Residential roof design

[Mike Sealander]

I feel compelled to post what I'm sure is a pervasive issue:
How is everyone modelling roofs, especially with special overhangs? For instance, let's say a 11.25" TJI roof has 2x6 outriggers? Do you include the ceiling finish (gwb, for instance) in the roof type?
I have one project where the roof family contains only plywood and shingles, the roof girders and purlins are modelled separately using structural members, and then the gwb ceiling is also modelled separately, using reference of the Revit roof family. Yet, it doesn't seem like the OOTB roof family is flexible enough to handle roofs, especially on the outboard side of exterior walls.

[kpaxton]

Mike,

First, thanks for your observations and comments! To be blunt, yes - the roof tools need a bit of work. We've got requests in the Wishlist Forum for the Factory to get more functionality, such as behaving somewhat like walls with 'unlockable & stretchable' elements (such as for the sheathing layer, etc.)

As to your question - how do we build roofs? I think you'll find that most everyone here builds them all a bit different. In your example, I could certainly do that - but I would only build the framing members IF they're going to be expressed/exposed to the living space. I can live with it being a 'generic' mass because I'll clean that up later when I do my detailing. Unless you're designing/building the same type of structure over and over, you'll find that you use different methods depending on what you need.

I do think that some have a tendency to 'over model' their projects - but it really falls to what you're comfortable with - and what your machine can handle! O.o The real bottom line is... "what do you need to do.... to convey what you need to convey... in the shortest amount of time that is available to you."

Kyle

[jvoight]

Mike,

I've been using your method on residential projects. I create the sheathing and shingles in one roof type. When I'm confident that the roof design is finished i copy the sheathing and shingle roofs and change its type to 11-7/8" TJI, adjust the overhangs to align with walls, align the two roofs and join geometry. I then use beam systems for the outriggers.

If you want to model your lighting use the ceiling tool for the gwb, if not add it to the 11-7/8" roof and place 2d lighting.

jim voight

[whittendesigns]

I have actually made families of rafters, valley/hips, jack rafters, girders, etc. and skinned the whole roof with a plywood layer. I feel for you.

I've done it many other ways also. I usually end up with a 5½" thick roof to simulate the thickness of 2x6's on a section cut. A vaulted, I'll do an 11¼" for 2x12 rafters and keep the overhang back to core, then 2x6 for that point on or something like a double cut on the tails. However, my fascia detail makes me use a very thin face on the fascia part, so I end up with roof sheathing thickness with shingle surface.

Only thing I really don't like about the roof stuff is the fact you can't place a surface pattern on curved surfaces (turrets)

[Mike Sealander]

Thank you everyone, it sounds like I'm not too far off the mark in how I'm approaching my project roofs.
Because I've been doing design-build, I've gotten used to being able to figure out framing issues during design, like how long a joist really is, what the angles are on compound cuts, how to get toilet waste pipes to miss floor joists. I did all this in AutoCAD.
Revit seems not quite there in its ability to automate the creation of some basic framing moves. I think I could model almost anything in Revit, but only if I make the decision to use in-place models of things.

[rjcrowther]

I agree with the last statement of Kyle's. Be wary of how much modelling you do. I did pick up some information somewhere (may have been on these forums) about what represents 'effective' modelling. The basic rule was model only if:

-if it is seen in more than one view
-if you need to sort out construction issues by seeing how things fit together
-if it required for a rendered presentation and you can clearly see it or the shadow it casts.

Roofs are one of those things where you really need to determine what you want from your efforts - again this is in concert with Kyle's thoughts. Personally, I try to avoid modelling individual components.

Rob

[mlgatzke]

Personally, I use a roof type that has 3.5" structure, .75" sheathing and about .25" for everything on top. Then again I don't render my roof structure and don't have to show each individual truss or rafter. When it comes to a building section, wall section, or detail I just use a filled region or detail component to represent the truss. Remember, if you're never going to see the individual trusses/rafters then don't model them.

Also, I place my ceilings as separate ceiling elements. I do not make them part of the roof. This allows me freedom of ceiling heights and shapes.

I'm afraid I've never seen the value in modeling framing. The builder isn't going to follow what you provide - he's going to build it the way he's used to building it. I'll detail it, yes, but only for liability reasons.

Sorry if this sound negative, I don't mean it to be. That's just my observation from my years of practice in the residential world.

To reiterate, I agree with Kyle (Hi Kyle), only model the framing if it's going to show and you're going to benefit from it. Only you can determine that. You've got to weigh investment and return.

[Mike Sealander]

Builders follow what I model, largely because the math on what I model is too complex to reasonably figure out without a computer.

[whittendesigns]

I agree to an extent. As a framer for over 20 years, the best tool in my toolbag is the Construction Master. Every person that comes to me looking for a job, that's the first question I ask them is if they have one. I would say 95% don't. I can't understand the logic of not having this in the field. Everyone should be made to have one.

It also depends on who is doing the building and the people doing the building will vary from job to job, even from the same builder. Everyone builds differently. Not once have I followed a set of blueprints completely.

On the design end I would say that you should be careful to take the liability of listing exact measurements on roof framing. Let them worry about it in the field. I've done irregular hip roofs in the field with no problems at all. That's about as complicated as it will ever get.