Adding Roof Geometry with Slope Calculations: Step-by-Step Tutorial

In this video, we are going to add our roof geometry. In order to do that, we need to see our roof geometry.

We have some geometry to pull from. Let's go to our Layer dropdown, and let's turn on our A-ROOF layer. There we go.

Now we can see our roof geometry. Remember, our slope established that the roof slides from the ridge here down to the left, and from the ridge here down to the right. If we take a look at our Roof Plan handout, we can see that the slope is 4:12.

That means it's a rise of 4 for a run of 12. That's 4 inches and 12 inches, or 4 feet and 12 feet. Also, if we look at the handout, we see that this datum here is called the Top of Plate.

What that means is that the structure of our walls ends at this line, and that is where the roof rafters would sit. So to combine all of this information, we need to know that this point right here—where my wall geometry lines up with that Top of Plate geometry—is where the bottom of our rafters will be. The rafters in this case are 3.5 inches, as they are two-by-fours.

So let's start by drawing our bottom line of that two-by-four, and it's going to come up in this direction here. Okay, so let's get going. I'll go Line, and in this case, our first point will be here, and our second point will be a relative coordinate.

We do not know the angle, and we do not know the point of this coordinate absolutely from where we just chose. We need to use a relative coordinate. So I'll type @12',4', and that's because I'm moving in the positive direction in X, and I'll move up, which is the positive direction in Y. Okay, I'll hit ENTER, Enter to say that I'm done, and there we go.

That's our first line of this roof. Now, 3.5 inches is our width of the two-by-four, so let's make that offset first. Offset, 3.5, Enter. I'll go up and click. Enter to say that I'm done.

That's the first part of our roof geometry. But then on top of that, there's probably about an inch of underlayment and roofing material—specifically, our composition shingles. So let's offset one more time a distance of 1, Enter. I'll click here and go up and click. Enter to say that I'm done.

Our two-by-four is not going to be visible on this drawing. It's actually hidden behind our two-by-six fascia board. So I can grab those two lines that represent our two-by-four and hit Delete.

This is the only line we need—the top of our roofing material. But you can see on the handout that we have a two-by-six fascia, and the two-by-six in nominal geometry is 5.5 inches wide. Now we need to offset from this point back down 5.5 inches.

Offset, 5.5, Enter. I'll grab this point and go down and click. Enter to say that I'm done. Now, I'm not going to clean up any more of that geometry.

Instead, we'll repeat that process on this side, and then we can clean it up together. Okay, let's turn off Ortho, and let's do that same process here. So I'll go Line, clicking this endpoint.

This time, I'm going in this direction. It's still a relative coordinate, but this time it's @-12',4'. We're going in the negative X and the positive Y. Enter. Then Escape, Escape, Escape.

Here, the offset is going up 3.5, and then 1. So our offset distance is 4.5. Enter. Here to here. Enter to lock it in.

Go back in one more time. Enter, 5.5, Enter. From this top line, back down and click. Enter to say that I'm done. Now this line right here we don't need anymore, so we can delete.

There we go. That's the outline of our fascia board. Let's clean it up a little bit.

At the top, that's a fairly easy solution. We just need some fillets. But how do we clean up our sides here and here? Well, we can see our geometry up above.

Here is where the roof goes—it's 1 foot away from the wall—and here. So let's draw some rays down so that we can use them for our geometry.

I'll draw a Ray here and here. I have a Perpendicular Snap, but I'll turn on Ortho. Clicking down. Enter. Enter to go back in.

This Endpoint—down and click. Enter to say that I'm done. Now two Rays have come down, and I can Snap or Trim or Fillet to that geometry. I'll turn off Ortho and Control + S to save.

Okay, so let's get this workflow done. I'm going to use the Fillet command for all of these connections. So follow along with me.

Fillet, and then Multiple, M, Enter. I'm going to click this line and then this line. That's cleaned up the point right there.

Then the top two—here and here. That's cleaned up both of these points now. Now I'm going to click this line and the bottom of my Ray.

And then I'll click this line and the top of my Ray to create a plumb cut. And then this line and the bottom. And then this line and the top.

Again, creating a plumb cut. Now, on the handout, you can see that we use a square cut—not a plumb cut. So while we used that geometry to clean up these lines, I can now delete these two plumb cut geometry lines, and we need to add in square cuts.

If we go to our Object Snaps, we can see Perpendicular is still on. So I can come in here with a new Line, draw from this Endpoint here to the Perpendicular here. Click. Enter to say that I'm done.

And I'll come over here and do the same thing—from this Endpoint to the Perpendicular here. Enter to say that I'm done.

Now we can Fillet or Trim these back together. In this case, I'll just use Fillet. Fillet—here to there.

And Fillet—here to there. Before we go away, there's one more small Trim that we can do. If we zoom way in, we see this yellow line crosses.

Let's go ahead and Trim that out on this side. Enter to say that I'm done. And pan over, go back to Trim, and Trim it out on this side.

Enter to say that I'm done. All right, I'll do a Zoom Extents and Control + S to save. In the next video, we are going to add our UCSs (User Coordinate Systems) and our named views.

We can start to put our geometry on our other views.