Roof Questions

[davidcobi]

Place a box exterior wall building with location line at face of core up to a top plate level.
Place a roof by footprint... Pick Walls... Extend to Wall Core (use Rafter not Truss roof)
Draw a section through the building.
Roof should be resting on top plate of wall.
Now select all your walls and change them to a wall type that has a different core dimension.

Revit doesn't update the roof so that it is still resting on the top plate the way a Rafter roof should. The roof ridge height also doesn't update which maybe you want, but now the roof isn't resting properly on the top plate. You have to go to the roof's properties and switch it to a Truss roof... Then switch it back to a Rafter roof for the change to take effect.

Also when you Build a Roof by Footprint using lines or if you build a roof by extrusion changing the wall core thickness or roof structure causes issues.

Also when you're in sketch mode and you mix Picking Walls and using Lines in the same roof you end up with hips that seem unpredictable.

Can anyone post examples of where lines are better than pick walls, Where mixing lines and pick walls is desireable or necessary, and where changing wall thickness, overhang, pitch, or roof thickness don't change framing dimensions in unpredictable ways?

For those of you who have to model false raftertails that are not as deep as the actual rafters: Do you model a framing roof and then a finish roof separately but directly on top of the framing roof so you can extend the roof finish out to the end of the false raftertails or do you just model a finish roof and draft in the rafter depth in sections later?

Thanks.

[Henry D]

Also when you're in sketch mode and you mix Picking Walls and using Lines in the same roof you end up with hips that seem unpredictable.

Can anyone post examples of where lines are better than pick walls, Where mixing lines and pick walls is desireable or necessary, and where changing wall thickness, overhang, pitch, or roof thickness don't change framing dimensions in unpredictable ways?

For those of you who have to model false raftertails that are not as deep as the actual rafters: Do you model a framing roof and then a finish roof separately but directly on top of the framing roof so you can extend the roof finish out to the end of the false raftertails or do you just model a finish roof and draft in the rafter depth in sections later?

Thanks.
DGCAD has a good tutorial on picking lines vs walls for roof sketches. I think you have to save the link in his post as a target to get it to work...here is the link to the post http://forums.augi.com/showthread.php?t=35515

The way I do the false rafter tails is by using voids. Some people use two roofs, but I prefer the voids because then there is only one roof to modify if it has to change.

[davidcobi]

Thanks, That cleared up the Align Eaves tool a bit for me. I think the answer is to just stay away from Lines and to always use Pick Walls. The tutorial doesn't show the walls or roofs in fine detail level and what happens to their relationship when someone makes a change to the wall or roof types later in the process.

[dbaldacchino]

Well, the roof is associated to the level, not to the walls. If you draw 20' walls and you associate a roof to level 2, which is at 10', the roof will be at 10' if you pick lines, or if you use pick wall and you add an overhang, the point over the picked walls will be at the level height. The lines created by using the Pick Walls command are different than the ones created by the line command. Create the two and check their properties. Note how the parameters differ.

I personally have not done a whole lot of sloped roofs, but when I needed to, I opted for the line option and then positioning the roof in a section roof to where it needs to be.

[davidcobi]

I think the real difference is that in Revit some tools are "constraining" tools and some are just loose components. When you use Pick Walls the roof is now constrained to the walls so when you relocate walls the roof moves. When you create a roof by Lines the roof is less constrained and requires adjusting manually when you change the overhang, plate height, pitch, or wall thickness.

To use Pick Walls or other "constraining" tools in Revit you have to know the "rules" required to get the component to behave properly when placing and modifying. If system families built with "constraining" tools are not constructed and modified using the proper "rules" you get those famous warning messages that ask you to delete or cancel and will not let you execute the command at all.

The family editor is the best example of this aspect of Revit because if you want to build in a lot of automation you have to use Revit's "constraining" tools to build the component. The more automation you want to build into parametric components the more you have to understand "constraining" type tools and the more training your staff is going to need to work with constrained components.

Using lots of "constraining" tools in family files is fine as long as you test the model and make sure it works before placing it in a project and as long as you explain to less savy staff that they should not be editing or trying to create highly constrained families until they are fully trained in the "rules" used when creating and modifying highly constrained components.

The danger of using "constraining" tools like Pick Walls in the project file is that if the project was constructed by someone who fully understands the "rules" associated with each "constraining" tools then any new staff asked to modify constrained components in the project file will very likely run into many warning messages and will need further training to know how to resolve these issues in the future.

[dbaldacchino]

Yep, you are correct. With drawing/picking lines, you have to create constraints yourself by checking the Lock checkbox, aligning & locking or placing dimensions and locking those values. The Pick Walls option knows what wall it was assigned to and it moves when the wall moves. It doesn't constrain like an align & lock, but like a locked dimension. When you manually move one of the lines created by the Pick Walls tool, Revit doesn't throw a fit about constraints not being satisifed, like if one manually constrains to a face with a lock or dims. to a face and locks it, so these "constraints" are all transparent and act like there's an invisible locked dimension that is automatically unlocked when such line is moved and re-locked automatically once it's released.

I think a simple, great enhancement would be to simply give us a unique subcategory for the two different types of lines so we can assign different colors to them. Then we can tell at a glance which is which. Right now the easiest way to tell them apart is to pick a line and observe whether the Options Bar gives you a greyed out "Overhang" listbox or not.

Thanks for brining up this topic as I honestly had not gotten this deep into sloped roofs! As I said, I had been manually sketching lines or by using the pick tool, and then adjusting the roof height in a section view.