8 things to know about a slate roof installation

One of those resources was Joseph Jenkins, a slate roofing consultant and author of The Slate Roof Bible. Jenkins warns that uninformed roofers are telling homeowners to have their slate roof replaced when it really isn’t.

“The main thing that people need to understand is that a slate roof can literally last centuries,” Jenkins said. “I am annoyed that a roofer would destroy someone’s roof, and it is unfortunate that the owners do not know what they have lost.”

How long your slate roof will last largely depends on the type of rock used. According to an identification guide on the Slate Roof Central website, some of the toughest and heartiest types are purple slate, non-fading green slate, and gray-black Buckingham slate, which can last every 150 to 200 years. Softer shales, especially those that were once mined in parts of Pennsylvania, have a lifespan of 75 to 90 years.

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This is the guy on my house from 1946 so I’m in the market for a new slate roof. The median age of homes in Washington is 75, so I’m not alone.

A slate roof can cost anywhere from $ 12 to $ 40 per square foot, according to websites and roofers I’ve consulted. Their price is on the low end if you’re using recycled slate or reinstalling your own. The price goes up if your house is complicated, your slate is particularly chic, or you live in an expensive area. That is two to four times more than an asphalt shingle roof. On the other hand, a slate roof can also last four or more times as long, which makes it a good value in the long run. However, in order for a slate roof to last a long time, it must be installed correctly.

Here’s what you need to know:

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Knowing the color and cost of the slate that you will put on your roof is not enough. Even knowing the name of the slate maker is not enough. “The most important thing you need to know is where it came from the ground,” said Jenkins.

In other words, you need to know the name and location of the actual quarry. This is important because some quarries have a better reputation – and a better guarantee – than others. Look for slate that has a lifespan of at least 75 years. One hundred is even better.

That guarantee should include a guarantee that the slate maker will pay to replace your roof if the slate develops pyrite stains – ugly, rust-colored streaks. The Slate Roofing Contractors Association maintains a list of reputable manufacturers and quarries on their website. You should also ask your installation company if they can reinstall or recycle your old slate and adjust the price accordingly.

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A critical factor is the amount that slates overlap to keep water out of your home. Skilled roofers will make chalk lines on the felt pad to make sure there is enough overlap.

Slates should overlap at least three inches on the sides, which is known as the side overlap. More importantly, the overlap at the top of each slate, known as the overlap. If your roof is steep – with a slope of at least 20 cm high per 30 cm width – you will need 3 cm head protection.

You can confirm the roof pitch with an online calculator. If your roof is shallower between 4:12 and 8:12, the slates should be at least 4 inches head height. Roofs that are shallower than 4:12 shouldn’t be made of slate, according to Traditional Roofing Magazine.

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One final note: there should be extra headgear 1 to 2 inches near the eaves to protect against ice jam.

Copper is the most common metal used in slate roofs. However, there are other options such as B. coated stainless steel, which cost less. Regardless of what metal your contractor is using for flashing and other purposes, consistency is the real key due to what is known as galvanic corrosion.

Put simply, some metals “eat” each other over time when they come into contact with one another. This is one of the reasons why the metal parts of slate roofs often fail long before the rock itself.

This caution applies to metals used in flashes, ridges, valleys, nails, rivets, drip edges, gutters, and downspouts. You don’t have to worry as much about the metal composition of your snow protection devices as they won’t come into contact with other metals.

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Slate nails should be made of copper, stainless steel, or at least hot-dip galvanized steel so that they can fight for as long as the slate itself. Galvanized nails are a no-no because they can rust in just a few years.

The nail length is also important. The correct length is twice as thick as your slate plus 1 inch. If the nails are the right length, they will penetrate the roof cladding boards but will not penetrate the other side.

After hammering in, the nail heads should be flush with the slate. If they’re pushed in too far, they can crack the slates that are designed to hold them in place. If not hammered in far enough, they can crack the slate layered on top.

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In this era of man-made materials, the underpayment of slate roofs has become a confusing and controversial issue. All but one roofer whom I interviewed wanted to use a so-called ice and water protection in the valleys of my roof under the slate. Jenkins said ice and water protection are not only unnecessary, but can also damage slate roofs.

He said this product prevents your slate roof from breathing because it’s synthetic and makes repairs difficult to do later because it’s sticky. So what underpayment is appropriate? Traditional 30 pound organic roofing felt.

The felt is primarily there to protect your home from the elements if it storms before the contractor installs the slate. It then dissolves in a couple of years and Jenkins said that was perfectly fine. “I’ve worked on well over 1,000 slate roofs in my life and none of them had a functional underlay,” said Jenkins. The stone itself is what spills water and protects your home, not the material underneath.

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The sheathing, also called decking, is the wood to which the slate is attached. Ideally, the wood will last 150 years – or long enough to support an average initial slate roof and a replacement slate roof.

The right choice for the cladding is individual planks. The boards can be anywhere from three quarters to 1½ inches thick and will work with many different types of wood. Plywood, particle board, and composite woods are not ideal because they are made with glue and will not last long enough, according to Slate Roof Central.

When replacing a lightweight roof, you should also make sure that your rafters and sheathing are strong enough to hold a heavy slate roof without sagging.

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Correct equipment and technology

Your roofer should choreograph the project so that the workers walk as little as possible on the slate, which can crack the stone. To achieve this, contractors should use roof mounts, known in the trade as mini-scaffolding, that roofers can work from.

Other traditional tools a good slate roofer should use: slate cutters, hammers, hooks, and rippers. To test the slate knowledge of potential roofers, you can ask them if they use these tools. Good roofers also know they need to mix up their supply of slate as they work, rather than pulling from a single pallet, to avoid sudden color changes.

What your contract should contain

As you’ve read, there’s a lot to know – and to insist on – especially since replacing a slate roof can be a five- or six-figure investment. However, when I requested quotes to replace our slate roof, three out of four roofers submitted half-page contracts without these specifications.

“That bothers me,” said Shaun Rowe of Brax Roofing of Gaithersburg, Md. “For a roof like this, which has been built for a century, it is better for both contractors and customers to have the materials and workmanship detailed become.” Brax has acquired the five-page slate roofing contract from Slate Roof Central, which savvy homeowners can request from other roofers.

At the very least, ask contractors to include a clause in their contracts stating that they will build your roof according to installation guidelines developed by the Slate Roofing Contractors Association. If the home remains family-owned, your children – and even grandchildren – will thank you.

Elisabeth Leamy is a 13-time Emmy Award winner and 25-year-old consumer advocate who has appeared on programs such as Good Morning America. Connect with her on Leamy.com.

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