How an Interlock Aluminum Roof Works
Quick answer
An Interlock aluminum roof is a system of shingles or panels that lock together on all four sides over a solid deck and underlayment, with concealed fasteners. The four-way interlock creates a continuous, wind- and water-resistant surface with no exposed screws, and the lightweight aluminum installs over most existing roofs. The result is a roof engineered to last a lifetime.
The four-way interlock
What makes an Interlock roof different is in the name. Each shingle or panel locks to its neighbors on all four sides, so the roof behaves as one continuous, mechanically connected surface rather than a field of separate pieces. There are no loose tabs for wind to catch and no exposed fasteners piercing the weather surface — the panels hook and lock together, fastened to the deck with concealed clips and nails. That geometry is what gives the roof its wind resistance and its clean, seamless appearance.
The layers of the system
A roof is a system, not just a surface. An Interlock roof starts with a sound, solid deck (minimum 1/2-inch sheathing), covered entirely with synthetic underlayment as a secondary water barrier, with ice-and-water protection at the eaves in cold climates. The interlocking aluminum shingles or panels install over that, from the eave up, finished with matching ridge caps, trims, and flashing. Each layer has a job — structure, secondary barrier, and the durable, finished weather surface — and together they keep water out and last for decades.
Why aluminum, and why over-existing works
Interlock builds in aluminum for two reasons: it cannot rust, so it lasts a lifetime and thrives in coastal and wet climates, and it is lightweight. That light weight is what lets an Interlock roof install over most existing roofs without added structure — saving tear-off cost — and it's gentle on the home's framing. Finished with the durable Alunar PVDF coating for color and UV resistance, the system delivers the strength and fire resistance of metal with corrosion immunity that steel can't match.
Frequently Asked Questions
How does an interlocking metal roof work?
Each shingle or panel locks to its neighbors on all four sides over a solid deck and underlayment, with concealed fasteners. This creates one continuous, wind- and water-resistant surface with no exposed screws.
Does an Interlock roof have exposed fasteners?
No. Fasteners are concealed — the panels hook and lock together and fasten to the deck out of sight. There are no exposed screws to back out, leak, or corrode, which improves both durability and appearance.
Why does Interlock use aluminum?
Because aluminum cannot rust and is lightweight. That means a lifetime roof that thrives in coastal and wet climates and can install over most existing roofs without added structure.
Can an Interlock roof really go over my old roof?
Usually yes. Its light weight allows installation over one existing layer where code permits, over solid sheathing, saving tear-off cost. An installer confirms the deck and code first.
Sources
- ICC-ES ESR-1790 — System description — Panel & fastening system
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Last reviewed 2026-07-11 · Reviewed by Scott Plumptree, Director of Marketing