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Thread: Roof Hip & Ridge Cap TRIG!

  1.    #1
    Junior Member cwasher's Avatar
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    Roof Hip & Ridge Cap TRIG!

    Long time lurker, sporadic contributor here. Over the years, I am grateful for the people on the RFO community. I have learned a lot. Figured it was time to share a solution to a problem I worked on a month or so ago.

    I wanted to make some roof accessory families to increase model accuracy. Specifically, I was looking at making some ridge vent/tile and hip cap tile/shingle families. Let us start with the easiest of the two:

    (I know some of these can be achieved via fascia sweeps, however, I did not care for the limitations it imposed)

    Ridge Vent
    All the math for these families is done in the profile family and then nested and linked into the parent line-based family. For a ridge cap there are two conditions: adjacent roof slopes equal or not equal.

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    In the profile family, all parameters are TYPE. This is so they can be linked to the parameters in the parent LB family. First, there is a check box to control the two conditions mentioned above. If slopes are equal it is checked, if not, uncheck. Next, the input fields define the slope conditions and size of the ridge vent.

    Lastly, the math. Pretty straightforward trig here. Using the slope input to convert to angle for each adjacent roof plane. RidgeAngle is a conditional statement that evaluates based on the two conditions we mentioned earlier. Pretty straight forward. Here is the profile with the parameters.

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    Hip Cap
    This is the solution that gave me the most trouble. Let us review what makes this challenging. A ridge is parallel to the ground plane. A roof Hip is the edge of two sloped planes whose slope is rising to meet the ridge. Again, we have two conditions: adjacent roof slopes equal or unequal. See below diagram:

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    Through many web searches. I came across the term backing angle in wood framing. This is the angle that the top of the hip framing member must be cut in order to allow sheathing to lay flush on the hip member. The few formulas I came across did not seem reliable, until I found this GEM!

    Martindales Bevel Angles a book from 1948 in which a PE produced formulas for all sorts of steel framing conditions.

    The two relevant formulas are on page 18 of the PDF, See the sketch on the proceeding page for mark references.

    Code:
    R1    Pitch of Hip or Valley Rafter.                                         tan R1 = tan S sin D
    C5    Angle between Roof plane and Hip or Valley Rafter flange.              tan C5 = sin R1 cotan D
    Essentially in order to solve for C5, we need the following variables:
    • R1 is the slope of the hip
    • S is the slope of the adjacent roof plane
    • D is the horizontal angles between the eave and hip


    We will use the first equation to derive R1 the slope of the hip member and then use that value to solve for C5. Lets look at how this translates into Revit parameters:

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    First, we have the condition checkbox like the previous family (equal or unequal adjacent roof slopes). Next, we have the inputs. We only have one Roof Slope input since we can utilize the horizontal angles to derive the backing angles.

    Convert Roof slope into decimal angle, RoofSlope1. Calculate RafterPitch (R1) rewriting Martindales formula. BackingAngle1 and 2 are using Martindales second formula. SumBackingAngles is the parameter that adds the two backing angles if the adjacent roof planes are equal or not. Here is the profile with the parameters:

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    See attached two families for your learning. Note, when using the hip ridge family, you must host it to the roof plane that you will be inputting into the Roof 1 Slope value. Also, it matters which direction you draw it. So after inputting the values and it still looks off, try swapping the end points around.

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    TO-DO
    I still need to work on a way of cleaning up the ends of the hip caps to account for them being trimmed at the eaves and where they would meet at the ridge. I think the best approach would be to have separate families for the ends and then join the line-based component to the freestanding end geometries.

    If not directly useful for you, maybe this math can be utilized for other types of families or modeling elements. Love to hear your thoughts.
    Attached Files Attached Files

  2.    #2
    Moderator cellophane's Avatar
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    Good Stuff!

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    Senior Member PijPiwo's Avatar
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    Roof capping was also discussed here some years ago - a work around though.

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    Forum Addict sdbrownaia's Avatar
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    could you use a void revolve to cut the ends of the family as needed. a revolve can specify its start and end angle so you could cut the ends unique as needed, or a void extrusion can be used but you need two angles.

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    Junior Member cwasher's Avatar
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    Quote Originally Posted by PijPiwo View Post
    Roof capping was also discussed here some years ago - a work around though.
    Thanks. Yes I like that approach for a "quick and dirty" solution.

    Quote Originally Posted by sdbrownaia View Post
    could you use a void revolve to cut the ends of the family as needed. a revolve can specify its start and end angle so you could cut the ends unique as needed, or a void extrusion can be used but you need two angles.
    Hmm... I like the revolve idea, will have to try that at some point. I'll have to flex my brain again to figure out the trig to get the angle based on the current inputs, seems promising!

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    Member d.stairmand's Avatar
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    That Steel Book is brilliant!

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