Friday, January 23, 2009

Rafter or Truss Roof Property

Ever wonder what the difference was between selecting Rafter or Truss when doing a Roof by Footprint and utilizing Pick Walls? (Notice, I mentioned Roof by Footprint and Pick have to use these tools/options to get the selection of Rafter or Truss.)  Well, the difference is quite simple but can be confusing to some when laying out the footprint lines.

 image image

When Selecting the Rafter Option, the slope starts at the INTERIOR face of the wall. If you use the Truss Option, the slope will start at the EXTERIOR face of the wall.  The confusing part for some is that the sketch line doesn't change when changing the Rafter or Truss parameter.  As you can see in the images, the overhang doesn't change but the "base point" of the wall does change height.  Notice how the dimension from the level to the top of the fascia line...the roof is moving vertically to adjust where the slope point starts.  So the sketch line doesn't change location to change where the slope starts, the Rafter or Truss option moves the roof up or down to change where the slope starts.

EDIT:  Forgot to mention one little thing...using Extend to Wall Core also works the same way.  The above images used the face of the wall for the overhang, not the face of the core.  If you check the box in the options bar to Extend to Wall Core, the slope point will be from the core face.  This would give a more realistic representation of the actual construction for most stud conditions, where the slope point would be in-line with the stud face and not a finish face.


GeoffB said...

Thanks. Simple yet confusing ;-)

I can see why it only happens with Pick, but why not just make the choices Interior or Exterior?

Dwane Lindsey said...

I think they are trying to use the construction terms and how each "sits" on the wall...and make you think about what you are actually using. ;-)

As an example, a rafter typically sits according to the interior face of the stud and have a birds mouth. Where as a truss typically has a bottom cord and extends to the exterior face of the stud.

That's my guess anyway...

GeoffB said...

True, but the Revit representation looks hardly anything like a true rafter and nothing like a true truss. If they did then the terms would be sensible. Since they don’t better to use terms that more close describe what is really happening.

Dwane Lindsey said...

I can't disagree with you on that one...they don't represent the true look! But the slope "base point" is the difference, not the look unfortunately.