Skylight Installation and Your Roof

Skylights add natural light and character to Massachusetts and Rhode Island homes, but they're also one of the most common sources of roof leaks. Understanding the roofing requirements around skylights - and how to maintain them - prevents the frustration of a leaking skylight.

Why Skylights Are a Common Leak Source

A skylight requires a penetration through the roof deck and all roofing materials. This penetration must be precisely waterproofed to prevent leaks. The challenge:

• •The skylight curb and the surrounding roofing materials expand and contract at different rates with temperature changes
• •New England's freeze-thaw cycles stress every joint and seal around the skylight repeatedly
• •Snow and ice accumulation on and around skylights adds physical stress
• •Poor original installation (which is common) creates problems that persist and worsen over time

The most important factor in skylight leak prevention is installation quality - specifically, proper flashing.

How Skylight Flashing Works

A properly flashed skylight uses a multi-component flashing system:

**Step Flashing (Sides)**

Small L-shaped metal pieces installed alongside the skylight, integrated with each shingle course - the same method used at wall transitions. Each piece overlaps the one below.

**Apron/Head Flashing (Bottom Edge)**

A piece of flashing at the lower edge of the skylight that diverts water sliding down the curb onto the surrounding shingles.

**Counter Flashing / Cap Flashing (Top Edge)**

Flashing at the top of the skylight that prevents water from running behind the step flashing.

**Integrated Flashing Kits**

Most major skylight manufacturers (Velux, FAKRO, Sun-Tek) offer pre-engineered flashing kits specific to their skylight models and specific roof pitches. These kits are designed to work with the skylight's geometry and are the recommended installation approach.

Attempting to "improvise" skylight flashing using standard roofing techniques without the manufacturer's flashing kit often results in leaks.

Common Skylight Installation Problems

**Improper flashing installation sequence:** The order in which underlayment, step flashing, shingles, and counter flashing are installed matters. Any deviation from the correct sequence allows water paths.

**Improper slope:** Skylights must be installed on roof sections with adequate slope (typically 15 degrees or more). Low-slope skylight installation requires special curb extensions or different product selection.

**Caulk as primary seal:** Caulk around a skylight is a temporary measure, not a permanent waterproofing solution. Caulk ages, cracks, and fails in New England's temperature swings. Proper mechanical flashing doesn't rely on caulk.

**Ice and snow accumulation:** In Massachusetts winters, snow can pile against a skylight. Properly designed skylights and flashing systems accommodate this, but low-quality or improperly installed systems fail under ice pressure.

When to Replace vs. Repair a Leaking Skylight

Repair (Flashing Issue)

If the skylight glazing itself is intact and the leak is at the flashing - common for skylights installed without proper flashing kits - a roofing contractor can replace the flashing without replacing the skylight. This typically costs $400-$800 and permanently resolves the leak.

Replace (Skylight End-of-Life)

Skylight glazing typically lasts 15-25 years. Signs of glazing failure:

• •Condensation between double-pane layers (seal failure)
• •Cracked or yellowed acrylic or polycarbonate glazing
• •Hardware failures (for operable skylights)
• •Frame corrosion or structural compromise

When replacing a skylight, it's most cost-effective to do it in conjunction with a roof replacement - the shingles around the skylight must be removed and reinstalled either way.

Skylight Maintenance

Annual inspection of each skylight:

• •Interior: Look for any staining or moisture around the frame
• •Exterior: Look for debris accumulation around the curb; check that water drains away from the skylight rather than pooling against it
• •Clear any debris from around the curb that could trap water or ice

After ice dam events, inspect each skylight for evidence of water intrusion - they're common secondary entry points when ice dams are present.

Getting Skylight Work Done Right

Skylight installation and flashing is specialized work. Verify that any contractor you hire:

• •Uses manufacturer-supplied flashing kits (not improvised solutions)
• •Has experience with the specific skylight brand being installed
• •Can demonstrate their flashing installation sequence

Roofing Doctors installs and re-flashes skylights as part of roof replacement projects and as standalone repair services across Massachusetts and Rhode Island.