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ARMORTHANE PROTECTING YOUR WORLD

PROTECTING YOUR WORLD

ARMORTHANE PROTECTING YOUR WORLD

Garage Door Insulation:
Kits, R-Values &
When to Replace

What a retrofit kit really adds, how to read a door’s R-value honestly, when a new insulated door is the better buy, and two calculators for kits and heat loss.
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Tell us the garage size, what is above and beside it, and how you use it. We will connect you with a certified applicator for the walls, ceiling and rim joist.

  • Garage size and door count
  • Attached, detached or room above
  • Heated, cooled or unconditioned
  • What insulation is there now
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Step 1 of 3
R-0.85
Calculated R-value of a bare single-layer steel door: just the two air films
DASMA TDS-163
R-8
Rating of a common fiberglass retrofit kit, 2.25 in. thick, for one door up to 9 ft wide
Owens Corning kit data
R-18.4
Top published rating for a 3-layer polyurethane-filled steel door
Clopay Classic Steel
$1,500
National average to buy and install a new insulated garage door
Angi, 2026 data

Garage door insulation is one of the cheapest garage upgrades there is, and one of the most oversold. A bare steel door is a sheet of metal with an air film on each side, so almost anything you add is a big gain. But the door is one surface, it hangs on springs balanced to its weight, and it leaks air at all four edges. We insulate garages and shops with spray foam every day; this guide covers the door itself: what a kit gets you, how to read a door's R-value, when a new door is the better buy, and two calculators.

Quick answer

For an attached or heated garage with an uninsulated single-layer steel door, a fiberglass or foam-board kit is worth it: it lifts the middle of each panel from about R-0.85 to roughly R-5 to R-9 for well under $200 per single door in materials. Replace the bottom seal and side stops at the same time, because air leaks around the edges often matter as much as the panels. If the door is dented, warped, or you want R-12 or more, buy a factory insulated door instead. Never spray foam onto a sectional door; the added weight throws off the springs and the foam cracks at the joints.

What's in this guide
  1. 1Is garage door insulation worth it?
  2. 2Garage door insulation options compared
  3. 3Garage door R-value vs U-factor
  4. 4Kit estimator
  5. 5Heated garage heat-loss calculator
  6. 6How to install a garage door insulation kit
  7. 7Kit or new insulated door?
  8. 8FAQ
Start here

Is garage door insulation worth it?

It depends on what is on the other side of the garage walls and on how you use the space. A standard double door is 16 by 7 feet, or 112 square feet. When that surface is bare steel, it is the weakest part of the garage envelope by a wide margin.

Worth it

Attached garage, room above

The garage is a buffer between the house and outdoors. Warming it a few degrees helps the shared wall and any bedroom floor above. Insulate the door, but put the real effort into the shared wall, the ceiling and the floor of the room above.

Worth it

Heated or cooled shop

If you run a heater or mini-split in the garage, the door is losing energy you pay for every hour. This is where the payback math below is real money.

Skip it, or do it last

Detached, unheated, open walls

If the walls and ceiling are bare studs and nobody heats the space, insulating only the door changes very little. Do the ceiling and walls first.

An insulated door is also quieter and rattles less in wind. In hot climates a reflective face cuts radiant heat from a sun-baked door, but only with an air space in front of the foil. The Department of Energy credits attic radiant barriers with 5 to 10 percent cooling savings in warm, sunny climates; a door is a far smaller surface, so expect comfort, not a visible line on your power bill.

Contractor tipClose the door on a sunny afternoon and turn the lights off. Every strip of daylight around the edges and under the bottom seal is an air leak. Fix those first; weatherstripping is the cheapest part of the job.
Materials

Garage door insulation options compared

Three ways to add insulation to an existing door, and two kinds of factory insulated door. R-values are center-of-panel figures calculated the door industry's way (insulation plus 0.85 for the air films), so they are the best case. Click a heading to sort.

OptionCenter-of-panel R-valueThicknessWeight addedWorks onOur take
Bare single-layer steel (baseline)R-0.85Skin onlyNonen/aCommon on older and budget doors
Fiberglass batt kit, vinyl faced (e.g. Owens Corning R-8 kit)About R-8.9 (R-8 + films)2.25 in.LightPan doors with a 2 in. or deeper frameBest R per dollar for a retrofit; held by clips pushed through the batt
Rigid foam board kit (EPS, foil or vinyl faced)About R-4.5 to R-8.41 to 1.5 in.LightPan doors; cut to fit between stilesTidy, rigid, easy to wipe down; a little lower R than fiberglass
Reflective bubble / foil kitR-4 claimed (needs an air space)Thin, under 1/2 in.Very lightAny door, including flat-back doorsMostly a hot-climate radiant product; little help in a cold garage
Factory polystyrene door (2-layer, steel + EPS)About R-5.5 to R-7.5 (varies by model)1-5/16 in. foam10 to 15 lb more than non-insulatedNew doorEntry-level insulated door; check the tested U-factor
Factory polyurethane door (3-layer steel sandwich)Up to R-18.4About 1-3/8 to 2 in.25 to 40 lb more than non-insulatedNew doorThe real upgrade for a heated shop: stiffer, quieter, best seal at the joints
Spray foam on the doorNot recommendedVariesHeavy, unevenNoneUnbalances the springs, cracks at section joints, can void the door warranty
Sources: DASMA TDS-163 (air films 0.68 + 0.17); Owens Corning garage door kit data; Bob Vila kit testing (reflective kit R-4); HomeGuide (rigid foam R-3.6 to R-5.0 per inch); Clopay Classic Steel data; Garage Door Handbook weight chart. Foam-board and polystyrene-door R ranges are our calculation from those per-inch figures using the DASMA method.

Fiberglass vs foam board vs reflective: which kit?

On a typical steel pan door (hollow back, 2 inch frame around each panel), fiberglass gives the most R-value for the money. Foam board is cleaner and stiffer, the better pick in a workshop where batts get snagged. Reflective bubble is weakest in winter. In Bob Vila's testing every kit read 8 to 10 degrees warmer on the inside face an hour after installation, which says more about how bad a bare panel is than about the kits. On a flat-back door, foam board is the only practical option; use an adhesive rated for foam, since solvent-based glues eat EPS.

Reading the label

Garage door R-value vs U-factor

Garage door R-values are not measured like wall insulation, and that trips up buyers. DASMA, the door industry's trade group, sets the method in Technical Data Sheet 163: the insulation in one section plus a fixed 0.85 for the air films (0.68 still air inside, 0.17 for a 15 mph wind outside). Steel skins count as zero. DASMA's worked example uses polyurethane with a k-factor of 0.12, about R-8.3 per inch, and gets R-16.47 for one section. That is how brochures reach the teens.

What DASMA says itselfThe section method ignores joints, stiles, hardware and perimeter seals, and DASMA says it should not describe a whole door. The whole-door number is the U-factor from ANSI/DASMA 105 testing, the method the International Energy Conservation Code names for garage doors. Lower is better: a U-0.20 door is twice as efficient as a U-0.40 door, and the U-factor is not simply 1 divided by the brochure R-value.

Compare new doors by tested U-factor. With a kit, the R-8 on the box describes the batt, not the door; the seams and the gaps at jambs and floor stay as leaky as before unless you fix them.

Calculator 1

Garage door insulation kit estimator

Enter your door size and pick a kit type to get the area, what to buy, the resulting center-of-panel R-value and how much heat flow you cut.

Estimator

What will it take to insulate my door?

Fiberglass kits are figured at 65.75 sq ft each (eight 22 x 54 in. panels) at a $128.47 list price; foam board as 4 x 8 sheets with 15% cutting waste; R-values by the DASMA section method.

16 for a double, 8 or 9 for a single
7 is standard
Same size
—
Area to cover
—
What to buy
—
Material cost
—
Center-of-panel R after

Calculator 2

Heated garage heat-loss and payback

If you heat the garage, this tells you whether the door is worth the money, using the standard degree-day method. Energy prices default to recent U.S. averages from the Energy Information Administration; change them to match your bill.

Heat loss

What does my garage door cost me to heat?

Annual heat loss = area x 24 x HDD / R. Upgrade costs use Angi 2026 ranges for new doors plus $300 to $500 install, or the fiberglass kit list price. Assumes the garage is held near 65°F.

Base 65°F; chips fill this
EIA, Feb. 2026
EIA, Mar. 2026
EIA, July 2026
—
Door heat loss now, per year
—
Yearly saving, best case
—
Upgrade cost
—
Simple payback

Treat the saving as an upper bound: the math uses center-of-panel R-values and covers conduction only. Air leaking past a worn bottom seal and loose side stops is not included, and on an older door it can matter as much as the panels.

Step by step

How to install a garage door insulation kit

The most common fiberglass kit is rated at under an hour per door; budget longer if you also replace seals. Our order of work:

  1. Check the balance before you start

    Pull the emergency release, lift the door by hand to waist height and let go. A balanced door stays put. If it drops or rises, have a garage door technician adjust the springs before you add weight; torsion springs can injure you badly.

  2. Fix the air leaks

    Replace a flattened bottom seal (match your retainer profile) and set the side and top stops so they lightly touch the closed door. Often the most noticeable improvement.

  3. Clean and measure each panel

    Degrease each pan so clips stick. Measure every panel; end panels are often narrower.

  4. Cut and fit

    Cut about 1/4 inch oversize so pieces press into the frame. Keep clear of hinges, rollers, struts, the lock bar and the opener bracket.

  5. Fasten

    Fiberglass kits use two-piece clips pushed through the batt. Foam board friction-fits or takes foam-safe adhesive. Reflective kits need their specified air space.

  6. Re-check the balance and the opener

    Repeat the halfway test, then run the safety-reverse test in your opener manual.

Do not do thisDo not spray foam the back of a sectional door. It adds uneven weight and cracks where sections hinge. A factory polyurethane door weighs 25 to 40 pounds more than the same door uninsulated and ships with springs sized for it; yours were sized for the door you have.

Fire and foam inside a garage

Exposed foam plastic is a fire question. The International Residential Code generally requires foam plastic to be separated from the interior by a thermal barrier such as 1/2 inch gypsum board (IRC R316.4) unless an exception applies. Factory doors are tested as complete products; if you add foam board yourself, use a faced kit sold for garage doors and ask your building official on a permitted remodel. Vinyl-faced fiberglass kits avoid most of the question.

Decision

Kit or new insulated garage door?

Angi's 2026 data puts a new insulated door at $1,500 on average, most jobs $1,100 to $4,200. Polystyrene doors run $400 to $1,100 and polyurethane $700 to $1,600 or more, plus $300 to $500 labor. A fiberglass kit for a double door is about $260.

Kit

Door is sound, garage is a buffer

Sound steel pan door, attached unheated garage, and you want it a few degrees warmer. A kit plus new seals is the best value.

New door

Heated shop or living space

You heat the garage most of the year or there is a bedroom over it. A polyurethane door seals better at the section joints, which a kit cannot fix.

New door

Door is dented, rusted or racked

Insulating a door near the end of its life is money spent twice. Sections that no longer close tight leak regardless.

Neither yet

Walls and ceiling are bare

Insulate and air-seal walls and ceiling first. The door is one surface of six.

Where spray foam does belong in a garage

We make spray foam, and we would not put it on a moving door. We put it where the garage leaks most and nothing moves: the wall shared with the house, the rim joist, the ceiling under a bonus room and the walls of a heated shop. Closed-cell foam air-seals and insulates in one pass. Our garage insulation guide walks through each surface and the code requirements, and our rim joist insulation page covers a leak that is easy to miss in any garage that adjoins the house. For material choices see closed-cell spray foam and the spray foam R-value guide, and for budgets see spray foam insulation cost.

Bedroom over the garage? Our floor insulation guide covers floors over garages and crawl spaces. Building a shop with living space? See barndominium insulation. The rest of this series covers roof insulation and basement ceiling insulation.

Garage and shop insulation

Door done? Seal the rest of the garage properly.

A certified ArmorThane applicator can spray-foam the walls, ceiling and rim joist of your garage or shop, so the insulated door is not the only thing keeping the heat in.

Get a free quoteFind an applicator

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FAQ

Garage door insulation questions

What is the best insulation for a garage door?

On an existing steel pan door, a vinyl-faced fiberglass kit: about R-8 in 2.25 inches. Foam board is close behind and tougher in a workshop. For a new door, a polyurethane-filled steel door, rated up to R-18.4.

How much does it cost to insulate a garage door?

A fiberglass kit for one door up to 9 feet wide lists for about $128, so a double door is about $260. Angi's broader range for insulating an existing door is $300 to $1,500. A new insulated door averages $1,500 installed.

Does insulating a garage door make a difference in winter?

For the door surface, yes: in Bob Vila's testing, insulated panels read 8 to 10 degrees warmer on the inside face. How much warmer the garage gets depends on the walls, ceiling and air leaks.

Will insulation make my garage door too heavy?

Fiberglass and foam-board kits are light, and most balanced doors handle them. Do the halfway balance test before and after. Never add spray foam, wood or drywall to a door.

What R-value should a garage door have?

For an unheated attached garage, the energy code does not set one, because the garage is outside the home's insulated envelope; the code looks at the wall, ceiling and door between garage and house. For a heated shop, we suggest a new door in the R-12 to R-18 range or an R-8 kit on an existing door, and compare new doors by tested U-factor.

Can I spray foam my garage door?

We would not, and we sell spray foam. It adds uneven weight, cracks at the section joints and leaves exposed foam plastic. Spray foam belongs on the walls, ceiling and rim joist.

Is a reflective garage door insulation kit worth it?

In a hot climate with a sun-facing door, it can help summer comfort if there is an air space in front of the foil. The Department of Energy notes that in cool climates conventional insulation is usually the better buy.

Polystyrene or polyurethane garage door: which is better?

Polyurethane. It is foamed in place between two steel skins, bonds to them, stiffens the door and has roughly twice the R-value per inch of polystyrene. It costs more: $700 to $1,600 or more versus $400 to $1,100 in Angi's 2026 figures.

AT
Written by the ArmorThane technical team. We have manufactured polyurea, polyurethane and polyaspartic coatings and spray foam insulation in Springfield, Missouri since 1989. We do not make garage doors or door insulation kits; brand names are used for reference only. Spring and opener adjustments should be done by a qualified garage door technician. Updated October 2026.

Sources

  1. DASMA Technical Data Sheet 163, garage door section R-value calculation: dasma.com/…/TDS163.pdf
  2. DASMA Technical Data Sheet 196, U-factor on garage doors and the IECC: dasma.com/…/TDS-196.pdf
  3. Owens Corning garage door insulation kit: owenscorning.com/…/garage-door-insulation-kit
  4. IDI Distributors, Owens Corning R-8 kit specifications and list price: idi-insulation.com/oc-garage-door-insul-kit-22x54x2-25-r-8
  5. Clopay Classic Steel insulation options: clopaydoor.com/classic
  6. Clopay Classic Steel 16 x 7 R-12.9 door listing: homedepot.com/…/204598364
  7. Angi, insulated garage door cost (2026): angi.com/articles/insulated-garage-door-cost.htm
  8. Angi, cost to insulate a garage (2026): angi.com/articles/cost-to-insulate-garage.htm
  9. Bob Vila, garage door insulation kits tested: bobvila.com/articles/best-garage-door-insulation-kit
  10. Garage Door Handbook, door weight by size and insulation: garagedoorhandbook.com/…/garage-door-weight-chart
  11. HomeGuide, insulation R-value per inch by material: homeguide.com/costs/basement-insulation-cost
  12. U.S. Department of Energy, radiant barriers: energy.gov/energysaver/radiant-barriers
  13. U.S. EIA, residential natural gas prices: eia.gov/dnav/ng/ng_pri_sum_dcu_nus_m.htm
  14. U.S. EIA, Electricity Monthly Update, retail prices: eia.gov/electricity/monthly/update/end-use.php
  15. U.S. EIA, heating oil and propane update: eia.gov/petroleum/heatingoilpropane
  16. U.S. EIA, British thermal units and fuel heat content: eia.gov/energyexplained/units-and-calculators/british-thermal-units.php
  17. ICC, 2021 International Residential Code, Chapter 3 (R316 foam plastic): codes.iccsafe.org/content/IRC2021P2/chapter-3-building-planning

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