A chimney chase cover protects the area where the chimney passes through the roofline, blocking wind driven rain, pests, and debris. Making a proper cover helps extend the life of your chimney and prevents water intrusion into the framing around the chase.
This guide walks you through measuring materials cutting and assembling a durable cover using screws flashing and sealant. Follow each phase carefully to create a cover that fits tightly and complies with most building practices.
| Cover Type | Material | Best For | Typical Lifespan |
|---|---|---|---|
| Metal Pan | Galvanized steel or aluminum | Low slope chases, commercial work | 20–30 years |
| Shingle Over Wood | Asphalt shingles + plywood | Residential roofs with slope | 15–25 years |
| Rubber Membrane | EPDM or TPO sheet | Flat or irregular chase profiles | 10–20 years |
| Custom Metal Cap | Stainless steel formed cap | Premium look, tight detail | 30+ years |
Metal Pan Chase Cover Details
Gauge and fastening
Choose 26 to 22 gauge steel or aluminum for the pan. Specify welded seams or approved lap seams and use stainless steel screws with rubber washers. Space fasteners every 6 to 8 inches along edges and every 12 inches in the field for uniform load distribution.
Cricket and saddle integration
Where the chimney meets the main roof slope, a cricket or saddle should be built to redirect water away. The chase cover must tie into the cricket with continuous flashing and drip edge to prevent channeling behind the chimney.
Slope Compatibility and Shingle Integration
Matching roof pitch
For steep slope roofs, a shingle over wood chase cover works well when the plywood base matches the roof pitch. Cut the plywood to extend at least 2 inches beyond the chase on all sides to allow for proper flashing attachment.
Shingle alignment
Stagger vertical joints and align shingles over the cover so water flows off the roof rather than pooling at the chase edge. Use starter courses and ridge cap shingles to finish the look and add extra weather resistance.
Material Selection and Venting Considerations
Choosing between metal and membrane
Metal covers suit areas with heavy snow or driven rain, while rubber membranes work well on flat or low slope chases. Avoid materials that degrade quickly under UV exposure if the chase is fully exposed.
Clearance for vent terminals
Mark vent pipe locations before cutting the plywood base. Leave a minimum 2 inch offset around plastic or metal vent pipes and use a flashing collar that compresses gently against the pipe for a watertight seal.
Step by Step Construction Process
Template and top measurements
Trace the inner edges of the chase onto template material, then transfer to plywood or sheet metal. Add the required overhangs and cut with a circular saw or snips, keeping cuts square for easier alignment on site.
Flash and fasten sequence
Install base flashing on the chase wall, lay the cover, then cover with apron flashing and cap flashing at the top. Secure the cover with corrosion resistant fasteners designed for the cover material and roof type.
Key Takeaways for a Durable Chase Cover
- Measure the chase opening accurately and add consistent overhangs for water control.
- Select material thickness and type based on roof pitch, climate, and exposure.
- Integrate a cricket or saddle to move water away from the chimney.
- Use compatible flashing and sealed fasteners to prevent leaks at penetrations.
- Check local code requirements for attachment methods and wind uplift ratings.
FAQ
Reader questions
How do I determine the correct overhang for a wood framed chase cover?
Extend the cover at least 2 inches past the vertical chase walls on all sides, and provide a drip edge to prevent water from wicking back under the cover.
Can I install a metal cap chase cover on a low slope roof without a cricket?
Yes, but you should add an internal cricket or peaked liner inside the chase to create positive drainage and prevent water from sitting at the low point.
What fastener type works best for rubber membrane chase covers on asphalt shingles?
Use rubber washers and corrosion resistant screws designed for membrane work, and seal each penetration with manufacturer approved seam adhesive or liquid rubber.
Should the chimney chase cover be attached to the roof rafters or the vertical chase walls?
Attach the cover to both the rafters for overall support and the chase walls for lateral stability, using proper flashing to bridge the connection.