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Flat Roof/Historic House/Must Get Help

Pnut | Posted in Construction Techniques on August 13, 2003 09:13am

O.K. all you roofing and waterproofing experts—I need your help.

I have a 120 year old Italianate home that I’m restoring. It is basically a square with 4 hips that form a flat 13 X 15 flat section at the top. Other than the flat section, the roof is a 6:12.

I plan on using asphalt shingles on the slopped section, but I’m trying to decide on what to do with the flat section (it has a slight slope, about one-quarter inch per foot)…My architect has recommended a product called Deck 70 from Universal Protective Coatings—it is an elastomeric polyurethane coating. Anyone have any experience with this???

On the flat section itself, I have the following obstacles

  1. There is a “hatch” for access to the top of the roof.
  2. There will be 6 areas for vents (toilet, sinks, attic exhaust, etc)
  3. There will be 8 areas of penetration of a Simpson post anchor for a widows walk
  4. There are two chimneys that rest next to the flat part (one part butts up against the flat section, the rest is on the sloping part)

What do you think? What do you recommend? What about underlayment (plywood, framing etc).

Changing the slope/appearance is not an option as this is in the historic district and there would be opposition…Thanks for the input….

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Replies

  1. FastEddie1 | Aug 14, 2003 01:20am | #1

    Where are you?  Weather coul;d make a difference in your options.

    Do it right, or do it twice.

    1. Pnut | Aug 14, 2003 01:28am | #2

      S.F. Bay Area--usually fair amounts of rain November through March, but nothing huge. 

  2. Robrehm | Aug 14, 2003 04:06am | #3

    http://WWW.duradek.com check it out. If it will hold up to golf spikes it will do what you need it to.

    1. roofdoc | Aug 14, 2003 05:50pm | #5

      Are planning on doing this yourself?if so the product that rob is refering takes a $400 heat gun to apply.I would suggest using one of the peel and stick modifieds like polyglass granule surfaced also has its own peel and base base sheet.A little more user friendly and repairs a lot easier

      1. Piffin | Aug 14, 2003 06:03pm | #7

        I like Polyglas but it's not a good choice with so many penetrations and flashings and such a low pitch, IMO.

        Excellence is its own reward!

        1. roofdoc | Aug 14, 2003 06:17pm | #8

          Piffin I have installed them in ponding water situations with no problems,The last company I ran for else we did 6 semi truck loads of the product in a year,yes edpm is a alright product but it somewhat overrated,have you ever seen one shrink to the point it pulls off the walls.If you review epdm product specs you will that the shrinkage is listed I do believe that most are in the 1-3% range 3% of 20 feet is?

          1. Piffin | Aug 14, 2003 06:52pm | #9

            7-3/16" but no,I haven't seen glued down shrink. Seems more applicable to ballsated or mechanical installed. or for parrapet walls.

            Ar e you talking cured APDM or uncured flashing material? I know poorly installed uncured will shrink bad..

            Excellence is its own reward!

          2. roofdoc | Aug 14, 2003 07:11pm | #11

            They all shrink with the least  being a reinforced dosen"t matter on the application  the sheet itself shrinks the only difference in adhered is most times thickness of sheet .045 verus.060.Even in the fully adhered I have seen shrinkage of up to 6to 8 inches.Don't get me wrong I think the product has it place but it is overated.One of the largest misconception is warranty I know of no manufactior that offers one in the residential market place,so when it come to common sense dollars why not spend them with a manufactor that stand behind its products where it is used

          3. Piffin | Aug 14, 2003 07:29pm | #12

            No manufacturer will stand behind the installation labour and that is where you will find most problems, especially in a roof like this one with so many penetrations..

            Excellence is its own reward!

          4. roofdoc | Aug 14, 2003 07:45pm | #14

            I would have to disagree as I know of three that do,it does mean getting ceritifed and letting the manufactuer know who you are GAF, Polyglass,Elk, and I do belivie that are several others that going the same way.Some of them even offer nonprorated full replacement warrantys on their shingle products,that is as long as your willing to have your installation inspected by their personal and correct any defects found

            I think that is great idea should put a end the pickup truck and hammer type of roofing contractor you know the one we read about here that don't use felt or flash properly.I have found that if the roofer knows that his work will be inpsected by someone thats know the difference they will usally not cut that cornor or their price

          5. Piffin | Aug 14, 2003 08:08pm | #15

            When I was specializing in roofing. I was certified with GAF and JM but as I remember it, the warrantee was not with the manufacturer but a sort of insurance bond carried by a separate entity ( with a similar or related name)and you paid for that type of warrantee. You did have to be "licensed " by the manufacturer in their installation technique to get it though.

            I agree that it is a good program but the manufacturer does not want to be totally on the hook for installations so they create these other corps or partner up with insurance underwriters for coverage.

            That comes back to the point. EPDM manufacturers do not want to increase their exposure. Commercial roofing has fewer penetrations / foot of coverage sold and installed and it is generally installed by factory trained personel. In my day, it was not possible to buy EPDM for residential. Each material purchase went through a program and the makers rep certified the installation.

            It is probably too much paperwoprk for them to handle to do the same on residential and there are certainly more residential installations being done by underqualified persons, increasing further the possibilities for leakage. It is not the material that fails, it is the seaming, IMO.

            I was called once to inspect a roof on a place under construcion still. It was all cut up in design with a small flat roof accessable from within the house. I stepped out to find a chop saw station set up over a peice of ply covering the EPDM ( that was the good part) and hundreds of scraps, sawdust, chips, nails, scrap flashing, you name it, being walked and ground into the EPDM. I was aghast and almost quit looking further but did a total inspection and found a bad lap seal where it ran under a wall that was doing the actual leaking.

            Nevertheless, I wrote it up that in addition to the bad lap, the siding crew had ruined the installed roof and that it needed to be replaced..

            Excellence is its own reward!

          6. Piffin | Aug 14, 2003 06:56pm | #10

            I just remembered that I installed a Polyglass on a 21' roof last spring and was up on it last week. Edges that I cut flush had shrunk back about a quarter inch on the edge metal. I guess that Polyglass will shrink too.

            I'm still having a hard time accepting that poly or anything else installed in ponding water will work or that the polyglas will be a s good around penetrations thirty years from now..

            Excellence is its own reward!

      2. Robrehm | Aug 15, 2003 05:47am | #22

        True Duradek does take an expensive heatgun to apply but you won't do it your self. It is only sold installed through dealers who have been trained & certified. It comes with up to a 10 year warranty and they will stand behind a dealers work. there are similar products on the market sold as a DIY but you do not get the training or factory support. Good luck getting them to honor a warranty issue.

         I should confess I am a dealer. My first job is still looking & holding up after the warranty has expired. This is for a hotel that hosts players & fans for the memorial golf tournament (& others) where the "guests" will wear their golf spikes from the room out to the course. I put this in 6 years ago.

  3. woodguy99 | Aug 14, 2003 04:49am | #4

    I don't have any experience with Duradeck, but their website makes it look pretty good.  I do have some experience with copper and EPDM and I know that it could be your solution.  You'll want boots and counterflashing for all the vents and the chimney, and the hatch will need a built-up curb.  It may be worth trying to find a good commercial roofer who is familiar with this stuff and will guarantee their work.  If you want to give it a try yourself, there's a wealth of information in old FHB's and JLC's on how to do this stuff.

  4. Piffin | Aug 14, 2003 05:59pm | #6

    I've done enough of these that I knew about the hatch and penetrations before you mentioned them. Most have a steeper pitch for the mansard portion though. Those with the lower pitch were more common out west, for some reason. Odds are good that your flat top was copper to begin with and it gor covered with a sequence of other asphaltic materials ovder time.

    EPDM gets my vote. If you are not removing older layers ( which you should do) or if the old sheathing is boarding with gaps, there are special gypsum underlayments made to go with EPDM.

    Your most critical junction will be the pitch break at top of the shingled mansard roof. you need to be sure the matal flashing detail allows for drainage off the upper roof and has enough coverage on the shingles so wind doesn't drive that water flowing off back up under to run behind the shingles.

    <Hi Mike - you boss finally letting you have a minute or two for BT??LOL>

    .

    Excellence is its own reward!

    1. woodguy99 | Aug 14, 2003 07:33pm | #13

      Hi Piffin. Actually I posted that message last night, but yeah, it's been a slow week in the design department so I've been redoing our New Client Questionaire and catching up on Breaktime and J**online. I'm finally used to the "new" format here; it's not so bad afterall.

  5. COH | Aug 14, 2003 11:33pm | #16

    Given what you have described I would recommend a copper roof using details prescribed in the National Roofing Contractors Association. Specifically that or sheet lead. The roof of the Vatican has this and it will hold up longer than the house. On of the modified bitumen roofing products, either hot or cold application would also work well. I have used torched on products over even galvanized subdecking, this reduces the chance of sparks, and this will weather well. Your main concern in a roof of this pitch is to frame and sheet it such that water drains off an doesn't remain on any of the surface. You could drain it into a copper swale.  Look for a roofing contractor with experience in any of these areas. Stay away from simple BUR.

    1. Piffin | Aug 15, 2003 12:09am | #17

      "The roof of the Vatican has this and it will hold up longer than the house."

      Maybe the vatican has had some special assistance from above, but i have seen perhaps a hundred of these copper roofs that have not held up longer than the house. They will wear through from water coursing over them, especially where acid rain is present..

      Excellence is its own reward!

      edit to add -

      From a historic preservation viewpoint, the copper is the best idea and has some merit from the fire prevention standpoint - sparks flying from neighbors.

      Edited 8/14/2003 5:17:34 PM ET by piffin

      1. COH | Aug 15, 2003 12:53am | #19

        Are you saying that the acid rain will eat through the lead coating?  Rain on the west coast just isn't that acidic.

        1. Piffin | Aug 15, 2003 01:22am | #20

          no. I wasn't thinking in terms of leaded copper. it's the plain old copper that I've seen gone by. Leaded would do it. When you mentioned lead, I thought you had plain lead sheets in mind..

          Excellence is its own reward!

          1. COH | Aug 15, 2003 01:26am | #21

            My mistake in writing, and thinking, in shorthand.

    2. seeyou | Aug 15, 2003 12:49am | #18

      Another option would be lead coated copper (20 oz). Get lots of references before hiring anyone.

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