by James Carlson

s we continue trying toTelate more and mOTe

! science to the art of ap-I plying steep-slope wateT-

shedding roofing mateTials, we maybe overlooking some of the basicsthat help make the most out of ourmost widely applied steep-slopematerial-thTee-tab shingles-

Although some of the majoTshingle manufacturers have suc-ceeded in turning the three-tab

calls and letters from contractorsand applicators alike, suggestingthis topic be discussed and clarified.

A review of steep-slope applica-tion techniques may reveal a partof the art that can affect initial roofperformance, as well as longevity-

There are three basic aspects ofapplying three-tab shingle roofsthat we often do not give muchthought to. If we did, certain roofs,on various slopes, in different cli-mates would perform moretrouble-free for the service life ofthe material.

Aside from the numerous flash-ing and counterflashing details thatcan assist performance, the threebasic aspects we should give addi-tional insight to are shingle offsetor "sidelap," exposure and valleyconstruction-

By applying shingles atthe optimum offsetpattern, we can providethree-tab shingle roofsthat perform for thelong-term.

asphalt shingle into a commodity,or mass-produced material, thereare a variety of grades and differ-ences in product quality. We, asknowledgeable craftsmen, designersand manufacturers, can enhancethai quality with some techniquesthat can assist in making three-tabshingle roof applications p('rformbetter.

Offset patternsShingle "sidelap" or "side-gauge" isactually the amount of shingle offset,a measured distance left or right,from the neighboring shingle inthe course below (see Figure 1). Thisoffset from course to course is whatmakes up the pattern for the roofwhen installing three-tab shingles.

There are three basic offset pat.terns used in three-tab shingling:

. Six-inch pattern. The AsphaltRoofing Manufacturers Associa-tion (ARMA) refers to it as the"6-inch method," while NRCArefers to it as "cutours thatbreak joinrs on halves" (seeFigure 2).

. Five-inch pattern. ARMA calls thisthe "5-inch method," and NRCAclassifies it as "random spacing"(see Figure 3).

. Four-inch pattern. ARMA refers tothis as the "4-inch method," andNRCA calls it "cutours thatbreak joinrs on thirds" (seeFigure 4).

In addition, there are variationson these basic offset patterns to ac-commodate metric-sized shingles,

Shingle offsetOne roofing problem that is notbeing monitored, is not beingresearched in different climates,and isn't even currently being dis-cussed, is one that numerous con-tractors and shinglers have beendeliberating over for several years:the often ignored issue of shingleoffset or "sidelap."

Three.tab shingle offset patternshave become somewhat of a "silentcontroversy" in some parts of thecountry.

On occasion, NRCA receives

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fOT certain slopes in certainclimates.

and these variations are not ade-quately documented.

In this day and age, most ex-perienced roofing contractors andapplicators should know the impor-tance of following the manufac-turers' written applicationinstructions, or obtaining writtenapproval for deviating from the in.structions on a particular project.However, this brings us to a two-

alone describe seven different ac-ceptable offset patterns. Consider-ing that some of these shingles willbe applied at their prescribedoffset -some with less than 4inches of side lap, on slopes lessthan 3 inches per foot-we maynot be building-in good long-termwatershedding characteristics tosome roofs.

There are reasons for using a

A closer lookNot all sidelaps or offsets are rightfor every job. To depict this moreclearly, it may be best to think ofoffsets as providing three basicfunctions.

First, they provide a form of pro-tection by ensuring sufficient side-lap to protect the roof system frommoisture migrating into shinglebutt joints or fastener punctures.Second, certain offsets can providea more advantageous avenue forrunoff over the surface of the roof.Third, they are a source of aesthet.ic appeal for certain visible roofareas.

The first offset pattern we willexamine is nicknamed "half-pattern," "half-tab" or "6s," becausewith this pattern the tabs are inter-rupted in the center by the cutoutin the shingle above and below(see Figure 2).

In climates where heavy, pouringrains are common, gauging theside lap so that the cutouts line upevery other course, as in "half-pattern" fashion (as many manufac-turers recommend for every roof),may not always be best. Those whohave had the opportunity to exa.mine aged shingle roofs in wet cli-mates have seen the evidence incutouts where the granules of theunderlaying shingle have been

Figure Gauging the shingle

particular shingle offset pattern.Maybe it is time to review the mostcommon of them, for the purposeof discussing the benefits anddrawbacks with certain offsets.

One particular offset techniqueis usually best suited to each in-dividual job, and roof longevity isaffected by specific offset patterns

part question. Does the roofing in-dustry as a whole understand theadvantilges and disadvantages ofdifferent offset gauging of three-tabshingles, and when should onetype be used in lieu of another?

Numerous shinglers think the in-dustry does not fully understand.An examination of bundle wrap-pers from 10 shingle manufac-turers is evidence that there aremore manufacturer-recommendedapplication offset patterns than thethree that ARMA recognizes in itsResidential Asphalt Roofing Manualand more than the three thatNRCA describes in The NRC'\ SteepRoofing Manual.

The side lap application instruc-tions on the back of these 10 wrappersrange from setting offset from aslittle as 3 inches to as much as60/16 inches.

Of course, this includes wrappersfrom standard- and metric-sizedshingles, but these 10 wrappers Figure 2: Six inch pattern

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the owner with the optimum lon-gevity that the new three-tab shin-gle roofing is capable of achieving.

There may be a few other draw-backs to always applying three-tabshingles at the 6.ind1 offset pat-tern- One that has been reported,

weathered, washed and erodedfrom the roof.

These cutouts on the downslopesides of the roof, with their erod-ed, granule-less, exposed material,suggest the cutouts have actuallybecome the "water slots" for runoff

one manufacturer's wrapper in-structs), the roof may be moreprone to leakage in its later yearsfrom ice damming aftd heavy moss.ing in the cutouts, as shingle buttjoints are aligned in every othercourse (see Figure 5)-

There are positive attributes toapplying shingles at the 6-inch off.set pattern. A few of the attributesI am aware of are:

. On long sloping roofs with nar-row fields, application can bequicker-

. When the pattern is staggered("stair stepped"), it providesmore material coverage beyondshingle butt joints, which can bebeneficial in climates with ex-treme freeze-thaw cycling proneto severe ice damming

. It provides a more rigid or boldappearance to steep visible roofareas.

. It can be easier to keep astraighter line for shingle tie-inaround dormers during application.

FlVeoinch offsetThe 5-inch offset pattern is probablymost widely used in regions wherefiberglass, metric-sized, three-tabshingles are common, such as onthe West Coast, though with metricshingles, the actual offset is 50/.inches. Some the advantages and

Figure 3: Five inch pattern

but is not documented, is if thepattern is not staggered diagonallyas when applying shingles in the"straight-up method" (as at least

migrating to the gutter_In fact,some shinglers refer to cutouts as"water slots."

Examining aged three-tab shingleroofs where the protecting granuleshave been eroded from betweenthe cutouts reveals the underlyingmaterials that are exposed toultraviolet radiation, and thus tofurther oxidation and more ex.treme weather degradation- There-fore, thermal cycling and heataging can be accelerated, as iswet/dry cycling of organic three-tabshingles where granules are miss-ing. The shingle condition underthe cutouts is typically worse alongthe downslope courses, because thedownslope areas are exposed togreater quantities of runoff overthe life of the roof.

In wet and extreme climates,specifying and applying three-tabshingles "per the manufacturer'sinstructions" may not be providing Figure 4: Four inch pattern

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possible disadvantages are asfollows:

Advantages:. Probably the biggest advantageis that cutouts and shingle buttjoints do not line up verticallyexcept in every seventh course.In climates with regular heavyrains, this pattern may allow fora more even distribution ofrunoff over all cutouts, thusminimizing granule erosion.

. Besides being suitable in areaswith heavy rains, the 5-inch pat.tern works well on large, open-field roofs because slight ir-regularities in shingle size andalignment are less noticeable.

. If the roof area is sizable, thispattern can be quicker to install.

. When using metric shingles, the5&/.-inch or "5-plus" pattern maybe the optimum offset for mostclimates when considering allFigure 5: Shingling in the straight-up method

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factors, including labor to installand minimizing material waste.

. The pattern is less rigid, and forvisible roof areas, some feel the ef.fect is more relaxed or calmingwith certain architecture.

Drawbacks:I am only aware of one drawback:It can be more difficult to keep thepattern straight when shinglingaround large dormers or obstructions.

Four-inch offsetThe 4.inch pattern may be theleast common. However, as WilliamJohnson states in the Roofer.s Hand-book, it is a pattern that a contrac-tor may wish to suggest to ahomeowner when desiring differ-

ent roof aesthetics in a neighbor-hood with all the same type andshade of three-tab shingle roofing(see Figure 3).

On lower-slope roofs in wet andextreme climates (prone to severefreeze-thaw cycling), the 4-inch pat.tern, or others with less than 4inches of offset, may not promoteoptimum service in the later yearsof the roofs life when age andweathering may cause organic andsome fiberglass shingles to lift fromthe roof plane.

A note about other offsets lessthan 4 inches: When consideringusing offset patterns less than 4inches on lower slopes, do not for-get that ice damming, mossing and

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vegetation fallout may affect howthe roof will perform.

The NRCA Steep Roofing Manualspecifically states: "Cutout center-lines of any course should be located at least 3 inches laterally fromthe cutout centerlines in both thecourses above and the courses be.low:' ARMA's Residential AsPhaltRoofing Manual is more conserva-tive: "Caution: Never use an align.ment system where shingle jointsare closer than 4 inches to oneanother:'

take another look at three-tabshingle offset patterns, and con-sider establishing general guide-lines for their most appropriate oroptimum use.

By applying three-tab shingles atthe optimum offset pattern. takinginto consideration the roofs slope;its layout; the region's climate; theroofs orientation into prevailingweather, and surrounding foliageor vegetation that may depositleaves, needles or debris on theroof, we can provide building own-ers with three-tab shingle roofs thatperform for the long-term.

James Carlsoo is an NRCA deputydirector of technoiOg)' and research.

References:The NRCA Steep Slope Roofing Manu-al, copyright 1989. Available fromthe National Roofing ContractorsAssociation's Publications Depart-ment at (708) 299-9070.

Residential AsPhalt Roofing Manual,copyright 1988. Available from theAsphalt Roofing Manufacturers As-sociation at (301) 231-9050.

Roofers Handbook, by W.E. john.son, seventh printing 1988. pub-lished by Craftsman Book.Company. Carlsbad, Calif.; tele-phone (619) 438-7828. Possibly themost thoroughly written "how to"book about asphalt shingle applica-tion published to date. -Note:Figures I, 4 and 5 were ad~edfrom the Roofers Handbook. ~

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