Roofing Systems, Substrates, and Preparation
Chapter Introduction
This chapter covers the essential knowledge related to the different types of roofing systems, the substrates on which they are installed, and the critical preparation steps. For the Red Seal exam, you must not only identify materials but also understand design principles, national standard requirements, and the consequences of preparation errors. Mastering this content is fundamental, as the majority of roofing defects (leaks, delamination, blistering) originate from inadequate substrate preparation or an incorrect system selection.
2.1 Classification of Roofing Systems
Roofing systems are classified according to two main criteria: slope and membrane type.
2.1.1 Classification by Slope
Slope is expressed as a percentage (%) or as a ratio x:12 (vertical rise in inches for 12 horizontal inches).
| Roof Type | Typical Slope | Drainage Method |
|---|
| Flat roof (low slope) | 1:50 (2%) to 1:12 (8.3%) | Internal or scupper drainage |
| Sloped roof (moderate slope) | 1:12 to 4:12 | Gravity drainage (eavestroughs) |
| Steep-slope roof | 4:12 to 12:12 and greater | Gravity drainage |
Key Rule: The National Building Code of Canada (NBCC) requires that roofs with a slope of less than 1:50 (2%) be equipped with a secondary drainage system (overflow) sized to discharge water without overloading. The minimum recommended slope for a bituminous membrane is 1:50 (2%), except for liquid-applied or elastomeric membrane systems designed for zero slope.
2.1.2 Classification by Membrane Type
Membranes are divided into three main families:
13.Bituminous membranes: based on modified asphalt (SBS – styrene-butadiene-styrene, or APP – atactic polypropylene) or oxidized bitumen.
14.Polymeric membranes (single-ply): PVC (polyvinyl chloride), TPO (thermoplastic olefin), EPDM (ethylene-propylene-diene monomer).
15.Liquid-applied membranes: polyurethane, acrylic, silicone, applied cold.
The choice of system depends on the slope, substrate, climate, building use, and expected service life.
2.2 Roof Substrates and Decks
The substrate is the surface on which the membrane is installed. It must be dry, clean, smooth, structurally sound, and compatible with the chosen system.
2.2.1 Wood Substrates
Plywood: exterior-grade (CSA O121 or O151), minimum thickness 12.5 mm (1/2 in) for steep slopes, 15.5 mm (5/8 in) for low slopes. Joints must be supported by joists or blocking.
Oriented strand board (OSB): conforming to CSA O325. It is sensitive to moisture at the edges; a 3 mm gap between panels is required to allow for expansion.
Lumber boards: rarely used alone, except in renovation work. They must be covered with an underlayment or a cover board.
Spacing Requirement: Plywood and OSB panels must have a 3 mm (1/8 in) gap at all joints to allow for thermal expansion and prevent warping.
2.2.2 Concrete Substrates
Cast-in-place concrete: must have a cure time of at least 28 days before applying an adhered membrane. Residual moisture must be measured (see Section 2.4).
Precast (prestressed) slabs: joints must be sealed and covered with a levelling layer.
Tapered concrete insulation (slope-to-drain): made with lightweight concrete or tapered insulation, it must have a minimum slope of 1:50.
2.2.3 Metal Substrates
Steel roof deck: must be clean, free of oil, rust, and primed if necessary. Fasteners must be spaced according to wind calculations (see Section 2.5).
Stainless steel or aluminum: requires a specific bonding primer for adhered membranes.
2.2.4 Insulation as Substrate
Rigid insulation boards (polyisocyanurate, extruded polystyrene, mineral wool) often serve as a substrate for single-ply membranes. They must be:
Compatible with the membrane (check technical data sheets).
Mechanically fastened or adhered according to manufacturer specifications.
Covered with a vapour barrier on the warm side (interior side) to prevent condensation.
Caution: Expanded polystyrene (EPS) must never be used in direct contact with a hot bituminous membrane, as it will melt. A thermal barrier (glass fibre mat) is required.
2.3 Vapour Barriers and Ventilation
2.3.1 Vapour Barrier
The vapour barrier is a material that limits the diffusion of water vapour from the building interior into the roof assembly. It is mandatory in Canadian climates to prevent condensation within the insulation.
Location: on the warm side of the insulation (interior side).
Materials: polyethylene (6 mil or greater), self-adhering bituminous membrane, or aluminum foil.
Permeance value: must be less than 1 perm (57 ng/(Pa·s·m²)).
NBCC Rule (Article 9.25.4.2): The vapour barrier must be continuous, without tears, and all joints must be sealed.
2.3.2 Roof Ventilation
For sloped roofs with a ventilated attic space, ventilation is essential to remove moisture and heat.
| Ventilation Type | Minimum Requirement (NBCC) |
|---|
| Intake vents (eaves) | 1/300 of the ceiling area |
| Exhaust vents (ridge) | 1/300 of the ceiling area |
| Total ventilation area | 1/150 of the ceiling area if no vapour barrier |
Formula: Ventilation area (m²) = Ceiling area (m²) ÷ 300 (or ÷ 150 without a vapour barrier).
Common Trap: Ridge vents must be installed with a 50 mm (2 in) gap on each side of the ridge to ensure adequate airflow.
2.4 Surface Preparation
Preparation is the most critical step. A membrane installed on a poorly prepared substrate will fail prematurely.
2.4.1 Moisture Assessment
Halogen lamp test (plastic sheet test): a simple method to detect relative moisture in a concrete substrate. A 450 mm × 450 mm polyethylene sheet is sealed to the concrete for 24 hours. If water droplets appear, the concrete is too damp.
Calcium chloride test (ASTM F1869): measures the moisture vapour emission rate (MVER). The typical limit is 3 lbs/1000 ft²/24 h (14.6 g/m²/24 h) for most adhered membranes.
Electronic moisture meter: for wood, moisture content must be below 19% (ideally 12–15%).
2.4.2 Cleaning and Priming
Cleaning: remove all dirt, oil, grease, laitance, or debris. Use a mechanical broom, industrial vacuum, or high-pressure water jet (followed by complete drying).
Primer: apply a primer compatible with both the substrate and the membrane. The primer improves adhesion and seals dust. It must be applied in a uniform coat and allowed to dry according to manufacturer instructions (typically 1 to 4 hours).
2.4.3 Substrate Repairs
Concrete: cracks wider than 3 mm must be repaired with a polyurethane sealant or epoxy grout. Honeycombing must be filled.
Wood: damaged or rotted panels must be replaced. Protruding nails or screws must be driven in or removed.
Metal: burrs must be ground down, and rusted areas treated with a rust inhibitor.
2.5 Fastening Calculations and Wind Resistance
Roofs are subject to wind uplift forces. Calculating wind resistance is essential for mechanically fastened membranes or insulation boards.
2.5.1 Design Wind Pressure
The design wind pressure (q) is determined according to the NBCC (Appendix C) and depends on:
The reference wind velocity (V) in km/h for the region.
The exposure factor (Ce) based on height and terrain roughness.
The gust factor (Cg).
The external pressure coefficient (Cp) and internal pressure coefficient (Cpi).
Simplified Formula: q = 0.5 × ρ × V² × Ce × Cg × Cp
Where ρ is the air density (approximately 1.2 kg/m³).
2.5.2 Fastener Spacing
For a mechanically fastened membrane, fastener spacing is determined by:
Spacing (m) = Fastener pull-out resistance (N) ÷ (Local wind pressure (Pa) × Membrane width (m))
Example: A 2 m wide membrane, fasteners with an 800 N pull-out resistance, local wind pressure of 1500 Pa.
Spacing = 800 ÷ (1500 × 2) = 0.267 m (267 mm).
Rule of Thumb: Fastener rows must be spaced a maximum of 300 mm apart in the perimeter (high wind zone) and a maximum of 600 mm apart in the field of the roof, according to calculations.
2.5.3 Wind Zones
The NBCC defines three roof zones:
Corner zone (perimeter): highest wind pressure, width = 10% of the smallest building dimension, but at least 1 m.
Edge zone: intermediate pressure.
Field (interior) zone: lowest pressure.
Common Trap: Candidates often forget to increase fastener density in the corner zones. This is a major cause of in-service failure.
2.6 Applicable Standards and Codes
The following standards are cited on the Red Seal exam. You must know their exact titles and scopes of application.
| Standard | Title | Application |
|---|
| NBCC | National Building Code of Canada | General design and construction requirements |
| CAN/CSA A123.21 | Standard for the wind resistance of membrane roofing systems | Wind resistance testing of membranes |
| CAN/CSA A123.5 | Asphalt shingles | Asphalt shingles |
| CAN/CSA A123.17 | Bitumen for roofing | Roofing bitumen |
| CAN/ULC S701 | Thermal insulation for buildings | Thermal insulation |
| CAN/ULC S705.1 | Polyurethane foam insulation | Polyurethane foam insulation |
| CSA B149.1 | Natural gas and propane installation code | Relevant if gas appliances penetrate the roof |
Rule 8-200 of the Canadian Electrical Code, Part I (CE Code): This rule concerns electrical installations on roofs (e.g., solar panels). It requires a 1 m working space around equipment and fall protection. Although this falls under electrical work, the roofer must coordinate their work with these requirements.
2.7 Installation Procedures by System Type
2.7.1 Modified Bituminous Membrane (SBS/APP)
96.Preparation: substrate dry, primed.
97.Laying: unroll the membrane, position it, then heat it with a torch (SBS) or weld it with hot air (APP).
98.Lap seams: sheets must overlap by 75 mm (3 in) on longitudinal edges and 150 mm (6 in) at the ends.
99.Welding: the weld must be continuous, without burning the bitumen (appearance of black smoke = overheating).
100.Terminations: wall flashings must have a minimum height of 150 mm above the finished roof surface.
Application Temperature: The torch must produce a blue flame (temperature of 1200 °C to 1400 °C). The bitumen must melt without running or burning.
2.7.2 Single-Ply Membrane (PVC/TPO/EPDM)
103.Attachment: mechanical (screws + plates) or adhered (adhesive or ballast).
104.Seam welding: hot air (PVC/TPO) or adhesive tape (EPDM).
105.Weld width: minimum 25 mm (1 in) for a hot-air weld.
106.Weld testing: a peel test must be performed on a sample to verify weld quality.
Common Trap: TPO and PVC must not be welded together. Their chemical composition is incompatible.
2.7.3 Asphalt Shingles (Steep Slope)
109.Underlayment: asphalt-saturated felt (15 lb or 30 lb) or synthetic underlayment, installed with a 50 mm (2 in) overlap on horizontal joints.
110.Shingle installation: start at the bottom, with a 1/2 shingle-width offset between rows.
111.Fastening: 4 nails per shingle (6 in high-wind zones), placed 25 mm above the cutout line.
112.Exposure: the maximum exposure is 145 mm (5 3/4 in) for standard shingles.
Calculating the Number of Shingles: Roof area (m²) ÷ Area covered by one bundle (m²) = Number of bundles. Add 10% for cuts and waste.
2.8 Flashings, Penetrations, and Counter-flashings
2.8.1 Wall Flashings
A flashing is the upturn of the membrane onto an adjacent wall. It must:
Have a minimum height of 150 mm above the roof surface.
Be mechanically fastened at the top (metal counter-flashing or termination bar).
Be sealed with a compatible sealant.
2.8.2 Penetrations
Penetrations (pipes, vents, stacks) must be sealed with:
A pre-formed pipe boot made of EPDM or TPO.
A two-piece metal counter-flashing.
A polyurethane or silicone sealant.
Rule: Every penetration must have a flashing height of at least 150 mm and a counter-flashing that overlaps the base flashing by a minimum of 75 mm.
2.8.3 Metal Counter-flashings
Metal flashings (aluminum, galvanized steel, copper) must be:
Fastened with compatible attachments (no galvanic contact between dissimilar metals).
Sealed with sealant at the joints.
Installed with a positive slope to shed water.
2.9 Safety and Fall Protection
Although this chapter focuses on systems, safety is a major exam topic.
Guardrails: mandatory if the slope is greater than 4:12 and the fall height exceeds 3 m.
Lifeline: must be anchored to a structure capable of supporting 18 kN (static load) or 8 kN (dynamic load).
Scaffolding: conforming to CSA S269.2, with guardrails at 0.9 m and 1.1 m.
Personal protective equipment (PPE): harness, lanyard, hard hat, safety glasses, and heat-resistant gloves for torch work.
Common Trap: Candidates forget that torch work requires a Class ABC fire extinguisher within 7.5 m of the work area, according to fire prevention regulations.
Pitfalls to Avoid
142.Confusing slope and pitch: a 2% slope is not the same as a 2:12 pitch. The former is nearly flat, the latter is approximately 9.5°.
143.Forgetting the spacing of wood panels: a 3 mm gap is mandatory; a tight joint causes warping and distortion of the shingles.
144.Applying a bituminous membrane over EPS insulation without a thermal barrier: the insulation melts and the membrane sags.
145.Neglecting wind zone calculations: fasteners must be more dense at the perimeter and corners.
146.Using a water-based primer on a frozen or damp substrate: the primer does not penetrate and adhesion fails.
147.Welding TPO and PVC together: chemical incompatibility, the weld will not hold.
148.Installing a vapour barrier on the wrong side: it must be on the warm side (interior), otherwise condensation occurs within the insulation.
149.Forgetting the overflow (secondary drainage): mandatory for flat roofs, otherwise water accumulates and overloads the structure.
150.Measuring concrete moisture too early: concrete with less than 28 days of cure has residual moisture that is too high.
151.Ignoring the minimum flashing height: 150 mm, not 100 mm. Insufficient height causes leaks from water back-up.
Summary
Roofing systems are classified by slope (flat, sloped, steep) and by membrane type (bituminous, polymeric, liquid-applied).
The substrate must be dry, clean, smooth, and compatible with the membrane. Wood panels require a 3 mm gap; concrete must have a 28-day cure.
The vapour barrier is placed on the warm side of the insulation and must have a permeance of less than 1 perm.
Attic ventilation must be at least 1/300 of the ceiling area (with vapour barrier) or 1/150 (without vapour barrier).
Surface preparation includes moisture assessment (calcium chloride test, limit of 3 lb/1000 ft²/24 h), cleaning, and primer application.
Wind fastening calculations use the formula q = 0.5 × ρ × V² × Ce × Cg × Cp, and fastener spacing is reduced in corner zones.
Key standards are the NBCC, CSA A123.21 (wind resistance), CAN/ULC S701 (insulation), and CSA B149.1 (gas, for penetrations).
Wall flashings must have a minimum height of 150 mm; penetrations require a two-piece counter-flashing.
Safety requires guardrails for slopes > 4:12, lifelines anchored to 18 kN, and a fire extinguisher within 7.5 m of torch work.
Priority Review Points for the Exam:
Know how to convert slope (%) to a ratio (x:12).
Know the moisture limits for each substrate.
Be able to calculate fastener spacing.
Identify material incompatibilities (EPS + hot bitumen, TPO + PVC).
Memorize minimum heights (150 mm for flashings, 25 mm for welds).
End of Chapter 2. Proceed to Chapter 3 for the study of waterproofing materials and their application methods.
