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Flat Roof - Chimney Flashing Question - Forno Bravo Forum: The Wood-Fired Oven Community

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  • Flat Roof - Chimney Flashing Question

    Hello everyone. Much thanks to all the helpful answers on this forum! I could not have gotten to this point without you people!

    I am now at the stage I will be cladding my frame work of my enclosure. I will have a flat 5' x 6' roof with a 6" 24" long ss duravent chimney. I will be enclosing the chimney also and covering with either brick or stone veneer. I've ordered a pond liner from HD for the roof.

    Question I have is, what is the best way to weather proof around the chimney? I will have to cut the pond liner to accomodate the chimney. I can fold the membrane up the wall on one side of it but will need to figure out flashing for the other 2 sides (chimney will be flush with the front face). I will have some pond liner left over when I trim for the roof. Given the colder weather (hovering around freezing and getting colder), is there a product that will make a weatherproof seal if I overlap the membrane at the chimney, or should I wait until spring and use a pond seam kit? I looked at Blueskin WB tape, but since it is bitumin-based, it may not work with the pond liner which is flexible pvc. Any suggestions most welcome. Thank you!

    Dan

  • #2

    Check back with the manufacturer of your liner for the recommended glue for seaming. Since it is a pvc product, I don't think that the temperature is as much of a concern as dampness and humidity. Even if temperature does figure into your product, you can maintain heat for the short times that pvc glues need to bond. Seaming the liner 360 degrees around your chimney is only a failsafe. That will be the last line of defense. You will still need to do a rigid flashing

    To cap the flashing around a chimney, I always use "shingle eaves drip flashing". I embed this into the brick. It caps which ever custom made flashing that I use that conforms to the roofing material. I use a punch to make holes that will help it set firmly into the into the mortar. Placing the flashing over a wood board works for punching the holes fairly quickly. A drill would also work.

    This is going to take couple or so posts due to pic size.
    Last edited by Gulf; 12-02-2018, 08:15 PM.
    joe watson

    "A year from now, you will wish that you had started today "

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    • #3
      For your application, another bend in the eavesdrip flashing is needed to turn it vertical up the backer wall. You can rip and place scraps of 3-4" backer board on all four sides of your chimney. One run will work, but two layers may work better with the bead that is in most eaves drip. It doesn't matter if it is thicker than the veneer that you choose.
      joe watson

      "A year from now, you will wish that you had started today "

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      • #4
        A metal bender can be easily made by clamping wood or metal at the exact spot of the bend. Sorry, I have no pics for this. HF has a very reasonably priced bender if you don't want to dyi. The bender can be used for the eaves drip and the metal taht conforms to the roof. The below pic shows the flashing as it conforms to the roof in my application. Since yours is a flat roof, it will look like this on all for sides.

        That being said, many contractors nowadays will just butt the roof to the brick veneer and silicone the heck out of it without any flashing. That gets them past the 1 year call back for the insurance. I like permanent fixes myself. I hope that this helps. I may be able to elaborate if there are more questions.
        joe watson

        "A year from now, you will wish that you had started today "

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        • #5
          Hey Joe, thanks for your message! This is the solid way to do it. I have a couple follow-up questions: The finished material on top will be random flag which is very uneven on its surface. Underneath will be a scratch coat at least 5/8" thick. Underneath the scratch coat will be the pond liner with molded rubber chimney flashing which I was going to put over the backer board (Densglass on roof and Durock for the chimney enclosure). I was also going to have the finished chimney enclosure flush with the front wall of the oven enclosure.

          Should I still do a rigid flashing, or just rely on the pond liner/scratch coat/mortar? I am thinking the water will be pooling slightly because of the flat roof, and because the rigid flashing will only be on three sides (because the front chimney wall and front oven wall will be flush). I think I am probably missing something regarding finishing. I really appreciate your comments and advice, Joe. I am totally willing to go the extra mile on this because I want it to last and be waterproof. So, given that it will be random flag on top, and front of chimney will be flush with front wall of oven, what would you recommend? Thanks again!!!

          Dan Lewczuk

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          • #6
            I want it to last and be waterproof.
            Dan,

            I haven't seen much long term success with flat roofs. Even those with proven roofing materials. I'm not sure that flagstone is a viable opton for even a sloped roof, considering your region. Freeze/thaw will probably do a number on the joints. Is there any possibility of rethinking the flat roof design and opting for another choice of roofing material?
            joe watson

            "A year from now, you will wish that you had started today "

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            • #7
              Hi Joe, thanks, you are the voice of reason! I am switching back to the first plan - gable roof! Question: what would you suggest for minimum roof pitch? I need to keep everything under 8'.

              I've got some steel panels (see photo). I am just trying to figure out what to finish the walls with, to match (any suggestions, I'm all ears). Probably go with stucco. I am thinking that the steel would be the most Maintenance-free (it was pulled from an old barn). I will probably end up painting them, but there's nicer ones underneath.

              Again, thanks sooooo much!!!

              Dan

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              • #8
                You need to check your local requirements. Ontario is snow country so snow load and pitch are different than Gulf's area where wind load is more of a concern than snow.
                Russell
                Build Link............... Picassa Photo Album Link

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                • #9
                  Good point and thanks for the message. Here, if the structure is less than 10 x 10 x 8' high, which it is, it is up to the owner as to how it's built. Anything over that and the municipal by-laws kick in, the structure needs an inspection, etc. Having said that, even though it's not required, I'd still want to also make sure it's conforming to my local by-laws. There are a lot of buildings with flat roofs here, as well, but the more I researched , the more timid I got about flat roofs...Gulf's advice has been very sound and I was just curious what he might suggest . I'm definitely finishing it with a gable roof.

                  On another note, we had our first pizzas this evening! I used 2 rolls of ceramic fibre (4 layers in the dome and 3 on the sides) and it was barely warm to the touch only at the hottest spots! Very pleased and very thankful for this forum!

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                  • #10
                    6 in 12 for the roof pitch. Thanks again for the post, sincerely.

                    Dan

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                    • #11
                      A 6/12 roof is a good looking pitch. You may have to lower the eaves to get it to work out with your height limitations. Russell is correct about snow loading codes. That is not an issue down here. However, shorter spans and proper bracing will increase the strength of any roof. If you can possibly do it, projecting the gable out over the front of the oven will vastly increase the number of days per year that the oven can be operated comfortably.
                      I am just trying to figure out what to finish the walls with, to match
                      I'm a very big fan of old corrugated metal. I would only seal it with a clear coat to halt the corrosiion if any is present. I have even artifically aged some new metal to match the older patina. I think that it will look good with what ever you decide.
                      joe watson

                      "A year from now, you will wish that you had started today "

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                      • #12
                        Joe, thanks again! Very encouraging. I hope to finish the roof within the next 2 weeks. I also ordered peak roof flashing for the duravent chimney. The chimney flashing will be vented, with a storm collar. We get a ton of rain in spring and fall.

                        I had planned to lay the corrugated sheets right over the framing of the roof (rafters every foot). Then I was going to use molded foam srtips under the bottom edges of the panels and ridge panel to keep out bugs, etc. Then I saw pictures of the roofs being clad on top with durock or other outdoor sheathing, and then the metal roof panels on top.

                        If I could trouble you and Utah with one more question: Which is best, with or without the durock sheets under the roof panels? Just wondering if this (durock panels under metal roof panels) would be necessary if I put proper flashing on edges and eaves, along with the foam strips. Thanks again for your patience and advice!

                        Dan

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                        • #13
                          Hello Dan! I put just metal roofing over my WFO in 2009 as a temporary cover during the oven's first Oregon winter. To my dismay, I noted that condensation from the underside of the roofing was dripping onto the oven every morning. I resolved the drip problem by taking the roofing off and putting plywood down with a Tyvec cover before replacing the metal sheets on top. On the permanent den rafters the next spring, we just put down tar paper on top of the plywood before the final metal roofing because I couldn't find a reasonable price/source on some type of heavier/sturdier roofing underlay or house wrap.

                          If it was my roof in your climate, I would use Durock or exterior plywood with a waterproof layer material under the metal roofing. There are some great materials now available as an underlay for roofing (shingles & metal)...as well as more variety of house wraps. If you have any builder friends, check to see if they have remnants from the big commercial rolls of the building wrap or check with some of your local roofers.

                          p.s. Glad Joe "turned" you back to a gabled roof. I'd plan as much overhang as you can to give you a bit of dry space around the structure. Also, think about putting in gutters with downspouts that direct water away from your entry/working area. With your heavy snow loads, make sure you look at installing the little roof "snow catchers" so the snow doesn't slide off and damage something on the sides of your enclosure. I've seen lots of deck railing destroyed when the house roof unloaded its snow buildup.
                          Last edited by SableSprings; 12-06-2018, 02:04 PM.
                          Mike Stansbury - The Traveling Loafer
                          Roseburg, Oregon

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                          • #14
                            I'll leave this to those who have done a roof. My build is out in the open.
                            Russell
                            Build Link............... Picassa Photo Album Link

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                            • #15
                              Thanks, guys!! The plan is coming together. Great call re: gutter, as I will have a counter on the right side of the oven. I hope to post pics soon...

                              Dan

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