Chimney Flashing: Common Leak Points and Better Details

Flashing leaks usually start with material aging and breakdown. Weathering, UV, and freeze-thaw cycles take a toll over time. Poor detailing lets water find a path behind the metal or membrane.

Movement from the roof and chimney, or shifting from framing, creates gaps and split seals. When components aren’t lapped or terminated correctly, water can follow the path of least resistance. Observed staining or rust often points to these root causes, not just a single bad seam.

Material degradation and corrosion

The lifespan of your chimney flashing heavily depends on the material used. Cheap, low-quality materials won’t hold up against weathering and heat.

• Corrosion: Rust weakens metal flashings. Look for red or orange stains. Use stainless steel or copper for better corrosion resistance.
• UV exposure: Sunlight degrades rubber and plastic flashings over time. Opt for materials rated for UV resistance.
• Freeze-thaw cycles: Extreme temperature changes can cause cracking in improperly selected materials. Choose freeze-thaw resistant materials, like aluminum or copper.
• Weathering: Prolonged exposure to rain and snow can degrade flashings. Regular inspections help catch issues early.
• Incompatible materials: Mixing incompatible materials (e.g., metal with rubber) can cause weak bonds, leading to leaks. Ensure all materials are compatible.

Structural movement and masonry issues

Chimneys are subject to movement due to settling, temperature changes, or wind. This movement can compromise flashing interfaces, leading to leaks.

Cracked mortar: Inspect your chimney’s mortar joints for cracks. Repointing may be necessary to prevent water entry.

Settling: If your chimney has settled, it may no longer be plumb or level, causing flashing to leak. Have the structure evaluated and repaired if needed.

Shifting stacks: A shifting chimney stack can cause flashing to bend, warp, or separate, leading to leaks. Ensure your chimney is properly secured and aligned.

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Start at the step flashing where it meets the roof plane; misalignment or gaps here invite seepage. Counterflashing terminations at the chimney sides are a common failure if not tucked under proper flashing.

Also check saddles or crickets that shed water poorly, and the chase-top transitions where the chase collar meets flashing. Each junction has its own failure mode, so inspect them as a group and note any loose or cracked parts.

Counterflashing Terminations and Mortar Joints

The end of the counterflash should be tucked under the shingles to prevent water from getting behind it. Here’s what to look for:

Check if the counterflash is properly tucked under the shingles at its termination.

Mortar joints around the chimney can crack and let water in. Inspect these joints, especially where they meet metal flashing.

If you see cracks or gaps, repoint the mortar using a tuckpointing technique. If the damage is severe, consider replacing the entire section of flashing.

Crickets/Saddles and Backwater Zones

Crickets or saddles are metal pieces that go over the chimney to direct water away. They’re crucial for preventing leaks:

Check if your cricket is present and in good condition. It should slope downwards, away from the chimney.

Backwater zones behind the chimney can trap water. Ensure these areas are properly sloped to drain water away.

If you find any issues with your crickets or backwater zones, repair them immediately to prevent chronic leaks. If you’re unsure, consult a professional.

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Look for loose or lifted flashing, corrosion, or broken sealant along chimney edges. Check for dark stains, spalling masonry, or efflorescence on nearby brick or stone surfaces.

Inside, watch for staining on ceilings or attic rafter bays, and any musty smells that hint at hidden leaks. Work safely from ground level or with appropriate fall protection, and avoid climbing on unstable roof sections.

Prioritize proper sequencing: install primary flashing first, then counterflashing, with overlaps that direct water away. Keep terminations tucked under adjacent flashing so water travels over, not behind, joints.

Use continuous bends and clean laps to reduce crevices. Favor durable materials and simple, continuous transitions over complicated stacks that invite failure. Focus on robust, repeatable details rather than brand specs.

Proper sequencing and layering techniques

Start with a solid base. Install underlayment first to protect against moisture from below.

Next, apply step flashing. Make sure each piece overlaps the one below it by at least 2 inches. This creates a staggered pattern that sheds water outward.

Now, install shingles. They should overlap the step flashing to maintain a continuous water-shedding path.

Lastly, add counterflashing. It should cover and be secured to the top of the step flashing, ensuring no gaps where water can seep in.

Secondary defenses: kickouts, crickets, and diverters

Kickouts are L-shaped metal pieces that divert water away from vulnerable junctions where the roof meets a wall. Install them at these intersections.

Crickets or saddles are used when one roof plane is higher than another. They sit on top of the lower roof, diverting water away from the chimney and preventing backups.

Diverters, like cricket-style diverters, can be used to direct water away from specific areas prone to leaks, such as where a dormer meets the main roof.

Use these secondary defenses in combination with proper sequencing and layering for maximum protection.

Termination methods and integration with masonry

For integrated counterflashing, the flashing is inserted into a vertical groove (reglet) cut into the chimney’s mortar joints. This method provides good protection but requires precise cutting.

Face-applied systems involve securing the flashing directly to the face of the chimney with nails or screws. They’re easier to install but may not provide as robust protection against water intrusion.

The best choice depends on your chimney’s construction and local climate. For example, integrated counterflashing might be better in areas with heavy rain, while face-applied systems could suffice in drier regions.

Regardless of the method chosen, ensure a tight fit and proper sealing to prevent leaks at termination points.

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Flashing comes in several forms; pick options that resist corrosion and suit your roof type. Consider tools that help you form tight bends, cut clean edges, and seal without relying on risky field workmanship.

When you check specs, verify compatibility with adjacent materials, installation temperature ranges, and warranty language. Always compare manufacturer instructions and local code requirements to your project site.

Material options and tradeoffs

Choosing the right material for your chimney flashing is crucial to prevent leaks. Here are some common options:

• Galvanized Steel: Common, affordable. Look for 24- or 26-gauge. Avoid thin gauges as they rust quickly.
• Aluminum: Lightweight, corrosion-resistant. Check for anodized finish for better durability. Avoid in areas with high salt content.
• Copper: Premium, long-lasting. Expensive but won’t corrode like steel. Not suitable for all applications due to its softness.
• Lead: Traditional, malleable. Used for custom jobs. Toxic if not handled properly; avoid if possible.
• Membranes: Flexible, waterproof. Great for repairs and as secondary defense. Check UV resistance and temperature range.

What specs and standards to check

Before purchasing materials, verify the following:

Corrosion Resistance: Check the material’s resistance to rust or corrosion. This is crucial in areas with harsh weather conditions.

Manufacturer Instructions: Always follow the manufacturer’s installation guidelines to ensure your flashing lasts as long as possible.

Local Building Codes: Check with your local building department to ensure your chosen materials comply with local codes and standards. Some areas may have specific requirements for chimney flashing.

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For temporary fixes, seal obvious gaps and keep water from pooling while you plan a longer repair. Assess whether you can handle a full flashing replacement or if a licensed contractor is the safer route.

When planning a DIY permanent repair, outline a logical sequence: remove deteriorated sections, clean surfaces, install new flashing, and verify proper terminations. If in doubt, prepare to hire help and gather any project guidelines or permits required by local rules.

Temporary Emergency Fixes

When a leak is active, these temporary fixes can buy you time until permanent repairs can be made. Remember, they are not long-term solutions.

Non-structural seals: Use roofing cement or caulk to temporarily seal leaks at the source. Apply liberally and allow to dry.
Limitation: Will degrade over time and in harsh weather conditions.

Temporary diverters: Install a makeshift diverter using plastic sheeting, tarps, or even large pieces of rubber to redirect water flow away from the leak.
Limitation: Can be unsightly, may not fully stop leaks, and can be dislodged by wind or weather.

While these fixes can help in a pinch, they should not replace permanent repairs. Always follow up with professional-grade flashing and proper installation techniques.

Replacing Step Flashing and Counterflashing (Overview)

This overview guides you through removing damaged flashing and installing new step flashing and counterflashing.

First, remove old flashing carefully to preserve the underlying structure. Then, install new step flashing, ensuring proper overlap with roofing materials.
Tip: Always start from the bottom and work your way up for correct overlapping.

Next, install counterflashing. Fit it over the step flashing, ensuring a tight fit against the chimney. Secure it in place using nails or screws.
Note: Counterflashing should be slightly shorter than the chimney’s width to allow for expansion and contraction.

Proper integration with roofing materials is crucial. Ensure all flashing is securely attached, properly overlapped, and sealed to prevent water intrusion.

Installing or Repairing a Cricket/Saddle

A cricket or saddle behind your chimney can improve drainage and prevent pooling. Here are decision points and general steps to consider.

Decision point: If water is pooling behind the chimney, causing leaks or damage, installing or repairing a cricket/saddle may be necessary.
General step: Build up the structure behind the chimney using roofing felt, plywood, or other suitable materials. Ensure it slopes away from the chimney to direct water flow.

Tip: The slope should be at least 1 inch per foot of length to effectively drain water.
Note: If your chimney is masonry, consult a professional before making any structural changes.

Once the cricket/saddle is installed or repaired, ensure it’s properly integrated with the roof and flashing system. Seal all joints and inspect regularly to maintain its effectiveness.

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Schedule seasonal inspections and address debris that blocks drainage around the chimney. Clear the roof edge and chimney base to prevent water from pooling near flashing.

After extreme weather, recheck seals and look for new gaps or movement. Keep maintenance records with dates and findings to catch recurring issues before they escalate.

Weather-related care and long-term preservation

Extreme weather conditions can degrade your chimney’s flashing over time. Here are some considerations to help preserve its longevity:

Freeze-thaw cycles: Water expands when it freezes, which can cause cracks in the caulking and sealant around your flashing. Ensure these areas are well-sealed before winter.

Prolonged wetting: Constant exposure to moisture can lead to rust on metal flashings. If possible, redirect water away from the flashing area using gutters or downspouts.

UV exposure: Prolonged sun exposure can degrade caulking and sealant, making them more susceptible to cracking. Apply a UV-resistant sealant for added protection.

Proper drainage and ventilation: Ensure your chimney has adequate ventilation to prevent moisture buildup. Install a chimney cap if you don’t have one, and consider installing a cricket or saddle to divert water away from the flashing.

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When leaks are ambiguous, trace water paths from the interior to the exterior while noting any related roof features. Avoid overusing sealants as a long-term solution, which can trap water behind flashing.

Prepare to hire by collecting photos, measurements, and a summary of observed conditions. Ask contractors about their approach to flashing terminations, overlap, and sequencing, and request references or past project details showing similar work.

Diagnosing intermittent or hidden leaks

Chimney leaks can be tricky to pinpoint, especially when they only appear during certain weather conditions. Here’s a systematic approach to trace these elusive problems:

First, isolate the roof area. Look for leaks near the chimney, but also check other potential entry points like valleys and eaves. Use tarps or plastic sheeting to block off sections of the roof during rain.

Next, use targeted water testing. With a helper inside the house, apply water to specific areas around the chimney while they monitor for leaks from within. Alternatively, consider hiring a professional leak detection service for a thorough inspection.

How to vet contractors and compare quotes

When hiring a professional for your chimney flashing repair, it’s crucial to do your homework. Here are some key factors to consider when evaluating bids:

Verify credentials and warranties. Ensure the contractor is licensed and insured. Ask about manufacturer warranties on materials used and labor warranties offered by the contractor.

Compare proposed details. Make sure each quote includes a detailed description of the work to be done, including materials to be used and any necessary repairs or upgrades. Ensure these align with your long-term waterproofing goals.

Ask for references and examples of their work. A reputable contractor should be able to provide references from satisfied customers and photos or videos of similar projects they’ve completed.

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