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Michael Wilson/3 min read

Adding Slope to a Flat Roof: Establishing Ridge Lines and Low Points

Roof Slope Setup

1

Add Slope Arrows

While editing the roof sketch, draw slope arrows from low to high.

2

Set Slope Values

Properties → set head/tail elevations or slope percentage.

3

Define Ridge Lines

Where slope arrows meet defines the ridge — adjust until correct.

4

Place Drains at Low Points

Add roof drain families at the lowest elevations to handle runoff.

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Now that we have the flat roof drawn, what we're going to do is we're going to go ahead and add our ridge lines and our low points so that we can establish the slope on the roof.

Now that we have the flat roof drawn, what we're going to do is we're going to go ahead and add our ridge lines and our low points so that we can establish the slope on the roof. To do this, we need to select our roof first. And I use the Tab method here, but always remember, you can always go in with the crossing, use Filter, and then only select roofs to select the roof as well.

Now, with the roof selected, and it's set to be flat, meaning we didn't assign any slope to the edges, we have these shape editing tools in the modify roofs contextual tab. The first thing I want to do is I'm just going to add my ridge lines, which will be at grid line B and grid line 3. And I'm going to do that with this Add Split Line option. So I'm going to find the midpoint here, because that's what this is.

And I'll just bring it all the way down until it hits the midpoint at the edge of the roof there. And you can kind of see it's that blue dashed line that we're hitting. So that's my first ridge line.

And I'll do the same thing to establish my second ridge line. The next thing I want to do is I'm going to establish the height of this ridge line. And it's going to be eight inches above our zero point, which is our drain locations here.

So I'm going to go to Modify Sub Elements. And what I can do is I can use a window to select all these points. And you can see that they're all selected here.

What I can do is in the Options bar, I can go ahead and I can add eight inches to that value. And it'll move all of these guys up eight inches. The next step here is we're going to add these low points.

So to add our low points, we can go in and we can select the Add Point option, which will allow me to add a low point on the roof. And to do this, I'm going to go ahead and I'm going to find that midpoint that's going through so that we have it set exactly in the middle there. And then I can use that Modify Sub Elements again by selecting these points and setting them to zero.

So you notice as I'm adding that in, it's going to go in and it's actually going to add the valley lines in for me. If we were to hit escape and go into our 3D view, you can now see that we have our roof sloping at these locations down to those low points. And that's how we can add slope to the roof by using a flat roof method.