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Thread: Custom Roof Truss Family Poll - Your opinion matters.

  1. #1
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    Custom Roof Truss Family Poll - Your opinion matters.

    Hello,

    I am in the process of creating a custom wood parallel chord roof truss and am curious as to how some of the guru's on this site would approach this task. A little background on the task first.

    So I had a project that had a fairly complex roof slope that sloped in 2 directions on each face. The framing was not perpendicular or parallel to either of the slopes. After trying to place the OOTB trusses and searching the interwebs for a truss family that I could manipulate the way that I needed to I was left with only 1 option to create the truss family myself. So the daunting task began with a generic model work plane based family. A few parameters and geometry and I was in business. Then another project came along with a similar roof design and with it some new roadblocks. Long story short the progression of the truss evolved slightly with each new project leading me up to my current task.

    The concept of this custom parallel chord truss family is to provide a sense of familiarity for the end user to what they were used to seeing in ACAD details with parametric control of many graphical options. I know this breaks 1 of the Revit cardinal rules, "This is Revit not ACAD. Do not expect the same results as you normally would." Breaking this rule proved to be relatively easy using a sweep or extrusion with voids, at first, then creating the voids in the extrusion sketch to be controlled via parameters. Its the additional graphical options that are beginning to become a little much.

    Now I am left with a list of options that aren't hard to create but with a sense that maybe the route I'm taking while creating this custom family might be longer than what it needs to be.

    The options are as follows:
    Control of the size of chord members. The top chord independently from the bottom and end chords.
    Control of the angle for the vertical end chords so that they can be set perpendicular to the finish floor when the truss is sloped.
    Optional outriggers that can vary in size or differ from the top chord.
    A sliding web panel for use in mid point bearing details.

    So after about the 4th time creating this truss I'm on path that seems like the family may become overweight with so many types.

    Family types is where I'm really ending up with this, What I've got so far is
    2x4 chord
    2x4 chords w/ 2x6 top chords
    2x4 chords w/ 2x8 top chords
    2x4 chords w/ 2x10 top chords
    etc.

    This continues on with 2x6 through 2x10 chords and none of these include the outrigger options yet which if I continue down this route will grow that family even more.

    Does anyone have a better solution or work flow that I could use to create a custom family for a parallel chord wood roof truss that will allow for options 2x4 - 2x10 for the top chord independently, the (2) end chords & bottom chord, and outriggers on both ends for all variations of the 2x members to be used?

  2. #2
    Forum Addict GMcDowellJr's Avatar
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    Use nested families with instance based family type parameters.


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  3. #3
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    Hello Greg,

    I'm going to give nested families a shot with this task. How you would implement the nested family approach? I am thinking that I need a nested family for a right and left outrigger family, a family to represent the web members that would contain a vertical and 2 diagonals, a family for the top chord and then a family that would have the end and bottom chords. A potential obstacle I could see occurring would be a joining issue for the nested families to remove the edge lines where members overlap in the host family. I'll keep you updated on my progress.

    Thanks,
    Kyle

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    Hello world,

    So I've been working on creating this truss using the nested families approach and have run into a little snag. I'm in the process of creating a family to nest into a host family that will represent the (2) end chords and the bottom chord of a wood truss. I found a walkthrough to create a rotation rig at The Simply Complex Blog: ROTATION RIGS THAT DO NOT USE THE ANGLUAR DIMENSION that helped to get over a hurdle I was having with the end chords having an adjustable angle for conditions such as a sloped parallel chord truss. The problem I'm having now is part of the rig does not behave how I'd hoped when the truss grows in length. I'm attaching the family as far as I've been able to get it so far. Any ideas or suggestions on how to solve this next puzzle would be greatly appreciated.

    Kyle
    Attached Files Attached Files

  5. #5
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    Hello world,

    I finished my truss using the nested family method as suggested by GMcDowellJr and everything is flexing as expected. The only hang ups I have with it is how the pull downs work for choosing the individual chord member sizes. Otherwise very happy with it. I'm attaching a 2015 version but also have versions for 2016 and 2017 available. This truss has optional outriggers on each end, options for setting the top chord, bottom and end chord sizes. I know the biggest criticism I'll probably get is regarding how I modeled the end chords and bottom chords but at this time it works just fine for my needs. There are few more parameters I'd like to add, such as having the bottom chord size drive the end chord sizes and how the web panel doesn't adjust its overall height to the bottom chord height, but the web panel was only added for the rare instance of needing to detail a mid-point bearing condition. Any rate feel free to take a look and play with my most complex family to date and share any input or suggestions you might have.

    Thanks,

    Kyle
    Attached Files Attached Files

  6. #6
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    without having plunged into the family itself, I would just say I handle outriggers with simple beams, no reason to try and put them in your family IMO but if you got them in there good on you.

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