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EPDM ( Mulehide ) and Green Roofs..

IronDog | Posted in Construction Techniques on October 9, 2004 01:58am

Hi,

Just attended a Green Roof Conference here in Md. and got a lot of contradictory information regarding installing a G.R. over epdm.
Mostly it was vendors saying that the roots would tear the seams apart and
( of course ) that won’t happen to our seams. But then you look closer at
what they do and even they put some sort of intermediate sheet between
the dirt and the waterproof membrane.

The reason I’m asking is that I’m doing a DIY re-do of a 66 K Sq. Foot warehouse here in Baltimore and don’t want to hire these guys with
their proprietary systems if I don’t have to.

I have installed Mule Hide Epdm and cannot imagine that shallow roots from
Sedum would have any meaningful effect on a 6″ wide seam. And even I plan to put some sort of sheet between the dirt and the rubber.

Thanks in advance for your thoughts and comments,

Tom

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Replies

  1. csnow | Oct 09, 2004 02:58am | #1

    I would think you could put down something like Tu-Tuf to protect the membrane and the seams.  It's very resistant to puncture.

    http://www.energyfederation.org/consumer/default.php/cPath/21_28_68

    1. User avater
      IronDog | Oct 09, 2004 06:18am | #3

      CS,

      Thank you for the link. That looks like a good candidate for a root barrier.

      Tom

  2. VaTom | Oct 09, 2004 03:44am | #2

     I have installed Mule Hide Epdm and cannot imagine that shallow roots from
    Sedum would have any meaningful effect on a 6" wide seam. And even I plan to put some sort of sheet between the dirt and the rubber.

    Unfamiliar with Mule Hide, but I have no trouble with 6 mil poly, overlapped if necessary.  We have min 12" earth cover over poly with our insulation umbrella of XPS and more poly overlying that.  Then 12" wet dirt to grow whatever in.  Assuming you have drainage (?), shouldn't be any problem.

    For more conservative use, if you have sufficient earth cover, bentonite rolls will give greater waterproofing than epdm. 

    Had visitors tramping on my roof today, picking tomatoes.  12 yrs, no leaks.  One thing I didn't consider, living in a forest, was that trees will attempt to take root there.  Poor place for an 80' tulip poplar.

    PAHS Designer/Builder- Bury it!

    1. User avater
      IronDog | Oct 09, 2004 06:30am | #4

      Tom,

      Have you done the ultimate DIY green roof?

      Just poly with dirt on top and the XPS?

      Mine is a 1/12 roof I'll be working with and we do have snow events that

      sometimes cause ponding, so the soil could get super saturated and back up between unsealed layers.

      Do you have 12" soil on your roof total or 24"? That's a lot more weight then we could handle in our situation. We are hoping for 4" lightweight soil mix and sedum.

      Interesting you mention the trees taking root. There was some discussion about that at the conference. Commericial installations have their soil blown on with a pump. If the pump had blown grass the day before it introduces that

      and clover which is harder to control.

      Thanks!

      Tom

      1. VaTom | Oct 09, 2004 02:17pm | #5

        Have you done the ultimate DIY green roof?

        Hi Tom, lol, no but it works pretty well.  This is just PAHS (Passive Annual Heat Storage, by John Hait, 1983).

        1/12 should be fine, just something to promote drainage, minimize ponding.  From the concrete roof deck we use: (1) 6 mil poly, carpet scraps for padding, (2) 12" dirt which is the heating/cooling system for PAHS (ideally should be 24" but roof structure has to be paid for), (3) PAHS umbrella of layers of 6 mil poly and XPS, (4) dirt to grow whatever in.  The top dirt could easily be as little as 4", depending on what you want to grow and how drought resistant you need.  Don't forget, you do need plant growth to keep the dirt there. 

        We get the occasional 12" snowfall.  Last house had 40' spans, 3/40.  Gotta be serious about the engineering with 300 psf total load.  I assume you do know what your roof will support.  One reason, in addition to low cost, we use 6 mil poly, is that it comes in huge sheets.  Fewer seams are better.  We also don't use 1 layer, 4-5 is typical.  First house, ours, I used bentonite rolls on the concrete.  We no longer waste the money.  Bentonite wouldn't work for you with only 4" dirt cover, not enough fill pressure.

        As we're looking for mass for heating/cooling (normal annual 65°-75°), the back wall is typically buried, making it easy to drive a tractor on the roof for soil transport.  We spend some time "roofing", but it's only once and provides most of the heating/cooling.

        When we first moved in I got busy with other things, letting weeds take care of the roof.  No lawn mower here.  The tulip poplars thought it looked just fine.  Now we have raised veggie beds up there with enough room to drive my compact tractor/loader between.

        You're welcome, good luck.PAHS Designer/Builder- Bury it!

        1. User avater
          IronDog | Oct 09, 2004 04:50pm | #6

          I was wondering what kind of roof you had in order to support all that soil!

          Yes, I'll be having a structural engineer figure the amount of soil I can use.

          Should be ok for the 4" of lightweight soil I'm looking for.

          Won't help me much for insulation in winter but should help in summer quite a bit and of course the epdm should last twice as long under the soil since it's not exposed to heating and cooling an UV.

          I'll post pics when the project gets underway.....

          T.

          1. VaTom | Oct 10, 2004 01:14am | #10

            I was wondering what kind of roof you had in order to support all that soil!

            Steel bar joists, K Series, are what do the work.  Probably not unlike your building, just more steel.  That 40' span was 2000 sq ft.  Cost of the bar joists, bracing, and galvanized decking was only $8300, delivered.  That was before the big steel price hike.

            Pictures, small ones for us dial-ups, are always welcome.  Here's an old construction photo of our place.PAHS Designer/Builder- Bury it!

  3. User avater
    MarkH | Oct 09, 2004 06:08pm | #7

    My thought on the root problem is that roots seek water. Unless you have a serious problem, the roots will not try to penetrate the seams. Of course I am only guessing.

    I did check out a good book on green roofs and I don't remember root penetration being a problem. These roofs are extensively used in European countries.

    1. User avater
      IronDog | Oct 09, 2004 06:54pm | #8

      Hi Martha Stewart,

      I think the seam penetration "problem" is something the vendors were throwing out

      so you would purchase their proprietary roof membrane systems.

      Even with their systems they put down layers of EPS and or PVC sheets over the waterproof membrane and under the dirt layer.

      One other thought I had is that I could reinforce the seams. One product I am considering is Geocel with geocel tape. Works very well with EPDM and can be painted on seams.

      How are you doing in your new digs? ;-)

      Tom

      1. georgeolivergo | Oct 09, 2004 09:39pm | #9

        hey Tom,

        here in the great PacNW we've been using 60 mil reinforced EPDM when we use EPDM, also TPO, and have tried most other proprietary systems available in our area. like you said we don't see a problem with root penetration using sedums. saplings might be another story! typically we use a drainage mat of some kind on low slopes, for example an Enka drain mat, or a cupped mat. of course we're on the west coastal side so we haven't had to deal too much with water ponding from melting snow/ice.

        friends of mine have described PAHS systems to me but I've never seen one installed, that sounds very cool. very 70s! (jk) But definitely coming from a different perspective than the extensive green roofs we're putting on.

        best, GO

        1. User avater
          IronDog | Oct 10, 2004 01:16am | #11

          Go,

          For this "test roof" I'm keeping costs down so I'm using unreinforced .045 epdm with

          a slip sheet and probably used synthetic carpet on top of that. I am also thinking of

          adding some drain pipes below the carpet. Would probably be 1/2" pvc that I would drill holes in.

          But really it's hard for me to imagine the soil staying so saturated for so long that it

          would harm the sedum.

          While we are having this discussion I'll tell you about this interesting farm

          we visited during the conference which is the only farm in the nation devoted to growing and studying green roof plants.

          http://www.greenroofplants.com/welcome.htm

          The owners family has lived on this farm for 5 generations and he decided some time ago that the family farm model was dying and decided to develop a niche. As a result

          he is now an internationally known expert on green roof plants.

          Also, professors from Penn State were there and their program is the only one

          devoted to the study of green roofs and how the whole system interacts together.

          The building, the plants, the soil, the roof membrane, storm runoff etc. I'll try to provide a link for that soon.

          However as they stressed their research is only applicable for the NorthEast US.

          They beleive similar centers have to be established in different areas of the US.

          Tom

          1. georgeolivergo | Oct 10, 2004 03:45am | #12

            Tom,

            funny that you mentioned greenroofplants.com, I have their extensive green roof plants poster hanging in my office right now, it's a beautiful poster!

            Anyway, maybe you could find some other industrial byproduct material that would make a good drainage plane between your membrane and the carpet, rather than the PVC, I just have to make that suggestion because PVC is such a worst in class material. I agree, I think the sedums will be OK, of course depending on your soil mix. You're absolutely right that all components of the green roof must work as a system and it's critical to have a solid understanding of each component, this is our philosophy. I didn't know about the Penn State research, thanks for bringing that up.

            best, GO

          2. User avater
            IronDog | Oct 10, 2004 05:23am | #13

            Yeah, I'm pretty sure there are lots of materials already in common use ( non - proprietary ) that would serve very well for green roof materials.

            The vendors had samples of various materials that I really doubted were something they dreamed up themselves and had manufactured.

            A lot of it is probably used in the industry that deals with storm water control.

            Anyway, got a lot of materials and info from the conference which I'll try to sort through and post for all.

            One thing that really struck me from the PSU research was the soil mix.

            They had done analyses of soil media from green roof vendors to look at the organic matter vs. material that holds water vs. how much air space capacity there was.

            They stressed how critical the mixture is.

            If there is a preponderance of organic material and you start out with a 4" roof you'll soon wind up with a 3" roof and then less as bacteria eat up the organics.

            Also, if there are too many fines then there is not enough air space for the plants.

            Again, this is East coast research only.

            Another factor was PH of the soil. Soil tended to become more acidic over time and lime (dolimitic) needed to be added every few years to maintain the right PH.

            The plants tend to make the soil acidic and acid rain and loss of organics as well.

            There was a lot of interesting detail. I was surprized how interesting it was.

            Tom

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