How to do tapered insulation?

[patricks]

For years I've tried to come up with the best way for showing tapered insulation on low slope roofs, and have never really found a GOOD solution. Part of the problem, it seems, is that apparently I've been doing it wrong all along. I'm used to showing tapered sections that slope 90 degrees to the main roof slope, almost like a very flat hipped roof, with ridges perpendicular to the roof, and valleys making 45° angles if the tapered is the same slope as the main roof, or around 22.5° if the tapered is half or twice the main roof slope.

The roofing contractors don't do it this way. They take the main roof slope, and lay down tapered boards at an angle, which reduces the number of valleys at each roof drain, usually from 4 valleys on my drawing to only 3 in the field.

The first attachment shows how I normally do it, with slope defining lines near the roof drain, with the tapered insulation roof element either extended to the main roof, or just sketched out that way. I used 1/8" and 1/4" sloped pieces, on a 1/4" sloped roof.

The second attachment shows how it's actually constructed, with 1/2" tapered boards. The blue circles are the roof drains. The tapered boards that start out at 1/2" thick run at an angle, up the roof slope. Because of this, I can't really make it out of a sloped roof object, unless I start with it flat, and do point elevation modifications, which would require a bunch of extremely tedious manual calculations. Laying it out this way means the tapered "ridges" (running up and down at the roof drains and between roof drains) are not actually level with the ground, as one might expect, like it is in my version. I can't really make a face-hosted family because there are just too many angles to deal with around a roof.

Any suggestions on how to model this?

[Rick Moore]

I model it using roofs and sub element modification so the variable thickness property works. It's a bunch of slope calculations but it works

[damon.sidel]

I second what Rick says, I use sub-elements with the variable thickness properties, too.

Instead of doing the calculations, I sometimes use another 3D program that allows intersecting geometry like SketchUp or Rhino. Then I measure it and translate the measurements to Revit. Thinking about it, couldn't you create multiple separate roofs, each with a simple slope, then join them all together? It might be a mess in your orthographic views, but you could use that "blob" to measure and create a cleaner roof with sub-elements.

Finally, and this may not be a useful suggestion, but it looks like your roof plan gets the point across and coordinates the things you need to coordinate, like roof drain locations and general approach. Wouldn't it be OK to let the contractor figure out the specifics, even if it differs from your more schematic approach?