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Few roofs look as good as slate. Walk through older neighborhoods in New Jersey and you will still see slate roofs that have been up for generations. But real slate is heavy, it breaks when you walk on it, and it takes special skills to install and repair.
Composite slate was made to solve those problems. It gives you the look of slate in a lighter, tougher tile. WDM Contracting installs composite and composite slate roofing on New Jersey homes, and this guide answers common homeowner questions.
Composite slate (also called synthetic slate) is a roofing tile made to look like natural stone slate. Instead of stone, it is molded from man-made materials. Depending on the brand, that can mean new plastic, recycled plastics, recycled rubber, or a blend. Makers add ingredients that help the tiles stand up to sunlight and fire.
The tiles are installed one by one, just like real slate. That is the big difference between composite slate and "slate-look" asphalt shingles. Slate-look shingles are asphalt shingles that are cut and colored to look like slate. They can be a good choice too, but they are a different product. Composite slate is a separate tile that copies the thickness, edges, and texture of real stone.
Composite slateNatural slateWhat it isMolded tiles made from plastics and/or rubberStone split from a quarryWeightMuch lighter (one major brand lists about 311 pounds per 100 square feet)Heavy (about 800 to 1,500 pounds per 100 square feet for common thicknesses)Walking on itMost brands say their tiles can be walked on carefullyBreaks easily; roofers avoid stepping on itTypical warranty50-year or lifetime limited warranties are commonSome quarries offer long warranties on the stone, but most of its value comes from its long track recordLifespanBacked by long warranties, but the products are much newer than slateAbout 60 to 175 years or more, depending on the quarryCostMore than asphalt shinglesUsually costs more than composite slate to buy and install
Here is what those differences mean for your home.
Real slate can weigh 800 to 1,500 pounds per 100 square feet of roof, depending on how thick it is. Many houses were never built to carry that much, so switching an asphalt roof to real slate often means strengthening the roof framing first.
Composite slate weighs a fraction of that. As an example, one major brand lists its tiles at about 311 pounds per 100 square feet. That is why composite slate is often an option on homes that could never hold real slate. It matches what the WDM roofing page says about composite slate: the look of natural slate "without the weight, fragility, or installation complexity."
Real slate is hard, but it is brittle. A misplaced foot can crack it, which is why slate roofers work from ladders and hooks and try to keep off the roof. Every future repair, chimney job, or gutter job on a slate roof has to be planned around that.
Most composite slate brands say their tiles can be walked on carefully, though they still advise keeping foot traffic to a minimum. Many products also carry the highest impact rating for roofing (UL 2218 Class 4). That rating is a lab test in which steel balls are dropped on the tile. Ratings vary by product, so ask which rating the exact tile on your proposal carries.
Many composite slate products can reach the top fire rating, Class A. But for several brands, that rating only applies when the tiles go over a specific fire-resistant underlayment (the protective layer under the tiles). Without that layer, some products drop to a lower rating. This is one reason the materials under the tile matter as much as the tile itself.
Natural slate is famous for lasting a very long time. According to the National Park Service, many slates from Vermont, New York, Virginia, and Pennsylvania last anywhere from about 60 to 175 years or more, depending on the quarry.
Composite slate is a much newer product, so no one has 100 years of real-world results yet. What you do get is a manufacturer warranty. Warranties of 50 years or "lifetime limited" are common for composite slate. Read the fine print on any warranty: most are limited, and the full coverage period is often shorter than the headline number.
At WDM, every roof comes with two layers of protection. The manufacturer's warranty covers the materials. WDM's own workmanship warranty covers the installation. If an issue comes up because of how the roof was installed, we fix it at no cost to you.
Some composite products can fade slightly over the years. Manufacturers limit how much fading their warranty will accept. If color matters to you, ask to see the fading terms in the warranty for the product you pick.
We don't post fixed prices, because every roof is different. As a general rule, composite slate costs more than standard asphalt shingles and usually less than a real slate roof. What moves the price is the size of the roof, how steep it is, how many chimneys, skylights, and vents it has, the material you pick, how many old layers have to come off, and how easy the roof is to reach. You can read more about what drives price on our pricing page.
Composite slate is not a "slap it on" product. A few details decide whether it lasts.
Roof steepness. Composite slate is made for sloped roofs. Most makers do not allow it on roofs flatter than about 3 inches of rise per 12 inches of run. On roofs that are just steep enough, they require a full waterproof layer under the tiles. Very low roofs need a different system, like the flat roofing options WDM also installs.
Waterproof layers at the weak spots. Major composite slate makers require a peel-and-stick waterproof layer in every valley (the low lines where two roof slopes meet). Some also require it along the lower edges of the roof, where ice can build up. That goes further than New Jersey's building code, which only requires the edge layer in the coldest part of the state.
Metal flashing. Flashing is the metal that seals the roof around chimneys, walls, and valleys. Slate-style roofs often use long-lasting metals such as copper, because the flashing needs to last as long as the tiles do.
A full tear-off. Building code does not allow a new roof to be installed over an existing slate roof. Even when you are replacing an asphalt roof, WDM generally recommends a full tear-off so we can check the wood boards under the roof (the decking) before the new roof goes on. You can read more about this in our post on roof repair vs. replacement.
Composite slate tends to make the most sense if:
It may not be the best fit if your roof is very low-sloped or if your budget points toward asphalt shingles. In that case, a thicker, higher-grade asphalt shingle (often called an architectural shingle) may be the smarter buy. See our breakdown of what a new roof costs in New Jersey for how the options compare.
If your home is in a local historic district, your town's historic preservation commission may need to review a change in roofing material before the work is approved. Some towns let you replace a roof with the same material without review but require approval to switch materials, for example from real slate to composite. If you are not sure whether your home is in a historic district, your town's zoning or construction office can tell you.
A historic review is separate from the building permit. WDM manages the building permit process with your town, from filing the paperwork to scheduling the final inspection. Our post on roofing permits in NJ explains when a permit is needed.
What is composite slate roofing?Composite (synthetic) slate is a roofing tile molded from plastics and/or rubber to look like natural stone slate. It is installed tile by tile like real slate but weighs much less.
How long does composite slate last?Manufacturers commonly back composite slate with 50-year or lifetime limited warranties. Natural slate can last about 60 to 175 years or more, depending on the quarry, but it is much heavier and more fragile.
Is composite slate cheaper than real slate?Generally yes. Composite slate usually costs more than asphalt shingles and less than a natural slate roof.
Can you walk on composite slate?Most brands say their tiles can be walked on carefully, though they advise keeping foot traffic to a minimum. Natural slate cracks easily underfoot.
Composite slate gives you the classic look of slate in a lighter tile that is easier to walk on and easier on your home's framing. It costs more than asphalt shingles, but it avoids most of the weight and breakage problems of real stone. The keys are the right product, the right layers underneath, and careful installation.
WDM Contracting is based in Monroe, NJ and installs composite and composite slate roofing for homes across New Jersey. We come out, look at your roof in person, and give you a written proposal that lists every material by brand and type.
Request your free estimate or call 848-360-6121.