EPDM is similar in that it has the seams joined together with an adhesive (which is also torched to make it "sticky") but also has a rubber "tape" that covers these seams - the seams should be caulked as well. Average life for this type of roof is 20 years plus or minus.

As to the differences in price, it is most likely due to a variety of things such as the material being used and the thickness (or millage) of the material (obviously thicker is better). Then there will always be a little bit of difference in how somebody prices things out. One guy might say he'll do it for $1 per square foot while the next guy estimates things at $1.50 per square foot (just example prices not meant to reflect cost of roofing). That extra 50 cents adds up over the whole roof (an extra $300+ in your case).

Make sure that the person you end up using is licensed and insured to help cover your own rear end.

The below are the 3 main types of flat roofs:

1. Built Up flat roofs or BUR

2.Single-ply flat roofing

3.Spray-on / paint-on roofs

What type of roof do you have?

EPDM is "rubber" modified bitumen is NOT rubber. It irks me when people call mod bit rubber, gah like nails on a chalk board. I'd throw that proposal away just for the fact that the guy called it rubber LOL. Modified bitumen is asphalt. Torching is one method of application. Modified bitumen may also be applied with cold process adhesives or self adhering. Be sure to check out the link I posted above as it explains the modified bitumen system ratings. The more layers, the longer lasting and the more expensive. Mod bit is rated 10-20 years.

EPDM seams are not torched. I have never in my life seen torchable EPDM. EPDM seams are sealed either with adhesive or self adhesive tape. Again, EPDM is rubber, much like the inner tube on a bicycle only much thicker. Put a torch to rubber and see what happens. EPDM is rated 10-30 years depending on thickness of membrane and method of attachment.

A restoration like KMS was referring to is sometimes an option. There must be no water saturation within the existing roof, and the roof must first be brought up to a maintainable condition. These liquid applied systems get a bad name because alot of roofers skip the necessary prep work, but in the right circumstances they are a good alternative. Learn more here: http://www.reliableamerican.us/services/roof...

Some things which affect price...

Tear off, are they all tearing off, or are some laying over. If some are laying over, is that allowed by code? If not allowed by code throw out the proposals for anyone who suggests a recovery / lay over, unless it is a liquid applied system which by my local code is acceptable as another layer.

Insulation, what insulation is being installed if any. If there is not at least the installation of a cover board over the substrate/decking I suggest throwing out the proposal. Insulation board may or may not be a good thing depending on how the roof is currently insulated. If you have a warm deck design, meaning the substrate/decking is insulated then opt for as much insulation now as you can afford. Typically polyisocyanurate insulation is used, at an R value of 6 per inch. However if your roof is a cold deck design, meaning you have insulated ceilings; I can install blown in fiberglass with an R value of 30, for the same price as installing polyiso insulation board with an R value of 9. Read this to learn more about cold decks and warm decks: http://www.reliableamerican.us/articles/warm...

System rating. I hit on that above and previously provided a link which goes into great detail about system ratings. But in my area many roofers are selling cheap 10 year modified bitumen roofs, and then customers wonder why they have to replace their roof every 10 years... Hmmmm? I only propose 15 year rated systems or better. Why? Because the investment is not that much greater and the roof will last longer, and I am usually urging my customers to opt for the 20 year rated roof.

details and flashings. What is being done around the edges, the drainage, the curbs... All this should be spelled out in the proposal, and it is not uncommon for guys in my area to completely neglect ALL the details. I was on a roof last week where there was no means of mechanically fastening the membrane to the wall. After a few years the membrane becomes unadhered and falls from the wall. This is just one example. Without knowing the size shape and details of your roof I couldn't possibly point out all the potential differences.

Flat roofs are their own monster. Being a great shingle roofer doesn't qualify one to propery install a flat roof. Make sure you deal with a roofing contractor who has extensive flat work experience. One thing is for sure about flat roofs, they are much less forgiving than sloped roofs. You can get away with lots of sloppy mistakes on sloped roofs, but a flat roof must be installed perfect. A good skilled flat roofing contractor will do that for you.

And that brings me to profit margin. Yes you should expect to pay a legitimate roofing contractor a greater investment for their experience and professionalism. I know I charge more than the "going rate" for my roofs, but that is because we deserve more. We are often doing more, plus we don't cheat our insurance nor do we cheat our taxes. We will actually fix our mistakes if/when they happen. These "hidden" costs do add up, but are what set apart a legitimate company from the guy kitchens today and roofs tomorrow. Is our profit margin higher? I actually don't think so. I once did the match and saw that the guy undercutting my price by sometimes 20% is actually making more money than me by installing that minimum code roof, but cutting those corners, and cheating. So they charge less, they get more work, they make more money on their jobs since they cheat, and they laugh all the way to the bank! I'm just the schukc trying to do things right and having to fight for every job because of hacks who undercut the market and ruin the "going rate".

A note on insurance, make sure whom ever you choose to hire to do what ever kind of work you choose to have done on your house is always INSURED. General Liability protects you against damage to your property. Workmans comp protects you should a worker get injured. Workmens comp is more important because it is more expensive and alot of guys skip out on in. Workmans comp (at the roofing rate 42% of payroll) costs me an average of $10-17,000 PER ROOFER PER YEAR. A 5 man roofing crew, you do the math. And that's JUST workmans comp and not liability nor vehicle insurance. I pay more in workmans comp than I take home in a year. See how some guys can increase their bottom line by cheating?