Photograph of  really worn out asphalt roof shingles Asphalt Roll Roofing Installation, Defects, Repairs

  • ROLL ROOFING, ASPHALT - CONTENTS: Asphalt based roll roofing installation, inspection, leaks, life expectancy. Definition of roll roofing materials, specifications, standards, applications. How and where should mineral granule coated roll roofing be used on buildings? What is the life expectancy of roll roofing
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Roll roofing installation, inspection, troubleshooting, repairs:

This article describes mineral-granule coated asphalt roll roofing roofing materials, choices, installations, inspection, defects, roofing repairs, and product sources. Our page top photo shows our client pointing to a low slope area on a roof where mineral-granule coated asphalt roll roofing was applied after shingles in that location had leaked repeatedly. This article includes a description of severe wear and early failure of a mineral-granule-surfaced roll roofing installation over an older metal roof.

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Asphalt Roll Roofing Materials, Choices, Costs, Life Expectancy, Characteristics

Roll roofing material (C) Daniel Friedman

As stated in Best Practices Guide to Residential Construction, chapter on BEST ROOFING PRACTICES:

Roll roofing is simplest product to install on a small section of low slope roof is 90-pound roll roofing.

This consists of a heavy, asphalt-saturated organic or fiberglass felt with a granular surface. Rolls are 36 inches wide and weigh 90 pounds. Single-coverage roll roofing typically has a 2-inch lap with exposed nails and is used mainly on utility structures.

Double-coverage roll roofing is installed with a full 19-inch lap joint, leaving a 17-inch exposure, with a 2-inch head-lap.

Nails are concealed under the lap joints that are sealed with asphalt lap cement. With two layers of protection, double-coverage roll roofing is acceptable for small roof areas and can be used on roofs as shallow as 1:12.

-- Adapted with permission from Best Practices Guide to Residential Construction.

In its earliest forms roll roofing consisted of sheets of felt canvas or cloth that were impregnated with asphalt, then rolled flat along a low-slope or even some steeper sloped roofs with the material's long edge parallel to the building eaves.

Modern 90-pound asphalt roll roofing is built of mineral-coated fiberglass-reinforced mat or organic-mat (bituminous impregnated paper) material very similar to asphalt roof shingles, in 36-inch wide material sold in 36-foot long rolls. Roll roofing is coated on both sides with asphalt and its upper or exposed side is protected with mineral granules.

Common roll roofing material colors are white, brown, black. You may find some roofers referring to roll roofing as "90-pound felt" since a 36-foot roll of the material, able to cover about 100 sq. ft. (one roofing "square") weighs close to ninety pounds.

Tips For Buying Roll Roofing Materials

Our roll roofing material photo (left) shows that this roll was a bit out of round. When buying roll roofing avoid rolls that are squashed as they may be difficult to roll out smoothly (give the material time to relax and flatten before nailing).

Also avoid rolls whose ends are badly damaged as it may make for uneven or raised seams.

This is an inexpensive roofing material often installed (over 15# felt underlayment) by homeowners and do-it-yourself-ers.

Installing Roll Roofing for Maximum Life

Roll Roofing Problems (C) Carson Dunlop Associates

Nonetheless roll roofing installations will have a longer life if installed according to the product manufacturer's instructions, nailed at proper intervals, and with seams properly sealed.

It's also important to install roll roofing over a smooth sound roof deck. If the roof decking sags, ponding on the roof surface after rain may reduce its life.

Overlapping strips of asphalt roll roofing are installed over the roof surfaces with overlapped edge joints sealed, usually with a heated asphalt compound, or cold-applied using a similar sealant that functions at lower temperatures.

Sketch courtesy of Carson Dunlop Associates.

Probably in part because asphalt roll roofing is typically used on low slope and nearly flat roofs, it can have an anticipated wear life of less than ten years, often five years.

The life of roll roofing may be extended by coatings.

Common Problems on Roll-Roofing Covered Roofs

Roll Roofing Problems (C) Carson Dunlop Associates

As Carson Dunlop Associates' sketch (at left) illustrates,

Not quite so common, but we also see misapplications of roll roofing such as:

Watch out: Because mineral-granule-coated modified bitumen roofing can be mistaken for roll roofing, and vice versa, readers should also see MODIFIED BITUMEN ROOFING. These products look a lot alike but their properties and installation procedures are different from one another.

Early Roll Roofing Failure When Installed Over Existing Metal Roof

Cracked worn out roll roofing installed over a metal roof (C)

Reader comment: details of failure conditions on a ten-year-old roll roofing installation over metal

Here is a good picture of severely degraded mineral surfaced roll roofing. It was mistakenly and unnecessarily placed on top of a metal panel porch roof, the type fabricated with U-shaped overlapping panels. You can see the lines of the vertical legs of the roof panels clearly in the surface of the roll roofing. These do not require a secondary roof membrane.

Also, mineral surfaced roll roofing requires a smooth and flat surface to ensure property bonding and for full support. This roofing sagged over time, allowing water to pond, and in my opinion, greatly shortened the lifespan.

However, based on permit information and my opinion on the condition, it was ten years old, which is at the end of the anticipated lifespan anyway, according to technical resources (like ). But the age was unconfirmed.

- 2016/06/10 - Andrew Kester, P.E. 60993 is a forensic and structural engineer practicing in Florida. Also see CELLOPHANE STRIP ENGINEERS' VIEW

Cracked worn out roll roofing installed over a metal roof (C)

Above: a closer look at the rapidly failed roll roofing installation over what looks like an exposed fastener metal roof panel system. [Click to enlarge any image]

Reply: it's quite likely that this roof needed replacement before the time of its observation at age 10

From the severity of the cracking and crack pattern, I'd bet that those cracks were gross 3-5 years back. Do you think we actually have two effects: linear cracking in the roofing where it bends over the metal roof joints and significant variegated cracking throughout the roofing material.

Would you agree that since this roof, as photographed and reported to be ten years old, has severe variegated cracking worse than we might expect even on a ten year old roof. In turn that might suggest that the cracks were evident 3-5 years ago, had the roof been inspected at that time?

If I'd seen these cracks on a 5 year old roof I'd have said it was failing faster than normal, perhaps because of a combination of bending at the roof panel seams and heat reflected from the metal roof surface over which it was installed?

I know that an engineer should avoid speculation but still, if you thought the text above were reasonable I'll include it.

As the metal roof below this roll roofing failure is clearly not a standing seam roof, I infer it's almost certainly what we call "barn roofing" or more properly, exposed fastener metal roof panel systems consisting of overlapping panels with raised lap joints rather than standing seams. Those lap joints are usually through-bolted to the structure below; the bolt heads may make additional wear points in any membrane roof later installed over the metal.


Here is what a typical manufacturer of roll roofing expects to find below an installation of their mineral-granule-surfaced residential roll roofing product:

Install roll roofing directly over clean, dry plywood minimum 15/32” (11.9 mm) decking or approved equal on slopes equal to or greater than 1:12 for the concealed nail method or 2:12 for the exposed nail method. - source: GAF Corporation, "Technical Advisory Bulletin - Options and Application Procedures for Roll Roofing Products", retrieved 2016/06/13, original source: Guard/Options_and_Application_Procedures_for_Roll_Roofing_Products_Steep_Slope_Technical_Point_TAB_R_2011_119.pdf

Roof Decks: For use on new or re-roofing work over well-seasoned, supported wood deck, tightly constructed with maximum 6" (152 mm) wide lumber, having adequate nail holding capacity and smooth surface OR minimum 3/8" (10mm) thick APA–Engineered Wood Association labeled exterior grade plywood/OSB decking. Be sure that there is no moisture on the surface of the deck or within the deck (which can have an adverse effect on product performance). Nail tin or other metal over gaps or knot holes larger than 1/4" (6.4mm). Sweep all dirt and debris from roof deck prior to application. - source: GAF Corporation, "Application Instructions for Mineral Guard® Residential Roll Roofing", retrieved 20`6/06/13, original source: / Residential_Roll_Roofing/Mineral_ Guard/Mineral_Guard_Residential_Roll_Roofing_Installation_Instructions.pdf

- Daniel F.

Reader follow-up:

... what you are suggesting is perfectly reasonable. I also thought the infrared rays reflected from the metal roof probably exacerbated the degradation of the roll roofing. Since I was not there to investigate that section of roof, I am comfortable you using that photograph and your commentary is reasonable.

I will keep sharing these types of dramatic photographs that make for good academic discussion. I have to dig up a few photos where you can see the huge difference in degradation on the same roof based on which slope it is on, i.e., south exposed roofs in Florida are always worse than other slopes. I am thinking of this one where they had recently removed large solar panels, and the rest of the roof was in bad shape but those areas covered by the panels looked much newer. UV rays and rain, shingles worst enemies!


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