Roof Axis Geometry

[Ed Wachter]

I would expect a roof face axis to be located either at the top surface or bottom surface of the roof face. It seems to be somewhere in between. Can anyone help me understand this geometry? I'd like to be able to set the axis Z in relation to wall height but I can never quite tell where the axis is. Is it a function of roof thickness?, or slope?, or something else?

Thanks

Ed

[CipesDesign]

The line drawn during creation is a line along the axis Z and perpendicular to slope. To more fully understand this, run the Create Roof command, then Ungroup and examine resulting Roof Faces.

[Ed Wachter]

I think that's helping. I see that the Create Roof command automatically places the axis at the inside face of wall and the axis Z automatically equals the height of the walls selected while making the roof. My convention has been to place the axis at the outside face of framing. I think if I keep it at the inside then I can just enter an axis ht. equal to my wall ht. We almost always create individual roof faces since we don't do very many hip roofs.

Thank you!

Ed

[CipesDesign]

Ed, it really depends on the exact construction method. With prefab trusses, for example, the bottom edge of the top chord generally intersects with the outside edge of the top plate. With a cut (stick framed) rafter, there is great variation, but generally the seat cut will place the intersection at (or near) the inside corner of the top plate. The best policy is to draw it in section, or verify it in section, to make sure you have what you want.

[Joe-SA]

One of my biggest complaints when comparing Roof Faces and Roof Objects. The Axis Z is an elevation that results from taking the lower outside corner of a roof face (looking in section) and extending it along the roof pitch up the slope for the length of the overhang to the point where you drew the inflection point of the slope in plan when you created the roof. Usually the face of the wall/sheathing. Depending on whether you have a double miter, vertical, or horizontal eave this point could be on the top or bottom or somewhere in the middle of the depth of the roof face. I never tried to predict it. Just adjusted the height after creation.

With the Roof Object tool having bearing height and bearing inset parametric input you get much more predictable results.

You might be interested in this recent thread.

Joe

http://techboard.vectorworks.net/ubbthreads.php?ubb=showflat&Number=181872&Searchpage=3&Main=35191&Words=shed+roof&Search=true#Post181872

[Ed Wachter]

I was afraid the axis Z might be determined by some complex method as Joe seems to be describing. My experiences with individual roof faces has not be nearly so neat and predictable as the Create Roof command seems to suggest. I've been checking by cutting sections from the model and sometimes drafting a 2D section to double-check. If I ever find some simple rule to easily predict how high my roof will be based on axis Z I'll post it here.

Ed

[CipesDesign]

It's not as difficult as you might think. Take a look at the attached step by step directions.

Also, you can use the MOVE command in Front View to move the Roof Face up or down...

[bc]

Nicely done Peter.

[ksmuland]

Hi, I am trying to learn VW, and am doing a shed roof. Following your tutorial here, I am not able to add surface when the roof surface and overhang rectangle are selected. the option is greyed out. What do you think I'm doing wrong, and is there an easier way to do shed roofs?