Roof Flashing Replacement: Chimney, Valley, and Wall Intersections

Roof flashing is priced by the detail being rebuilt, not simply by the length of visible metal. Chimney sidewalls, roof-to-wall intersections, valleys, and penetrations each shed water differently. Ask for a sketch or photos showing which layers are being removed and replaced. GAF’s installation guidance illustrates that wall flashing works as a layered system: leak barrier, step flashing, and wall or counterflashing must overlap so water drains downslope (GAF roof accessory instructions).

Read the scope by roof detail

Detail	Minimum useful description	Cost drivers to separate
Chimney	Step flashing, back-pan or cricket, and counterflashing condition	Chimney width, masonry joints, access, surrounding shingle age
Roof-to-wall	Step flashing and wall counterflashing, plus siding clearance	Number of courses, siding removal, corner transitions
Valley	Valley lining or woven/open detail and adjacent roof replacement	Valley length, roof material, ice or debris exposure
Plumbing or vent penetration	Boot or metal flashing matched to pipe and roofing	Pipe size, brittle shingles, access and underlayment

The word “flashing” can mean replacement metal, a sealant patch, or a complete layered repair. Those are not equivalent. GAF’s field guide identifies ponding behind chimneys and side seams as leak concerns and explains why a cricket may divert water around a wide chimney (GAF steep-slope field guide). A bid for a chimney should therefore say whether it includes a cricket or only side flashing.

What to ask for in a complete bid

Request photos before and after removal, the flashing metal or system specified, underlayment and leak-barrier work, shingle or tile replacement, disposal, and a workmanship warranty. Ask whether counterflashing is cut into masonry joints, surface-mounted, or left untouched. Masonry work and roof work may be performed by different trades; the proposal should name who owns the water-tightness detail.

For a roof-to-wall repair, ask whether siding or trim will be removed to expose the upper leg of the flashing. A contractor who replaces only the exposed lower metal may leave a concealed failure. For a valley, ask whether the quote includes the underlayment beneath the valley and replacement of adjacent damaged decking. The visible stain is not the measurement.

Comparing bids without a fake unit price

Put each bid into the same columns: roof detail, demolition, substrate repair, flashing system, finish replacement, access, disposal, and warranty. A lower bid that includes sealant and two replacement shingles is not cheaper than a higher bid that removes enough roofing to inspect the deck and rebuild the water path. Do not use a per-foot comparison until the two contractors have defined the same detail and removal width.

Flashing manufacturers also limit warranty protection to specified systems and installation methods. If the roof is under a material warranty, keep invoices, product labels, and photos. The manufacturer’s guidance can explain compatibility; it does not promise that every installer’s repair is covered.

These sources explain flashing performance and compatibility; they do not establish what a local crew will charge for removal, access, and restoration. Geography, roof material, height, and hidden damage change the work. Ask for a written site-specific quote and a separate allowance for deck or masonry repair, with the allowance converted to an actual price after removal.