In my last blog I was discussing this prevalent question about the longevity of a new tile or slate roof. Below you will see a picture of a new Spanish tile roof such that is sold at Burbank Roofing Supply, where contractors buy our materials.
Slate is a natural product. Some manufacturer’s make a smooth surfaced “slate” look (versus a rougher shake look) but it is just concrete or sometimes other man-made materials. Slate is completely different in look and feel and cost to a man-made slate imitation product.
Slate will be similar to one piece tile. (See my last blog.) Many people believe that slate will always remain leak free longer than interlocking one piece tile and this is not, strictly speaking, true. In fact, I can argue it’s the other way around.
The reason slate roofs have been observed to last 100 years or more, probably has more to do with a combination of simple factors that aren’t immediately obvious: slate roofs are usually steep and steep roofs last longer.
If you’re putting slate on, which is extremely expensive, you’re more than likely going to select the superior underlayment system of the time, a high quality crew (if for no other reason than low-quality crews usually avoid slate or have no idea how to do it) and a good contractor.
But all things being equal, the interlocking one piece tile will usually prevent more water from entering a system, on its own, than slate will. If you don’t believe me then get 10 pieces of one piece tile, and 10 pieces of slate, nail them properly on a piece of plywood and hit it with a hose. Take them off and see which one let more water through.
I’ve taken apart plenty of circa 1920s one piece tile roofs that had no felt under them, but I’ve never taken apart a slate with no felt under it. It can be done under the right conditions but I doubt anyone would try it!
Because slate is natural stone, the slate itself will outlast manmade concrete tiles without question but we’re talking about how long the system will remain watertight.
Using upgraded rubber-modified felts will increase the life of the roof, particularly with a double layer. There are other felts, particularly new synthetics which are not time tested. I use them sometimes, under the right circumstances and I think they will hold up but they are not for every situation. I don’t use synthetics under two-piece tile, at least, not by themselves.
My go-to choice most often is a double layer of rubberized 35 lb. or a torch-down roofing membrane. I stopped using the non-rubber modified felts ages ago. Since a double 35 lb. would only cost about $1500 more than a single 30 lb. or even a double 30 lb., it seems a small price to pay to ensure a very long lasting roof that you may never have to redo again.
AltaDena roofer, Matt Glass, is co-owner of J and J Roofing, offering roofing contractor services in all areas including Burbank, Studio City, Tarzana, Woodland Hills, Encino, Northridge, Pasadena, Sherman Oaks, Los Feliz and Silverlake for all roofing needs.