Existing Commercial Bldg - Flat Roof, Which system best?

I’m new to the forum, and know very little about roofs. I hope that someone in this forum may be able to give me some much needed advice. I own a 2800 sq. ft commercial bulding with a flat roof in Broken Arrow, Oklahoma (Near Tulsa). The roof has many leaks and needs replaced. I have rec’d several bids, with varying scopes and I’m trying to determine which is the best system.

System # 1 - Single ply Duro-last ($11k to $12k) {One bid mentioned 1/2" insulation, the other didn’t}

System # 2 - 1" Insul mechanically fastened to roof + 3 plies fiberglass felts + flood coat entire roof with hot steep asphalt ($8k)

System # 3 - 1 layer emulsion base coat + 1 layer elastomeric top coat ($3k)

System # 4 - Mob base sheet + 2 plies of fiberglass felt with hot asphalt. ($6k)

System # 5 - Install a pitched roof on top of existing roof. ($25k)

I know that the quality of the contractor plays a huge role, and I’ll need to do some research to try to determine if the contractors are good.

A) Are any of these roofing system not worth pursuing?
B) Any suggestions on how to verify if a contractor is good?
C) Should I read much into the warranty they offer? For example, I would expected the pitched roof to be one of the best systems, but their warranty was only 3 years.



Based on the bids you have recieved so far, The Duralast is your best “value”.
Unless there is a site condition on your building that would require re sloping your roof ( if that is what you mean by installing a pitched roof) it wont be necessary to speak to #5 again.
System #2 is not a bad choice if you have a limited budget but you should put a reflective coating over the system when the asphalt roof has set for about 4 weeks. You will spend about another $1500 to do that.

Systems 3 and 4 are junk.

System #1 Duralast hasnt been through a real warranty cycle yet so " Buyer beware" There have been some conflicting results in their longterm performance. They have reinvented thier product several times so their oldest roofs are not the same as the ones they sell today. Hopefully they got it right.

Good luck.


How many units are on the roof?

Are any of these guys tearing the old roof off?

My answers are based on value and longevity of the roof.

Duro-Last their sheets in the beginning were the best sheets they ever had. Fibertite made them. With the choices you have I would not put it on. And I install Duro-Last.

No. 2 seems like the best system.

No. 3 If you have alot of leaking. This system needs a good base.

No. 4 is a less expensive no.2

No.5 You need a strutural enginer to make sure your building can hold the added stress.

The contractor is a major part of your roof.

Forget about systems 3, 4, and 5, they aren’t even worth considering. As for systems 1 versus 2, I have to say from a consultant’s stand-point, without knowing much about your roof, I’d opt for system #2. If you were to provide more information I might could be of more help, but given the information that you’ve provided I have to go with #2.

More in the morning, but I dont like #2 without a base sheet and gravel.

Thank you to each of you for your helpful responses and suggestions. It sounds like everyone universally agrees that only System 1 and 2 are worth pursuing. So I’ll try to answer your questions about those systems:

Will the old roof be removed?
System 1 - I think they are not removing the old roof, nothing is stated in their bid. We will need to verify.

System 2 - They stated that they would be removing the old roof.  

How Many Units on the roof?
There is one HVAC Unit. I have uploaded some pictures of the roof and building at the link below:

mecaconsulting.com/Downloads … 0Building/

There were a couple of suggestions you have made about System # 2:

  • Reflective coating
  • Base sheet with gravel

Do these vary based upon the personal preferences, or are they something I need to consider revising in the System # 2 proposal?

Any suggestions on the best way to verify if a Contractor is good?

Thank you again for all of your help!!! :smiley:

ask for references.find out if they are an approved contractor by the manufacturer of the system they install.ask to SEE other work they have installed.research the system they want to install.your roof looks to be an easily removed,installed situation.good luck.

Here are the warranties they offer:

System # 1 (Duro-last) - 15 yrs Material and Labor

System # 2 (3 Ply Fiberglass Felts) - 2 yrs Workmanship and 10 yrs Material

I know now that Duro-last has not been through a warranty cycle, so there is some risk with their warranty. But given the big difference in warranty, wouldn’t I be better off with System # 1?

Alright, after looking at the photos here is what I would consider. I would probably go with system #2, but like Aaron said I would want a base sheet or a 4th ply of membrane. I’d also be curious as to what type of insulation the contractor is proposing, though I suspect it is perlite/fesco. That also brings up the question of what type of roof deck do you have? It is a fluted metal deck, corrugated metal with lightweight concrete, wood, etc.??? Are you planning on getting your R-value from the roof board insulation, or is the ceiling and/or underside of deck insulated? Does the existing roof system have insulation, and if so is it wet? Where is this building, i.e., Houston, Texas or Anchorage, Alaska? How long do you plan on owning the building?

Anyway, if you could answer the questions above I could give you a much better answer. But without knowing, here are my thoughts for now:

Remove the existing roof system, and install new insulation as needed for R-value, maybe some polyisocyanurate overlaid with perlite. The polyisocyanurate will provide a high R-value, and it should be mechanically fastened to the roof deck. The perlite would be mopped overtop the iso board in Type III or IV asphalt, and would provide a suitable surface for the roof membrane. Then I would probably just have the roofing contractor install a 4-ply asphalt built-up roof system. Instead of flood coating the roof, you could have the roof coated with an emulsion and a few days later have the roof coated with Aluminum Coating. You could also go the route of installing an asphalt flood coat and gravel on the roof if you need the fire rating, and if the roof can support the added weight.

You could also remove the existing roof, and install a two ply modified bitumen roof system, or even a base sheet and one-ply modified bitumen if you are looking to save money and don’t plan on keeping the building very long. Another option, and I hate to say it, is you could cover the roof with spray polyurethane foam (ask Aaron for particulars, I don’t much like the system but your roof would not be a bad candidate from what I saw in the photos).

I will also say, it looks like you have a relatively new HVAC unit, but the duct work is rusted and old. You should definitely have the roofing contractor address the flashing around the duct penetration, and you should either install a metal shroud over the ductwork or clean and coat the ductwork with a urethane coating (acrylic coating would probably also work fine if you want).

Anyway, if you could answer some of my questions it would help and might totally change what I would recommend for a new roof.

Thanks Cerberus. Here are answers to your questions:

That also brings up the question of what type of roof deck do you have? It is a fluted metal deck, corrugated metal with lightweight concrete, wood, etc.???

==> It is a corrugated metal roof. There is not any insulation underneath, it is bare. No concrete, wood, etc… We have offices in the front 1/2 of the building, and there is a drop ceiling (with insulation) about 6 to 7 feet below the corregated metal roof. We basically have offices inside a warehouse.

Are you planning on getting your R-value from the roof board insulation, or is the ceiling and/or underside of deck insulated? Does the existing roof system have insulation, and if so is it wet?

==> No insulation currently. We have a drop ceiling with insulation above the ceiling tiles. The “warehouse” is not currently climate controlled, but could be in the future.

Where is this building, i.e., Houston, Texas or Anchorage, Alaska?

==> Broken Arrow, Oklahoma (near Tulsa). We get pretty hot summers, and we get snow/ice a couple of times each winter.

How long do you plan on owning the building?

==> Probably for 10 to 15 yrs.

Currently my Duro-last quote is for $11k, and the “System 2” is $8K. If I make the changes proposed by some of the members here, then I suspect System 2 is going to be comparable in price to the Duro-Last. With the better warranty, would I be better going with Duro-Last?

First of all, don’t get too caught up in the warranty side of things, as most manufacturer’s warranties aren’t worth the paper they are written on (or something like that). If you look at most warranties there are several things you must do to keep it intact, and there will be several exclusions for damage by other, acts of God, etc.

Now, on to your system and your question. First, yes you will likely be bumping up the price for a built-up roof if you comply with several of the suggestions on this board. In fact, the polyisocyanurate insulation I recommended will drive the price up substantially, but you may recoup that money down the road in heating/cooling costs. However, if you are well insulated above the acoustic celing, then you may want to go with some basic insulation just to provide a suitable roofing substrate.

You say you have a fluted metal roof deck, so that tells me you need to mechanically fasten roof board insulation to the metal deck using insulation screws and stress plates. Depending on the location of your building, height, ground roughness, etc., you may or may not want to install the insulation to comply with FM (Factory Mutual) wind up-lift loss prevention guidelines. You would need to have it determined whether you should go with FM I-60, I-90 or I-120. Basically, you would probably be looking at I-60 or maybe I-90. I personally would probably opt for I-90 if you have many straight-line winds or tornadoes in the area.

Next you need to decide what type of insulation to use. Since you would be using it strictly as a substrate, and not for its R-value, I would probably opt for a nominal 1-inch thick fiberglass insulation at the minimum (I would prefer 2-layers with staggered joints), rather than organic wood fiber or perlite. The fiberglass will stand up better to moisture intrusion if you ever have leaks. Still, choice of insulation is certainly something you can value-engineer down.

Now you have to decide what type of roof membrane to use. This would also affect your insulation choice. First off, I would recommend either a built-up asphalt roof membrane or a modified bitumen roof membrane. However, you could opt for PVC, spray polyurethane foam (applied over existing roof), EPDM, or any number of membranes. I think my first choice would be a built-up roof (BUR) for your building. You could go with the modified bitumen or even a BUR with a modified bitumen cap sheet, but you probably would be fine with just a BUR. Now, you need to determine whether to go with a 3-ply system or a 4-ply. In my way of thinking, the cost for a fourth ply is not going to be that much more, and the roof system will be so much better.

Alright, so by now you should either be deciding upon a 4-ply BUR or a spray polyurethane foam roof. Once again, you would want to talk to Aaron if this is the route you want to go, and with your building it might be the best alternative. You wouldn’t have to worry about tear-off, and the foam would add reflective and insulating qualities to the roof. Anyway, if you go the BUR route, you have to decide whether to go with a glaze coat (not recommended), flood coat and gravel (provides fire rating) or emulsion and aluminum coating (possibly the best option for the money). The other option would be a 2- or 3-ply BUR with a modified bitumen cap sheet, but that would probably be too costly when compared to your other bids. At the same time, remember this roof is going to serve you for years to come and will be the most important part of the building structure.

Back to warraties for a minute. You keep mentioning Durolast’s warranty, but with a BUR system you can also get a NDL (No Dollar Limit) warranty. Depending on the BUR system and manufacturer, you can generally get 10-, 12-, 15- and 20-year warranties standard.

Okay, now lets move on. The next thing you will want to consider is flashings and counterflashings. If you go with the BUR or mod. bit. roof, I recommend modified bitumen flashings along base of walls, curbs, parapets, etc., and I recommend minimum 24 gauge prefinished (Kynar 500) galvanized/galvalume metal counterflashings that are shop fabricated.

Good luck. If you have any more questions, let me know.

Please consider this option as well gaf.com/Content/GAF/RES1/ROO … berty.html

The last job I did was a flat roof, so I build a pitched roof on top the old one just like you said and installed this liberty low slope system.

It was my first time doind this system and it really looks like a best option for low slope today in my opinion.

Self-adgereds are fine, but I like a watertight roof. There is nothing preventing water infiltration at ANY seam with SA. They are only good for uni-directional waterflow to a roof edge with no gutter, IMO.

Good politicing, Cerb. :slight_smile:

That would be a nice roof to do. I would go with the tear off, and depending on the insulation situation, either 2" of polyiso and a 1/2" wood fiber then a 2 ply base, and a torched cap sheet. If you wanted to be really fancy, go with a torched smooth cap, and then a granulated cap on top of that for the ultimate protection.

What most people dont realize is that materials are a sliver of the roofing project cost. Nearly all the cost of the project is LABOR. Well, tear off labor is the same, the install labor is a variable depending on the system. It usually makes the most sense to go with the best system you can at the present to offset rising labor costs and inflation over the expected life of the roofing.

For instance, I can install a 20 year spec roof for about 25% more than a ten year spec, in most sitautions. Double the roof, a quarter added cost translates to BIG savings over repalcing the ten year spec roof in ten years, due to the installation process, labor (at a higher rate later), profit, and overhead. Not to mention the added hassle/aggravation of doing it twice in the same time frame. I hope this helps.

I really do appreciate all of the feedback, but I’m more confused now than ever. I think I need an English to Roofing translator, because I don’t understand half of the options being suggested. Do they make a roofing for dummies book? Believe it or not I am an Engineer, but this I design steel stacks, vessels and piping.

What is a tear-off roof?

I meant to say tear the existing roof off. It is a far better job.

I like the mulitple plies for flat roofing because of the redundancy factor, as well as it being a tough tough roof.

Ok as for system #1, you say there is a 15 yr material and labor warranty, does their price include the warranty fee, and are they approved by duro-last. Second I would call mulehide and find out if they have an approved contractor in your area and then get a bid from them. True most “residential” manufacturers material only warranties cover very little, commercial material and labor warranties cover a lot, even if your contractor installs it incorrectly. mule-hide 800-786-1492.