Join Paul F. Aubin for an in-depth discussion in this video Using slope arrows, part of Revit: Tips, Tricks, and Troubleshooting.
- There's a few different ways you can define slope in roof elements. You can use slope defining edges, you can use points with the shape editing tools, or you can use slope arrows. The subject of this movie is going to be slope arrows. I was presented this roof by a client some time ago and they knew some of the points on the roof, but they were having difficulty identifying the final point. So I've got a different view here that shows what we knew. We knew that this point here was zero, this one was four, it sloped up to eight here, but they were having a hard time figuring out what this point should be in order to build the roof and have it maintain a flat plane, so it was really important that this plane here didn't become canted.
It needed to stay a flat plane. So we looked at a few potential solutions to solve it, but I consulted a good friend of mine who's an engineer, and she helped me with some of the calculations, and I often go to Desi when I have some advanced math to do because she's very generous with her time and often helps me figure out some of the calculations. So I have a view over here called slope calculations, and it's just a drafting view, and I've got a scan in here of the diagram that Desi drew, and the calculations that she came up with, and it turns out that it was a fairly complex problem to solve when you start getting into all the diagonals, and figuring out the angles, and the different delta heights, and the changes and so forth.
But if you read through it, it's all very logical and flows nicely, and the formulas work and get you to the point that we needed to determine what that height was. Well Desi's an engineer, and so she tends to solve problems using math. My background is in architecture, so I tend to solve problems using graphics, using drawings and diagrams. So, I took what she drew over there, and I said "Well, there's got to be a way that I can simplify this a little bit, and do it a little bit more graphically.", because I was having a hard time getting my head around all of those formulas.
So I did a to scale sketch of one little wedge of that roof, and you can see it here sketched out in these bold lines, and reminding you what the heights were, and what we were looking for. And I sort of had the intuition to say "Well, if we extend these two points out and make this a parallelogram, then we know that this is four, but that should mean that this point up here is also four.", and in fact when I was discussing it with Desi, she agreed and she said "Well, take that a step further, that means that you've actually got a diagonal going across your entire parallelogram there, where the height is four along that entire line." When she said that a light bulb went off and I said "Wow, OK.
Well if that is true, then doesn't that mean that we can draw a perpendicular to that and that's our slope arrow?" Because what a slope arrow does is it just defines the direction of the slope. So I drew this perpendicular line, and I said "Well great! Now all we need to do is figure out what the height is at that end of the line and we're good to go." And so Desi figured it out this way, with a bunch of formulas, and I attempted to figure it out with a couple diagrams. So I drew a triangle this way and a triangle this way, and kinda overlapped them together here, and we both ended up at this number here, which is kind of an ugly looking number.
There's two things that I don't like about that number, I'm not a big fan of fractions to begin with, and I'm a little concerned that it might be rounding off a little bit too much, and so It might not quite work exactly. But it did actually work and it was fine, but we were talking again about the solution, and then Desi just said to me "Well, this is four remember? So why wouldn't you just take your slope arrow and snap it back to here, and then set the height at four and you're done?", and I looked at her and I went "Wow", and all of a sudden the light bulbs went off again, and it was like "Of course that's the solution!", and it's so much more elegant than either of the other ones that we were contemplating.
And so, this is what ultimately ended up using to build the roof that you saw back in the 3D view. So what I'd like to do right now is go to the roof plan and kind of walk through that process and kind of build that roof again for you there. So I'm going to work over here off to the side, and I'm going to build just one of these wedges to start off with. So I'll go to architecture, I'll click on the roof by footprint, and I'll start the sketch. The long side here is 25', and then in this direction it was 11'6".
Now here I'm going to go up just one, because it's not at a 90 degree angle here, this is actually slightly sloped. I'll delete that line right there, and then I'll just copy this 25' line here, and copy the diagonal line here, and that gives me that parallelogram that we started with. Now if I were to finish this right now, and we were to look at it in 3D, all that gives me is just a completely flat roof slab, so let's continue with this and start adding the slope now.
So I'm going to edit the footprint, and I want to draw that diagonal, because that's the key to the whole solution is where that 4' height is, that diagonal line going across the parallelogram. Now if you do it with a boundary line you're going to have to erase it before you can finish the sketch. So it's actually much better to draw a reference plane in here, and I'm going to snap right from that endpoint to this endpoint and that gives me that constant diagonal at 4'. Now I'm ready for the slope arrow. A slope arrow is quite literally, just an arrow that has a height at it's tail, and a height at it's head, and that defines the slope.
It's also possible to take the slope arrow, and change it to slope and say that it's 4:12, or that it's 8:12 or whatever slope you want. Well the only rule about the slope arrow that's critical, is the tail of the arrow has to touch the sketch. So this arrow would fail, but if I draw an arrow that touches this sketch-line anywhere, then it won't fail. Now in our case, we know that this point right here is zero, so what I'm going to do is actually, tell my slope arrow to start right there, because by default the height offset at the tail is zero, and I don't need to change that.
But I do want to change the height offset at the head and make that four. Then I want to take this other end of the slope arrow and make sure it's snapping to this reference plane at a perpendicular. And that's all we need to do. So now that shape is complete. Now if I finish that, that's still a parallelogram shaped roof, but it now has the slope, and you can probably see that best if you go to a front view and you can see that it's sloping now.
So we're almost there. That gives us close to what we want, but remember this was a wedge shape or more of a pie shape there, so I'm going to edit the footprint again, and the distance off of here is about a foot and a half. So I'll just do a quick reference plane for that, and then I'm going to take this line, snap it right to that intersection, and then use trim and extend to clean that up. And the beauty of these reference planes is, you can leave them in the sketch. You don't have to delete them, they can stay there, and when you're finished, you get your roof at the correct slope.
My original solution was to go ahead and mirror these now and create six separate wedges. But then it dawned on me, there's no rule that says you can only have one slope arrow, you can actually have multiple slope arrows. So if I edit this sketch one more time, and I'm going to select everything on this side, plus this little short line here, and I'm going to mirror it along this diagonal. Now I'm going to select this, and you have to delete it because if you keep it there the sketch will fail. Remember you have to have an enclosed sketch, so let's just delete that there.
Now what is that going to give us? It looks a little odd, but both of these slope arrows are at zero right here and they slope up to 4' and 4', which means you're going to get a valley right where that diagonal line that I just deleted used to be, and when I click finish and look at that in 3D, that's exactly what you get. And that is the key to getting this roof exactly where we need to be. We don't even need to know what the height of that point is, these are perfectly flat planes, because by definition, that's what slope arrows do, and if you just continue to mirror the sketch, you end up with this shape over here, and if I just edit this sketch and show you what it looks like, you can see that that's all I did.
I just mirrored it a total of six times, and then when you finish the sketch, you get the final result.
NOTE: The exercise files for this course can only be opened in the most recent version of Revit (Revit 2017).
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