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Discussion Forum

Penetrating a membrane roof

VinceR | Posted in General Discussion on January 27, 2007 05:16am

I have to mount a 2 x 8 on top of a membrane roof, to serve as a base for a small structure.  Is there a safe (leakproof) way to do this? (8-inch side down.)

Several years ago I did the same thing on a rool-roofing surface by putting a dollop of asphalt cement/patch under the wood, where the fastening screws were to penetrate.  That setup was leakproof for more than 10 years, before dismantling.

Will the same thing work for a membrane?  Should I use silicone or other caulk instead of roofing cement?

Thanks,

 

Vince

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  1. roofguy | Jan 27, 2007 07:08am | #1

    What kind of membrane roof? EPDM? PVC? Something else? The manufacturer should have details for this application. It's usually better to flash the curbing fully rather than hoping that some caulking will keep the assembly watertight.

    getting a little chatty...

  2. theslateman | Jan 27, 2007 02:47pm | #2

    Roofguy is right-flash the wood with the same material as the roof itself,don't just depend on caulk or tar.

  3. Piffin | Jan 27, 2007 03:09pm | #3

    You were extremely lucky before.

    And if this is an EPDM membrane, asphalt dollops can eat their way through the material. You need to identify what the material is to use the right complimentary patch.

    You should also describe what this project and structure is overall, to get the best, most accurate responces and ideas for ways to get to your end goal.

     

     

    Welcome to the
    Taunton University of
    Knowledge FHB Campus at Breaktime.
     where ...
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    1. VinceR | Jan 27, 2007 06:00pm | #4

      Thanks for the replies.  The project is construction of a decorative railing.  The old installation used 2 X 8 X 8-inch bases to support posts, eight feet apart.  The rail will enclose three sides of an 8 x 16- foot roof, so there are six bases.  I do not expect any load, other than the posts and rails plus balusters.

      The old railing was taken down prior to reroofing, now the "boss" want the rail back up. (I don't know what the rush is, it has only been two years!)

      The roof was "torched."  Does that give any indication of what the material is?  (I have a small leftover piece, but I don't see any identifying markings.  It is about 3/16" thick and not vey flexible.

      While I am picking your brains, does anyone have an idea where I can get vinyl rails and balusters of 18-inch height?  Evrything I find is 36" high, and the vendors look at me like I'm crazy.

      Thanks again,

      Vince

      1. User avater
        dedhed | Jan 27, 2007 10:05pm | #5

        Half of 36" is 18 ". Cut them in half, the ones I have delt with have the same profile all the way thru. Weather Best I think

      2. Piffin | Jan 27, 2007 10:59pm | #6

        I see quite a few problems here, Vince.But to start - the membrane is a modified bitumen torch down roof material. I will have about a ten year life expectancy unless you use a coating about every five years and are extremely careful about traffic on it. It is compatable with most roof repair products in a bucket like you mentioned. But that does not make that a good choice for mounting these posts. First problem - a 36" high railing is code. That is why any body looks askance at the idea of an 18" one. I have done historical replacement that is 22" high and that even scares me. It is more of a trip hazard than a railing.Mounting posts always need firm framing base to screw/lag into. If you did not do layout for this railing before roofing, odds are that you are only screwing into the sheathing/deckintg under the modified. That will not give you the strength to meet codes which require that a railing be capable of withstanding a 250# lateral load force.That said - I did do something similar once. Every post was a junction for railing sections at a 90° or 45° so each section counter-braced the adjacent to achieve load resistance.I used 2x12 and a tablesaw to bevel the edges to a long slope. Then I seated them in caulk the way that you describe, and screwed them down with #12 or #14 structural screws, galvanized.after that, I torched a piece of modified onto the roof over this plate so that it laid out 8" or more al the way around, except of course, right at the outer edge, where there was only about 4" useable. This technique means a couple of slits at corners to keep it from showing a 'fishmouth' that will scoop up water and trap it.Then posts mount.The proper way to do this is to mount posts and build pitchpans around them, then pour full of bitumen, but that is beyond the possibilities of a DIY.Your better way is to build a sleeper deck and incorporate post mounting platens but it sounds like you want to merely walk on the deck as is....Many more threads on this exist if the advanced search is working and not too homonal today. Search using terms like EPDM + IPE + deck 

         

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

        1. VinceR | Jan 28, 2007 12:06am | #7

          Piffin, Dedhed, roofguy, et al,

          Thanks for the information, tips and leads.  I'll need to do some research.

          If not too troublesome, I will probably ask for more advice, once I know a little more of what I'm talking about.

          Thanks very much.

          Vince

      3. IdahoDon | Jan 28, 2007 10:28am | #8

        Are there ever any people actually up on the roof, or is the railing purely a decrative thing?  If it's purely decrative, then railing codes don't apply, at least as codes are interpreted here.

          

        Beer was created so carpenters wouldn't rule the world.

        1. VinceR | Jan 28, 2007 06:42pm | #9

          Idaho,

          No, the roof is almost never walked on.  Maybe two or three times a year, by me, for maintenance or something.

          I found many references to this problem as a result of Piffin's suggestions, and I am now a little smarter, but also a little more confused.

          For example, there were statements made that a membrane roof should last ten years - unless a coating is used.  Is that the aluminum-bearing tarlike stuff?  How often should it be applied?

          And then I saw some of Piff's pictures where it appears that a deck was laid over a membrane roof.  Would the deck have to removed in ten years to repalce the membrane?

          And then I saw membranes that appeared to be many feet wide, quite different from my 36-inch (or so) stuff.

          And then there was some discussion about "floating" the railing.  Does that mean the  2 x 8 x 8 rail-post supports just lay on the roof?  Of course that would mean no penetration, but would anchoring only at the ends be sufficient?

          Also, my roof has a 5-inch wide mesh along the edge, which was "cemented" down, but is now beginning to loosen, i.e., the cement seems to have washed away.  Why was the mesh there?  Should I replace it?

          Forgive me for being so pesky, but I saw from the many posts I read that you guys are super knowledgeable and helpful.  So, thanks very much in advance.

           

          Vince

          1. Piffin | Jan 28, 2007 07:32pm | #10

            Welcome to class...;)Good Questions BTWYou have modified torch down, which comes 36-40" wide and is applied single ply. It is an asphalt re-inforced product which suffer=s from exposure to UV rays, thus the need to use paints or coatings of varipous kinds to keep it protected from exposure to increase it's life expectancyEPDM comes 12' wide and is a rubber membrane which can last forty years all by itself. When covered by a floating dcck, it sees little UV exposure, so the friction of sleeps wearing on it is the greatest detriment to long life.For either, some guys like to build decks as a palletized system so they can theoreticly lift sections off for repairs.
            I have never built one that way, but have repaired under such in the paast and my experience is that since these smaller sections are more prone top movement, the dends and corners abutting one another sometimes warp up and truip people and that is also where excessive wear happens, creating added need for repairs...I'm not sure of the context where you found ref to a floating railing - but here is aphoto of how I prepare for locating posts.
            My preference for a deck mounted post is what Fypon sells. The post is hollow and the mounting hardware is a plate that is lagged to the deck. The center of that plate has a threaded hole for wallbolt which extends up inside the length of the post. This is tightened down at the post top to make the assembly a torsion box thing. I'll see if I have any detail photos of that for you too. 

             

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

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