The copper cap over your bay window may have years of service left. That does not automatically make it compatible with the standing seam roof you want below it. Before you approve the panel order, have the roofer identify the existing metals and trace where their water goes. Copper does not have to touch a new roof panel to create a material compatibility problem.
This matters on a St. Louis house where the roofing work covers only part of the building. You might be replacing shingles over a porch while keeping a copper dormer roof, chimney flashing or decorative roof above it. The decision is whether those retained pieces can stay with the proposed panel system, and what detail will make that possible.
Material and spec
Check both direct contact and runoff. These are separate questions. A drawing can show two metals safely separated at a joint while missing the water that travels from one surface onto the other. Ask the contractor to mark the retained copper and the direction of drainage on a roof photograph before discussing a fix.
MBCI's guidance for Galvalume roofing says panels must not contact copper or receive its runoff. Galvalume is steel protected by an aluminum-zinc coating. The restriction concerns the material combination, even if the copper piece itself remains watertight. See MBCI's guidance on metal roof corrosion.
For example, picture a copper-covered dormer above the new standing seam section. Rain leaves the dormer and crosses several feet of the proposed panels. Keeping a gap between the dormer flashing and those panels does not remove that drainage path. The roofer needs to address where the water lands, as well as how the two roof sections meet.
Name the metal beneath the color
A proposal that says only "brown standing seam" leaves this question unanswered. Ask for the panel manufacturer, product name, base metal and protective coating. Brown paint does not tell you whether the panel beneath it is steel or aluminum. Likewise, a copper-colored trim piece may be painted metal rather than copper.
Have the contractor identify existing pieces through inspection and available records. Do not order changes solely from a photograph or the color visible from the driveway. An older flashing detail may also contain more than one material, with a previous repair covering part of the original work. If its identity remains uncertain, that uncertainty belongs in the inspection notes before the material order is released.
The Metal Construction Association treats dissimilar-metal contact and water runoff as distinct corrosion concerns in its technical guidance. Its technical resource library includes "Dissimilar Metal Corrosion in Roofing Installations." For your house, ask the panel supplier to review the actual combination being proposed rather than relying on a general statement that all the pieces are roofing metal.
A separator needs a defined job
If the proposed solution is a separating material, ask exactly where it goes and what it accomplishes. Does it address contact at a joint? Does the design also keep copper runoff off the panels? A strip tucked between two components is not an explanation of the whole drainage arrangement.
Ask for a detail accepted by the manufacturer of the selected panel system. It should identify the adjacent materials and any specified separator, fasteners and sealant. "We will put something between them" is too vague to approve. The installer should be able to show how the detail fits the roof you have, including the corners and ends where the materials meet.
Do not assume that repainting an old copper piece settles the issue. If coating it is proposed as the solution, request written manufacturer acceptance of that specific arrangement and an explanation of any continuing maintenance it requires. Otherwise, you are agreeing to an unresolved material question beneath a fresh finish.
What it costs
There is no useful flat allowance for keeping copper beside a new metal roof. The price depends on which piece creates the conflict, whether it can be removed independently and whether the drainage path can be changed. A small, accessible flashing replacement and a retained copper dormer roof are different jobs.
Ask for the compatibility work to appear as a separate part of the scope. That lets you see whether the price includes replacing existing metal, fabricating a transition or changing drainage. It also lets you compare two proposals that otherwise appear to supply the same standing seam panels.
If you want to retain a visible copper feature, ask the contractor to price a documented way to keep it, if one is available. Then compare that with replacing the affected piece using a material accepted for the new assembly. Include any work needed to reach the flashing, such as opening adjacent siding or arranging masonry work. The price should identify who restores those disturbed areas.
A material change may affect the appearance of a dormer or entry roof. Review that consequence before ordering panels. If your address has an applicable exterior review requirement, establish whether the proposed alteration needs approval. Across St. Louis County, confirm the responsible municipal office for your address rather than assuming the roofing permit answers every exterior design question.
The expensive surprise is discovering the conflict after the panels arrive. You may then be choosing between altering a feature you meant to preserve and revising an order already in production. Have the compatibility decision recorded before authorizing fabrication, with any unresolved inspection item clearly assigned to someone.
What to ask
Start with one direct question: "What existing copper will drain onto or meet this roof, and what does the panel manufacturer allow?" Ask the roofer to answer it using your roof photographs and the proposed product information. A general assurance about experience with metal roofs does not identify the detail your house needs.
Then ask for these points in writing:
- Which existing metal pieces will remain, and how their material was identified.
- The manufacturer and product name of the proposed panels.
- Where water from each retained copper surface will discharge.
- The accepted detail for any joint between different materials.
- The price and responsibility for replacing or modifying conflicting pieces.
- Any manufacturer response used to approve the arrangement.
If the answer is that the copper sits below the new roof, have the contractor show that on the drawing. That is a different drainage arrangement from copper above the panels, but the attachment and contact details still need review. Location is useful evidence; it is not a substitute for checking the assembly.
Keep the accepted detail with your roof paperwork. If someone later replaces a dormer cap, adds decorative metal or changes an upper gutter, give that contractor the panel information before they select materials. A future alteration should be checked against the roof already installed.
To discuss a standing seam project in St. Louis or the greater St. Louis area, call Keys Roofing, the contractor behind Standing Seam STL, at (314) 220-2333. Mention any copper you intend to keep when arranging the visit. Have a ground-level photo ready that shows both that feature and the roof section below it.