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Roof shingle exposure distances: this article provides a definition of roof shingle exposure and gives the range of acceptable shingle exposure amounts. Too little shingle exposure may at least cause a cosmetic issue while too much shingle exposure risks leaks or shingle blow-off and wind damage.
Roof shingle exposure is defined as the amount of a shingle whose upper surface is not overlapped by the next successive shingle course or in some roofing patterns, the amount of the shingle that is not overlapped by a side-adjacent shingle.
In our sketch at left, the asphalt shingles are being installed with a 5-inch exposure - the distance between th two red arrows.
Roof shingle exposure amount is the portion (measured in inches or cm) of asphalt shingle that remains exposed to weather as successive courses of shingles are installed up the roof slope.
We measure shingle exposure as the distance from the lower edge of an exposed roof shingle or shingle tab down-slope to the lower edge of the shingle in the shingle course (row) just below.
5-inch shingle exposure: The typical or "standard" asphalt roof shingle exposure amount is 5". For 12-inch wide shingle materials this means that the head lap or covered portion of each shingle course will be 7".
4-inch shingle exposure: On lower slope asphalt shingle roofs with slopes uner 4/12 the roofer may use a 4" exposure in order to increase the resistance of the roof to wind-driven rain.
According to GAF, In some cases, this can be an acceptable
practice, but there are risks for which CertainTeed will not take
responsibility. A shortened exposure can harm the appearance of the
applied roofing, especially those with shadow lines, and it can reduce
shingle ability to resist wind blow-offs by shifting the adhesive seal line
away from the bottom edge of the shingles. - "GAF-Elk Timberline
High Definition Roofing Shingles
Product Information" (2008) [discontinued product]
Exposure Amount for Other Roofing Methods
The allowed exposure amount for other roofing methods and products will vary. For example, in a built up roof (BUR roofing) using multiple plies of tarred felt, the exposure width will usually be defined as the width of an individual felt ply minus 2".
Nineteen-Inch Selvage membrane roofing, also referred to as Double-Coverage or Split-Sheet roofing uses a prepared roofing sheet that includes a 17 inch (430mm) granule surfaced area intended to be exposed to the weather, and a smooth, non-granule surfaced 19 inch (485mm) selvage edge. Selvage membrane roofing is also referred to as SIS, double-coverage or "Wide Selvate" roofing (ASTM Standard D 371-89, Standard Specification for Asphalt Roll Roofing (Organic Felt) Surfaced with Mineral Granules, Wide Selvage).
Maximum shingle tab exposure amount
The manufacturer's maximum recommended shingle exposure amount varies depending on the shingle brand and model, but a typical industry asphalt shingle exposure amount would be between 5" and 5 5/8" for architectural grade shingles. Some shingle brands permit much larger exposure amounts.
For example, GAF/ELK Timberline Grande® 40 High Definition® asphalt shingles, designed to resemble a wood-shake roof, permit an exposure of 8 1/4" - a feature intended to provide more area of roof coverage per shingle course, thus using fewer total shingles and reducing material cost for the roof.
Adjusting the shingle tab exposure amount near the ridge
Square-tab asphalt roof shingles are normally installed uniformly on the roof with all courses using the same exposure amount, with this exception: when the distance from eaves to ridge would not result in finishing the last or upper-most shingle course with a whole shingle, the roofer may start adjusting the shingle tab exposure perhaps 6 courses below the ridge so that the shingle tab exposure on final course will be a whole tab.
We may stretch or shrink the exposure amount slightly, typically by 1/4" or less per course, to make this final detail work out properly.
Deliberately random shingle tab exposures & widths
In other shingle designs and installation patterns, the manufacturer and/or roofer may deliberately vary the shingle tab exposure amount in a pattern called "random tab shingles". However even when the shingle exposure amount is varied, there will be an upper limit or maximum allowed exposure amount.
Avoid excessive asphalt shingle exposure amount
Watch out: spreading shingle courses too widely apart, that is, installing with excessive shingle exposure may result in a shorter roof life if portions of the shingle head that were not intended for exposure to the weather are in fact left exposed.
Reader Question: is this shingle exposure correct?
8 Sept. 2014 Pam said:
Is anyone familiar with this type of roofing installation? We could be wrong, but it seems as if the rows are too far apart? We would be very grateful for any information or insights. Thanks in advance!
Pam I took a look at your photo and will also post it here for others to comment. It looks as if there was a deliberate effort to expose a black shadow-line between courses. I can't know if this is a shingle appearance feature or if the roofer separated the courses by more space than the usual 4-5" of asphalt shingle exposure. Make some measurements and tell us the shingle exposure amount: that is, the distance from the lower edge of a course of shingle tabs down to the lower edge of the successive course below.
If you know the shingle brand and model number that would also be useful.
Watch out: on typical 3-tab asphalt roof shingles, using an exposure amount greater than 5 5/8" risks leaving the shingle nails exposed to the weather - asking for roof leaks.
And as the location of self-sealing tabs (protection against wind uplift) begins at about 6 1/8" up from the shingle's lower edge, exposures in this range may prevent the shingles from self-sealing against wind damage, increasing the risk of shingle blow-off.
Thank you so much for your prompt reply! We are considering purchasing the home, and the seller was gracious enough to allow our contractor friend take a look around this weekend before the home inspection this coming week. He's in excavation and said he knows nothing about roofing, but he seemed to think the courses were spaced a little bit further apart than they should be. I could see if the seller could provide more information on them.
The only thing stated in the disclosure is that it was approximately 3 years old. Here are the only other pictures our friend took on the roof. Again, thanks so much for your time assistance! We are very grateful. Any information you would be willing to provide would be very much appreciated. That way we can compare notes with the inspector we hire, too! Here are links to the other pictures:
Your photos show that the shingles are not properly installed in my opinion because at least where you show the plumbing vent,
I can see a shingle cutout that extends over and above the top edge of the plumbing vent flashing (red oval): this will certainly be a roof leak.
It is also an example of inexperienced or sloppy workmanship. Perhaps the roofer was "extending" the shingle coverage on the roof by using wider exposures, thus saving money on material cost.
Measure the distances of shingle tab exposure and compare them with the data we give in our article above.
If you see shingle exposure more than 5 5/8" OR if you see exposed shingle nails or self-sealing tar strips then the shingles were over-extended and most likely will have a reduced life. More, if the shingles were not installed according to the manufacturer's specifications, the shingle warranty will probably not be honored.
If our mutual hypothesis (excessive shingle exposure) is found by measurement and inspection to be correct, then your experience shows that a "new roof" is not necessarily an assurance that all is well, durable, and leak-resistant overhead.
Asphalt Roof Shingle Manufacturers
Atlas Roofing Corp.
Fiberglass and organic felt shingles
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"GAF-Elk Timberline ® Prestique ® Grande ® 40 High Definition Roofing Shingles Product Information" (2008) GAF-Elk Corporation 5/08 13 61 Alps Road, Wayne, NJ 07470 www.gaf.com, retrieved 9/8/2014, original source: http://www.gaf.com/Other_Documents/ Legacy_Products_Discontinued/Timberline_Prestique_Grand%C3%A9 /Timberline_Prestique_Grande_40_Info_Spec_Sheet.pdf [Note that this is a discontinued product]
GAF Materials Corporation, Grand Timberline Premium Architectural Shingle Application Instructions.
http://www.gaf.com/Content/Documents/20573.pdf discusses the requirements for successful asphalt shingle installation including the condition of the roof deck, the use of roofing felt underlayment, the selection of roofing nails by type and length and penetration of the roof decking, and the role of glue strips on the back side of asphalt roof shingles.
Roofing The Right Way, Steven Bolt, McGraw-Hill Professional; 3rd edition (November 1, 1996), ISBN-13: 978-0070066502, p. 350 for one of many citations on this point.
"Hurricane Damage to Residential Structures: Risk and Mitigation", Jon K. Ayscue,
The Johns Hopkins University, Baltimore, Maryland, published by the Natural Hazards Research and Applications Information Center, Institute of Behavioral Science, University of Colorado, November 1996. Abstract: "Property damage and loss from hurricanes have increased with population growth in coastal areas, and climatic factors point to more frequent and intense hurricanes in the future. This paper describes potential hurricane hazards from wind and water. Damage to residential structures from three recent intense hurricanes - Hugo, Andrew, and Iniki - shows that wind is responsible for greater property loss than water. The current state-of-the-art building technology is sufficient to reduce damage from hurricanes when properly applied, and this paper discusses those building techniques that can mitigate hurricane damage and recommends measures for mitigating future hurricane damage to homes." - online at www.colorado.edu/hazards/publications/wp/wp94/wp94.html
"Evaluating OSB for Coastal Roofs," Paul Fisette, Coastal Contractor, Winter 2005, online at coastalcontractor.net/pdf/2005/0501/0501eval.pdf . Fisette cites: "Jose Mitrani, a civil engineer and professor at Florida. International University in Miami, was ... Florida’s official damage assessment team. ... After Hurricane Andrew, Florida code advisers ruled OSB sheathing inferior to plywood."
ARMA - Asphalt Roofing Manufacturer's Association - http://www.asphaltroofing.org/
750 National Press Building, 529 14th Street, NW, Washington, DC 20045, Tel: 202 / 207-0917
ASTM - ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA, 19428-2959 USA The ASTM standards listed below can be purchased in fulltext directly from http://www.astm.org/
NRCA - National Roofing Contractors Association - http://www.nrca.net/, 10255 W. Higgins Road, Suite 600,
Rosemont, IL 60018-5607, Tel: (847) 299-9070 Fax: (847) 299-1183
"Applying Shingles on Extreme Slopes", Dave Flickinger, RRO, Professional Roofing, July 1999. [PDF copy] - National Roofing Contractors Association - http://www.nrca.net/,
10255 W. Higgins Road,
Rosemont, IL 60018-5607,
Tel: (847) 299-9070
Fax: (847) 299-1183,
Office hours: 8 a.m. to 5 p.m. CST
UL - Underwriters Laboratories - http://www.ul.com/
2600 N.W. Lake Rd.
Camas, WA 98607-8542
Tel: 1.877.854.3577 / Fax: 1.360.817.6278
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