Roofing Systems & Installation

Everything in a building eventually answers to the roof. You can pour perfect foundations, erect flawless steel, frame beautiful walls — but if the roof leaks, you’re the one getting the call at 6 a.m. on a Sunday morning while the congregation watches water drip onto the communion table. Roofing is the trade where good work is invisible and bad work is a catastrophe.

On church projects, roofing presents unique challenges that you won’t find on a typical commercial box store. Church buildings involve complex geometry — steeples, clerestory walls, dramatic roof pitch changes, massive clear-span sanctuaries with cricket systems, and decorative cupolas that look gorgeous from the parking lot but are an absolute puzzle to waterproof. Membrane systems on flat sections mix with standing seam metal on visible slopes, sometimes on the same building. That means crews need to be versatile.

This guide covers the full range of roofing systems installed on church projects — single-ply membranes (TPO, EPDM, PVC), built-up roofing, modified bitumen, standing seam and exposed fastener metal panels, flashing, insulation, drainage, skylights, and even green roof assemblies. If you’re working toward your Roofer (449A) certification or your Sheet Metal Worker (308A) ticket, this material maps directly to the competencies you’ll be tested on.

1. Single-Ply Membrane: TPO

Thermoplastic Polyolefin — TPO — is the workhorse membrane on church projects. When putting a flat or low-slope roof on a fellowship hall, classroom wing, or gymnasium, there’s about an 80% chance it’s white TPO. It’s reflective (keeping cooling loads down), cost-effective, and when welded properly, those seams are stronger than the sheet itself.

Attachment Methods

• Mechanically attached: The most common method on church projects. Membrane is laid over insulation, fastened at seam overlaps with plates and screws into the structural deck. Seams are then hot-air welded over the fastener row. This system handles wind uplift well and doesn’t require adhesive — which means it works in cooler temperatures when bonding adhesives won’t cure.
• Fully adhered: Membrane is bonded to the substrate with adhesive or self-adhering backing. Gives a cleaner look with no flutter in the wind, and performs better in high-wind zones. Used on projects where aesthetics matter — visible low-slope sections adjacent to occupied areas, or roofs with rooftop mechanical equipment that congregations see from the parking lot.
• Ballasted: Membrane laid loose and held down with river rock or pavers. Rarely used on church projects because church roofs tend to have too many penetrations (HVAC, plumbing vents, steeple connections) for ballast to be practical.

Hot-Air Welding

This is where TPO roofing becomes a skill, not just labour. Hot-air welding fuses the membrane sheets together using a controlled stream of heated air — typically between 450°C and 550°C depending on ambient conditions, membrane thickness, and wind speed. The two standard tools:

• Leister Varimat V2: The automatic welder for field seams. Drives itself along the overlap at a consistent speed and temperature. You set it, guide it, and watch it work. Produces 38 mm minimum weld width on every pass.
• Leister Triac AT: The hand welder for detail work — patches, corners, penetration boots, and any spot the Varimat can’t reach. Think of it as your roofing scalpel. Mastering the Triac is what separates a roofer from a membrane installer.

Field Verification

Every TPO seam gets probed. That means a blunt-tipped probe run along the entire length of every welded seam, applying moderate pressure, checking for any fish-mouths, skips, or unbonded areas. If the probe catches, you stop and repair. No exceptions, no “it’ll be fine.”

2. Single-Ply Membrane: EPDM

Ethylene Propylene Diene Monomer — EPDM — is the old reliable of single-ply roofing. It’s a synthetic rubber membrane, black in colour, and it’s been keeping buildings dry since the 1960s. While TPO has overtaken it on new construction, you’ll still encounter EPDM on renovation projects and on buildings where the original spec calls for it.

Seam Methods

Unlike TPO, EPDM seams are not welded — they’re glued or taped. The two primary methods:

• Splice tape (3-inch): A factory-cured butyl tape applied between cleaned, primed membrane laps. This is the modern standard. Clean both surfaces with EPDM splice wash, apply splice primer, lay the tape, roll it with a steel roller. Sounds simple, but contamination or cold temperatures will ruin the bond.
• Liquid adhesive (splice cement): The older method. Contact cement applied to both membrane surfaces, allowed to flash off, then mated. Still used for some detail work but largely replaced by tape for field seams.

TPO vs. EPDM — Honest Comparison

3. Single-Ply Membrane: PVC

Polyvinyl Chloride membrane is the premium single-ply option. It’s hot-air welded like TPO (same Leister equipment, similar technique), but PVC brings superior chemical resistance and fire performance to the table. On HCMI projects, PVC gets specified when the roof will be exposed to kitchen exhaust grease, generator fuel vapours, or any environment where animal fats or petroleum products might contact the membrane.

When PVC Gets Specified

• Commercial kitchen areas: Church fellowship halls with commercial cooking equipment — the exhaust fan discharge will destroy TPO over time, but PVC handles it.
• Generator pads: Rooftop backup generators with diesel fuel storage. One fuel spill on TPO and you’re re-roofing. PVC shrugs it off.
• High fire-rating assemblies: PVC is inherently fire-resistant (it self-extinguishes) and can achieve ULC Class A ratings more easily than TPO in certain assemblies.

The downside? Cost. PVC runs 15–25% more than TPO installed, and the membrane is less flexible in extreme cold. For most HCMI church roofs without chemical exposure concerns, TPO remains the better value. But when the spec says PVC, there’s a reason — don’t try to value-engineer it out.

4. Built-Up Roofing (BUR)

Built-up roofing is the grandfather of flat roofing systems — multiple plies of reinforcing felt embedded in hot asphalt, built up layer by layer to create a monolithic waterproof membrane. It’s been used for over 100 years, and while single-ply membranes have taken most of the market share, BUR still gets specified on projects where long-term durability and redundancy matter more than installation speed.

System Components

• Base sheet: Mechanically fastened or adhered to the insulation. Provides the foundation for subsequent plies.
• Interply felts: Fibreglass or organic felts mopped in hot asphalt. Typically 3 or 4 plies for commercial applications. Each ply adds redundancy — a puncture has to go through all layers to cause a leak.
• Hot asphalt: Heated in a rooftop kettle to approximately 200°C (equiviscous temperature varies by asphalt type). Applied by mop or mechanical spreader between each ply.
• Surfacing: Either gravel (flood-coated with asphalt and embedded aggregate) or a mineral-surfaced cap sheet. Gravel provides UV protection and ballast; cap sheet is lighter and easier to inspect.

5. Modified Bitumen (SBS/APP)

Modified bitumen sits between BUR and single-ply — it’s asphalt-based like BUR but comes in rolls like a membrane. The asphalt is modified with polymers to improve flexibility and temperature performance. Two types dominate:

• SBS (Styrene-Butadiene-Styrene): “Rubberized” asphalt. Stays flexible in cold weather — critical for Ontario winters. Can be torch-applied, hot-mopped, or self-adhered. Most common on church projects.
• APP (Atactic Polypropylene): “Plasticized” asphalt. More heat-resistant, always torch-applied. Less common in Ontario due to cold-weather brittleness.

Application Methods

• Torch-applied: An open-flame propane torch melts the underside of the roll as it’s unrolled onto the substrate. Produces an excellent bond but introduces significant fire risk. This is the primary method for APP and is common for SBS cap sheets.
• Self-adhered: Factory-applied adhesive backing — peel the release liner and roll it out. No flame, no fumes, no hot work permit. Becoming the preferred method for base sheets and in areas where open flame isn’t practical (near combustible walls, over occupied spaces).
• Hot-mopped: Traditional method using hot asphalt from a kettle, same as BUR. Less common now but still used for multi-ply mod-bit systems.

6. Standing Seam Metal Roofing

This is the signature roofing system on church buildings. When a congregation looks up at their church from the street, it’s usually standing seam metal they’re seeing — on the main sanctuary roof, the steeple, the entrance canopy, the bell tower. Standing seam metal roofing is where function meets aesthetics, and on a church project, aesthetics matter more than almost anywhere else in commercial construction.

System Components

• Panels: Typically 24-gauge steel (Galvalume or pre-painted) or 0.032” aluminum for specialty applications. Panel widths range from 305 mm to 457 mm (12” to 18”). Panels are roll-formed on site with a portable panel machine or pre-fabricated in the shop. Panel profiles: snap-lock, mechanical seam (single or double lock), or batten seam.
• Clips: Concealed fastening clips attached to the substrate — the panel floats on the clip, allowing thermal expansion and contraction. Fixed clips at the ridge, sliding clips toward the eave. Clip spacing per engineering — typically 600 mm o.c. for standard wind loads, tighter in high-wind zones.
• Underlayment: High-temperature self-adhering ice and water shield over the entire deck (not just at eaves and valleys like residential). On HCMI projects, we underlay 100% of the metal roof deck — it’s the secondary waterproofing layer.
• Ridge cap and trim: Custom-fabricated ridge caps, valley pans, eave drip edges, rake trim, and transition flashings. All fabricated in the shop by 308A sheet metal workers using the brake.

Seaming

After panels are set on clips, the raised seam legs are folded together using a mechanical seaming machine. For double-lock seams, the machine makes two passes — the first folds the seam over 90°, the second folds it flat against itself, creating a weather-tight 360° lock. The seaming machine rides along the seam at a controlled pace; forcing it or going too fast produces inconsistent folds and potential leak paths.

7. Exposed Fastener Metal Panels

Not every roof on a church project needs the premium treatment. Support buildings, storage sheds, maintenance garages, and covered walkways often get exposed fastener metal panels — R-panel (trapezoidal rib) or AG-panel (agricultural profile). They’re less expensive than standing seam, faster to install, and perfectly functional for utilitarian applications.

Installation Essentials

• Fastener pattern: Screws with EPDM washers driven through the panel flat (not the rib) into purlins below. Typical pattern is every other rib at purlins, every rib at eaves and ridges. Over-driving crushes the washer and creates a leak point; under-driving leaves the washer loose and creates a leak point. Get it right.
• Sealant: Butyl tape sealant at all panel laps, ridge caps, and trim interfaces. Don’t rely on screws alone to keep water out — sealant is your second line of defence.
• Trim: Eave drip, rake trim, ridge cap, and transition flashings. Pre-fabricated or shop-bent. Even on a utility building, trim should be straight, tight, and clean — standards should not lower just because the building is a garage.
• Panel overlap: Minimum one rib overlap at side laps. End laps minimum 150 mm with sealant tape. Always lap panels so the prevailing wind hits the lap edge, not the open seam.

8. Roof Flashing

If there’s one section in this entire guide that you should read twice, it’s this one. Flashing is where roofs leak. Not in the middle of a membrane field, not in the centre of a metal panel — at the edges, the penetrations, the transitions, the curbs, the walls. Every point where the roofing system meets something else is a potential failure point, and flashing is what keeps water out at those joints.

Common Flashing Locations

• Pipe penetrations: Plumbing vents, electrical conduit, gas lines. Each one gets a pre-formed or field-fabricated boot or pitch pan, integrated into the membrane or metal roofing.
• HVAC curbs: Rooftop units sit on raised curbs. The curb is flashed with base flashing that extends up the curb face and over the top, lapped under the unit’s factory flange. This is a high-failure area — the curb deflects under load, the unit vibrates, and the flashing fatigues over time.
• Roof-to-wall transitions: Where a low roof meets a higher wall (extremely common on church buildings with stepped roof planes). Counter-flashing is set into a reglet cut in the wall, with base flashing extending up behind it. The counter-flashing sheds water over the base flashing — two layers, one system.
• Valleys: Where two roof planes meet at an inside angle. W-valley or open valley with a fabricated metal pan. On standing seam roofs, valleys are custom-fabricated sheet metal with a standing water dam on each side.
• Edge details: Drip edges, gravel stops, coping caps. The perimeter is where wind uplift is highest — edge flashings must be mechanically fastened, not just adhered.

Sheet Metal Brake Work

Most custom flashings on church projects are fabricated on site or in the shop using a sheet metal brake. This is 308A Sheet Metal Worker territory — the compulsory trade. Bending clean, accurate flashings requires understanding material behaviour, bend allowances, and hem details. A flashing with a wavy bend or an inconsistent leg height doesn’t just look bad — it creates gaps where water enters.

9. Roof Insulation

Roofing insulation isn’t just about keeping the building warm — it’s a structural component of the roof assembly, it controls condensation, and it creates the slope that directs water to drains. On HCMI church projects, where sanctuary ceilings can be 10 m high and heating costs are a perpetual concern for congregations, getting the insulation right has a decades-long financial impact.

Insulation Types

Tapered Cricket Systems

Flat roofs aren’t actually flat — or at least they shouldn’t be. The Ontario Building Code requires a minimum 1:50 slope (2%) to drains. On HCMI projects, we achieve this slope using tapered insulation — factory-cut polyiso or EPS boards that increase in thickness from drain to high point, creating a built-in slope without structural changes to the deck.

Crickets are tapered insulation saddles placed behind penetrations and along structural members to redirect water toward drains rather than letting it pond. Every HVAC unit, every pipe cluster, every structural beam that projects above the roof plane gets a cricket. Ponding water is the enemy — it degrades membranes, adds dead load, and breeds mosquitoes in the summer (which is somehow also the roofer’s fault).

10. Roof Drains & Scuppers

All the slope in the world doesn’t matter if the water has nowhere to go. Roof drainage is the final piece of the waterproofing puzzle, and it requires tight coordination between the roofing crew, the plumber, and the structural engineer. On HCMI church projects, we typically use interior roof drains on flat-roof sections and scuppers or gutters on sloped metal roofs.

Interior Roof Drains

• Drain body: Cast iron or ABS body set flush with the structural deck, connected to the storm piping below. The plumber sets the drain body; the roofer integrates the membrane flashing into the drain flange. This handoff is critical — if the membrane-to-drain connection fails, every drop of water on that roof is going into the building.
• Clamping ring: A compression ring that sandwiches the membrane between the drain body and the ring. Bolts torqued evenly — uneven clamping creates gaps. Use a star pattern, just like torquing a wheel.
• Strainer (dome): The visible dome that prevents debris from clogging the drain. Must extend minimum 100 mm above the roof surface. Clean them. Seriously. A clogged drain turns your carefully sloped roof into a swimming pool.

Overflow Protection

The OBC requires secondary (overflow) drainage on all flat roofs. If the primary drain clogs, water must have somewhere to go before it exceeds the structural load capacity of the deck. Options include:

• Overflow scuppers: Openings in the parapet wall set 50 mm above the primary drain level. Water hits the scupper before it reaches dangerous depth.
• Overflow drains: Secondary drain bodies set at a higher elevation than the primary drains, connected to separate storm piping.

11. Skylights & Roof Hatches

Skylights are common on church projects — natural light in a sanctuary or fellowship hall reduces electrical costs and creates beautiful worship spaces. Roof hatches provide maintenance access. Both are penetrations through your carefully waterproofed roof, and both require meticulous curb and flashing details.

Skylight Installation

• Curb construction: Skylights sit on raised curbs — typically minimum 200 mm (8”) above the finished roof surface to prevent water ingress during rain and snow accumulation. Curbs are framed with pressure-treated lumber or metal, insulated, and clad with the roofing membrane extending up and over the curb top.
• Setting the unit: Skylight is set on the curb and fastened per manufacturer instructions. Gaskets, sealant, and weep holes all matter. Never skip the weep holes — they let condensation escape. Block them and you’ll get interior dripping that looks like a leak but isn’t.
• Flashing integration: The skylight manufacturer provides a flashing kit, but the roofer is responsible for tying it into the field membrane. Laps must follow shingle-style — lower pieces under upper pieces so water sheds outward at every layer.

Smoke Vents

Ontario fire code requires automatic smoke vents on certain large-area buildings, including church sanctuaries over specific size thresholds. These are essentially skylights with fusible link releases that pop open in a fire to vent smoke and heat, aiding firefighter operations. The roofing crew installs the curb and base flashing; the fire protection contractor installs the vent mechanism. Coordinate early — the curb opening must match the vent unit exactly, and the fusible links must not be painted, sealed over, or obstructed by roofing materials.

12. Green Roof Systems

Green roofs are becoming more common on church projects, particularly where congregations want rooftop community gardens, stormwater management credits for municipal approvals, or simply want to be good stewards of the environment. A green roof is a living system built on top of a waterproof roof assembly, and getting it right requires understanding both roofing and horticulture.

System Layers (Bottom to Top)

1. Waterproof membrane: PVC or TPO, fully adhered. This is the most critical layer — once 150 mm of growing medium is on top of it, finding a leak is an archaeological excavation. The membrane must be flood-tested before any green roof components go on.
2. Root barrier: A chemically treated sheet that prevents plant roots from penetrating the membrane. Some PVC membranes have built-in root resistance, but HCMI specs always call for a separate barrier — belts and suspenders.
3. Drainage layer: Dimpled plastic sheet or granular drainage mat that channels excess water to roof drains. Without it, the growing medium becomes waterlogged and the plants die — and the added water weight stresses the structure.
4. Filter fabric: Geotextile that prevents fine soil particles from washing into and clogging the drainage layer.
5. Growing medium: Engineered lightweight soil mix — not garden soil. Typically 100–150 mm deep for extensive (sedum) systems, 200–400 mm for intensive (garden) systems. Weight when saturated is the critical structural consideration — the engineer must design for it.
6. Vegetation: Sedum and drought-resistant plants for extensive systems; vegetables, herbs, and perennials for intensive church community garden systems.

13. Roofing Day Checklist

Every roofing day on a church project starts and ends with a checklist. Roofing is weather-dependent, safety-critical, and unforgiving of shortcuts. This checklist keeps crews consistent and protects both the building and the people on top of it.

Pre-Work Inspection (Before 7:00 a.m.)

• Check weather forecast — current conditions, precipitation probability, wind speed, and temperature. No membrane installation below 5°C without manufacturer approval and supplemental heating. No metal panel work above 40 km/h wind. No torch work if gusts exceed 25 km/h.
• Inspect fall protection systems — guardrails, anchors, lifelines, harnesses. Check harness webbing for cuts, fraying, or chemical damage. Check lanyards and SRLs for proper retraction.
• Walk the roof surface — look for overnight damage, ponded water, debris, or displaced materials. Report any issues before work starts.
• Verify hot work permit (if torch or kettle operations are planned). Confirm fire extinguishers are charged and positioned.
• Review the day’s scope with the crew — what areas are being worked, what materials are needed, what coordination with other trades is required.

Material Staging

• Membrane rolls, insulation boards, fasteners, and adhesives staged on the roof in the work area — not scattered across completed sections where foot traffic will damage finished work.
• Materials stored flat and weighted or strapped down. An unsecured membrane roll in a gust of wind becomes a 40 kg projectile.
• Adhesives and sealants stored within manufacturer temperature range. Bonding adhesive that froze overnight is garbage — don’t use it.

Weather Monitoring (Ongoing)

Roofing crews watch weather the way farmers do — constantly. Ontario weather changes fast, and getting caught with open membrane laps and exposed insulation when a thunderstorm rolls in is a disaster. The foreman monitors weather radar on a phone or tablet throughout the day. If rain is within 30 minutes, all open work gets sealed or tarped — no exceptions.

End-of-Day Tie-In

This is the most important 30 minutes of the roofing day. Before anyone leaves the roof, all exposed edges must be sealed:

• Membrane: All open laps temporarily sealed with membrane adhesive or weighted. Exposed insulation covered with tarps or temporary membrane. Water that gets under the membrane overnight causes blistering, delamination, and insulation degradation.
• Metal panels: Loose panels clamped or screwed at minimum two points to prevent wind displacement overnight.
• Flashing: All incomplete flashing work sealed with temporary sealant or taped. An unfinished flashing in an overnight rain puts water directly into the building.
• Tools and debris: All tools, fasteners, and scrap collected and secured. Loose metal on a roof in a windstorm is a projectile hazard.

Codes, Standards & Trade References