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3. When to replace a roof

# When is the best time of year to replace a roof around Brantford and Hamilton?

Around Brantford and Hamilton, May to September is the easiest time to replace a shingle roof: Environment Canada's normals for Hamilton airport show daytime highs above 10°C on nearly every day of those months. A roof can still go on in the cold. Shingle makers say cold shingles turn brittle and can take weeks to seal, so a winter roof is laid with extra care and hand sealing.

Updated 16 October 2026 by Straight Arrow Roofing & Siding

## What is the weather like for roofing, month by month?

These are Environment Canada's climate normals for the Hamilton A weather station at the airport in Mount Hope, which sits between Brantford and Hamilton. Normals are 30-year averages, here 1981 to 2010, so they describe a typical year, not this one.[1]

| Month | Average high | Average low | Days above 10°C | Days with 5 mm or more of rain or snow | Thunderstorm days | Snowfall |
| --- | --- | --- | --- | --- | --- | --- |
| January | −1.7°C | −9.3°C | 1 | 4 | 0 | 41 cm |
| February | −0.5°C | −8.6°C | 1 | 4 | 0 | 35 cm |
| March | 4.3°C | −4.5°C | 6 | 4 | 1 | 26 cm |
| April | 11.8°C | 1.5°C | 17 | 5 | 2 | 8 cm |
| May | 18.5°C | 7.1°C | 29 | 6 | 4 | 1 cm |
| June | 23.9°C | 12.6°C | 30 | 5 | 5 | 0 cm |
| July | 26.5°C | 15.2°C | 31 | 5 | 6 | 0 cm |
| August | 25.3°C | 14.5°C | 31 | 4 | 6 | 0 cm |
| September | 21.2°C | 10.4°C | 30 | 5 | 3 | 0 cm |
| October | 14.1°C | 4.5°C | 24 | 5 | 1 | 1 cm |
| November | 7.5°C | −0.2°C | 9 | 5 | 1 | 11 cm |
| December | 1.2°C | −5.8°C | 2 | 5 | 0 | 33 cm |

"Days above 10°C" counts days whose high is warmer than 10°C. "Days with 5 mm or more" counts days with at least 5 mm of rain, or snow measured as water. Both are averages, so they are not whole numbers in the source; we have rounded them.[1]

## Why does temperature matter so much for shingles?

Because of the seal strip. Asphalt shingles are made with a strip of sealant that bonds each course to the one below it, and the sun does the bonding. Owens Corning puts it this way: "Direct exposure to the sun's energy activates the sealant, allowing shingles to bond to the course below."[2] In the cold that takes longer. For temperatures "at or below 40°F (4°C)", the company says "Shingles installed in cold weather may not immediately seal until warmer temperatures are present for the sealant to activate."[2]

IKO says the same, and says why it matters: "it might take up to several weeks for shingles to seal together", and "Shingles that do not seal together have a higher propensity for blow-off which could result in roof leaks."[3] It also warns that asphalt shingles "can become more brittle in cold weather", at 10°C and below, so bundles must never be bent, dropped or thrown.[3]

## Can you replace a roof in winter?

Yes. IKO says "it is possible to shingle year-round", with extra care.[3] Three things change on a cold-weather roof:

- **Warm shingles.** IKO notes that some contractors bring bundles into a heated space for a few hours before they go up, so they bend without cracking.[3]

- **Hand sealing.** If the shingles will not have time to seal before winter, IKO recommends sealing them by hand with asphalt plastic cement.[3] Owens Corning asks for four 1-inch dabs of roof cement under each shingle around the whole edge of the roof when it is 4°C or colder.[2]

- **Shorter days.** Snow, ice and early dark cut into the working day, so the same roof takes longer in January than in June. A good crew only opens as much roof as it can close the same day.

## Which months bring the most rain, storms and wind?

Rain is spread through the whole year: every month averages three to six days with 5 mm or more. Summer is when it arrives as storms. July has the most precipitation, 101 mm, and the most thunderstorm days, about 6, so summer re-roofing is planned around the forecast day by day.[1] Wind runs the other way: the station averages about three days a month with winds of 28 knots (52 km/h) or more from October to April, against one or fewer a month from June to September.[1] That is one more reason a winter roof gets hand sealed.

## What if the roof is leaking now?

Do not wait for the season. A leak does more damage the longer it runs, and [repairs](https://straightarrow-dev.pages.dev/services/roof-repair/) are done all year. A full replacement can be planned for warmer weather once the leak is stopped, and the [inspection](https://straightarrow-dev.pages.dev/services/roof-inspections/) tells you how much time the roof really has.

## Can I share or reuse this table?

Yes. The table is free to use, quote or link to. The numbers belong to Environment and Climate Change Canada; we have only picked the ones that matter for a roof. We read them, and both manufacturer bulletins, on 16 October 2026.

## Sources

1. [Canadian Climate Normals 1981 to 2010, Hamilton A (climate ID 6153194)](https://api.weather.gc.ca/collections/climate-normals/items?STN_ID=4932&f=html), Environment and Climate Change Canada, MSC GeoMet API, read 16 October 2026.
2. [Cold weather shingle installation, technical bulletin 10022497-A, April 2026](https://www.owenscorning.com/dms/10022497), Owens Corning, read 16 October 2026.
3. [Installing shingles in cold weather, residential information bulletin R-52, August 2012](https://www.iko.com/na/document/tbr52-installing-shingles-in-cold-weather-product-bulletin), IKO, read 16 October 2026.

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Source: https://straightarrow-dev.pages.dev/guides/best-time-to-replace-a-roof/