A smart upgrade — with a dangerous shortcut
When it comes to upgrading your home’s exterior, a metal roof is one of the smartest long-term investments you can make. Metal roofing offers exceptional longevity, sleek modern curb appeal, and unyielding resistance against severe seasonal weather — from heavy snow load to high winds.
However, during the planning process, homeowners often come across a common shortcut designed to cut initial labour costs: installing new metal panels directly over existing asphalt shingles.
While it might sound like a convenient shortcut that saves time and disposal fees, “roofing over” your old system is a major gamble.
Keen Roofing’s policy: we do not metal over shingles
At Keen Roofing, we hold ourselves to an uncompromised standard of craftsmanship and care for every home we touch. Because we care deeply about protecting your home and delivering results that genuinely stand the test of time, we maintain a strict company policy: we do not install metal roofing over old shingles.
We refuse to compromise our brand’s standard of quality — or your long-term peace of mind — by cutting corners on the single most critical structural component of your roof.
Here is why covering old shingles with metal panels is a risk that simply isn’t worth taking, and how it can compromise your investment from the inside out.
1. You hide structural rot and water damage
The primary deck of your roof — the plywood or OSB structure underneath your shingles — is its foundation. Over time, aging asphalt shingles can develop hidden leaks, severe moisture buildup, and wood rot.
If metal panels are laid directly over an old roof, there is no opportunity to inspect and repair the decking beneath. Securing heavy-duty metal panels into compromised or rotten wood guarantees structural sagging, loose fasteners, and eventual failure.
2. Trapped moisture causes hidden mold and corrosion
Metal reacts quickly to temperature changes. When warm air rises from your attic and meets a cold metal panel, condensation naturally forms on the underside of the panel.
When installed over old, uneven shingles, this trapped condensation has nowhere to escape. Over time, the trapped moisture rots out the remaining original underlayment, encourages mold growth in your attic space, and can accelerate corrosion on non-treated fasteners and metal components.
3. Uneven surfaces ruin aesthetics and seal integrity
Asphalt shingles curl, cup, and lose granules as they age, creating a rough and uneven surface.
Metal panels — especially standing seam systems — require a smooth, level plane to sit correctly. Fastening rigid metal panels over uneven shingles distorts the metal (a visual flaw known as oil canning) and prevents the panels from expanding and contracting properly during thermal shifts. This puts artificial stress on the fasteners, stretching out screw holes and creating potential leak points over time.
4. Excessive weight stress on your home’s frame
While individual metal panels are relatively lightweight, combining them with a saturated, heavy layer of old asphalt shingles creates unnecessary dead weight on your roof trusses. Add a heavy winter snow load on top, and you are putting severe, uncalculated stress on your home’s framing structure.
5. It may void your manufacturer warranty
A high-quality metal roof system is designed to last anywhere from 40 to 70 years, often backed by robust long-term manufacturer warranties. However, many top metal panel manufacturers specifically state in their fine print that failure to install their product over a clean, flat, and newly underlaid substrate voids their warranty coverage entirely.
Saving a modest tear-off fee is a poor trade for losing decades of manufacturer protection on a premium metal system.
The Keen Roofing difference: done right, every time
A metal roof is built to last a lifetime, but it is only as strong as the deck it sits on. Skipping the tear-off phase might save a modest amount upfront, but it compromises the integrity, safety, and comfort of your home.
Because we care about doing right by our homeowners, our process always includes a full tear-off — stripping old layers down to the bare deck to reveal true structural conditions; deck inspection and repair — replacing compromised wood to ensure a solid foundation; high-performance underlayment — installing climate-rated moisture barriers before panel attachment; and precision metal craftsmanship — delivering flawless standing seam and metal tile installations backed by our solid workmanship warranty.
Planning a metal roof upgrade? Contact the certified team at Keen Roofing today for an honest assessment and a transparent, itemized quote.
