roof by footprint - hip with differing fascia height - images inside

[3dway]

Hi Gang. Me again.

I'm doing a hip roof with a feature that we often do. The fascia height is interrupted by another roof but jumps up by 6 or 12 inches on the other side of the interruption.

I haven't been able to figure out how to do it with roof by footprint. I am reluctant to try to do it by masses. Masses are very messy in my mind and make changes difficult because you have to delete roof, change masses, remake roof, for every change. Later the fascia disapears with the roof and also has to be redone.

Right now I'm going into sketchup to see if it's even geometrically possible without making different soffit depths. I forgot to mention that the design sketches show all 24" overhangs. I'm suspecting that this is something that takes advantage of 2d's shortcomings.

Anything you guys can do help me do this by footprint would be great. Attaching is working although it's finicky.

In sketchup I can concentrate on the problem instead of how the tools work, so for now it's a crutch.

[muttlieb]

That roof isn't possible the way you have it drawn. You need to reconcile the fascia height some way (the fascia on the left side is higher than the right side). As you acknowledged, one way to do that is to reduce the fascia overhang on the lower fascia, but I'm not sure that's going to give you the look you want.

[3dway]

Here is the sketchup solution, so far. Where it's impossible [for me] to acomplish this in Revit, I was able to quickly come up with someting in sketchup.

I'm reluctant to use this as a mass family for roof by face because I find you cannot change roof by face without deleting it. Please correct me on this... please... no really.

[muttlieb]

How big is the SU model? Can you post it here?

[jeffh]

That roof isn't possible the way you have it drawn. You need to reconcile the fascia height some way (the fascia on the left side is higher than the right side). As you acknowledged, one way to do that is to reduce the fascia overhang on the lower fascia, but I'm not sure that's going to give you the look you want.

That is what I thought when I looked at it.

It reminds me of a time the principal in my office (old guy, no computer) looked at one of my AutoCAD Architecture models of some roof condition and said it was not what he wanted. He sketched what he wanted on a piece of paper. What he sketched was geometrically impossible. I "faked it" for the drawings to make him happy. Then it got built the way I modeled it in the field. He never knew the difference.

[3dway]

I've been able to model the roof in revit using several roofs. Problem no. 1 was that as I was modelling them, if I tried to edit a roof that I had already created, I'd get a "cannot create roof" error. I coule make a new one from scratch including change I was trying to make, but couldn't change one that had been created. Weird.

Problem No. 2 is that it refuses to join these! Which means it's all for naught. I haven't even got to cleaning up the inside of the roof so it sections nicely.

This is one of those situations where I can do it in a couple of hours in sketchup, but in Revit I can't do it at all. Nothing works the way I expect it to. Roofs are a huge part of our designs (though this one is unrefined at the moment). I can't affort not to be able to do out of the ordinary things like a staggered fascia.

I'm dying for some help here. I'm supposed to have the elevations resolved and I've spent a day on the roof. This killed me on the last project too.

[3dway]

one more .................................................................................
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[3dway]

Any one have any luck using a slab as a roof and using the slope lines to make ridges and peaks?

[muttlieb]

I'd still like to have a look at that SU model, if possible...

[3dway]

it's 2 meg and the messy geometry from revit is embarassing.

[muttlieb]

Can you strip out some of the geometry that's not relevant to the roof? I don't care about messy geometry, I just want to see what you had to do to the SU model to get it to work and it's not clear from the 2D images you've posted...

[3dway]

Please excuse the ****** geometry. This was intended to be a quick exercise in ensuring that the roof was possible. It's quite unfinished and quite a mess at the back.

3ds files are way smaller than skp.

[3dway]

Can anyone shed any light on the "remake" button when using roof by mass? How successful is it generally?

[muttlieb]

In the SU model, you've offset a wall to get it to work. You'll have to do the same in Revit. My advice is, model it like you'd build it and Revit will become much easier for you...

[3dway]

You did that in one roof?

Can you show me the plan view of the roof sketch - magenta lines?

...Model it like you would build it?

I'm kind of stumped by this. To model it like I'd build it would require lofting it out of several truss shapes. If Revit will loft, that's dandy, but I don't think it will.

Thanks for the sketch by the way.

The jog in the roof that you're showing there is hidden by the low roof that runs up onto the main. If I model the roof you've got there, then model the one that runs up onto it, how do I get rid of the **** on the inside? Maybe my approach is wrong here, but when I section this, I expect to show the roof as the truss top chord, sheating, shingles. I expect to have to show the bottom chord as part of the ceiling. We don't show truss webs on our drawings anyhow so I could even cover this on the section with a masking area, but I'd rather not. In the spirit of BIM, it should be modelled accurately.

Now, if the roof tool let me include the truss outline, that would be useful.

[muttlieb]

This one consists of three roofs. Attached is the Revit file for you to reverse engineer ;)
By 'model it like you'd build it', I just meant you need to at least get the geometry correct. The reason your original revit try wasn't working is that you were trying to get it to make a roof that was impossible to make. It worked in SU, but you had to offset a wall to get it to work.

HTH.

[3dway]

After a night's sleep and a fresh cup of coffee, I now see what you mean by having offset the wall. I determined that the ceiling space at the back is a scissor truss and the little square of wall on that back corner actually happens on top of the great room trusses and does not cut into the space so it doesn't matter where it occurs. I'll have to look back at this with the fresh mind to see if it holds up. Things come to me in my sleep.

[3dway]

Ok, I'm mercilessly thrown back into yesterday's helplessness.

It seems to me like the order of events is important here because I keep getting a "can't make roof error.

What I'm trying to do here is recreate the situation as though I were starting the roof, but this time with the knowledge that you've given me; which is basically proof that it can be done (reasonably) elegantly with Revit.

First I make it with the fascia at (call it) zero all around. It includes the main roof and the right "peninsula hip". Next I do the left "peninsula hip and set it up at the right height. Then I look at it from the front elevation and realize that I need to shift the ridge over to keep the overhangs the same while and still align the left plane of the main roof with the left plane of the high left peninsula hip. If I move the roof footprint line associated with that it will shift the ridge, but I'll have to cut an opening to cut off the overhang.

With the knowledge you've given me, I realize that I have to put a jog in the right side. I do the math, edit the roof plan and put the jog in the right side and set the lines to not define slope. I get the right side to cut up to the right height with the reduced overhang (offset wall by your explanation) but there's a tail hanging down at the back. How did you get the new fascia height to continue around the corner to the back roof footprint line, while keeping the same overhang? I've looked at the properties of the lines to see if you're doing something not obvious, but I can't find anything.

I assume you cut the overrunning roofs in after making the main roof. Or did you sketch with ref planes?

Is it a process thing?
I think I neeed to understand what Revit uses to make a roof instead of thinking how I would build it. I think about the trusses. The top plate, the heel height, the overhang, the slope. I think about the trusses in terms of the dimensions that the truss suppliers call and ask for if we didn't dimension the details right. We dimension roofs to the truss members. Everything else after that doesn't matter, the trades just follow the trusses.

[3dway]

Am I missing the boat by thinking about roofs the way that Revit is asking me for the information?

Roof by footprint - Revit is asking me what the boundary of the roof is when looking at it from above. OK. I draw that.

Defines Slope - OK. I tell it which lines define the slope. Having looked at this example file provided a few posts up it feels like one trick is that you only want one line defining the slope on each side (more or less). The right side of the example file has four lines, only one defines slope.

So if I cut a fascia back by moving the footprint line in, I usually get a "can't make roof error"

... just so lost. It's actually more frustrating now to see a complete example in front of me and not being able to figure it out.

[muttlieb]

Trust me, I understand your frustration. While it's important to keep in mind how the roof will be built, you also need an understanding of the logic behind how revit creates roofs, and that will come with experience and trial and error - at least that's how I figured it out ;) I think you were on the right track. The most difficult part of your roof is getting the main hip with the offset fascia height. You actually need two offsets in the roof - obviously the fascia needs two points to transition from the lower height to the upper height. You've got the jog in the right wall that is hidden by the overlapping roof. The other place it jogs is at the front wall where it dies into the higher hip on the left. I started the roof by using the pick walls tool with overhang, and I selected the walls in the lower right that have the lower plate height. The rest of the roof defining lines were done with sketch lines - some are slope defining and some are not. You are correct that typically each roof 'face' only has one slope defining line. Hopefully the attached image will clarify what I'm trying to describe. Also attached is the revit file.

[3dway]

I got the roof to work using three roofs.

I have some more information on specifying the fascia height by each footprint line.

Did you adjust the fascia height on the lines? Either the higher ones or lower ones? Logic tells me your walls with an overhang valued from the wall are "zero" height, and you've set the other up a certain amout. Is that correct?

Thanks for all of the help on this.

[muttlieb]

I did not manually adjust the fascia height on the higher fascias. The lower ones at '0' that were set using 'pick walls' define the starting point of the slope. Since the other ones were drawn with lines and do not define the slope, they form the fascia at a higher point, depending on the distance setback from the slope defining line. Hope that makes sense... You might want to try it out on a simpler roof to see how it works.