This article explains the most common mistakes that lead to leaks, focusing on flashing, ventilation, and underlayment. Many leaks that appear within a few seasons trace back to a few details that are easy to overlook during installation. Understanding these details helps homeowners ask the right questions before work begins. Call
517-404-7606 today to schedule a roof replacement inspection.
Why Flashing Matters in a Roof Replacement
Flashing is the metal or membrane that seals joints where the roof meets chimneys, vents, walls, and skylights. Reusing old flashing is one of the most common causes of leaks after a re-roof. Flashing and drip edge cannot be reused reliably, so they should be replaced with the new roof.
Skipping step flashing or improperly lapping it at walls can also let water move behind the shingles. Each joint should shed water downward. Inspect these areas after installation and again after the first heavy storm.
How Ventilation Affects a New Roof
Attic ventilation keeps air moving so moisture and heat do not build up under the roof deck. Poor ventilation can cause condensation, shorten shingle life, and contribute to ice dams in Michigan winters. Adding new shingles over an old layer can also reduce airflow, which is why full tear-off is generally recommended.
A balanced system of intake and exhaust vents works best. Blocked soffits, closed vents, or insulation that covers the eaves can undo the benefit of a new roof. Ask whether the attic ventilation will be checked as part of the roof replacement.
Underlayment and Decking Mistakes to Avoid
Underlayment is the water-resistant layer that sits between the deck and the shingles. Damaged or missing underlayment allows water to reach the deck during heavy rain or snowmelt. A complete underlayment installation is a standard part of a well-run project.
Soft or rotten decking should be replaced before new shingles go down. Installing shingles over damaged sheathing can trap moisture and create uneven surfaces. Ask the contractor how decking is inspected and whether any repairs are included in the estimate.
Common Warning Signs After a Roof Replacement
Leaks often show up first as stains on ceilings, damp insulation in the attic, or water near a vent or skylight. Light staining after heavy rain can still signal a problem that needs a closer look. Early attention keeps a small repair from becoming interior damage.
Homeowners should look at the attic after the first few storms and check the flashing at each penetration. Any new stain should be photographed and reported to the contractor, since warranty claims depend on documentation.
Skylights and Other Penetrations Need Extra Care
Skylights, chimneys, plumbing vents, and exhaust fans all pierce the roof and must be sealed carefully. Each penetration creates a point where water can enter if the flashing is missing, mis-lapped, or poorly sealed. These spots deserve close attention on every roof replacement.
A thorough installer checks each penetration after the new shingles are in place. Look for clean flashing lines and sealant only where the manufacturer allows it. Ask the contractor how penetrations will be flashed before work starts.
Ice Dams and Michigan Winters
Ice dams form when snow melts on warm spots of the roof and refreezes at the cold eaves. The water can back up under the shingles and reach the attic or interior walls. Ice dams are a common reason homeowners in Michigan call about leaks after a new roof.
Good attic ventilation, air sealing, and proper underlayment at the eaves reduce the risk. Ask whether ice and water protection will be installed along the eaves and in valleys as part of the roof replacement scope.

Another warning sign is a stain or bubble in the drywall near a wall that faces the prevailing wind. Wind-driven rain can push water under flashing and shingles from a direction that was not expected. Checking the exterior walls and the roof edges after a storm can reveal a problem before it spreads.
Sagging ceilings, a musty smell in the attic, and frost on the underside of the roof deck in winter also deserve a prompt inspection. Each of these signs points to moisture that is getting through the system and needs to be traced to its source.
