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Does Changing Roofing Material Make Existing Flashing and Vents a False Saving?
I’m comparing reroofing bids for a property with an approximately 15-year-old asphalt shingle roof. One proposal keeps asphalt shingles, while another changes to a metal roofing system. The metal material price looks competitive, but I’m concerned the total scope may change once the existing accessories are considered.
For each bid, I’m checking whether it clearly states replacement or reuse of:
- Drip edge and other perimeter edge details
- Step and counterflashing
- Pipe boots and plumbing vent flashings
- Skylight flashing
- Underlayment and ice-and-water protection
- Ridge vents, intake vents, and vent adapters
I don’t want to assume that components installed for asphalt shingles will work with a metal panel system, or that older flashing and vent boots are worth reusing just because they’re still present. The reverse may also apply if a new shingle system has different underlayment, ridge vent, or edge-detail requirements.
How do you compare these bids in practice? Do you require a line-by-line compatibility review, including the existing roof material and approximate age, before approving the lower material price? Also, which components are commonly reusable when staying with shingles, and which should normally be replaced when switching to metal?
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3 replies
The metal bid should name the actual panel system and its approved details, not just say “metal roof.” Flashing, vent adapters, closures, and underlayment compatibility can vary substantially between exposed-fastener panels, concealed-fastener panels, and standing-seam systems.
I’d ask each contractor to identify:
- The panel profile and manufacturer
- The manufacturer-approved pipe boots, skylight and wall flashing details, and ridge vent
- Whether the existing intake vents and roof penetrations are compatible
- The specified underlayment and ice-and-water protection
- Which existing components are being reused, with their age and condition documented
A 15-year-old pipe boot or vent flashing might still look serviceable, but it’s a poor place to create a future leak just to preserve a line item. For the metal proposal, missing system-specific accessories can easily erase the apparent material savings. Staying with asphalt may allow more reuse, but only where the components match the new shingle system and can be removed and reinstalled without damage.
The “competitive” metal material price can be misleading if the bids aren’t comparing the same installed scope. I’d put the following on a separate line-by-line comparison:
- Tear-off, disposal, and any second-layer removal
- Deck or substrate repairs, including the unit price for damaged areas
- Eave, rake, ridge, and wall trim
- Closures, sealants, fasteners, and underlayment
- Labor to remove, replace, or adapt vents, skylights, boots, and other penetrations
- Cleanup and any required repairs around intake ventilation
Those costs can outweigh the difference in the roofing material itself, particularly if the metal proposal assumes more custom trim or accessory work. The asphalt bid may also look cheaper if it assumes existing flashing and vents can simply be reused, while the metal bid prices compatible replacements.
I’d ask both contractors to state the same assumptions explicitly, including what happens if the deck is found damaged after tear-off. A low allowance or vague “as needed” wording makes the bids hard to compare, even when the panel and shingle prices are clear.
The “same installed scope” comparison should also cover roof-to-wall transitions and chimney flashing. Those details are easy to omit when a bid focuses on panels, shingles, and general perimeter trim.
For similar bid comparisons, have both contractors state whether they will:
- Remove and replace step flashing at sidewalls, rather than bend it around the new covering
- Install the specified headwall and sidewall flashing for that roof system
- Reuse, replace, or modify chimney counterflashing
- Include masonry cutting and repointing if new counterflashing has to be reglet-cut into the chimney
- Price custom metalwork separately if the existing chimney or wall details aren’t standard
A metal roof may need different transition geometry and custom trim even where the underlying wall or chimney hasn’t changed. Conversely, an asphalt reroof bid can look attractive if it quietly assumes the old counterflashing remains usable. Treat any “flashing as needed” allowance as a comparison gap until the contractor explains exactly what’s included and gives a unit price for masonry or custom-sheet-metal work.