Asphalt Roof Shingle Wind Damage Causes & Evaluation
InspectAPedia^®  -    

• Workmanship as a cause of wind damage to roofs
• Shingle sealant defects as a cause of wind damage
• Disaster-resistant roofing shingles
• Do we need to remove the protective cellophane strips from the glue strips on asphalt shingles? No.
• Asphalt roof shingle blow-off, photographs

Roof Installation Workmanship: Fasteners/Nailing Problems, Wind Damage appeared to have led wind blow-off of these Atlas shingles, though an investigation of whether or not the shingles had self-sealed was also needed.

Weather: Wind damage can happen to any asphalt shingle roof in severe weather conditions. However if shingles are not properly nailed, shingles are far more likely to blow off of the roof in even a modest windstorm.

Proper roof shingle nailing: Roofing product manufacturers are careful to specify where shingle nails should be placed in each shingle and the number of nails required. These specifications may vary by shingle type and building location, with more nails specified for high-wind areas such as asphalt shingle roofs applied in coastal areas.

Components of roof shingle wind damage resistance: Asphalt shingle wind resistance combines several factors including the effectiveness of the glue strips on the shingle backs which adhere the shingle courses against wind-uplift, roof pitch, roof orientation with respect to prevailing winds, and importantly, proper shingle nailing patterns.

Not only must nails be properly placed and spaced, improper nailing itself, such as driving a nail through the shingle, leaving a nail sticking up to cut a shingle above, or using a roofing stapler improperly leaving cocked staples or shingle-cutting staples will all encourage shingles to fly away with the wind.

If an new roof has the bad luck to encounter a severe wind storm shortly after asphalt shingles have been installed, it is possible that the shingles will blow off of the roof because their self-sealing tabs have simply not had time (or warm enough weather or enough sun) to adhere.

Roofing Shingle Glue Strip or Glue Tab Adhesion Failure as Contributor to Wind Damage to Asphalt Shingle Roofs

Our photo (left) shows a typical 3-tab asphalt roof shingle (this one is made by GAF™). The shiny black strips form the "glue line" on the shingle. This adhesive is intended to bond to the three tabs of the next shingles nailed atop of this one when the roof is later warmed by sunlight.

On occasions, particularly during high wind conditions such as hurricanes, defective glue strips or adhesive strips on the underside of asphalt shingles may not provide sufficient adhesion, or if the shingles were not properly handled and the glue strip was dirty, an adhesion failure can lead to failure of the shingle tabs to adhere to the nailed-down header of the shingle above. In this case exposure to high winds can cause shingles to tear or blow off of the roof, increasing the degree of water damage inside the building when such winds are accompanied by rain.

In most climates exposure to even a few weeks of normal sunlight will cause the glue tabs on the under-side of asphalt roof shingles to soften and adhere to the surface below.

We discuss the function of asphalt shingle adhesive strips, handling the protective cellophane strip, and shingle uplift wind damage prevention in more detail below.

Should the Cellophane Strip on the Back of Asphalt Shingles be Pulled Off?

Our photo (left) shows the cellophane strip found on the back or "down"
side of a typical asphalt roof shingle. This one is a GAF™ product.

No: In answer to a common reader question, not normally: according to roofing manufacturers, it is not required to remove the cellophane strip on the back of roof shingles before they are nailed. Below we quote from a major manufacturer's instructions.

Yes: as we discuss in more detail below, experts familiar with wind damaged roofs (in coastal areas exposed to hurricanes and in other high-wind areas) previously recommended both the removal of the cellophane strip and the installation of double-sticky-sided roofing adhesive mastic tape or roof cement under shingle tabs at the time of asphalt roof shingle installation. As Cramer reported in 2009 (see "More on the "yes" answer" just below, currently asphalt shingles sold in high wind areas adhere and cannot be pulled apart by wind (nor hand).

Certainly if you wait to remove the cellophane strip until the moment that the shingle is about to be nailed, taking it off will do no harm, and it may speed the adhesion between shingles that is intended to resist wind blow-off of roof shingles. We suspect that few professional roofers will add to their roofing time and cost by taking a step that is not recommended by the product manufacturer.

More on the "no" answer to removing roof shingle cellophane strips

Asphalt roof shingle manufacturers recommend that installers leave that piece of cellophane in place. It does not need to be removed before, during, or after roof shingle installation. The cellophane tape on the back side of asphalt roof shingles is intended to prevent the glue strips from becoming activated prematurely, in storage or shipping, and equally important, to keep the glue-area clean during the roof installation process: jobsite debris (sawdust, dirt) can prevent the sealant from adhering. Once the roof is installed the heat from sunlight will activate the sealing mastic through the cellophane. It does not need to be removed as part of the roofing process.

Actually, trying to remove the strip after installation might also risk damaging the shingle since you'd have to run along the roof slope lifting nailed-down shingle tabs to try to (unnecessarily) pull off the cellophane - risking tearing shingles and causing also extra foot traffic wear.

Here is what the GAF Materials Corporation, Grand Timberline™ Premium Architectural Shingle Application Instructions say about the glue strips and cellophane. You'll note that we are to leave the cellophane in place, but if site conditions (high wind) require immediate shingle sealing, an extra step, using additional shingle tab adhesive, is permitted.

WIND RESISTANCE/HAND SEALING: These shingles have a special thermal sealant that firmly bonds the shingles together after application when exposed to sun and warm temperatures. Shingles installed in Fall or Winter may not seal until the following Spring. If shingles are damaged by winds before sealing or are not exposed to adequate surface temperatures, or if the self sealant gets dirty, the shingles may never seal. Failure to seal under these circumstances results from the nature of self-sealing shingles and is not a manufacturing defect.

To insure immediate sealing, apply 4 quarter-sized dabs of shingle tab adhesive on the back of the shingle 1" (25mm) and 13" (330mm) in from each side and 1" (25mm) up from bottom of the shingle. Press shingle firmly into the adhesive. For maximum wind resistance along rakes, cement shingles to underlayment and each other in a 4" (102mm) width of asphalt plastic roof cement.

NOTE: Excess tab adhesive can cause blistering of the shingle. [The company is referring to the use of additional roof shingle adhesive, not the factory-applied glue strip -- InspectAPedia]. The film strips on the back of each shingle are to prevent sticking together of the shingles while in the bundle and to keep dirt and debris out of the adhesive material so that after installation the adhesive will work. Their removal is NOT required during application.

More on the "yes" answer to removing roof shingle cellophane strips.

One of our readers, Leonard Wheeler, reported that independent analysis of wind damaged roofs concluded that "... many shingles and attachment adhesives used were not adequate for the wind speeds that occurred. The most common failure mode was lifting of the tabs due to failure of the self-seal adhesive, and subsequent tearing of the shingles at the fasteners (Smith, 1994)." Our associate, Mark Cramer, a Florida home inspector and educator in the field, reported that houses suffering damage during Hurricane Andrew were generally those not built to code, and that code-built homes survived the hurricane with minimal damage. Mr. Cramer provides this update:

Asphalt roof shingles sold today (2009) in high wind zones are totally different from what we used in the early 90’s. Forget the number of nails also, four is fine for most shingles used today. The problem was not number of nails but failure of adhesion. Today’s high wind shingles can’t be pulled apart once they seal.

Other measures to reduce water damage to buildings in coastal or high wind areas include use of roof flashing tape or strips of ice-and-water-shield type products over the butt joints between sections of plywood or OSB roof decking. The presence of roofing felt under shingles won't prevent roof leaks after shingles are installed, since the shingle nails will have made thousands of penetrations in that membrane.

Other Examples of Wind Damaged Shingle Roofs

The photographs here include examples of improperly or inadequately-nailed shingles which blew off in modest windstorms of far less than hurricane strength. In the first photograph below, our correspondent has laid-out shingles retrieved after the storm, showing the location and pattern of nail holes in each shingle - clear evidence of just how they were nailed. Our ridge cap shingle loss (above left) is plainly due to wind damage. The shingles falling off of the barn roof (above right) appear due to a combination of wind damage and possibly inadequate nailing.

• 
  Workmanship: Fasteners/Nailing Problems lead to holes or wind blow-off. Roofing manufacturers provide recommendations for the type of shingle fastener (nails are recommended), the type of roofing nail, and the length of roofing nail required. Yes, it is proper for roofing nails to penetrate through the roof decking so that the tips of the nails are visible inside. This is particularly important where 1/2" roofing plywood or OSB decking are used (as opposed to thicker roof decking materials). Here is a representative example comment on roofing nails from the GAF Materials Corporation Grand Timberline™ Premium Architectural Shingle Application Instructions:

  
  FASTENERS: Use of nails is recommended. Use only zinc coated steel or aluminum, 10-12 gauge, barbed, deformed or smooth shank roofing nails with heads 3/8" (10mm) to 7/16" (12mm) in diameter. Fasteners should be long enough to penetrate at least 3/4" (19mm) into wood decks or just through the plywood decks. Fasteners must be driven flush with the surface of the shingle. Over driving will damage the shingle. Raised fasteners will interfere with the sealing of the shingles.

  Experts discussing measures to reduce asphalt roof shingle blow-off in coastal or other high-wind areas recommend against using roofing staples to install shingles.
  

• Workmanship: Fasteners/Nailing Problems lead to holes or wind blow-off. Notice that not only has one shingle already fallen or been blown off of the roof, but its neighbors are sliding down. Diagnosis from a photograph is questionable but there appears to be a nailing problem here.
  
  
  
• Workmanship: Installation Pattern Problems:Laddering [Photo: Carl Gerosa, New Rochelle, NY.]
  
  
  
  
  
• Workmanship, condition of roof deck, roof flashing, roofing felt underlayment: Flashing and underlayment problems: Here is a representative example comment on the use of roofing felt underlayment and roof decking condition, from the GAF Materials Corporation Grand Timberline™ Premium Architectural Shingle Application Instructions:

  UNDERLAYMENT: Underlayment beneath shingles has many benefits, including preventing wind driven rain from reaching the interior of the building and preventing sap in some wood decking from reacting with asphalt shingles. Underlayment is also required by many code bodies. Where an underlayment is to be installed, use a breather-type underlayment such as GAF Shingle-Mate® underlayment.

  ROOF DECKS: Wood decks must be well-seasoned, supported, and tightly-constructed with maximum 6" (152mm) wide lumber, having adequate nail-holding capacity and a smooth surface. Plywood decking as recommended by The Engineered Wood Association is acceptable. Where a Class A rating is required over decks less than 15/32" thick, an underlayment is required. Do not fasten shingles directly to insulation or insulated deck unless authorized in writing by GAF. Roof decks and existing surfacing material must be dry prior to application of shingles.

• Workmanship: Improper materials/roof-slope problems - installing shingles on low-slope roofs, for example.
• Holes and nail-pops in shingle roofs, mechanically damaged roof shingles.
• Choice of roofing, shingle type, underlayment, and roof decking materials: In a 2005 article Paul Fisette cited Mitrani who, more than a decade earlier, concluded that in areas of coastal high winds and storms, OSB was an inferior roof decking product to plywood. Opinion among Florida consultants currently is that OSB is fine and performs as well as plywood. -- Cramer (personal communication 4/1/09).

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