Best Time to Replace a Roof in Michigan, Month by Month

September is warm without being hot. The normal daily high at Grand Rapids is 73.9°F and the normal low is 53.1°F, so shingles stay flexible, the sealant strips activate in the sun, and self-adhered ice and water shield sticks the way it's meant to.

It's also the driest month from April through October, with 3.43 inches of precipitation in a normal September and no snow, and it comes after the June to August stretch that NWS Grand Rapids calls the peak of Michigan's severe weather season. A roof finished in September has the rest of the fall to seal before November's snow.

October is still a good month. Normal highs run 60.7°F and normal lows 42.2°F, and October is the last month of the year when the average low stays above 40°F. Snow is rare: the normal October total is 0.3 inches.

The catch is rain. October is the wettest month by the normals at 4.02 inches, narrowly ahead of May and April, so expect a weather day or two. The month also cools as it goes, so a late-October roof gets less warm sun to seal before winter than one finished early in the month.

Summer is ideal for the shingles themselves. Normal highs run from 79.4°F to 83.1°F and the lows stay near 60°F, so the sealant strips bond quickly and there's no question of cracking a cold shingle.

What keeps summer out of the top two is the weather. NWS Grand Rapids calls meteorological summer the peak of the severe weather season in Michigan. In the SPC records, July and June are the top two months for damaging-wind reports statewide, and June has more Michigan tornadoes than any other month. A good crew only opens as much roof as it can close up the same day, which matters most in thunderstorm season.

By May the average low is 48.6°F, above the 40°F line, and the normal high is 69.8°F. Temperature isn't the problem.

Rain is. A normal May brings 4.00 inches, the second-wettest month of the year, and May opens the hail peak: May through July account for about 65% of Michigan's hail reports. Plan for weather days and a contractor who watches the forecast.

These are the shoulder months. The normal daily high is above 40°F (57.8°F in April, 47.2°F in November), but nights fall below it, so mornings can mean frost on the deck and a later start. A crew works the warmest hours and follows the manufacturer's cool-weather steps, including hand-sealing the shingles.

April is wet, with 3.99 inches of precipitation and 2.0 inches of snow in a normal year. November is drier at 3.10 inches, but it averages 7.1 inches of snow, and shingles installed late in the month may not seal on their own until the sun warms the roof in spring.

March has a normal high of 44.5°F, just over the 40°F line, and a normal low of 26.9°F. It still averages 7.6 inches of snow, about as much as November.

A March replacement is doable on a dry stretch, with the same cold-weather steps as November. Expect the schedule to follow the forecast.

Winter is the worst time to plan a replacement. The normal daily high stays below 40°F all three months (36.1°F, 31.0°F and 33.7°F), and together they average more than 60 inches of snow. Shingles are stiff, the sealant won't activate, and CertainTeed says its self-adhered underlayments lose most of their stickiness below 40°F.

It can still be done when the roof can't wait. GAF allows installation below 40°F when the contractor follows its mandatory precautions, and says the warranty is not affected when all of its application instructions are followed, including the cool-weather ones like hand sealing. If the roof only needs to stay dry until spring, an emergency repair may be the smarter call.