How Long Will My New Slate Tile Roof Last?

While there are many homes throughout Southern California with tile and slate roofs, I was recently in Pasadena when a client asked me “How long will my roof last?”  I decided that I should answer this roofing question thoroughly. My home in Altadena has a tile roof, as well.

Slate tile roof underlayment

First, one must understand that in addition to slate or tile, a “felt” is installed on this type of new roof. A “felt” is a fiber mat impregnated with asphalt and is used beneath roofing materials to provide protection for the wood deck the roofing materials are placed on.  Tile or slate roofing is a watershed and a decorative roof covering. The actual waterproofing is provided by the underlayment, or felt installed underneath the tile.

I must say that there are so many variables with slate and tile roofing, that the answer is quite broad. I’ve seen a slate or tile roof last 23 years and would not be surprised if a few might last one hundred years. On the average I would say that what I’ve seen here in the SoCal area is maybe around 28 years.

This is largely due to the inferior felts available in the 80s to 90s as well as the low-quality roofer using a single felt, since that time.  A good tile roof can and should last longer than that.  Any tile roof I install should be expected to last 45 to 90 years.  I always use high-quality felts, and double them up. If you’re going to spend that much money on a roof, you should not have to buy a new roof again in your lifetime.

A tile is manufactured while slate is natural stone. There are many kinds of tile, but in principle, there really are just two types; one-piece, and two-piece. One piece tile is usually concrete, sometimes lightweight concrete, and they interlock.  They are called one-piece because it only takes one piece of tile connecting to the next to make the “system”.

Two-piece tile is your traditional Spanish tile, and it is called two-piece because in order for it to work as a system, two pieces must be involved (even though the pieces are fundamentally the same).  Each tile is shaped the same but some are flipped upside down and made as “pans” – the channels between the tile rows – down which the rain will flow to the gutter.

It’s important to understand that with tile the felt underneath should be thought of as the principle barrier against rain.  Whereas, for composite shingles and flat roofing, it is not, it serves a different purpose, either as a vapor barrier, or in the case of flat, a vapor barrier and a suitable surface to melt your tar to.

Back in the day, one piece tile was sometimes installed without felt and, it worked, if you knew what you were doing you could make a one piece interlocking tile system not leak without the use of any felt.  But with a two-piece system (Spanish tile), you must have the felt and it must be good felt and a double layer.  All tile and slate nowadays is installed with felt, normally one is used and better roofers use two layers.

Since the felt is perhaps the single most important factor, I will suggest some roof life expectancies based on the types of felts that are widely available and used.  This is a rough guideline and, naturally, will vary depending upon your situation:

•    30 lb. felt: 15 to 20 years
•    30 lb. felt x 2 layer: 20 to 30 years
•    35 lb. rubber modified felt: 20 to 25 years
•    35 lb. rubber modified felt x 2 layer: 35 to 75 years
•    105 lb. flame applied smooth torch (rubber): 50-plus years, under the right conditions, could last over 100 years.

You can expect the lower numbers with two-piece tile, as it won’t last as long.

The bottom line is that because we used a double felt on his new roof – that owner in Pasadena can expect to have his roof last well past his stay in his home.

AltaDena roofer, Matt Glass, is co-owner of J and J Roofing, also servicing all areas including Sherman Oaks, Studio City, Woodland Hills, Pasadena, Tarzana, Burbank, Encino, Northridge,  Los Feliz and Silverlake for all roofing needs.