, thermal breaks and weather seals in place. The two are not interchangeable, and the second one tells you how the door will behave on your house.
DASMA, the association that writes the test standards, is blunt about it: door section R-values do not indicate the complete door's thermal performance, and you cannot take the inverse of a section R-value to get a whole-door U-factor. If a salesperson quotes only an R-value, ask what was tested.
R-value vs U-factor: what is the difference?
R-value is thermal resistance, and higher is better. U-factor is thermal transmittance, the rate heat moves through the whole assembly, and lower is better. For a single material the two are reciprocals. For a garage door they are not, because a door is not a single material.
A sectional door is steel skins, a core, thermal breaks between the skins, a row of section joints, a bottom seal and perimeter seals. Heat crosses all of it, and the joints and edges are where it crosses fastest. ANSI/DASMA 105 exists because a lab test of the assembled door is the only way to capture that.
So when a brochure says "R-18", it usually means the calculated value of the insulated section. That's not a lie. It's also not a whole-door rating, and a door with a lower section number and a real thermal break can outperform a higher one bolted into a crooked opening.
What R-value do I need for a garage door in BC?
Short answer: there is no published target to hit, and no single R-value that is right for every garage. Work from the garage, not the number. If it is attached, heated or under living space, the door is part of the building envelope, so buy the best sealed, thermal-broken assembly you can justify and ask for its U-factor. If it is detached and unheated, insulation is a comfort purchase.
Natural Resources Canada's guidance for an attached garage is that the walls, ceiling and door adjoining the house be insulated and air sealed, both to cut heat loss and to keep exhaust fumes out of the house. That is the standard worth designing to, and it's about the whole assembly and its seals, not one figure on a label.
| Door type | Typical advertised section R-value | What you are actually buying |
|---|---|---|
| Single-skin steel, uninsulated | None quoted | A metal sheet. No useful thermal resistance, loud in hail, and it sweats on the inner face in a heated garage. |
| Polystyrene core | Roughly R-6 to R-9 | The common mid-range door. Lighter and cheaper, reasonable on noise. |
| Polyurethane or polyisocyanurate core | Roughly R-12 to R-18 | Denser foam in a thicker section, usually with a better thermal break. Quieter as well. |
| Premium high-performance | Sometimes a whole-door U-factor | Thicker sections and real thermal breaks. Ask whether the U-factor came from ANSI/DASMA 105 testing. |
Those bands are typical market ranges, not measured facts about any particular door. Section thickness, foam density and the thermal break decide where a given door lands, and the number worth trusting is the one the manufacturer can document.
Does garage door insulation lower your heating bill?
Only if the garage is part of the heated envelope, or you heat it yourself. A door on a detached, unheated garage is not costing your house much heat, so insulating it will not show up on a gas bill. What changes is comfort, condensation and noise.
Attached garage, or a room above it: the door is a real part of the envelope, and insulation and air sealing both matter. NRCan is explicit that the walls, ceiling and door adjoining the house must be insulated and air sealed, to reduce heat loss and to stop garage fumes migrating inside.
Heated workshop: the door is usually the largest uninsulated surface in the room, so it is the first place to spend. Do not solve a cold garage by running a heating duct out from the house. NRCan calls that dangerous and a code violation, and it also pushes garage air back into the rooms you live in.
Be skeptical of any payback figure quoted without a blower door test or an energy assessment. A door upgrade is a comfort, condensation and noise decision first, and an energy decision second. Anyone who gives you a number of years is guessing at your house.
Why is an insulated garage door still cold?
Because the panel core was never the weak point. In this climate the losses are at the edges:
- The bottom seal. Cold air and water come in under the door, and a seal that freezes to the slab can tear away when the door lifts.
- Perimeter seals on the jambs and header, which harden and shrink with age.
- Section joints on a worn or twisted door. No amount of core insulation closes a gap between panels.
- The ceiling and walls, if the garage is a workspace. Insulating the door while the ceiling is bare puts the money in the wrong place.
A cheap door with good seals beats an expensive door in a crooked opening. That's not a slogan, it's how air moves. If the door stops short of the floor or sits unevenly, fix that first: a door that will not close flat is an open window with a lock on it.
Does a garage door insulation kit actually work?
Partly. A kit is foam board or batts cut to fit the inside of each section. On a dry, sound, uninsulated door it takes the edge off temperature swings and makes the garage noticeably quieter. It is a reasonable DIY job with a tape measure, a knife and an afternoon.
What it cannot do is create a thermal break between the steel skins, seal the section joints, replace a perished bottom seal, or turn an uninsulated door into a tested assembly. Expect the garage to feel better and the door to sound duller. Expecting the gas bill to move is where these kits disappoint people.
Two practical notes. Do not trap moisture against bare steel on a door that runs wet, and check the balance afterwards, because a kit adds weight across every section and the springs were sized for the door as built. If it no longer stays halfway up when you release it, it needs adjusting.
How much does garage door insulation cost?
We're not going to print a number here, because the honest range is wide enough to be useless. Garage door insulation cost comes down to a short list, roughly in order of impact: door size, single versus double; core material; windows and panel design; whether the old door and track come out; and whether the opening, springs or opener need work before a new door can hang straight.
A retrofit kit sits at the cheap end and a pro-installed insulated door at the expensive end. Ask for a quote that separates the door, the hardware, the removal and any opener or spring work, then compare like with like. Two quotes for "an insulated door" can differ by a lot because one includes new track and one does not.
Our Langley garage door cost guide covers what labour and parts run locally, and the quote you get from us is the price you approve before anything starts.
Seal it, insulate it, or replace it?
Three routes, in rising order of cost.
1. Air sealing only
New bottom seal, new perimeter seals, straighten what can be straightened, adjust the door so it sits flat. Cheapest option, and often the biggest single change in drafts and comfort. Sensible when the door is structurally sound. Our maintenance checklist covers the seal checks worth doing each season.
2. An insulation kit on the existing door
Cheap, DIY-friendly and honest about its limits, as above. Fine as a stopgap on a sound door you are not replacing yet.
3. A new insulated door
The only route that gives you a tested assembly: core, thermal break, sealed joints, new perimeter seals, and a door that closes flat. It also buys quiet operation and, on a tired door, the curb appeal that counts at resale. Residential door installation covers what that involves.
If the door is straight and the hardware is sound, route 1 or 2 is usually the sensible spend. If it is dented, rusting along the bottom or 25 years old, a new door starts to make sense. Our guide to repairing versus replacing covers where that line falls.
What should you ask before buying an insulated door?
- "Is that R-value a section calculation or a whole-door test?" Then ask for the U-factor.
- "Was the U-factor tested to ANSI/DASMA 105?" A number without a test method is marketing.
- "What is the section thickness and the core material?" Polystyrene and polyurethane are not equivalent at the same thickness.
- "Does this door have a thermal break?" Without one, the steel skins conduct heat straight past the foam.
- "Which seals are included, and are they new?"
- "Will it sit flat in my opening?" A high-performance door in an out-of-square opening still leaks.
An installer who cannot answer the first two is selling a number, not a door.
Will insulation help with condensation and noise?
Noise, usually yes. A polyurethane-core door with good seals is noticeably quieter than single-skin steel, and a belt-drive opener on new rollers removes most of what is left of the mechanical noise.
Condensation is more conditional. A warmer inner surface stays above the dew point more often, so the door sweats less. But if the garage is sealed and heated without ventilation, moisture off a wet car has nowhere to go. Insulation is not ventilation, and neither one fixes a wet slab.
When is insulation not worth it?
- The door is structurally failing. The money belongs in a new door, not a kit.
- The garage is detached, unheated and used for storage.
- The ceiling and walls are bare and staying that way.
- The door does not close flat. You would be insulating a hole.
We install and service doors across Langley, Surrey and the rest of the Lower Mainland, and we'll tell you when the honest answer is a new bottom seal rather than a new door. Call 604-388-9868 or send a photo of the inside of the door and the opening, and we'll tell you which of the three routes fits what you have.
Sources and standards
- DASMA Technical Data Sheet 163 — U-factor and R-value for residential and commercial garage doors — why section R-values are calculated and whole-door U-factors are tested to ANSI/DASMA 105
- DASMA — the difference between R-value and U-factor — codes and standards base door thermal performance on the U-factor of the entire assembly
- Natural Resources Canada — Keeping the Heat In, Section 7 — insulating and air sealing the walls, ceiling and door adjoining a garage