Reroofing around a 42-inch-wide brick chimney.

For a 42-inch-wide masonry chimney, you need a full two-piece flashing system (base/step + counter-flashing) plus a cricket (saddle). Code (IRC R903.2.2 / IBC 1503.2) requires crickets on chimneys >30 inches wide.

Material: 26-ga galvanized steel (G-90 min), copper (16 oz), or aluminum (.032"). No roll flashing. Match roof life expectancy.

Package Components:

1. Apron (Head) Flashing: One piece, full width + 8" min each side (58" total). Extends 4" min up chimney face, 4" min onto roof deck. Hemmed drip edge at bottom.
2. Step Flashing: 5"x7"x8" (min) pieces, one per course (approx. 20–25 pcs). Bend: 4" up chimney, 4" on deck. Install under shingles, over underlayment. Turn top corner 1" into mortar joint.
3. Counter-Flashing (Cap Flashing): Reglet-set into mortar joint 1.5" min deep (IRC R903.2.2). Not surface-mounted/caulked. Sections: two sides, rear (over cricket), front (over apron). Overlap base flashing 2" min. Solder seams (copper) or seal with polyurethane (steel/alum).
4. Cricket (Saddle): Required (width >30"). Frame 2x on roof deck, sheath, ice & water shield full coverage. Valley flashing (W-style) at roof-cricket intersection. Cricket slope ≥ roof slope. Cover with roof cladding (shingles/metal) then install rear counter-flashing over it.
5. Ice & Water Shield: Full deck coverage under cricket & 3 ft up roof from chimney. Wrap 12" up chimney faces before base flashing.

Critical Details:

• No exposed fasteners on vertical legs.
• Counter-flashing must be removable for repointing.
• Seal reglet with polyurethane, not silicone.
• If chimney >48" wide, cricket needs internal drainage (scupper) or double valley.

Verify: Masonry condition. Repoint open joints before flashing. If flue tiles project <4", extend crown.

For a 42-inch-wide brick chimney, proper flashing is critical to prevent water intrusion. The flashing package must include:

1. Base flashing (step flashing): Install corrosion-resistant metal (e.g., 26-gauge galvanized steel, aluminum, or copper) along the sides of the chimney where it meets the roof. Each piece should be L-shaped, at least 4" wide on the roof and 4" up the chimney, overlapping shingles by at least 2" and each successive piece by 2". Install one piece per shingle course, bent to follow the roof slope.

1. Counterflashing: Embedded into the chimney mortar joints (at least 1" deep) and bent down over the top of the base flashing. Must be at least 4" wide and made of compatible metal (same as base flashing). Seal the reglet (cut groove) with polyurethane or silicone sealant rated for masonry and metal.

1. Cricket (saddle): Required by IRC R903.2.1 and IBC 1503.2 for chimneys wider than 30" on the downhill side. Since your chimney is 42" wide, a cricket is mandatory. It should be framed at least 2x4 lumber, sheathed, and covered with the same roofing material as the main roof, with flashing integrated into the step and counterflashing system. The cricket diverts water around the chimney to prevent ponding.

1. Apron flashing: At the bottom (downhill) edge, install a continuous L-flashing extending at least 6" onto the roof and 4" up the chimney, overlapping the step flashing.

All joints must be lapped shingle-style (upper over lower) to shed water. Use compatible metals to avoid galvanic corrosion. Sealant alone is not sufficient — mechanical lapping and embedding are required.

If the chimney is on a steep slope or in a high-wind/rain area, consider using preformed flashing kits or consult a roofer. Improper flashing is a leading cause of leaks. If unsure, hire a licensed roofer — this is not a DIY-friendly detail for long-term reliability. (IRC R903.2, R905.2.8)