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Commercial roof – PVC or modified bit

RichBeckman | Posted in General Discussion on June 20, 2007 06:01am

As previously announced, my wife, Debby, is the new executive director of the Fort Wayne YWCA.

As she took on the job, they were in the middle of purchasing a new building to move to. The building needs a new roof.

They have two quotes (which they arranged for before Debby started the job). It is approx 7,780 square feet (per one of the bids).

Both call for total removal of old roofing.

One is installing a modified bit (“Performance Derbibase modified base sheet into a coating of Permastic adhesive” followed by “Performance Derbicolor modified roof system into a coating of Permastic adhesive”)
$68,770

The other is installing a fully adhered .06″ PVC white membrane (brand not specified, but sample of Johns Manville product enclosed.
$96,930

Roof has three or four roof top units which will be removed for the roof work and reinstalled on new curbing.

Is the PVC worth $28,000 more??

Rich Beckman

You are here.

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Replies

  1. Piffin | Jun 20, 2007 02:25pm | #1

    I am guessing the reason they have not pursued a bid for EPDM is that it more expensive than either, but it would be the better choice.

    Between those two, if the DB mod installer has a good background and reputation with the stuff, I would take that over PVC.

     

     

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    1. vintage1 | Jun 20, 2007 03:01pm | #4

      Piffin,

      Why do you think that EPDM is a better choice than either a PVC or Mod Bit system? 

      While I think EPDM is well suited to many of the residential (small) applications for low slope roofing, it is generally considered to be a lower commodity in commercial roofing.  I would expect an EPDM bid for this project to be less than either of the other two. 

      1. Piffin | Jun 21, 2007 04:45am | #6

        You seem to have your prejudices based on what you have seen and I have mine based on what I have seen.The two may be equivalent for all I know, but my background has the installers of mod bit being lesser skilled guys trying to compete with BUR,, while EPDM was a whole new thing - a true single ply membrane with a good history behind it in European commercial work. When I first got qualitfied for EPDM, it was not possible to get it for residential work. Now things seem turned around in the past 25 years to where you are saying it is only used for residential where you are. That alone is onfusing to me. Everywhere I go when I travel, I look out over the falt roofs and see probably 80-90% that are EPDM now where they used to be all BUR.The pvc had a lot of problems still to be worked out when I was introduced to it. Maybe they have it worked out now, but the basic physical properties of PVC make me doubt that. There was and maybe still is a time when fully adheered was the only way possible to get it to stay in place for more than a couple of years because it traps vapours which expand and because of the thermal expansiveness of the membrane.I see Grant mentions they still have some sort of problem with it. I don't know if it is the same probs that left me cold on it 25 years ago or not, but I have a strong predjudice against PVC borne of olde and a mild predjudice againsty mod from what I have seen, while my experiences with EPDM have been universally positive. 

         

        Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

        1. vintage1 | Jun 22, 2007 01:09am | #7

          Piffin,

          I respect your contributions to this forum and was just looking for some insight into your opinions.  You have a proven track record of successfully installing EPDM on your projects.     

          My background in low slope roofing is virtually all commercial or industrial so I  tend to automatically think in terms of what will be well suited to a 500 square roof on a mfg. facility, rather than what would work on the 10 square residential addition.

          A few comments to clarify my perspective:

          IMO, EPDM is a decent system, when properly installed.  It has a few limitations (membrane shrinkage and the inability to thermally fuse the seams) that can make its use in the wrong enviornment really problematic. 

          I agree that you will see it all over the country on roofs that used to be BUR.  (Its less expensive and goes down faster than a 3 ply BUR).  I'd even bet that half of those roofs are recovers w/ mech. fastened or worse yet, fully/adhered EPDM over an old, wet, leaky BUR.  In the commercial realm, people tend to think, "out of sight out of mind" when it comes to roofing.  They want good, fast and cheap!

          My experience has been that virtually anyone can be come a "certified" installer.  I can even buy EPDM at a local big box if I wanted to.    This translates to a lot of low quality installs that lack the proper design and spec. criteria.  And this is why I tend to think of EPDM as a lower commodity system.  Too many installers offering cheap (and sometimes inappropriate) roofing "solutions".

          As far as PVC-

          Like many of the thermoplastic single ply membranes, PVC has a checkered past.  There is abundant evidence of theromplastic single ply membranes failing in previous years. (Google Hypalon + shattering) However, there are at least 2 mfg's I know of that can show a 35+ year in-service use of a PVC based single ply membrane. 

          The material is fully weldable, isn't adversely affected by ponding water, can be repaired  by welding patches to punctures or other damage, and is UV reflective which makes them attractive on projects where you have to meet energy code requirements.  (They aren't cheap, but then quality comes at a price. :>))  That isn't to say that all PVC or tp single ply's are created equal, in fact I did recommend the mod bit to the OP over the single ply option he was presented, especially at the premium price difference.

          We all learn from our own experiences as well as the information shared here.  Thanks for sharing your experience.

           

           

           

          1. Piffin | Jun 22, 2007 02:42am | #8

            The same good stuff to you. Since your experience is in commercial, yours is probably the more valid opinion here, and we both made the same rec for this particular case anyway. ThanksBut for correction, probably half of the EPDM I see commercially is ballasted. Of course, I don't know how much is overlaid, but you probably made a valid assumption there. 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          2. User avater
            RichBeckman | Jun 22, 2007 03:31am | #9

            Thanks to all for the responses! A good discussion of what's what.Just what we wanted to hear, the cheaper bid might actually be the better bid.I printed the thread and gave it to Debby.

            If I had to put money on it, I'd bet on the mod bit (when you're a non-profit, thirty grand is a lot of money).

            Rich BeckmanYou are here.

          3. Piffin | Jun 22, 2007 04:26am | #10

            Thirty grand is thirty grand, and it can be the difference between being a non-profit or a profitable enterprise too.Just check the specs written and the rep of the company for sure.I bid a job once for a non profit sort of elderly home. I bid three ply BUR for around 24K and there were three other contractors right in the same ballpark. Four of us within less than two grand.The job went to a new outfit that bid about 19K! I figured close to 17K in materials for me, but knew they could be boughten for less some places - still, I wondered how they could make any money....two years later, the roof was leaking and I was called to fix it. I t was only a two ply job installed - not up to bid specs - and it was very poorly done - a total waste of money that could have been avoided by checking reputation ( there was none really) I made a couple patches and recommended that they replace the roof. Five years later they were still going from one company to another buying patches.I know you know that with roofing, the installation is more than half the quality of the job, just as with painting, it is 2/3 prep with the painting the easy part. 

             

            Welcome to the Taunton University of Knowledge FHB Campus at Breaktime. where ... Excellence is its own reward!

          4. User avater
            RichBeckman | Jun 22, 2007 06:09am | #12

            It is my understanding that the low bid is from a long standing reputable roofer. I'm not sure about the high bid.

            Rich BeckmanGoing to the Fest? Don't forget to bring pencils!!!1

  2. vintage1 | Jun 20, 2007 02:55pm | #2

    Rich,

    I would take the 2 ply Performance system over a JM PVC roof. 

    I actually like several single ply membranes including PVC, just not that particular mfg. 

    Need more info, but I would guess that the single ply roof system is actually a less labor intensive install and therefore should be equal or less expensive than the mod bit.  There isn't that much difference in material cost. 

    The mod bit system has the advantage of redundancy with 2 plies.  I would want to see another one of their jobs before allowing them to put it down in adhesive.  Great system if your set up to do it, but it can be one huge mess, if they aren't used to doing it.  Adhesive will be all over the place including all the areas you don't want it and the finished roof will look like shid.

  3. seeyou | Jun 20, 2007 02:55pm | #3

    Rich, I just went to a day long PVC/TPO seminar a couple of months ago. Sounded kind of like both products were still being developed, ie, problems have arisen and they're adjusting the formulas. One big selling point for PVC or TPO over EPDM would be their resistance to kitchen grease which is probably not relevant here. If installed properly, Modified is the most tried and true system of the two you're looking at, IMHO.

    http://grantlogan.net/

  4. alwaysoverbudget | Jun 20, 2007 04:34pm | #5

    with the roof airs up there and needing serviced often ,i would go with the modified. it's more forgiving of foot traffic.

    i'm shocked at the price though . around here i can get a tear off and modified roof put on in the 3.50 - 4.00 a foot range. last year  i had a bid on a 32,000ft building,tearoff,redeck 3000' for 110k. i'm not sure what the cost of removing airs and resetting runs. larry 

    hand me the chainsaw, i need to trim the casing just a hair.

  5. ponytl | Jun 22, 2007 04:56am | #11

    WOW....  70k (low bid) for  80sq....

    if they went with torch down... (which i happen to like but wth do i know)  ur look'n at less than 6k in materials... and what i believe is better than a 25yr roof...

    i know there are other costs involved  but  dang.... 

    I think for a non profit there might be other options that would serve them well

    without have'n seen the roof or whats involved it might be a fair price...(70K)  but then again it might be 50k high

    p

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