Roof Flashing Repair: Chimneys, Skylights, and Sidewalls

Quick Answer: Roof flashing is the metal barrier where the roof meets a penetration or vertical surface, and it's the second most common Calgary leak source after pipe boots. Repair varies by location: chimney flashing involves step flashing, counter flashing, and sometimes mortar joint work; skylight flashing on VELUX-system installs replaces an integrated kit; sidewall and valley flashing requires removing surrounding shingles. Calgary flashing repair typically costs $800 to $2,500 per location.

Flashing is the highest-stress point on any roof. Constant thermal expansion and contraction, freeze-thaw cycles, and direct exposure to wind-driven water make it the place where most leaks eventually emerge. The good news is that flashing repair is well understood and durable when done properly: a quality flashing repair lasts 15 to 25 years. This guide walks through the four main locations (chimneys, skylights, sidewalls, valleys) and what each repair involves.

At a Glance

• Flashing lifespan: 15 to 25 years for a properly installed flashing system

• Most common Calgary chimney flashing failure: Counter flashing pulled out of mortar joints

• VELUX skylight flashing system: Integrated underlayment + side + head flashing kit

• Sidewall flashing failure rate: Higher on homes built before 2005

• Chimney flashing repair cost: $800 to $2,000 (more with masonry)

• Skylight flashing replacement cost: $1,500 to $3,500 including new skylight

• Valley flashing replacement cost: $1,200 to $2,500

• Open vs closed valley lifespan: Open valleys typically last 25+ years; closed valleys 12 to 18

What Flashing Does

Flashing is the metal piece that bridges the join between two different surfaces or transitions on a roof. Common locations:

• Where the roof meets a chimney

• Around skylights

• Where the roof meets a vertical wall (sidewall, headwall)

• In valleys where two roof slopes converge

• Around plumbing vents (sometimes called pipe boot flashing, though this is technically a separate component)

Flashing redirects water away from the join so it can run off the roof normally. When flashing fails, water enters at the join and tracks into the building.

The material is usually aluminum, galvanized steel, or copper. Aluminum is most common in Calgary residential work; copper is premium and rare in residential.

Chimney Flashing Repair

Chimney flashing has three components that work together.

Step flashing

L-shaped metal pieces installed in alternating layers with shingles up each side of the chimney. The L bends one way against the chimney and the other way under the shingle course. Each piece typically covers 5 to 7 inches of vertical chimney height.

Counter flashing

A metal cap that tucks into a mortar joint on the chimney and folds down over the top edge of the step flashing. The mortar joint holds it in place; sealant prevents water entry at the seam.

Cricket (or saddle)

A small slope on the high side of a chimney that diverts water around rather than against the chimney wall. Required by Alberta Building Code on chimneys wider than 30 inches.

Failure modes:

• Counter flashing pulled out of mortar joint (most common; mortar deteriorates with freeze-thaw)

• Step flashing rusted through or punctured

• Cricket damaged or missing on wider chimneys

• Sealant cracked at the counter flashing seam

Repair scope:

• Remove surrounding shingles

• Inspect masonry condition; repair mortar joints if needed

• Replace step flashing in courses up the chimney

• Reset counter flashing into the cleaned mortar joint

• Apply manufacturer-approved sealant at the seam

• Re-shingle around the flashing

Cost: $800 to $2,000 for typical residential chimneys. Brick chimneys requiring tuckpointing (mortar joint repair) add $200 to $600.

A chimney that needs full flashing replacement often also needs crown repair (the cement cap on the top of the chimney). Crown repair adds $400 to $1,000 to the scope but extends total chimney life by 15+ years.

Skylight Flashing Repair

Skylight flashing varies significantly by installation generation.

Older non-flashed-kit skylights (typically pre-2005) use a generic step-and-counter system similar to chimneys, often with caulked seams that fail within 10 to 15 years. These are the skylights most commonly leaking in Calgary repairs today.

VELUX deck-mounted skylights (current standard) use a manufacturer flashing kit that includes:

• Underlayment skirt that integrates with the deck waterproofing

• Side flashings that interlock with shingle courses

• Head flashing at the top

• Sealant at specifically designed locations

Curb-mounted skylights use a separate raised curb (typically wood or aluminum frame) with flashing similar to a small chimney.

Failure modes:

• Caulked seams failed on older units

• Sealant degraded around VELUX systems at 15+ years

• Frame damage from impact or settling

• Glazing cracked (different from flashing failure but often discovered together)

Repair vs replacement: 

For older non-flashed-kit skylights, full replacement with a VELUX system is usually the better long-term answer. The unit cost ($600 to $1,500 for the skylight itself plus $900 to $2,000 for installation) is significantly more than resealing but provides another 25+ years of reliable service.

Angel's Roofing's VELUX certification covers the full flashing-system installation, including the integrated underlayment and warranty preservation on the manufacturer's "no leak" guarantee.

Cost: 

Reseal of existing skylight $400 to $900. Full VELUX skylight replacement including flashing $1,500 to $3,500 depending on size and access.

Sidewall and Headwall Flashing

Sidewall flashing appears where a roof slope meets a vertical wall (often at a dormer, addition, or bump-out). Headwall flashing is similar but at the top of a slope where it meets a wall (such as the back of a porch roof meeting the main house).

Common failures:

• Flashing not tucked properly behind siding (most common installation error on homes built before 2005)

• Sealant at the flashing-to-wall joint cracked

• Flashing rusted or punctured

• Improper kick-out flashing at the bottom of sidewalls (sends water into wall cavity instead of into the gutter)

Kick-out flashing is the single piece most often missing on older Calgary homes. It's the small piece at the bottom of a sidewall flashing that redirects water into the gutter rather than letting it run down the wall behind the siding. Missing kick-outs cause siding rot and interior wall damage that homeowners attribute to other causes for years before the diagnosis.

Repair scope:

• Remove surrounding shingles

• Loosen siding to access flashing tuck

• Replace flashing, including proper kick-out

• Re-tuck siding to enclose new flashing

• Re-shingle and seal

Cost: $700 to $1,800 per location depending on siding access difficulty.

Valley Flashing

Valleys are where two roof slopes meet at an angle. They handle large water volumes during rain or snowmelt and need durable flashing.

Open valleys show visible metal in the V. They last 25+ years and are the longer-lived choice. Calgary's hail exposure makes open valleys preferred over closed in many newer installations.

Closed valleys use shingles woven across the V. They look cleaner but typically last 12 to 18 years before the shingles in the V wear faster than the surrounding roof.

California valleys are a hybrid (one slope's shingles run through, the other's stop short). Less common in Calgary.

Failure modes:

• Open valley: metal rusted through or punctured by ice or hail

• Closed valley: shingles in the V worn through

• Improper underlayment causing premature failure

Repair scope:

• Remove shingles 12 to 18 inches on each side of the valley

• Remove old flashing

• Inspect deck condition

• Install new ice-and-water shield underlayment

• Install new valley flashing (typically open valley with W or hemmed-edge metal)

• Re-shingle each side with proper offset

Cost: $1,200 to $2,500 for typical residential valleys; longer valleys higher.

When Flashing Repair Requires Shingle Work

Almost every flashing repair requires removing surrounding shingles. This is the main reason flashing repairs cost more than they might appear to need.

Typical shingle removal:

• Chimney flashing: 8 to 15 shingles

• Skylight flashing: 10 to 20 shingles

• Sidewall flashing: 6 to 12 shingles per linear section

• Valley flashing: 20 to 40 shingles depending on valley length

Those shingles often need replacement after removal (older shingles crack on removal even when handled carefully). The shingle work portion of a flashing repair is typically $200 to $800 of the total quote.

Frequently Asked Questions

How can I tell if my flashing is failing?

Look for visible rust, separation from the chimney or wall, missing sealant at joints, and water staining on interior ceilings near a chimney, skylight, or wall. A roof-level assessment confirms; ground-level identification is often unreliable.

Will my flashing repair void the manufacturer shingle warranty?

Not when performed by a certified installer using approved materials. Angel's Roofing's GAF, IKO, Malarkey, and VELUX certifications preserve the relevant warranties when work is done under those product lines.

How long does flashing repair take?

Most flashing repairs complete within a single workday. Chimney flashing with masonry repair can extend to 1 to 2 days depending on mortar work scope.

Can I reseal flashing myself with caulking?

Touching up cracked sealant at a flashing seam can temporarily extend service life by 1 to 3 years. It's not a permanent repair and doesn't address underlying flashing degradation. Use only sealants rated for roof use (not generic silicone).

Do I need new flashing every time I replace shingles?

Best practice is to inspect flashing during shingle replacement and decide based on condition. Flashing under 10 years old often gets reused; older flashing usually gets replaced as part of the shingle work to align lifespans.

Why is skylight repair so expensive?

A full skylight flashing replacement typically means installing a new skylight unit since the manufacturer's flashing kit is designed for current production. The unit cost plus the flashing system plus access drive the total. Older non-kit installations can sometimes be repaired without unit replacement at lower cost.

About Angel's Roofing: Angel's Roofing provides Calgary residential roof repair throughout Calgary and surrounding areas, specializing in chimney, skylight, sidewall, and valley flashing repair with VELUX-certified installations and 25+ years of Calgary climate experience for homeowners requiring durable flashing work.

Ready to fix flashing leaks at your chimney, skylight, or sidewall before they spread? Angel's Roofing helps Calgary homeowners protect their investment with VELUX-certified skylight systems, manufacturer-warranty-preserving repairs, and written assessments documenting every flashing junction.

Contact us today at 403-569-2643 to book your complimentary flashing repair assessment.

Disclaimer: Roofing involves safety risks; consult licensed professionals for work beyond ground-level visual checks. Costs and specifications provided are estimates based on typical Calgary market conditions and may vary based on specific project requirements and current material pricing.