A chimney chase is the boxed enclosure around a flue (often finished in siding, stucco or masonry) that rides up through the roof plane. Where that chase meets the roofline is one of the most vulnerable spots for water intrusion because it concentrates seams, transitions, and changes in plane — and in Denver those seams see wet snow, freeze-thaw cycling and wind-driven rain. Left unchecked, leaks at the roofline will wick into framing, sheathing and insulation, causing rot, staining and costly repairs to both envelope and interior finishes.
Waterproofing a chase at the roofline is a system of layered details, not a single seal. We install a continuous through-wall flashing at the base of the chase, then a combination of base flashing (step flashing) interleaved with each course of shingles and a counterflashing that terminates into the chase material or mortar joint. Common step-flashing pieces are about 8″ x 8″ with roughly 4″ turned up the chase and 4″ over the shingle; all flashing pieces should lap each other by at least a couple of inches. For additional protection we use self-adhered membrane flashing across the chase roof interface and a metal counterflashing—stainless steel or copper where longevity is essential—rather than relying on sealants alone. Wide chases typically get a cricket (saddle) behind the chase to divert water, and a properly sloped concrete crown and metal chimney cap prevent ponding and entry from above.
Best practice ties these details into the roof underlayment and the chase wall assembly during construction so each layer sheds water to the exterior. Sealants are a last line of defense, not the primary waterproofing; the flashing must be mechanically sound and interlocked with the roof covering. We also recommend annual inspections after winter and prompt attention to cracked crowns, missing cap fasteners or deteriorated mortar, because small failures escalate quickly. As a Denver builder that designs and constructs homes on our clients’ lots, RKM Homes coordinates these roof-to-chase details during design and framing to ensure durable performance and minimize costly remedial work later.
What types of flashing are used around a chimney chase and what are the proper installation standards?
On custom homes I build we specify heavy-gauge flashing materials that will outlast common roofing—copper or stainless-steel are my go-to choices because they resist corrosion and solder or weld cleanly. Galvanized and painted aluminum are cheaper but tend to fail sooner, especially where dissimilar metals meet (copper on top of galvanized will cause accelerated corrosion). For a framed chimney chase you’ll typically see an apron (continuous) flashing at the low side, step flashing where the roof slope meets the chase, and counter-flashing or reglet at the chase face; for masonry chimneys there’s usually a through-wall or reglet-mounted counter-flashing tied into the mortar joints. Specify material and gauge in your contract so you’re not surprised by thin roll flashing that relies on caulk to keep water out.
Proper installation standards matter more than the material alone. Step flashing must be installed one piece per shingle course with the vertical leg slipped tight against the chase and the upper edge of the flashing tucked under the shingle above—each piece should overlap the next by at least 2–3 inches. Counter-flashing should be recessed into a reglet cut into the chase or masonry (or attached with a removable cleat system) and overlap the top of the step flashing so water sheds outward; sealant is only a backup, not the primary waterproofing. Fasteners should be stainless or copper (never plain steel) and driven where they’ll be covered by the next layer; where seams are required, solder or mechanically seam the joints rather than relying solely on caulk.
As a homeowner there are a few practical things you can ask for and look for: request that the ice-and-water underlayment be taken up the chase wall a minimum of a foot and that step flashing be installed over that membrane so the underlayment and flashing form a continuous path for water. Insist the contractor show you the reglet or removable counterflashing detail (this makes future repairs far simpler) and list the flashing material and fastener type in the scope. On finished roofs, watch for quick signs of trouble—shiny new caulk around the chase, rust stains, or visible gaps where flashing pieces should overlap—and have a roofer who understands step/counter-flashing replace or re-seat pieces rather than just slapping on more sealant.
How should the chimney crown, cap, and chase top be sealed at the roofline?
As a custom home builder I treat the crown and cap as the first line of defense where the chimney meets the roof. A properly formed masonry crown should be sloped away from the flue and extend 1½–2″ past the chase walls so water sheds clear of the masonry. On framed chases the factory-made metal chase-top or welded stainless cap performs the same job: keep rain off the top of the chase and shed water away from the corners where leaks usually start. Homeowners can spot trouble early by looking for hairline cracks or spalling in a concrete crown, rust or loose screws on a metal cap, or wet staining inside the chase or ceiling below after a storm.
When I build or repair a chase-top I follow simple, verifiable details that hold up in Denver’s freeze-thaw cycles. For a concrete crown the surface must be pitched (about 3/4″ per foot) and at least 2″ thick over the bearing brick or blocking; the crown should break over the edge so water doesn’t run down the face of the chase. For framed chases I specify a welded, hemmed-edge metal cap with a continuous drip edge and a back lip that overlaps the chase wall — fastened with stainless screws and neoprene washers so the fasteners won’t leak. The cap should be seated on a smooth, level surface and not simply caulked to deteriorating mortar or treated lumber; if the top surface is treated with a membrane, place the cap over that membrane and mechanically fasten through it so water can’t track under the cap.
Sealing and ongoing care are what prevent small problems from becoming costly leaks. Use an elastomeric, UV-stable sealant made for masonry/metal transitions (polyurethane or modified-silane polymers), tooling the joint against a backer rod so the bead adheres to two faces only and accommodates movement — avoid ordinary household silicone. For small crown cracks I recommend routing out the crack, filling with a high-quality masonry patch, then sealing the perimeter where the cap meets the chase. Inspect the cap and sealant after every winter and reseal every 5–7 years or sooner if you see cracking or separation; replace a cracked crown or a rusty, loose cap rather than relying on repeated caulking. If you find persistent damp spots inside the chase or the ceiling, call a contractor — that usually means the crown/cap interface is compromised and needs a pro-level repair.
How should a chimney chase be integrated with the roof assembly and my roofing material?
The roof’s underlayment and the chase’s weather barrier must be lapped and tied together before shingles or panels go on. On a practical jobsite that means the roofer brings the underlayment up the chase wall a few inches (or over a peel‑and‑stick ice & water shield where required), the base flashing is set at the roof line, and shingle step flashing is interwoven with the shingle courses so water sheds onto the roof instead of behind the chase. Ask your builder to show you photos of the underlayment lap and the first course of step flashing before the roof finish is completed so you can verify the sequence was followed.
Different roofing materials need different flashing interfaces and clearances, so get specifics for your roof type up front. For asphalt shingles the step‑flashing pattern is standard; for standing‑seam metal or tile roofs you’ll require custom formed flashings and larger clearances where the flashings bend and attach to the chase. Also make sure the metal used for flashings is compatible with your roof finish (for example, avoid plain galvanized against copper) so you don’t get accelerated corrosion where materials meet.
Coordination between the roofer, siding/chase contractor and your builder prevents failures at the roofline. Ask that the chase have a continuous weather‑resistant membrane under its cladding that overlaps the roof underlayment, that counterflashing be either reglet‑embedded or mechanically fastened into a trim receiver on the chase, and that the trades confirm the lapping order in writing or with install photos. As a homeowner, request these details in the scope of work: underlayment height up the chase, flashing attachment method, and material compatibility so you avoid callbacks for water intrusion later.
How does a chimney cricket (saddle) keep water off the roof and prevent leaks at the chase?
A chimney cricket is a small peaked roof built on the uphill side of a chimney to split and divert running water around the chase instead of letting it pond at the junction. On sloped roofs the uphill face of a chimney becomes a collection point for sheets of water and snowmelt; without a cricket that water either hits the back of the chase or gets forced into the flashing joints. On my builds I treat crickets as a fundamental water-control feature whenever the chimney sits on the uphill slope or the chase is wide enough that water can stagnate — asking your contractor to show you the proposed cricket location on the roof plan is a simple way to avoid future leaks.
Practical construction details make the difference between a cricket that works and one that causes problems. The cricket should form a peaked ridge centered on the uphill side of the chimney and be sized so it extends several inches beyond the chimney’s edges — I typically extend 6–12 inches past the chase to ensure flow clears the masonry. The cricket plane is built on solid blocking and sheathing, covered with a continuous waterproof layer, and given a steeper slope than the main roof so water sheds quickly; where space allows I aim for a noticeably steeper pitch (roughly 1:12 or steeper) than the surrounding roof. The ridge and seams must be tight and tied into the chase cladding so water is directed into the roof drainage paths rather than around the edges of the chase.
Homeowner-level maintenance keeps a cricket doing its job for decades. Inspect the uphill side of the chimney after heavy storms and in spring — look for debris build-up, leaves, or roofing material that’s pulled back at the cricket seams, and clear anything that would trap water. Watch for staining on the ceiling below the chimney or visible streaks on the chase; those are early signs the cricket or its joints are failing. If you notice persistent ice build-up at the cricket in winter, have your builder check attic insulation and ventilation first (ice can indicate heat loss that contributes to ice dams) and then repair or reinforce the cricket flashing and waterproof layer as needed.
What chase construction materials, waterproof membranes, sealants, and maintenance are needed to keep a chimney waterproof at the roofline?
As a custom home builder I start with the chase substrate — it needs to be a stable, water‑resistant assembly. Use exterior‑grade plywood or oriented strand board (OSB) sheathing covered with a continuous water‑resistive barrier (WRB) and provide a rainscreen gap behind whatever cladding you choose (metal, fiber cement, or siding). Metal framing or pressure‑treated blocking at the top of the chase prevents rot where fasteners concentrate. Avoid burying the WRB under siding edges; the WRB should be continuous from the roof plane up the chase walls so any water that gets behind the cladding can drain down and exit at the roofline.
For the waterproof layer itself I install a fully bonded, self‑adhesive membrane that is lapped onto the roof deck and carried up the chase walls and over the top surface beneath the cap. Choose a high‑quality rubberized asphalt or polymeric peel‑and‑stick that bonds to the WRB and to the roof deck; lap seams a minimum of 3–4 inches and extend the membrane at least 6–12 inches onto the roof to create a positive transition. Use compatible, flexible joint sealants where the chase meets metal trim or cap components — opt for a polyurethane or an advanced MS‑polymer/elastomeric sealant rather than generic silicone, and back deep joints with a closed‑cell backer rod sized slightly larger than the joint so the sealant only sees surface adhesion and movement, not three‑sided adhesion.
A practical maintenance plan keeps the system working: I recommend a visual check twice a year and after major storms—look for peeling membrane edges, cracked sealant joints, gaps at fasteners, and blocked drainage at the chase top. Re‑seal joints every 5–10 years or sooner if you see shrinkage or cracking; replace membrane laps or patches immediately where adhesion has failed. Keep the chase top clear of debris, document the materials used (membrane type, sealant type, fastening details) so future roofers can match products, and call a licensed roofer or builder for membrane repairs rather than relying on surface patches that won’t address underlying adhesion or substrate problems.