Metal Slate Roof vs. Real Slate: Weight, Cost Drivers and Durability

What are the main differences between metal slate and real slate?

The main differences are weight, fragility, installation and cost. Natural slate is split stone, laid piece by piece and fastened with corrosion-resistant nails. Metal slate is formed aluminum panels that interlock and fasten to the deck. Natural slate is many times heavier than aluminum, so it needs framing designed for that load. Aluminum slate weighs roughly 0.4 to 0.7 lb per square foot, which most existing roofs carry without reinforcement. Slate is hard but brittle: it can crack under a misplaced foot, a falling limb or ice. Aluminum bends rather than shatters and can be walked on carefully. Slate also requires specialist roofers, who are in short supply in parts of New England. Metal slate is installed by trained crews using a defined system, which makes the result more consistent from roof to roof.

Is a real slate roof better than a metal slate roof?

Real slate is better if you want authentic stone and your house is built to carry it. High-quality slate can last a very long time, and on a historic building nothing else is the same material. For most homeowners, though, the practical weaknesses of slate matter more. Older slate roofs in Massachusetts, Vermont and Maine often fail because the nails rust through or the flashings wear out long before the stone does, and fixing that means careful, slow work by a slate specialist. Metal slate trades the authenticity of stone for lighter weight, simpler repairs and resistance to cracking. Interlock aluminum is backed by the Guardian Lifetime Limited Material Warranty for the original purchaser while they own the home, transferable once with the second owner covered to 50 years from substantial completion; workmanship is excluded.

How do installation and repair compare?

Metal slate is faster and simpler to install and repair than natural slate. Each Interlock panel covers several slate faces at once and locks to its neighbors, so the crew covers the roof more quickly than setting individual stones. Natural slate is laid one piece at a time, each one punched and nailed, with careful overlaps. It is skilled, slow work, and mistakes are hard to fix later. Repairs follow the same pattern. Replacing a broken slate means working around brittle neighbors, often with special tools. A damaged metal panel can be replaced without breaking the ones around it. In winter, that difference shows up when a fallen branch or ice cracks slates and a repair has to wait for safe conditions on a slippery, fragile roof.

What drives the cost difference between metal slate and real slate?

Natural slate generally costs more to install than metal slate because of the material, the weight and the labor. Quarried stone is expensive to produce and ship, heavy framing may need reinforcement, and slate work is slow and specialized. For either roof, cost depends on size, pitch, the number of chimneys, dormers and valleys, how much decking needs repair, access to the site and the tear-off involved. Prices on our cost page are a rough guide only — every roof is priced individually, and structural or other site conditions can move the number. An in-home roof consultation is the only way to get accurate pricing for your home. Our metal roof cost guide explains these drivers in more detail.

How do they handle New England weather?

Both handle New England weather, but in different ways. Sound natural slate does not absorb much water, though poor-quality or old slate can flake and delaminate after years of freeze–thaw cycles. Aluminum does not absorb water at all. On the coast, from Cape Cod to the Maine shoreline, salt air attacks the metal parts of any roof. On slate, that means nails and flashings. Aluminum panels do not rust, which removes the main corrosion concern. In nor'easters, slate can be broken by wind-blown debris, and individual stones can slip if nails have failed. Interlock panels lock together on all sides and are rated for 120 mph wind when installed to manufacturer specification. Neither roof prevents ice dams; those come from attic heat loss and ventilation.

Which should you choose for your home?

Choose natural slate if your house is a true historic building, your local historic district commission requires it, or you specifically want stone and your framing can carry it. Choose metal slate if you want the slate look with less weight, simpler maintenance and a lower installed cost. Many owners who replace failing slate pick a metal slate profile because their framing, budget or plans do not justify new stone. Owners of Capes, newer Colonials and ranch homes often choose metal slate simply because they like the look and never had slate to begin with. Whatever you choose, check with your local historic district commission first if your home is in a district. Our job book lists 2,366 Interlock Slate roofs across New England, so there is likely one near you to see in person.

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