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Thurman 08-11-2009 05:42 PM

Nosy as to flat roof construction
A friend owns a old office building of approximately 10K sq. ft. down here in hot S. Ga. It has a flat roof constructed in 1958. It also has one very bad leak, and two bad leaks. I have been around industrial buildings with built-up flat roofs and have seen that they have sheet metal on top of the joist with some type of composite materials and then tar/gravel. This roof has some type of composite material made of large strands of something on top of the steel bridge joist, and who knows what on top of that, then tar/gravel. The only roofing company in town which will do this roof says it has to be completely torn off, and rebuilt from scratch, $133,000 for the new roof, with sheet metal panels, and their inspector/estimator told me there are no sheet metal panels in this type roof. Another company is coming from out-of-town which installs rubber membrane roofs to look at it. What is the composite material sitting on top of the steel bridge joist? Thanks, David

Ed the Roofer 08-11-2009 09:06 PM

In 1958 the most likely products used on top of a steep deck would have been a perlite based insulation board.

There could be other options if the decking had a poured on and/or troweled product, such as gypsum, but if it were tectum, it would be exposed from the interior.

The rib panel configurations may not be available for an exact match, but there are deck roll forming companies who have many of the old profile dies on hand for special occassions.

A re-roof, going over the top would be based on the integrity of the decking and if there were any insulation that had gotten excessively saturated.

Core samples and IR thermography would be prudent before making a decision.

A Roof Consultant or Commercial Building Inspector would be able to possibly utilize those methods of testing, as do some of the larger roofing contractors.

Additionally, by contacting a Consultant, they may know of a local contractor who could provide the services required from a local company.


Thurman 08-15-2009 07:07 PM

Second contractor came Thursday to look things over and he was much more friendly. The material we see, with the interior dropped ceiling panels removed, are in his words: Those are panels of a "dis-oriented" strand material that is four or six inches thick. He says he has seen many of these and that as soon as water gets through the tar and felt covering on top, this material starts to disintegrate much like particle board. He used a pointed metal rod to penetrate the roof during his exam and as I had stated, there are no metal panels at all. This roofer suggested removing any panels that have had water migrating into them, replacing them with a newer material, and using a membrane roofing material over the entire roof. About half the other pricing also. Thanks for the info Ed, David

Leftyho 08-16-2009 08:27 AM


So you are saying the first roofer is giving you the best solution to your problem. This decking does not hold up under any water penitration.

But, the second roofer is telling you what you want to hear. I am going to save you lots of money. So he is friendlier?

The second roofer may be right. But the first is definitly not wrong. Does not sound like the decking will hold up to well to all the screws he needs to put in to hold his system down.

Thurman 08-16-2009 09:55 AM

Leftyho- -maybe I wrote it wrong. And, it's not my building, it's a friends who I work for often. He hired me to be the middle man with the roofers as he can't work the phone/counter and talk to them. The first roofer has many years of experience in our area with flat roofs particularly tar/gravel roofing. He does not do any of the newer roofs such as rubber membrane, or built-up foam/silicone and will tell you that they are not worth the monies. IF they are not then why are so many buildings in my are going to them? Now, roofer #1 want to tear off the existing roof completely and start over because the existing roof does not have metal decking to build up from. He will us metal decking, then some type of composite materials, then tar/gravel. His cost do not include removing/re-installing two large A/C units, that is the building owners responsibility. Roofer #2, says that he will totally remove two areas of roofing, one area of 20 x 20, and the other is 10 x10. He will build up with somewhat the same composite panels as needed, remove all the existing rocks they can, smooth the roof (how) and put the rubber membrane over all of this, with a twenty year guarantee of some type. It's not just the money. The first roofer had a bad attitude over all, telling us that the existing roof was a piece of *&^% and should have never been allowed to be put on. Guess what? I'm this type person- I went downtown and pulled records on this building, as it was built for the State of GA. to start with. Roofer #1 put the existing roof on the existing building. When I called him on this he was correct in that "That was before I bough the roofing company", actually I think this building was built before he was born. Thanks for the input, two more roofers to talk to this coming week and then hopefully we can "Get er done". Thanks, David

Leftyho 08-16-2009 11:07 AM

Hi Thurman,

I understood you.

It is common for people to think that I do not understand what they say. I very often will have a lone veiw of things.

I am not familiar with the decking you are talking about. But if it falls apart when water touches it like osb, and you have a lot of damage. I would question the integrety of the rest of the decking. Also the holding power of the decking. As you will need to use a lot of screws for the other membranes.

Tar and gravel roofs are very good roof systems. The roof you have now lasted how long?

I do not install tar and gravel because of the investment of equipment and manpower. They last a long time. They are a proven, long lasting system. It will easily last 20 years.

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