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AZ Roofing Contractor practice questions

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Question 1Roofing Materials, Components, and System Selection

One roofing square of coverage equals how many square feet of finished roof area?

  1. 120 square feet
  2. 100 square feet Correct answer.
  3. 225 square feet
  4. 150 square feet

Explanation

A square is the standard roofing unit of area and equals 100 square feet of finished surface. Material takeoffs for shingles, underlayment, and tile are all converted to squares so quantities can be ordered and priced consistently.

Question 2Roofing Materials, Components, and System Selection

Which fastener is the standard method for attaching asphalt shingles to a wood deck?

  1. Roofing staples
  2. Construction adhesive
  3. Roofing nails Correct answer.
  4. Drywall screws

Explanation

Asphalt shingles are designed to be fastened with corrosion-resistant roofing nails of the proper length and head diameter, driven through the nail line and into the deck. The fastener must penetrate the deck enough to develop holding power without cutting the shingle.

Question 3Roofing Materials, Components, and System Selection

A built-up roof membrane is produced by alternating layers of bitumen with which component?

  1. Reinforcing ply Correct answer.
  2. Rigid foam board
  3. Loose gravel
  4. Aluminum foil

Explanation

Built-up roofing is assembled in the field by mopping bitumen and embedding reinforcing plies, usually asphalt-saturated felt or fiberglass mat, in alternating layers. The finished membrane typically receives a surfacing such as gravel, mineral cap sheet, or coating.

Question 4Roofing Materials, Components, and System Selection

Where eave protection is required, the underlayment must extend from the eave edge to a point at least how far inside the interior wall line?

  1. 20 in.
  2. 12 in.
  3. 18 in.
  4. 24 in. Correct answer.

Explanation

Model codes require eave protection to run from the eave edge to a line measured horizontally at least 24 inches inside the interior warm wall line. This keeps water that backs up behind an ice dam above the conditioned space rather than over it.

Question 5Roofing Materials, Components, and System Selection

What is the primary purpose of a metal drip edge at the eave?

  1. To hold the gutter in place along the eave line
  2. To spread the dead load of the roof covering
  3. To shed water clear of the fascia board Correct answer.
  4. To bond the underlayment to the roof sheathing

Explanation

Drip edge is installed along eaves and rakes to move water past the fascia and deck edge so it does not wick back into the sheathing. At the eave it also directs runoff into the gutter.

Question 6Roofing Materials, Components, and System Selection

How should wood structural panel roof sheathing be oriented to its supports?

  1. Face grain perpendicular to the supports Correct answer.
  2. Face grain parallel to the supports
  3. On the diagonal across the supports
  4. Randomly, to spread panel joints

Explanation

Wood structural panels carry their greatest bending strength along the face grain, so panels are laid with the strength axis perpendicular to the supports. The long panel dimension therefore runs across the rafters or trusses.

Question 7Roofing Materials, Components, and System Selection

What role do soffit vents play in an attic ventilation system?

  1. They exhaust hot air at the ridge
  2. They block wind-driven rain at the ridge
  3. They filter dust from incoming air
  4. They supply intake air low on the roof Correct answer.

Explanation

Soffit vents admit cooler outside air at the lowest point of the attic, where it enters and sweeps upward toward the exhaust vents. Without adequate intake area, ridge or static exhaust vents cannot move air effectively.

Question 8Roofing Materials, Components, and System Selection

What is the main purpose of underlayment installed beneath a concrete tile roof?

  1. To bond the tiles to the sheathing
  2. To act as a backup water barrier Correct answer.
  3. To add dead load for wind resistance
  4. To insulate the roof deck thermally

Explanation

Tile roofs shed most water at the tile surface, but wind-driven rain and capillary action can drive moisture beneath the tiles. The underlayment provides the secondary weather barrier that keeps that water out of the structure.

Question 9Roofing Materials, Components, and System Selection

Below what roof slope must asphalt shingles be installed over a doubled underlayment?

  1. 6:12
  2. 3:12
  3. 4:12 Correct answer.
  4. 2:12

Explanation

Shingle roofs between 2:12 and 4:12 are permitted only when a double layer of underlayment is applied in shingle fashion. At 4:12 and steeper, a single layer is generally acceptable. Slopes below 2:12 require a different roof covering.

Question 10Roofing Materials, Components, and System Selection

How is step flashing installed where a roof plane meets a masonry sidewall?

  1. Only at the top and bottom of the wall
  2. Sealed only with polyurethane caulk
  3. As a single continuous L-shaped piece
  4. In short pieces woven with each course Correct answer.

Explanation

Step flashing consists of individual L-shaped pieces, each installed over a shingle course and lapped by the next, so water is stepped down the wall. The pieces are embedded against the wall and lapped shingle-fashion.

Question 11Roofing Materials, Components, and System Selection

Which modifier gives modified bitumen sheet its elastomeric, rubber-like behavior?

  1. Ground limestone filler
  2. Styrene-butadiene-styrene Correct answer.
  3. Talc-based surfacing agent
  4. Atactic polypropylene (APP)

Explanation

SBS is a rubbery block copolymer blended into asphalt to create an elastomeric sheet that stretches and recovers. APP instead produces a plastomeric sheet with different heat and flexibility characteristics.

Question 12Roofing Materials, Components, and System Selection

How are seams in thermoplastic polyolefin (TPO) membrane joined?

  1. With adhesive primer
  2. With butyl tape
  3. With solvent-based cement
  4. By hot-air welding Correct answer.

Explanation

TPO is a thermoplastic, so seams are fused by hot-air welding to create a continuous, monolithic membrane. Solvent cements and tapes do not develop the same seam strength on TPO.

Question 13Roofing Materials, Components, and System Selection

Which galvanized coating designation indicates 0.90 ounces of zinc per square foot?

  1. G30
  2. G185
  3. G90 Correct answer.
  4. G60

Explanation

The number in the coating designation states the zinc coating weight in ounces per square foot, so G90 denotes 0.90 oz/ft2. Heavier coatings such as G185 are used where corrosion exposure is more severe.

Question 14Roofing Materials, Components, and System Selection

In a closed-cut valley, how are the shingles from the intersecting slope finished?

  1. They are cut parallel to the valley centerline Correct answer.
  2. They are cut on a diagonal to the ridge
  3. They are woven over the valley centerline
  4. They stop short so a metal pan stays exposed

Explanation

In a closed-cut valley, shingles from one slope are run through the valley and the shingles from the intersecting slope are cut along a line parallel to the valley centerline. The cut edge sits on the underlying shingle field, keeping the valley closed to view.

Question 15Roofing Materials, Components, and System Selection

How should net free intake vent area compare with net free exhaust vent area?

  1. Intake should roughly equal the exhaust area Correct answer.
  2. Intake should be at least twice the exhaust area
  3. Intake should be about half the exhaust area
  4. Intake area has no effect on system performance

Explanation

A ventilation system works as a balanced loop, so intake area is sized to approximately match exhaust area, and is often made slightly larger. Undersized intake starves the exhaust vents and reduces airflow through the attic.

Question 16Roofing Materials, Components, and System Selection

What does a Class A rating for a roof covering indicate?

  1. The covering carries the lowest dead load
  2. The covering offers the highest fire resistance Correct answer.
  3. The covering resists hail impact damage
  4. The covering resists uplift in high winds

Explanation

Class A, B, and C roof coverings describe fire resistance from external fire exposure, with Class A being the most severe rating. Wind and impact performance are graded under entirely separate classification systems.

Question 17Roofing Materials, Components, and System Selection

A Class 4 impact rating for a roof covering is established by which test method?

  1. A pressurized air blast on a panel
  2. A sandbag dropped on the field
  3. A steel ball dropped from a set height Correct answer.
  4. A fire-hose stream on a mock-up

Explanation

Impact ratings are assigned by dropping a steel ball onto a test deck from increasing heights and checking the underside for damage. Class 4 is the highest impact rating and indicates the covering survived the most severe drop.

Question 18Roofing Materials, Components, and System Selection

Under the model residential code, what is the general ratio of net free attic vent area to attic floor area?

  1. 1/50
  2. 1/150 Correct answer.
  3. 1/100
  4. 1/300

Explanation

The general rule is one unit of net free vent area for every 150 units of attic floor area. The ratio may be relaxed to 1/300 where a vapor retarder is installed on the warm side of the ceiling insulation.

Question 19Roofing Materials, Components, and System Selection

Why are standing-seam metal panels typically attached with concealed clips rather than through-penetrating fasteners?

  1. To eliminate the need for underlayment
  2. To allow thermal movement of the panels Correct answer.
  3. To improve the fire rating of the roof
  4. To reduce the number of fasteners needed

Explanation

Metal expands and contracts significantly with temperature changes, so the panels must be free to slide. Concealed clips anchor the panel to the deck while letting the seams and pan move, which prevents fasteners from wallowing out or panels from buckling.

Question 20Roofing Materials, Components, and System Selection

Why must a spray polyurethane foam roof receive a protective coating?

  1. The foam is combustible when coated
  2. The foam shrinks without a top load
  3. The foam degrades under ultraviolet light Correct answer.
  4. The foam needs weight for wind uplift

Explanation

Polyurethane foam is damaged by ultraviolet exposure, which breaks down the foam cells and causes surface deterioration. A coating or granule surfacing blocks UV and also provides protection from traffic and weather.

Question 21Roofing Materials, Components, and System Selection

Why are field fasteners in asphalt shingles spaced closer in roof corners and perimeters?

  1. Drainage is concentrated there
  2. Peak uplift pressures occur there Correct answer.
  3. Building code requires it at hips
  4. Felt laps are doubled there

Explanation

Wind pressure on a roof is not uniform; it is highest at corners and along edges where airflow accelerates around the building. Closer fastener spacing in these zones increases the shingle's resistance to being peeled back.

Question 22Roofing Materials, Components, and System Selection

Why should asphalt-based sealants not be used on TPO or PVC membranes?

  1. They can attack the membrane or its seams Correct answer.
  2. They cure too slowly to seal a lap
  3. They are not rated for exterior use
  4. They lose adhesion below 60 degrees

Explanation

Asphalt and many solvent-based products contain oils and plasticizers that are incompatible with TPO and PVC, and can cause swelling, softening, or seam failure. Only sealants and cleaners approved by the membrane manufacturer should contact these sheets.

Question 23Roofing Materials, Components, and System Selection

Why must a roof deck be dry before a self-adhering underlayment is applied?

  1. The membrane will not unroll when cold
  2. The release film will bond to the deck
  3. Trapped moisture prevents full adhesion Correct answer.
  4. The primer will not cure below 40 degrees

Explanation

Self-adhering membranes depend on full contact with clean, dry sheathing to develop their bond. Moisture trapped under the sheet can turn to vapor, blister the membrane, and cause adhesion failures once the roof heats up.

Question 24Roofing Materials, Components, and System Selection

What is the primary structural concern when replacing asphalt shingles with clay tile on an existing roof?

  1. Additional dead load on the framing Correct answer.
  2. Higher thermal movement at the eave
  3. Slower installation on steep slopes
  4. Reduced uplift resistance at the ridge

Explanation

Clay tile weighs substantially more per square than asphalt shingles, so the rafters, trusses, and connections must be checked for the increased dead load. A structural evaluation is normally required before the heavier covering is approved.

Question 25Roof Decking, Substrate Preparation, and Underlayment

What is the minimum weight of asphalt felt underlayment permitted beneath asphalt shingles on a roof slope of 4:12 or steeper?

  1. No. 30 asphalt felt
  2. No. 8 asphalt felt
  3. No. 10 asphalt felt
  4. No. 15 asphalt felt Correct answer.

Explanation

The code requires not less than one layer of No. 15 asphalt felt, or an approved equivalent, under asphalt shingles on slopes of 4:12 and steeper. Heavier felts are permitted but are not the minimum.

Question 26Roof Decking, Substrate Preparation, and Underlayment

When asphalt felt underlayment is applied shingle fashion, side laps between courses must be at least:

  1. 6 inches
  2. 2 inches Correct answer.
  3. 4 inches
  4. 1 inch

Explanation

Felt underlayment is lapped 2 inches on the sides and 4 inches at the ends so that water running down the roof is always shed onto the course below. The larger end lap compensates for the greater chance of displacement at horizontal joints.

Question 27Roof Decking, Substrate Preparation, and Underlayment

What gap should be left between the edges of adjacent roof sheathing panels?

  1. 1/32 inch
  2. No gap is permitted
  3. 1/4 inch
  4. 1/8 inch Correct answer.

Explanation

Panel edges are spaced about 1/8 inch apart to allow for expansion of the wood-based panel as it absorbs moisture. Panels installed tight together can buckle and lift fasteners.

Question 28Roof Decking, Substrate Preparation, and Underlayment

Roof sheathing panels must be fastened along supported panel edges at a maximum spacing of:

  1. 6 inches on center Correct answer.
  2. 24 inches on center
  3. 16 inches on center
  4. 12 inches on center

Explanation

The standard fastening schedule calls for fasteners at 6 inches on center along supported panel edges and 12 inches on center in the field of the panel. Edge fastening is closer because edge joints are the most likely place for panels to lift.

Question 29Roof Decking, Substrate Preparation, and Underlayment

What is the purpose of H-clips placed between roof sheathing panels?

  1. They create a drainage path for trapped moisture
  2. They eliminate the need for nailing along panel edges
  3. They tie the panels down to the rafters below
  4. They keep the edge gap and stiffen unsupported panel edges Correct answer.

Explanation

H-clips, also called panel edge clips, fit into the 1/8-inch gap and support panel edges that fall between framing members, which lets thinner sheathing be used. They are not a fastener and do not replace edge nailing.

Question 30Roof Decking, Substrate Preparation, and Underlayment

How is metal drip edge installed at the eave in relation to the underlayment?

  1. Drip edge is sandwiched between two layers of underlayment
  2. Drip edge is applied first, and the underlayment laps over it Correct answer.
  3. Drip edge is installed after the shingles are in place
  4. Drip edge is applied over the underlayment along the entire eave

Explanation

At the eave the underlayment is lapped over the drip edge so that water draining down the roof passes onto the metal and off the edge. The reverse relationship applies at the rake, where the drip edge is applied over the underlayment.

Question 31Roof Decking, Substrate Preparation, and Underlayment

Asphalt shingles are to be installed on a roof with a slope between 2:12 and 4:12. Which underlayment is required?

  1. Underlayment applied only at the eaves and valleys
  2. Two layers of underlayment applied shingle fashion Correct answer.
  3. A single layer of No. 15 asphalt felt
  4. No underlayment, because the slope sheds water

Explanation

On slopes from 2:12 up to but not including 4:12, asphalt shingles require a double layer of underlayment applied shingle fashion because the low slope drains slowly. At 4:12 and steeper, a single layer is sufficient.

Question 32Roof Decking, Substrate Preparation, and Underlayment

Valley lining installed beneath asphalt shingles must be centered in the valley and be at least how wide?

  1. 24 inches
  2. 36 inches Correct answer.
  3. 12 inches
  4. 18 inches

Explanation

Valley lining is required to be at least 36 inches wide, centered on the valley line, so that the extra water channeled into the valley is carried over a fully protected surface. The lining is installed before the field underlayment and the shingles.

Question 33Roof Decking, Substrate Preparation, and Underlayment

Synthetic underlayment is being fastened to wood roof sheathing. Which fastener is appropriate?

  1. Narrow-crown fine-wire staples
  2. Plastic cap nails driven through the cap Correct answer.
  3. Drywall screws driven flush with the surface
  4. Sixteen-penny common nails

Explanation

Synthetic underlayment is normally fastened with plastic cap nails, or with wide-crown staples where the manufacturer permits them, spaced as directed by the manufacturer. The cap spreads the holding force so the membrane is not torn away by wind.

Question 34Roof Decking, Substrate Preparation, and Underlayment

An attic space has no vapor retarder and a roof slope of 6:12. What is the minimum net free ventilating area?

  1. 1/150 of the vented area Correct answer.
  2. 1/100 of the vented area
  3. 1/300 of the vented area
  4. 1/600 of the vented area

Explanation

The base requirement is a net free ventilating area of at least 1/150 of the area of the vented space. The ratio may be reduced to 1/300 only where a qualified vapor retarder is installed or where a balanced arrangement of high and low vents is provided.

Question 35Roof Decking, Substrate Preparation, and Underlayment

A roof sheathing panel is stamped with a span rating of 24/16. What does the number 24 indicate?

  1. The panel weighs 24 pounds per sheet
  2. The panel suits roofs with a 24:12 slope
  3. The panel may be used on walls at 24-inch stud spacing
  4. The panel may span 24 inches between roof supports Correct answer.

Explanation

In a span rating such as 24/16, the first number is the maximum roof support spacing in inches and the second is the maximum floor support spacing in inches. A 24/16 panel is therefore approved for rafters spaced up to 24 inches on center.

Question 36Roof Decking, Substrate Preparation, and Underlayment

Wood structural panel roof sheathing should be installed with its long dimension oriented:

  1. At a 45-degree angle to the rafters
  2. Randomly, because orientation does not affect strength
  3. Parallel to the rafters
  4. Perpendicular to the rafters Correct answer.

Explanation

Panels are strongest along their long axis, so they are laid with the long dimension across the supports to develop the rated span. Laying them parallel to the rafters reduces the effective strength and does not match the span rating.

Question 37Roof Decking, Substrate Preparation, and Underlayment

Asphalt shingles may be installed only on roof slopes of at least:

  1. 4:12
  2. 1-1/2:12
  3. 1:12
  4. 2:12 Correct answer.

Explanation

Shingles are limited to roofs sloping at least 2:12; below that, water moves too slowly for the laps to shed it and a low-slope covering such as a membrane must be used. Slopes between 2:12 and 4:12 are permitted but require a double layer of underlayment.

Question 38Roof Decking, Substrate Preparation, and Underlayment

During tear-off, a plywood roof panel is found to be delaminated across more than half of its area. What is the correct action?

  1. Nail a new layer of sheathing over the entire roof
  2. Fill the delaminated area with roofing cement before covering
  3. Remove and replace the damaged panel Correct answer.
  4. Refasten the plies with screws and continue

Explanation

A panel that has lost its bond across a large part of its area can no longer carry loads or hold fasteners reliably, so it must be cut out and replaced with new sheathing of the same thickness. Localized surface damage can be patched, but widespread delamination cannot.

Question 39Roof Decking, Substrate Preparation, and Underlayment

An ice barrier membrane is required along the eaves of a roof where:

  1. The roof has ridge vents but no soffit vents
  2. The building is in a designated flood zone
  3. The roof slope is steeper than 8:12
  4. The average January temperature is 30 degrees F or lower Correct answer.

Explanation

Where the average January temperature is 30 degrees F or less, an ice barrier is required from the eave edge extending up the roof at least 24 inches inside the exterior wall line. Its purpose is to stop meltwater from backing up under the shingles and leaking into the building.

Question 40Roof Decking, Substrate Preparation, and Underlayment

When sheathing is laid in successive rows, the end joints between panels should be:

  1. Aligned in straight lines from eave to ridge
  2. Staggered between adjacent rows Correct answer.
  3. Placed over the same rafter in every row
  4. Located only at the ridge and the eave

Explanation

Offsetting end joints from one row to the next spreads the discontinuities across different framing members and avoids a continuous hinge line through the deck. Aligned joints concentrate stress and produce a weaker, more flexible roof surface.

Question 41Steep-Slope Roofing Installation (Shingle, Tile, Metal, Slate, Wood)

What is the minimum roof slope at which asphalt shingles may be installed, provided a double layer of underlayment is used?

  1. 4:12
  2. 3:12
  3. 2:12 Correct answer.
  4. 6:12

Explanation

Asphalt shingles are permitted down to a 2:12 slope only when the underlayment is applied in two layers; anything flatter requires a low-slope roof system. At 4:12 and steeper, a single layer of underlayment is sufficient.

Question 42Steep-Slope Roofing Installation (Shingle, Tile, Metal, Slate, Wood)

Where an ice barrier membrane is required at the eaves, how far must it extend up the roof?

  1. From the eave edge to 24 inches inside the exterior wall line. Correct answer.
  2. From the ridge down the full slope of every roof plane.
  3. Only within 6 inches of the eave edge and the rake edges.
  4. Covering the valleys and all roof penetrations only.

Explanation

The ice barrier must run from the lowest roof edge upward to a point at least 24 inches inside (past) the exterior wall line of the building, which is where ice dams back water up. It is a supplementary waterproofing layer under the underlayment, not a full-roof covering.

Question 43Steep-Slope Roofing Installation (Shingle, Tile, Metal, Slate, Wood)

What is the main function of a starter strip at the eave?

  1. To seal the cutouts of the first course and resist wind uplift at the eave. Correct answer.
  2. To provide a finished appearance along the rake edges.
  3. To take the place of underlayment along the lower edge of the roof.
  4. To hold the drip edge away from the fascia board.

Explanation

A starter strip is a reversed or purpose-made first course that fills the cutouts of the first shingle course and provides a continuous bonded edge at the eave. That solid edge resists wind uplift, which is greatest at the eave and rake.

Question 44Steep-Slope Roofing Installation (Shingle, Tile, Metal, Slate, Wood)

How far must roofing nails penetrate into or through the roof decking under asphalt shingles?

  1. 1/2 inch
  2. 1/4 inch
  3. 3/4 inch Correct answer.
  4. 1-1/4 inches

Explanation

Shingle fasteners must penetrate the roof decking at least 3/4 inch, or extend completely through the decking where it is thinner than that. This depth develops the holding power the shingle needs against wind uplift.

Question 45Steep-Slope Roofing Installation (Shingle, Tile, Metal, Slate, Wood)

How is the drip edge detailed at the eave relative to the underlayment?

  1. Underlayment overlaps the eave drip edge. Correct answer.
  2. The drip edge is installed only at the rake, never at the eave.
  3. The eave drip edge is applied over the underlayment.
  4. The drip edge replaces the underlayment along the eave.

Explanation

At the eave the underlayment is laid over the drip edge flange so that any water reaching the underlayment drains out onto the metal and away from the fascia. At the rake the relationship reverses, with the drip edge applied over the underlayment.

Question 46Steep-Slope Roofing Installation (Shingle, Tile, Metal, Slate, Wood)

Where should nails be placed on a standard three-tab asphalt shingle?

  1. Along the very top edge, above the sealant strip.
  2. Directly through the cutouts so the tab hangs from the nail.
  3. Anywhere within 1 inch of the shingle's side edge.
  4. Just above the cutouts, beneath the sealant strip. Correct answer.

Explanation

Nails belong in the nail line just above each cutout, where the next course will cover them. Nailing in the cutout or in the exposed area leaves fasteners exposed to water and violates the manufacturer's fastening pattern.

Question 47Steep-Slope Roofing Installation (Shingle, Tile, Metal, Slate, Wood)

How far should shingles overhang the rake drip edge?

  1. 1/4 to 3/4 inch Correct answer.
  2. A minimum of 3 inches
  3. Flush with the drip edge
  4. 1 to 2 inches

Explanation

Shingles should project roughly 1/4 to 3/4 inch beyond the rake drip edge so runoff clears the fascia. Excessive overhang droops in heat, breaks in wind, and prevents the edge from being supported.

Question 48Steep-Slope Roofing Installation (Shingle, Tile, Metal, Slate, Wood)

Which fasteners are suitable where roofing materials contact preservative-treated lumber?

  1. Coated drywall screws
  2. Aluminum roofing nails
  3. Electro-galvanized common nails
  4. Hot-dipped galvanized or stainless steel Correct answer.

Explanation

The chemicals in preservative-treated wood are corrosive to plain steel and thin electro-galvanized coatings, so fasteners must be hot-dipped galvanized, stainless steel, or otherwise rated for the exposure. Using under-rated fasteners leads to premature fastener failure.

Question 49Steep-Slope Roofing Installation (Shingle, Tile, Metal, Slate, Wood)

How is step flashing installed where a shingle roof meets a vertical sidewall?

  1. Pieces are placed beneath the underlayment with the wall leg behind the sheathing.
  2. One continuous piece of flashing is run the full length of the wall over the shingles.
  3. One piece is installed for each shingle course, and the shingle covers the horizontal leg. Correct answer.
  4. Pieces are laid on top of the finished shingles and sealed with plastic cement.

Explanation

Step flashing is installed in individual pieces, one per shingle course, with the vertical leg against the wall and the horizontal leg lapped over the shingle below and covered by the next course. The shingle-and-flashing layers then interlock so water cannot get behind the wall.

Question 50Steep-Slope Roofing Installation (Shingle, Tile, Metal, Slate, Wood)

What is the effect of high nailing asphalt shingles above the nail line?

  1. It leaves the nail above the exposure line and weakens the shingle against wind. Correct answer.
  2. It has no effect on performance as long as the nail reaches the deck.
  3. It increases resistance to wind uplift at the eave.
  4. It improves sealing by driving nails through the adhesive strip.

Explanation

High nails miss the reinforced nail line and sit above the top of the underlying course, so the shingle is not positively held at its base. The result is a loose, exposed fastener location and greatly reduced wind resistance, a common cause of blow-off failures.