Joseph Jenkins authored the Slate Roof Biblein 1997. He is also the founder and executive director of the nonprofit Slate Roofing Contractors Association of North America, Inc., which is a member of the International Federation for the Roofing Trades (IFD). When he isn’t providing consulting services or contracting work as the president of Joe Jenkins Inc., he conducts presentations about slate roofs throughout the country and internationally, as well as on radio and TV. He spoke to Roofing Contractorabout his presentation for the 2012 IRE.


Roofing Contractor:Could you tell us a little bit about your background?

Joe Jenkins: I climbed on my first slate roof in 1968 at the age of 16. I was a roofer’s helper during my high school years in Butler, Pennsylvania. I worked on all kinds of roofs for my boss, a first-generation Ukranian named Peter Odrey, who was 63 at the time and who learned roofing and sheet metal work in trade school. I remember well that day when I first climbed up a wooden hook ladder and straddled myself over the peak of a slate roof, like I was sitting on a horse. I was scared of the high, steep roof and I moved very slowly, like a sloth. The seasoned roofers who were working with me nimbly walked the ridge like a tightrope, laughing at my trepidation, perhaps remembering their own first experience on a scary roof. But what I remember most is how impressed I was that the roof was made of stone. I told myself then and there that if I ever built a house, I would put a stone roof on it. Today, my house does have a slate roof. So does my doghouse, chicken house, wood shed, compost bins, and shop. I have personally worked on well over a thousand slate roofs and have installed slate roofs on many buildings. My two sons do the slate work now.


RC:What can contractors look forward to at your IRE session on slate roofs? Can you share some highlights with us?

JJ: What I like most about the IRE is that it gives me an opportunity to share my knowledge with younger and less experienced roofers. Now that my sons are doing the roof work, I have more time to work as a slate roofing consultant nationwide. My work as a consultant takes me to many new slate roofs that have serious problems, some of which are in litigation. Almost all of the problems I see could have been easily avoided by some training or education. Even catastrophic roof errors that require the removal and replacement of an entire new roof can easily be avoided. It’s frustrating for me to see unnecessary errors occurring and it hurts the slate roofing industry. The IRE provides a perfect opportunity to help out the industry by fostering education.


RC: What are the most common installation mistakes you see with slate roofs?

JJ: I’d have to say that the number one mistake is lack of headlap. This is because a lack of headlap can’t be repaired. Instead, the roof has to come off and be re-laid with the correct overlap on the slate shingles. Needless to say, this can be a devastating mistake for both the contractor and the owner. Another mistake is not realizing that the roof, if installed correctly, can last 150 years or longer. Therefore, all of the essential components of the roof (fasteners, substrate and flashings) should be selected for that level of longevity. Another very common error is the contractor not staging the roof correctly and instead walking all over the slates during installation. This damages the slates and causes a condition known as “shedding,” where many slates will break and fall off, sometimes hundreds, during the months or years immediately after installation.

RC:When it comes to slate roofs, can you highlight some important details that might get overlooked? What about flashing?

JJ: What a lot of people don’t realize is that slate roof assemblies are generally simple. Remember that most existing slate roofs were installed before roofers had electricity and trucks. Many of the beautiful old, classic slate roofs you see on churches and institutions were done completely by hand, with only hand tools, using horses and wagons to haul the material. Today, hand tools are still used to install slate roofing. In fact, the slate shingles themselves are still split by hand out of rock at the quarries using hammers and chisels.

As far as specific details that are overlooked during installations are concerned, again, the big one is headlap. Also, sidelaps tend to be ignored, and starter course details are overlooked (there are five common mistakes made when installing starter slates). Contractors and owners also need to understand that there are many different types of slates and they have different characteristics — some good, some not so good. So it pays to know what kind of slates you’re using and where they come from. Slates also require installation techniques that differ from other types of roofing. You can’t use power nailers on slate, for example. Even hand nailing benefits from some experience so the slates aren’t “over-nailed” or “under-nailed.”

Slate roofs have a phenomenal life expectancy when correctly installed. This means that the roof must be installed with very long-term maintenance and repair in mind. A well-installed slate roof can be taken apart and put back together. Essentially, any part of the roof can be removed and replaced, like parts on a car. Screws and glue do not belong on a slate roof. Even ring-shank nails are problematic because they break instead of pulling out when repairing the roof. The broken shank remains under the slate and prevents the new slate from being installed. These details are the sorts of things I talk about in my presentations.

Flashings are another entire issue. Flashing metal must have a suitable longevity. Copper is usually recommended, as are stainless steel and sheet lead. All metals must be galvanically compatible. You can’t mix copper and steel, for example. When soldering metals, you have to allow for expansion and contraction.

There are many types of slate roof styles. There is the standard installation, random width installation, staggered butt, ragged butt, graduated slate, mixed colors, mixed shapes, and even intricate patterns. Slate roofing is an art and the roof is the palette.


RC: What advice would you give contractors looking to get into slate work?

 JJ: Some of the advice I would give would pertain to any contractor. Take pride in your work. Do the best job you can. Be honest at all times. Educate yourself before diving into a new project. Your reputation is your most important asset. Concentrate on quality and integrity and the money will follow. If a contractor wants to specialize in slate, they should know that they are becoming part of a community of craftsmen who date back a thousand years. Their work, if properly executed, could be admired by their adult great-grandchildren. There are books, videos, resource materials and organizations available to benefit slate roofers. I would highly recommend joining the Slate Roofing Contractors Association of North America, Inc. (, a nonprofit trade association, whether you do slate work full time or just occasionally. Google “slate roof.” It will open a whole new amazing world to you.