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Need help with variable thickness roof for drainage on a 'flat' roof

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    Need help with variable thickness roof for drainage on a 'flat' roof

    Variable thickness roofs seems to be the way to deal with 'flat' roof drainage slopes. You cant seem to set a slope though, I have to pick individual points and give them elevation offsets. So I draw it up in CAD in section at the proper slope just so I could measure the height of those points and then input those dimensions into revit at the same locations.

    This seems like a pretty involved process, is there a better way? I'm wondering how others deal with this.

    Also, If I dont get the point placements just right, revit has to create additional split lines/ridgelines where the slopes dont match up perfectly, which you can see on the left side of this roof plan.

    roof plan.PNG

    #2
    You can use ''modify sub elements'' to give the points an offset
    www.jansenengineering.nl

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      #3
      We use a generic model cricket family that goes on top of the roof. It has its quirks, but it is easier to quickly adjust the size of, has a set slope, and can be copied when there are multiple similar items (like skylights) that need to have crickets.

      Edit: We primarily work with external drainage (scuppers/downspouts). The one time I've done internal drainage they were close to the edge and overflow scuppers anyways.
      Last edited by jmk; January 25, 2021, 10:26 PM. Reason: Spelling
      Julie Kidder
      Architect + BIM Director
      Hartman + Majewski Design Group

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        #4
        There really is not a good way to do this. In reality, the roofers install tapered insulation with the thinnest edge near the roof drains, and then work their way away from the drains. Then the elevation at the parapet edges just ends being whatever it is. Revit doesn't really work like that. You could try doing separate tapered roof pieces, for each "face" of the sloping areas. Start with a short edge near the roof drain and give it a slope like 1/8 in 12 or 1/4 in 12. If you want you can make them bigger than needed, see where the different pieces overlap, then trim them back to those intersecting edges. It can get tedious, but so can individual families, or point editing or any other method.

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          #5
          Originally posted by jmk View Post
          We use a generic model cricket family that goes on top of the roof. It has its quirks, but it is easier to quickly adjust the size of, has a set slope, and can be copied when there are multiple similar items (like skylights) that need to have crickets.

          Edit: We primarily work with external drainage (scuppers/downspouts). The one time I've done internal drainage they were close to the edge and overflow scuppers anyways.

          Thanks, I think modeling the general roof slope like normal, then adding a cricket family of some kind later makes the most sense (other than not modeling the crickets at all and just calling out slopes and drain points in plan).

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            #6
            Sometimes just showing some model lines is more appropriate. Sure we would all like to have everything modeled exactly how it should be, but sometimes that just takes too long. And in fact, unless you're really knowledgeable about tapered insulation, they'll probably install it a bit different than you draw it anyway. Case in point: tapered crickets typically don't slope perpendicular to the main roof slope, like I used to think anyway. If the roof structure slopes, the tapered insulation ends up getting installed so that the slope runs at an angle compared to the main roof slope, parapet walls etc.

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              #7
              In your example above, the tapered insulation would be installed this way:

              tapered.JPG

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                #8
                I agree with you on the cricket slopes Patrick, but not on the using model lines in lieu of modeling. I'd rather have the model correct for the building and wall sections....and not have the team resort to filled regions.

                I don't concern myself with hitting an exact 1/4" slope -- i just make sure that i exceed it. The contractor can figure out the exact slopes from that point forward. It's fairly easy to model using shape editing, so long as you follow the rule of rectangles. If the shape of the roof is complex, i'll set my roof boundary to the largest extent, establish my roof slopes with shape editing, then trim away the excess portion with a vertical opening. This is assuming though that i either have tapered insulation or rippers w/ sheathing, i.e. the bottom is flat (variable depth enabled).

                Not sure where or how i stumbled across this ppt presentation on tapered insulation, but it is really helpful and explains the odd cricket slopes you mentioned (p 37-39). And i can't tell you how many times the juniors model/draw something like page 17; i make them fix it to be like p18.

                Jon
                Attached Files

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                  #9
                  Thanks for that document, lots of good info. In regards to using lines, I will do it if it's a really small, fast project with only a couple of drains/crickets needed. The amount of time it would take to model it properly would not justify the gains from having it modeled properly. For larger jobs, and/or big re-roofing jobs, then yeah I'll take the time to try to model it as accurately as possible. One of these days I hope I can figure out a way to get family components to work like we need them to for creating tapered crickets.

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