Thread: Tar and Gravel Roof

Never seen a tar and gravel roof on a residential roof, what's the life expectancy and what should I be looking for ?

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Originally Posted by Sam Morris

Never seen a tar and gravel roof on a residential roof, what's the life expectancy and what should I be looking for ?

Old Coal tar and gravel roofs could sometimes last 30-40 years. That pitch is too steep for a typical coal tar roof so I assume it is built-up asphalt. It really depends upon the number of plies, etc. Could last as little as 10 and possibly up to 30 years, but 20 max would be more realistic. Where I see them they are usually on flat roofs with parapets so I look for deterioration at the parapets, etc. to get an idea what condition it is in. I would not quite an average service life for a roof like that, and if you do not have an idea of the age I would say the service life cannot be predicted. Other that looking at visible flashing details it is hard to judge condition.

that roof should be gauged by the age of the home, which is?

Originally Posted by Sam Morris

what's the life expectancy and what should I be looking for ?

About 10 years *before* that green mossy stuff begins to grow on it.

In South Florida where that used to be a common roof, life expectancy was quite long as the gravel ballast (the gravel is there to help hold the roof covering down - and to protect the underlying roof materials from the sun and weather) - 25-40 years was not uncommon when not on a nearly flat roof (roof slope allows for relatively quick drainage of water off the roof). On flat roofs the life expectancy was somewhat less.

That is for the old built-up roofs with gravel ballast as those old roofs were laid with more care - newer built-up roofs were pretty much like all newer stuff - knock it out as quickly and cheaply as possible, which means using thinner (lighter weight) felts, less asphalt, and fewer layers (plies, 5-ply was common, now you seldom see anything more than 3-ply ... when you see a roof like that - which is seldom as that takes a 'tar kettle' and those can be quite dangerous to use, especially if the temperature is allowed to get too high and the kettle bursts into flames. I've seen that happen, and the person(s) near the kettle are covered with hot asphalt of about 450 degrees, and that burns the skin right off, and the heat stays there as long as the hot asphalt does - ever try getting hot asphalt off your shoes? It is a bad scene and the people are seriously burned, sometimes they don't make it. Even when the kettle is not allowed to get too hot and explode, the hot asphalt is dangerous to handle and you do not want any spilled on you.

Roofers who use those tar kettles pay *A LOT* for workmen's compensation insurance, even more than other roofers pay because working a roof can lead to falls, and the fall is not from a standing position to the ground, the fall is from the roof to the ground.

You should look for bald spots (no gravel or rock); alligatoring asphalt; crazed asphalt; "humped" sections that indicate previous repairs (which would be either a flood coat of hot asphalt or a 5 gallon bucket of Bull, depending on who did the work); ponding and other low spots; soft sheathing when walked upon; weird or non-standard flashings (many people don't know how to work on these roofs). If it looks wrong, it probably is...

Originally Posted by Dom D'Agostino

If it looks wrong, it probably is...

I second that!

Originally Posted by Jerry Peck

I second that!

Thanks for all the info, very helpful

T&G can be rejuvenated by removing the gravel, applying a fresh layer or two, and laying down new gravel. The only sure way to know the thickness is by destructive testing.

I have T&G on one half of the house, and it makes a fine roof, that is safe to walk on. My roof is over 40 and well cared for. I would to cap it with a waterproof deck and solar panels. But that will have to be for the next owners.

The moss grows on organic debris. Rake it off.

Time for replacement. The moss is feeding on the materials and is usually a sign of failure.

Ref. Raymond Wand:

The T&G materials are inorganic, hence, there is nothing for the moss to "feed on".

The organic debris particles that bed the moss, & the covering moss itself, will retain moisture and can cause expansion especially in freezing conditions.

Expansion will create minute cracking and will often displace the gravel.

Moss on any surface should be removed.

AAMOI: I know of a built in 1948, San Leandro Ca. duplex that has the original T&G roof.
The T&G is in great shape.

We have a fair amount of tar and gravel roofs out here in the Bay Area. If I saw something like that in your pictures, I would say it's probably due for replacement! Recommend a qualified roofing contractor...