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A Footprint roof is often the easiest way to create the most common forms of roofs and offer the simplicity of being to draw them in Plan view. Extrusion roofs allow us to sketch the profile of a roof rather than its footprint. So these are more suitable for more complex forms, like barrel vaults or undulating forms and so on. So let's take a look at a simple extrusion roof here in this dataset. To create an Extrusion roof, we actually work in a plane other than Plan view. So I'm looking at a three-dimensional view, and I'm going to hold down my Shift key and just kind of drag with my wheel to spin this thing around.
And I have this little exit way over here. Now let's assume that the designer wanted to not only put a little covering over that, but they wanted to have a little bit of fun with it and make it something freeform. So this is where we might to choose to do an Extrusion roof. To draw this Extrusion roof, we're actually going to work on the surface of the wall. So the wall that I have pre- highlighted right there, we need to work on that surface, rather than a Floor Plan view. Now I could work directly in 3D, but it's actually going to be a lot more convenient to work in Elevation.
So this is the West elevation, and I'll zoom in on the wall in question. So let's go ahead and start an Extrusion roof. To get there, we need to use the dropdown portion of the Roof button and then do Roof by Extrusion. And the first thing that Revit will say is, well, it'll recognize that we are not working in a floor plan anymore and so it will say, well, you need to do a sketch. This is a sketch-based object.
What plane do you want to do your sketching in? Because remember, they are just two-dimensional. So they just work on 2D planes. So we need to indicate a plane somewhere that we want to do our sketching. Now, if we had a plane predefined, we could choose off the list, but there are no choices there so that's not going to work. So why don't we just go with what it's offering us here and choose Pick a plane. When you do that, you can move your mouse around onscreen, and you'll see how it will highlight pretty much any geometry. And what I want to do is just highlight that wall right there.
So basically I'm just telling Revit, I'm going to work on that surface of that wall. Now, the next question it'll say, all right, great. I got that. That's the surface you want to draw on, but what about the height of the roof? What level should I associate it with? And it automatically suggests your top level, and in this particular project there is only Level 1 and Level 2. So that ought to do the trick. I'll go ahead and click OK. So next, I'm in Sketch mode. So again, everything grays out, and unlike our Footprint roof that we saw in the Adding Roofs movie, we don't have any Pick Walls in this case, because we're not working in Plan view, we're doing an extrusion.
So we just draw the shape. Now, we can draw any shape we like. Let's have a little fun with this. And let's let this also be our first time that we actually look at an arc in Revit. Drawing arcs works pretty the same way, no matter what tool we're working in, so we're doing it here in the context of a roof, but you can use the same technique to draw any kind of arc shapes. So basically what you do is you click anywhere for your starting point of your arc, and then anywhere for your ending point of your arc. And then you can see the arc will appear, and your next click is determining essentially the radius. So it's somewhere along the curvature of the arc itself and you pick a point, and that gives you the radius.
Now, you could stop here and just do that single curve, or we could go in and create a second curve. And notice when you do, Revit will even look for things like tangential relationships and so on. You could switch to Lines, and you could draw additional shapes, starting at that end point, maybe going out horizontal, and whatever you want to do. So just to show you that it doesn't have to be just one shape; it can actually be multiple shapes. The thing that's very different about this sketch versus either the floor sketch or the footprint roof sketch that we've looked at previously is that this sketch is not a close sketch.
Do not come and draw it around and make the total form. That will actually generate an error. So in this case you want to leave it open-ended like it is now. And when I click Finish, the reason for that is, you see how the thickness gets applied anyway? That's because in this case I'm using the Generic 12'' roof. And so the 12 inches gets determined by the thickness of the roof material. That's why we didn't need to sketch that. Now, it looks a little odd here what happened, and it's a little easier to understand in 3D view. I'm not really sure why Revit always does this, but it always goes the depth of your building.
It just sort of has to assume something, so rather than ask us another question, they just make an assumption. And in my opinion, they always assume poorly, because I always have to come over here and select this and make adjustments. Now, I can do this manually with these little control handles at the end. I can type in numbers, make that 55 feet. I can pull this one all the way out here, make that 10 feet. I guess that's not a good value.
Let me spin this around. If I can get it to a good angle, what I can show you is this may actually be the design you want where it sits away from the building, maybe it's held up by some structure, but if you wanted to actually attach the building, we can use our Align tool for that. So I'm going to go to Align, and what's really neat about Align is it actually works here in 3D. So I'm going to click the face of the wall, and then you see how it'll actually let me highlight the face of the roof object.
And then it will just go ahead and stretch that for me. So instead of my struggling with the grips there, the Align will do a much better job. So there you have it: That's an Extrusion roof. You can use it for any similar type shape: barrel vaults or undulating forms like this, and simple sketch, and you're good to go.
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