Why Modern Roofs Fail in Moderate Winds — and What the Ontario Building Code Requires

Why modern roofs fail in moderate winds

Modern roofs fail in moderate winds because of installation defects, not weather: nails driven above the manufacturer's nail line, adhesive strips that never sealed on cold-weather installs, and missing starter strips at the eaves. A roof installed to spec should shrug off far more than a moderate wind — architectural shingles are rated for roughly 130 km/h when properly nailed and seated, well above anything a typical GTA summer storm delivers.

That's the answer in one paragraph. The rest of this guide is the evidence.

When we do post-storm assessments across Toronto after a 70–90 km/h event, the pattern repeats: two houses side by side, same age, same wind. One loses nothing. The other loses thirty tabs off a roof installed four years ago. The weather was identical — the workmanship wasn't. The three defects below account for nearly every 'new roof, moderate wind, shingles on the lawn' call we take, and every one of them is invisible from the ground on the day of installation.

Defect 1: nails above the manufacturer's nail line

Every shingle has a printed or specified nail zone — a band where the nail passes through the shingle *and* catches the top edge of the shingle in the course below. One nail placed there fastens two shingles.

Drive the nail an inch too high and two things go wrong at once:

• The nail misses the course below entirely, so every shingle is now held by half the intended fasteners
• The nail sits in a thinner part of the mat, where it can pull through under uplift

Why does it happen? Speed. High nailing is the signature of a crew being paid by the square and moving too fast to place the gun precisely. It's also completely invisible once the next course goes on — the roof looks perfect from the driveway, and it stays looking perfect until the first real wind gets under an edge. Then shingles don't tear; they come off whole, nail holes intact, because nothing below was holding them.

This is why we photograph nail placement on every job. It's the one moment in a roof's life when the defect can be seen, and a photo record settles arguments before they start.

Defect 2: adhesive strips that never sealed

Asphalt shingles arrive with a factory-applied adhesive strip. It isn't sticky in the wrapper — it's heat-activated. The shingle gets nailed down, the sun warms the roof, and the strip bonds each shingle to the one below it. That bond is where most of a shingle's rated wind resistance actually comes from; the nails hold it to the deck, but the seal is what stops wind from getting underneath.

Here's the failure: below roughly 5°C, those strips can't activate. A roof installed in late November may sit through the entire winter with every shingle nailed down but none of them sealed — hundreds of loose flaps waiting for a gust. If a windstorm arrives before a stretch of warm sunny weather does, the roof fails at wind speeds it was rated to triple.

Cold-weather installation isn't automatically wrong — sometimes an emergency replacement can't wait for spring. But it demands hand-sealing each shingle with roofing cement, which is slow, and which the low bid never includes. Many manufacturers void their wind warranty on cold installs done without it.

Defect 3: missing starter strips at the eaves

The first course of shingles at the eave is the most exposed row on the roof — it's where wind hits first and where uplift pressure concentrates. That course is supposed to sit on a starter strip: a dedicated product (or a properly cut shingle) that puts a continuous adhesive bead directly along the eave edge, sealing the first course down at the exact line where wind attacks it.

Skip the starter strip and the bottom edge of the first course has nothing bonding it. Wind gets a fingerhold under the eave, peels the first course, and then works up the roof like a zipper — which is why wind damage so often shows as a strip of missing shingles running up-slope from the gutter line.

Crews skip starters for the oldest reason there is: it saves a bundle of material and an hour of work, and nobody can see the difference from the ground. Some cut costs halfway by flipping field shingles upside-down as starters — which puts the adhesive strip in the wrong position and seals nothing. From the ladder, we can spot a missing starter in seconds. From the lawn, you never will.

3-tab vs. architectural: the wind-rating gap

Installation defects aside, the product on the roof sets the ceiling on what any roof can survive.

• Older 3-tab shingles may lift at 60–80 km/h, especially once aged and brittle. Each tab is a single-layer flap with one adhesive bond, and decades of freeze-thaw leave the tabs stiff enough to crack rather than flex.
• Architectural (laminated) shingles are rated for approximately 130 km/h sustained when properly nailed and seated. They're heavier, doubled in layers, and bond over a larger area.

For context, Toronto has recorded 80–110 km/h gusts during several GTA storm events in recent years. That's the uncomfortable overlap: routine summer storms now sit squarely above the failure point of an aged 3-tab roof and comfortably below the rating of a well-installed architectural one. If your roof is 3-tab and past its mid-teens, moderate-wind damage isn't a possibility — it's a schedule.

One more thing the ratings don't show: winds that don't remove shingles can still break adhesive seals and leave the roof vulnerable to the next event. A roof can pass a visual check after a storm and fail two storms later from damage done the first time. That's why post-storm assessments check seal bonds, not just missing tabs.

Which part of the Ontario Building Code addresses roofs

Section 9.26 of the Ontario Building Code covers roofing for houses — materials, slopes, flashing, and eave protection. Larger buildings, including most commercial and multi-unit properties, fall under Part 5 of the Code, which governs environmental separation — the building envelope's resistance to wind, water, and vapour. If your building is a house or small residential building, Section 9.26 is the part that addresses your roof.

In plain language, here's what each does:

• Section 9.26 (Part 9 buildings — houses and small buildings) is prescriptive. It sets out acceptable roofing materials, the minimum slopes each material may be installed on, how flashing must be handled at intersections and penetrations, and eave protection — the membrane requirement at the roof edge that defends against ice damming, a distinctly Ontario concern.
• Part 5 (larger buildings) is performance-based rather than prescriptive. Instead of listing acceptable materials and slopes, it requires the roof assembly to demonstrably resist wind loads, precipitation, and moisture transfer for the building's location and exposure. Commercial flat roofs, mid-rises, and institutional buildings live here.

Two honest caveats. First, the Code is a minimum — the floor, not a quality standard. A roof can meet 9.26 and still carry every wind defect described above, because the Code inspector isn't checking nail placement against a manufacturer's spec sheet. Second, manufacturer installation instructions are frequently *stricter* than Code, and it's the manufacturer's requirements that govern your warranty. Every Blue Knight installation is spec'd to meet or exceed both.

What to ask your installer

Five questions separate crews that build wind-resistant roofs from crews that build roofs that photograph well:

1. 01

   'Where will the nails go, and will you photograph it?' The right answer names the manufacturer's nail zone and offers photo documentation without flinching.

2. 02

   'What starter product are you using at the eaves and rakes?' You want a named starter strip product — not silence, and not 'we cut field shingles'.

3. 03

   'What happens if it's below 5°C during the install?' The right answer involves hand-sealing with roofing cement or rescheduling — not 'the sun will get it eventually'.

4. 04

   'What wind speed is this shingle warrantied for, and what installation conditions does the warranty require?' This forces the product spec and the workmanship requirements into the same conversation.

5. 05

   'Is your workmanship warranty in writing, and does it cover wind loss?' The manufacturer covers the shingle failing as a product; only the installer's warranty covers the shingle failing because of how it was nailed.

The insurance implications of installation defects

Here's where installation defects get expensive twice. Home insurance in Ontario typically covers roof damage from a sudden event — a windstorm, hail, a falling limb. It does not cover gradual wear, and critically, insurers can contest claims where the real cause was defective installation rather than the wind itself.

Picture the adjuster's view: a four-year-old roof lost shingles in a 75 km/h storm. The shingle was rated for 130 km/h. The adjuster's reasonable question is why a roof rated for nearly double the recorded wind speed failed — and if the answer is high nailing or missing starters, the claim conversation shifts from the insurer toward the installer's workmanship warranty. If that installer is unreachable, uninsured, or out of business, the homeowner is standing in the gap.

What protects you, in order of usefulness:

• Installation documentation. Photos of nail placement, starter courses, and flashing from the original install. This is why we photograph every stage.
• A written, transferable workmanship warranty from a contractor who will still exist in year eight.
• A prompt post-storm assessment with photos and a written cause finding. We document whether damage traces to the weather event or to a pre-existing defect — honestly, either way — because that written cause is what gives you the strongest possible case with your insurer.
• The permit record. Unpermitted roof work can void coverage outright, before anyone even discusses nails.

A moderate wind should be a non-event for your roof. If it wasn't, the wind is rarely the interesting part of the story — and finding the real cause quickly is worth more than any patch.