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ARMORTHANE PROTECTING YOUR WORLD

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ARMORTHANE PROTECTING YOUR WORLD

Aluminum Roof Coating:
Heat Numbers, Coverage
& Where It Fits

What aluminum roof coatings are made of, how they compare with white coatings on real reflectance and emittance data, how much you need, and when to put it on.
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0.63
Initial solar reflectance of a fibered aluminum coating, 0.55 after 3 years
Karnak 97 data (CRRC)
0.46
Thermal emittance of that coating, about half of a white acrylic's 0.90
Karnak 97 and 529 data
90 days
New asphalt roofs should weather before an aluminum coat goes on
Karnak data sheets
1–1.5 gal
Per 100 sq ft for a fibered aluminum coating (16–24 wet mils)
Karnak 97 data

Aluminum roof coating is the silver paint you see on old flat roofs, mobile homes and farm buildings: asphalt loaded with aluminum flake, brushed or sprayed over built-up roofing, modified bitumen and metal. It is cheap, it protects asphalt from sun, and it reflects a good share of solar heat. What most product labels skip is that aluminum has low thermal emittance, so it does not shed absorbed heat as well as a white coating, and an aluminum roof coating runs noticeably hotter than its reflectance number suggests. We spray polyurea for a living and our ArmorSeal roofing liner is itself aluminized, so we like aluminum for the right job. This guide explains what aluminum roof coatings are, how they compare with white coatings on real heat numbers, where they work, and how much you need.

Quick answer

Aluminum roof coating is an asphalt-based coating pigmented with aluminum flake (ASTM D2824). It is best for protecting and adding reflectivity to built-up, modified bitumen, roll roofing and metal roofs that drain well. A fibered product goes on at about 1 to 1.5 gallons per 100 sq ft, a non-fibered one at 0.5 to 1. Apply at 50°F to 120°F, keep moisture off it for 24 to 48 hours, and let new asphalt weather 90 days first. It reflects well (about 0.63 initially), but its low emittance means it stays hotter than a white acrylic or silicone, so choose white when cooling a conditioned building is the main goal.

What's in this guide
  1. 1What aluminum roof coating is
  2. 2Aluminum vs. white: the heat math
  3. 3Roof surface temperature tool
  4. 4Reflectance and emittance compared
  5. 5Where aluminum coating fits
  6. 6Coverage and timing calculator
  7. 7How to apply it
  8. 8FAQ
The basics

What aluminum roof coating is made of

A traditional aluminum roof coating is asphalt cut with solvent, loaded with aluminum paste, and often reinforced with fibers. Brushed or sprayed out, the flat aluminum flakes float to the surface and overlap like fish scales, giving the bright silver face that reflects sunlight and shields the asphalt underneath from UV. ASTM D2824 is the standard for these aluminum-pigmented asphalt roof coatings and defines three types:

  • Type I, non-fibered. Thinner, smoother and sprayable. Karnak's 169 is an example, applied at 0.5 to 1 gallon per 100 sq ft (8 to 16 wet mils) on modified bitumen, smooth BUR, corrugated metal and steep asphalt roofs.
  • Type II, fibered with asbestos. A historical category. If you are scraping an old silver roof, have it tested before you disturb it.
  • Type III, fibered without asbestos. Today's fibered products, such as Karnak 97, applied at 1 to 1.5 gallons per 100 sq ft (16 to 24 wet mils). The fibers build film and bridge fine cracks.

Two newer variations are common at the store. Water-based versions, like Henry's 558 Aqua-Brite, suspend aluminum flake in emulsified asphalt instead of solvent. Rubberized versions, like Henry's 869, add SBS rubber polymers for flexibility. Solvent-based products carry real VOCs (Karnak 97 lists 450 g/L maximum), so check your local air rules before you buy.

Not the same thingAn aluminized polyurea like our ArmorSeal 100 AL uses aluminum for reflectivity too, but it is a 100% solids, spray-applied waterproofing membrane, not an asphalt maintenance coat. Different job, different price.
Heat

Aluminum roof coating vs. white: the heat math

Two numbers decide how hot a roof gets in the sun. Solar reflectance is the share of sunlight bounced away. Thermal emittance is how well the surface radiates away the heat it does absorb. Bright metals are the classic case of high reflectance and low emittance.

The Cool Roof Rating Council data published for Karnak's products makes the trade-off concrete. Their fibered aluminum coating starts at 0.63 reflectance and 0.46 emittance, for a Solar Reflectance Index (SRI) of 62. Their white acrylic starts at 0.85 reflectance and 0.90 emittance, for an SRI of 107. After three years the aluminum sits at SRI 52 and the white at 90. Both beat a dark roof by a wide margin, since most dark roofing reflects only 5 to 20 percent of sunlight, but white wins by a clear step.

That gap matters most on air-conditioned buildings in hot climates. The Department of Energy notes that conventional roofs can reach 150°F or more on a sunny afternoon and that reflective roofs can run more than 50°F cooler. On an unconditioned barn or a roof you mainly want to protect from UV, aluminum's lower price and asphalt compatibility may count for more. Our cool roof coating guide covers the energy side in more depth.

Tool

Roof surface temperature tool

This tool solves the same heat balance used in ASTM E1980, the standard behind the Solar Reflectance Index: full sun at 1,000 W/m², 98°F air, and a 80°F effective sky. Pick a coating or type in your own product's CRRC values. With medium wind it reproduces the published SRIs for the products listed (62 for the aluminum, 107 for the white acrylic), which is a good check that the math is right.

Heat balance

How hot will this roof surface get?

Solves absorbed sun = emitted radiation + convection: (1 − R) x 1000 = e x σ x (T⁴ − 300⁴) + h x (T − 310), with h = 5, 12 or 30 W/m²K for low, medium and high wind (ASTM E1980 conditions). SRI = 100 x (T black − T) / (T black − T white).

Used when Custom is selected
Dark roofs: 0.05–0.20
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Coated surface temp
—
Current roof temp
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Cooler by
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Calculated SRI

Side by side

Aluminum roof coating vs. other reflective surfaces

Click a heading to sort. Values are rated or published numbers for the specific products named, so use them as representative, not universal.

SurfaceReflectance, newReflectance, 3 yrEmittance, newSRI, newSRI, 3 yrBase
Fibered aluminum (Karnak 97)0.630.550.466252Solvent asphalt
White acrylic (Karnak 529)0.850.730.9010790Water-based acrylic
White silicone (Karnak 670HS)0.870.70Not listedNot listedNot listedHigh-solids silicone
Bare Zincalume steel0.75Not listed0.0568Not listedMetal, uncoated
Typical dark roofing0.05–0.20SimilarHighNear 0Near 0Asphalt, dark membranes
Sources: Karnak 97, 529 and 670HS product data (CRRC-rated values); bare Zincalume from LBNL data via The Roofing Brief; dark roofing range from The Roofing Brief. "Not listed" means the source did not publish that value (sorted as 0).
Fit

Where aluminum roof coating fits, and where it does not

Good fit

Smooth BUR and modified bitumen

The classic use. Aluminum protects the asphalt from UV and oxidation, and fibered Type III products carry UL Class A ratings over specified modified bitumen systems. See our asphalt roof coating guide for the black-coat alternatives.

Good fit

Metal roofs that drain

Non-fibered aluminum is listed for corrugated metal. For rust prep and when paint is the better choice, see our metal roof paint guide.

Good fit

Roll roofing and outbuildings

Barns, sheds and garages with roll roofing, where you want UV protection and some heat relief at low cost, and nobody is cooling the space.

Think twice

Air-conditioned buildings in hot climates

A white elastomeric with high emittance usually runs cooler. Compare our acrylic roof coating and silicone roof coating guides.

Think twice

Mobile homes and RVs

Many older mobile homes wear aluminum coating. RV roofs are usually EPDM, TPO or fiberglass and need products made for them; see mobile home roof coating and RV roof coatings.

Wrong product

Ponding roofs, shingles, active leaks

Data sheets require no standing water 48 hours after rain. Aluminum is a maintenance coat, not a membrane; it will not fix leaks or survive ponds. Shingles are a separate question entirely.

Calculator

Aluminum roof coating coverage and timing calculator

Aluminum coatings are often bought by the pail and applied by the owner, and two things go wrong: buying too little, and coating new asphalt too soon. This calculator handles both.

Coverage

How much aluminum coating, and when can it go on?

Rates from Karnak data: fibered 1–1.5 gal per 100 sq ft, non-fibered 0.5–1. Smooth surfaces use the low end, rough or weathered the high end. New asphalt waits 90 days; a primer coat on weathered asphalt needs 3–5 days to cure. Adds 10% for waste.

Metal roof? Enter 999
Enter your supplier's price
Options
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Gallons needed
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5-gallon pails
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Material cost
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Earliest topcoat

Past the maintenance-coat stage?

Seal it for good with an aluminized polyurea membrane.

When a flat or metal roof leaks, blisters or ponds, certified ArmorThane applicators spray a seamless, 100% solids membrane that reflects heat and stops water. Ask for a site visit and an honest opinion on whether you need it.

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Process

How to apply aluminum roof coating the right way

  1. Check timing and weather

    New BUR and asphalt roofs should weather at least 90 days so oils can leave the surface. Apply between 50°F and 120°F, and plan for no moisture on the coating for 24 to 48 hours. If water stands on the roof 48 hours after rain, fix the drainage first.

  2. Make repairs first

    Cut and patch blisters, reseal splits and flashings with roof cement and fabric, and let repairs cure. Aluminum coating covers repairs; it does not make them.

  3. Clean and prime old asphalt

    Sweep or wash off dirt and loose granules. Badly weathered, dry asphalt drinks coating; Karnak recommends priming it with an asphalt emulsion and letting that cure 3 to 5 days before the aluminum coat.

  4. Mix thoroughly

    Aluminum paste settles to the bottom of the pail. Box the pails or mix with a drill paddle until the color is uniform, or you will put plain asphalt on half the roof and silver on the rest.

  5. Apply at the full rate in one direction

    Brush or spray at the data sheet rate, finishing strokes in one direction so the flakes lie flat and leaf to the surface. Overworking dulls the finish and lowers reflectance.

  6. Inspect and recoat on schedule

    As the silver dulls and asphalt shows through, reflectance falls (the Karnak product drops from 0.63 to 0.55 in three years). Clean and recoat before the asphalt starts to craze.

SafetySolvent-based aluminum coatings are flammable and give off vapors; keep ignition sources away and follow the SDS. OSHA requires fall protection for roofing work 6 feet or more above a lower level.
FAQ

Aluminum roof coating questions

Is aluminum roof coating better than white roof coating?

For cooling, usually not. A white acrylic like Karnak 529 rates SRI 107 new and 90 after three years, while a fibered aluminum rates 62 and 52, mainly because aluminum has low thermal emittance. Aluminum is cheaper and very compatible with asphalt roofs, so it is a good choice for protecting BUR, modified bitumen and roll roofing on buildings that are not air-conditioned.

How long does aluminum roof coating last?

It depends on thickness, sun exposure and drainage. Treat it as a maintenance coat: inspect yearly and recoat when the silver dulls and asphalt shows through, before the roof surface starts to crack. Reflectance drops over time; one rated product goes from 0.63 to 0.55 in three years.

What is the difference between fibered and non-fibered aluminum roof coating?

Fibered coatings (ASTM D2824 Type III) contain non-asbestos fibers, build a thicker film at 1 to 1.5 gallons per 100 sq ft and bridge small cracks. Non-fibered coatings (Type I) go on thinner at 0.5 to 1 gallon per 100 sq ft, spray easily and suit smoother surfaces and metal.

Can you put aluminum roof coating on a metal roof?

Yes, non-fibered aluminum coatings are listed for corrugated metal roofs. Clean the metal, treat any rust and make sure the roof drains. If the roof leaks at seams or fasteners, it needs repairs and a real coating system first.

How soon can I coat a new asphalt roof with aluminum?

Manufacturers such as Karnak call for new asphalt roofs to weather at least 90 days before coating. If you primed with an asphalt emulsion, allow 3 to 5 days for it to cure before the aluminum coat.

How much aluminum roof coating do I need?

Plan on 1 to 1.5 gallons per 100 sq ft for fibered products and 0.5 to 1 gallon for non-fibered, using the high end on rough or weathered roofs, plus about 10% for waste. A 1,500 sq ft rough roof with a fibered coating at 1.5 gallons per 100 sq ft takes about 25 gallons with waste, or five 5-gallon pails.

Does aluminum roof coating stop leaks?

No. It is a protective, reflective maintenance coat. Leaks need repairs at the source, and a roof with widespread leaks or ponding needs a membrane system. For a price comparison across coating types, see our roof coating cost guide.

Is old aluminum roof coating dangerous to remove?

Possibly. ASTM D2824 still lists a fibered-with-asbestos type, a holdover from older products. If you plan to scrape or grind an old silver roof, have a sample tested for asbestos first.

AT
Written by the ArmorThane technical team. We have manufactured polyurea, polyurethane and polyaspartic coatings in Springfield, Missouri since 1989, including the aluminized ArmorSeal 100 AL roofing liner, and support certified applicators across North America. For a full overview of roof systems, see our roof coating guide. Updated October 2026.

Sources

  1. ASTM D2824, aluminum-pigmented asphalt roof coatings: store.astm.org/d2824_d2824m-18.html
  2. Karnak, 97 fibered aluminum roof coating (CRRC values, coverage, weathering): karnakcorp.com/product/97-fibered-aluminum-roof-coating
  3. Karnak, 169 non-fibered aluminum roof coating: karnakcorp.com/product/169-non-fibered-aluminum-roof-coating
  4. Karnak, 529 Renu-White acrylic (CRRC values): karnakcorp.com/product/529-renu-white
  5. Karnak, 670HS silicone (reflectance): karnakcorp.com/product/670hs
  6. Henry, aluminum roof coatings (555, 558 Aqua-Brite, 869): henry.com aluminum roof coatings
  7. The Roofing Brief, solar reflectance and SRI reference (2026, citing LBNL): theroofingbrief.com/roofing-solar-reflectance-sri-reference-2026
  8. U.S. Department of Energy, cool roofs: energy.gov/energysaver/cool-roofs
  9. OSHA 29 CFR 1926.501, fall protection: osha.gov 1926.501

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