Asphalt Shingle Applications and Related Coverings
Chapter Introduction
This chapter covers all the knowledge required for the Red Seal exam concerning the installation of asphalt shingles and related coverings. You will find the fundamental principles, installation methods, material calculations, national standard requirements, and common pitfalls. Mastering this content is essential, as asphalt shingles represent approximately 70% of residential roofing in Canada.
Definitions and Essential Terminology
Asphalt shingle: a roof covering composed of a base (organic felt or fibreglass mat) saturated with asphalt, covered with mineral granules. Fibreglass mat base is now the standard in North America, offering better fire resistance and greater durability.
Underlayment: a membrane installed over the decking before shingle installation. It acts as a temporary moisture barrier and protects the decking during construction.
Roof slope: the ratio between vertical rise and horizontal run, expressed in inches per foot (e.g., 4/12) or as a percentage. The minimum slope for asphalt shingles is 4/12 (33%), according to CAN/CSA A123.5.
Exposure: the visible portion of the shingle after the next course is installed. For a standard 1 m (36 in) shingle, the typical exposure is 145 mm (5 ¾ in).
Decking: the supporting surface on which the covering is installed. It must be dry, clean, and compliant with the National Building Code (NBC) for the snow and wind loads of the region.
Drip edge: a metal profile installed along the rakes and eaves to direct water toward the gutter and protect the decking.
Flashing: a metal piece or membrane used to waterproof the junctions between the roof and vertical elements (chimneys, walls, vents).
Applicable Standards and Codes
The following table summarizes the main national standards you need to know for the exam:
Shingle Classification According to Fire Resistance
Class
Resistance
Typical Use
**Class A**
High resistance
Residential buildings, municipal requirements
**Class B**
Moderate resistance
Certain commercial applications
**Class C**
Minimum resistance
Limited applications, mild climates
Fibreglass mat shingles with granule coating are generally classified as Class A, which is the standard for most residential roofs in Canada.
Decking Preparation and Prerequisites
Decking Requirements
The decking must be inspected before any installation. The following conditions are mandatory:
23.Dryness: the wood must have a moisture content below 19%. Wet decking causes shingle curling and layer delamination.
24.Cleanliness: no dust, debris, or oil residue may remain.
25.Fastening: the decking must be fastened in accordance with the NBC, using nails or screws suited to the material thickness.
26.Ventilation: a ventilation space beneath the decking (between the insulation and the decking) of at least 25 mm (1 in) is required to prevent condensation and ice formation in winter.
Ventilation Calculation
Roof ventilation must comply with the 1/300 ratio (1 unit of ventilation for 300 units of floor area) for unheated attics, according to the NBC. This ratio increases to 1/150 if a vapour barrier is not installed or if the slope is less than 1/3.
Calculation formula:
Total required ventilation area = (Attic floor area) ÷ 300
Example: for an attic of 120 m², the total required ventilation is 120 ÷ 300 = 0.4 m². This area must be split 50% into low ventilation (eaves) and 50% into high ventilation (ridge).
Underlayment Installation
Underlayment is mandatory for all asphalt shingle roofs. The types of underlayment are:
Type
Material
Typical Weight
Use
**Bituminous felt (Type 1)**
Organic felt saturated with asphalt
15 lb (6.8 kg) per roll
Slopes ≥ 4/12
**Bituminous felt (Type 2)**
Organic felt saturated with asphalt
30 lb (13.6 kg) per roll
Slopes ≥ 4/12, high-risk areas
**Fibreglass mat**
Fibreglass mat impregnated with asphalt
18–25 lb
Superior resistance, freeze zones
**Self-adhesive membrane**
Modified bitumen with adhesive
Variable
Drip edges, valleys, ice zones
Underlayment installation method:
36.Roll out the underlayment horizontally, starting at the bottom of the roof.
37.Each course must overlap the course below by at least 50 mm (2 in) for slopes ≥ 4/12.
38.Vertical overlaps (at the ends) must be at least 150 mm (6 in).
39.Fasten with staples or wide-head nails, spaced 300 mm (12 in) on centre, in a staggered pattern.
40.For slopes of 4/12 to 6/12, the underlayment must be installed in two layers in valley and drip edge areas.
41.For slopes less than 4/12, a self-adhesive membrane type underlayment is required over the entire surface.
Common pitfall: on slopes of 2/12 to 4/12, asphalt shingles are not recommended by CAN/CSA A123.5. If the client insists, a self-adhesive membrane over the entire surface is mandatory, and the absolute minimum slope is 2/12 with this method.
Asphalt Shingle Installation
Required Tools and Equipment
Roofing hammer or pneumatic nailer
Shingle knife (hook knife)
7.5 m (25 ft) measuring tape
Chalk line (blue or red chalk)
Carpenter's square
Shingle snips
Nail pouch
Personal protective equipment (PPE): harness, lanyard, safety glasses, gloves
Calculating the Quantity of Shingles
Unit of measurement: the square equals 100 ft² (9.29 m²) of roof surface.
Calculation formula:
Number of squares = (Total roof surface in ft²) ÷ 100
Example: for a roof of 2,400 ft², you need 24 squares of shingles.
Waste factors:
Roof Type
Waste Factor
Simple roof (2 slopes)
5–10%
Roof with valleys, chimneys, dormers
10–15%
Complex roof (multi-level)
15–20%
Calculation with waste:
Number of squares to order = (Total surface ÷ 100) × (1 + waste factor)
Example: roof of 2,400 ft² with valleys: (2,400 ÷ 100) × 1.12 = 26.88 squares, rounded up to 27 squares.
Number of nails: for each 1 m (36 in) shingle, you need 4 nails (6 nails for high wind zones ≥ 160 km/h). Each square of shingles requires approximately 320 nails (for 4 nails per shingle).
Drip Edge Installation
Drip edges must be installed before or after the underlayment, depending on the method. The recommended method is:
66.Install the drip edge along the eaves, fastened with aluminium or stainless steel nails spaced 200 mm (8 in) apart.
67.Install the drip edge along the rakes (gables), overlapping the eave drip edge at the corners.
68.The drip edge must extend at least 10 mm (3/8 in) beyond the edge of the decking to direct water into the gutter.
Self-Adhesive Membrane Installation at Drip Edges
The self-adhesive membrane (ice and water shield) is mandatory in the following areas:
Along the eaves, over a width of at least 900 mm (36 in) measured from the outer edge of the interior wall.
In valleys, over a width of 600 mm (24 in) on each side of the valley centreline.
Around penetrations (chimneys, vents) within a 300 mm (12 in) radius.
This membrane is particularly critical in regions where the risk of ice dams is high (Canadian climate). It must be installed directly on the decking, before the underlayment.
Shingle Installation: Detailed Procedure
Step 1: Laying Out Reference Lines
77.Measure the width of the roof (from left rake to right rake).
78.Mark the centre of the roof and snap a vertical chalk line.
79.Snap a horizontal reference line at 145 mm (5 ¾ in) above the lower edge of the drip edge.
Step 2: Installing the Starter Course
The starter course is crucial for waterproofing. It consists of shingles with the tabs cut off, or prefabricated starter shingles.
82.Cut the tabs off the starter course shingles (or use starter shingles).
83.Install the starter course along the drip edge, leaving an overhang of 6 to 10 mm (¼ to ⅜ in).
84.Fasten with nails at 25 mm (1 in) from the top edge, at each end and at the centre.
85.The starter course must be installed so that the vertical joints do not coincide with those of the first full course.
Step 3: Installing the First Full Course
87.Install the first full shingle over the starter course, aligning the bottom edge with the bottom edge of the starter course.
88.The vertical joints of the first course must be offset by at least 150 mm (6 in) from the joints of the starter course.
89.Fasten each shingle with 4 nails (or 6 in high wind zones), placed at:
25 mm (1 in) below the adhesive line (sealant line)
25 mm (1 in) from each end
25 mm (1 in) on each side of the centre slot (for 3-tab shingles)
Step 4: Installing Subsequent Courses
94.Each subsequent course is installed with an exposure of 145 mm (5 ¾ in) for standard shingles.
95.Offset the vertical joints by 150 mm (6 in) from the previous course (half a shingle for 3-tab shingles).
96.Use the chalk line to verify horizontal alignment every 3 to 4 courses.
97.For 3-tab shingles, the exposure is 145 mm; for architectural shingles, it may vary from 140 to 150 mm depending on the manufacturer.
Step 5: Installing the Rakes (Gables)
99.Cut the shingles flush with the edge of the rake drip edge.
100.Leave an overhang of 6 to 10 mm (¼ to ⅜ in) beyond the drip edge.
101.Apply bituminous cement (roofing cement) under each tab along the rake to prevent wind uplift.
Step 6: Installing Valleys
The valley is the most critical area for waterproofing. Two methods are accepted:
Open valley method:
105.Install the self-adhesive membrane over the full width of the valley (600 mm on each side).
106.Install the underlayment over the membrane.
107.Snap two chalk lines parallel to the valley centreline, spaced 100 to 150 mm (4 to 6 in) apart.
108.Install the shingles, cutting them along these lines, leaving the valley visible.
109.The shingles must extend past the chalk line by at least 50 mm (2 in).
Closed valley method:
111.Install the self-adhesive membrane as above.
112.Install the shingles from one side of the valley, extending them 150 mm (6 in) beyond the centreline.
113.Install the shingles from the other side, cutting them at 50 mm (2 in) from the centreline.
114.Apply bituminous cement along the cut line.
115.This method is faster but less aesthetic and more prone to leaks.
Step 7: Installing Flashings
Chimneys:
118.Install a step flashing on each side of the chimney, extending 100 mm (4 in) up the wall and 75 mm (3 in) onto the roof.
119.Each flashing piece must be installed with each course of shingles.
120.Install a counter-flashing embedded into the mortar joint of the chimney, to a depth of at least 25 mm (1 in).
121.Seal all joints with polyurethane or silicone sealant.
Vertical walls:
123.Use step flashings of 100 mm × 100 mm (4 in × 4 in).
124.Each piece is installed with each course of shingles.
125.The flashing must be covered by the shingle over at least 75 mm (3 in).
Vents and penetrations:
127.Install a preformed flashing (boot) made of EPDM rubber or lead.
128.The base of the flashing must be installed over the shingle, and the next shingle must cover the base of the flashing.
129.Apply bituminous cement under the base of the flashing.
Step 8: Installing the Ridge
131.Use ridge cap shingles or cut standard shingles into three sections.
132.Each section must have an exposure of 145 mm (5 ¾ in).
133.Fasten each section with 2 nails on each side, at 25 mm (1 in) from the edge.
134.The nails must be covered by the next section.
135.For ventilated roofs, install a ridge vent before installing the ridge cap shingles.
Fastening: Nails and Staples
Parameter
Nails
Staples
Minimum length
19 mm (¾ in)
19 mm (¾ in)
Shank diameter
3.0 mm (11 ga)
1.6 mm (16 ga)
Head diameter
9.5 mm (⅜ in)
9.5 mm (⅜ in)
Penetration into decking
At least 6 mm (¼ in)
At least 6 mm (¼ in)
Recommended use
All types of decking
Plywood decking only
Fastening rule: nails must be placed on the adhesive line (sealant line) of the shingle, at 25 mm (1 in) below the top edge. A poorly placed nail (too high) may be exposed to the elements; a nail placed too low may not be covered by the next course.
Advanced Calculations for the Exam
Slope Calculation
Slope is expressed as the ratio between vertical rise and horizontal run.
Formula: Slope = Rise (in) ÷ Run (in)
Example: a rise of 8 in for a run of 12 in gives a slope of 8/12.
Conversion to percentage: (8 ÷ 12) × 100 = 66.7%
Conversion to degrees: arctan(8 ÷ 12) = 33.7°
Calculating the Actual Roof Surface
The actual surface (sloped surface) is greater than the ground surface (footprint).
Formula: Actual surface = Ground surface ÷ cos(slope angle)
Example: for a ground surface of 200 m² with a slope of 8/12 (angle of 33.7°):
cos(33.7°) = 0.832
Actual surface = 200 ÷ 0.832 = 240.4 m²
Quick method with slope factor:
Slope
Multiplier Factor
4/12
1.054
6/12
1.118
8/12
1.202
10/12
1.302
12/12
1.414
Example: ground surface of 200 m² with a slope of 6/12: 200 × 1.118 = 223.6 m².
Calculating the Ice Dam Barrier Height
The height of the self-adhesive membrane at the eaves depends on the local snow load and the width of the eave overhang.
Rule of thumb: the membrane must extend at least 900 mm (36 in) beyond the interior wall line. In regions with heavy snow loads (≥ 3.0 kPa), this height may reach 1,800 mm (72 in).
Common Errors and Pitfalls to Avoid
Installation Pitfalls
160.Poorly positioned nails: a nail placed too high (above the adhesive line) remains exposed and may puncture the shingle of the course above. A nail placed too low is not covered by the next course and causes leaks.
161.Excessive exposure: an exposure greater than 145 mm (5 ¾ in) reduces the lifespan of the shingle and voids the manufacturer's warranty. Always check the maximum exposure specified by the manufacturer.
162.Insufficient underlayment: neglecting the underlayment or using an inappropriate type for the slope is a frequent error. For slopes of 2/12 to 4/12, a self-adhesive membrane over the entire surface is mandatory.
163.Poorly executed valley: a closed valley without adequate cement or an open valley with incorrect spacing (less than 100 mm) causes water infiltration.
164.Inadequate ventilation: a ventilation ratio below 1/300 causes heat and moisture accumulation, leading to shingle curling and mould formation.
Calculation Pitfalls
166.Forgetting waste: ordering exactly the calculated surface without a waste factor leads to a material shortage on the job site.
167.Confusing ground surface and actual surface: using the ground surface to calculate the number of squares significantly underestimates the requirements.
168.Ignoring underlayment overlaps: the 50 mm (2 in) horizontal and 150 mm (6 in) vertical overlaps increase the actual underlayment surface needed by approximately 10%.
169.Incorrect nail count calculation: for a roof of 24 squares with 4 nails per shingle, you need approximately 7,680 nails. Add 10% for waste and drops.
Code and Standard Pitfalls
171.Minimum slope: installing asphalt shingles on a slope less than 4/12 without a full self-adhesive membrane is a violation of CAN/CSA A123.5.
172.Fire classification: using Class C shingles in an area requiring Class A is an infraction of the National Fire Prevention Code.
173.Decking fastening: decking fastened with nails that are too short or spaced more than 150 mm (6 in) apart does not comply with the NBC and may detach under wind loads.
Exam Tips
175.Memorize the key values: exposure of 145 mm, underlayment overlap of 50 mm, overhang of 6–10 mm, nail spacing of 25 mm below the adhesive line.
176.Understand the ratios: ventilation 1/300, minimum slope 4/12, joint offset of 150 mm.
177.Practice the calculations: actual surface, number of squares, waste factors, ventilation.
178.Know the standards by their full names: CAN/CSA A123.5, CAN/CSA A123.2, National Building Code.
179.Visualize the procedures: the exam may include questions on the order of operations (drip edge → membrane → underlayment → shingles → flashings → ridge).
Summary
Asphalt shingles require a minimum slope of 4/12 (CAN/CSA A123.5).
Underlayment is mandatory, with overlaps of 50 mm horizontal and 150 mm vertical.
Self-adhesive membrane is required at the eaves (900 mm), in valleys (600 mm on each side), and around penetrations (300 mm).
The standard shingle exposure is 145 mm (5 ¾ in).
Nails must be placed at 25 mm below the adhesive line, with a penetration of at least 6 mm into the decking.
Vertical joint offset must be at least 150 mm (6 in).
Ventilation must comply with a minimum ratio of 1/300 (or 1/150 without a vapour barrier).
Material calculations must include a waste factor of 5 to 20% depending on roof complexity.
Step flashings are mandatory at junctions with walls and chimneys.
The ridge is installed last, with an exposure of 145 mm and nails covered by the next section.
Pitfalls to Avoid
Never install asphalt shingles on a slope less than 2/12, even with a self-adhesive membrane.
Never use staples on OSB (oriented strand board) decking — only on plywood.
Never install underlayment with insufficient overlaps in valley areas.
Never install a ridge vent without having verified the low ventilation (eaves) — an imbalance creates negative pressure that draws moisture into the attic.
Never use ordinary steel nails for aluminium flashings — galvanic corrosion will destroy the fastening.
Never install a course of shingles without checking alignment with the chalk line — a drift of 2 mm per course becomes 40 mm over 20 courses.
Never cut shingles with a circular saw — use a hook knife to avoid damaging the granules.
Never apply bituminous cement on a wet or frozen surface — adhesion will be compromised.
Never install ridge cap shingles with visible nails — each nail must be covered by the next section.
Never neglect the local wind load calculation — coastal areas and prairie regions require 6 nails per shingle instead of 4.
