Mastering Roof Plan Geometry Using Layers, Offsets, and 45-Degree Logic

Let's jump right in and work on our roof plan geometry. The first thing we'll see is that our A-no-plot has this line. This line was the line we generated back when we were doing our A-wall masonry, the brick on the outside of our building.

We migrated this layer to the A-no-plot layer instead of deleting it so that we could use it in this workflow. But if you don't have this line, don't worry. You can just draw it again using the A-wall layer.

That's why I turned on A-wall. Just to remind us that this is the outside of our A-wall layer. And that is what needs to be represented on the A-roof outline layer, A-roof outline.

So I'm going to select this line that's currently on A-no-plot and migrate it to A-roof outline. That is all that needs to be done because it is the wall outline for our roof. We can see that we have a few other layers here.

A-roof dimensions, A-roof downspouts, A-roof gutter, A-roof outline, which we're just using, and A-roof vent. All of our other geometry for the roof itself is going to go on A-roof. So I'm going to select A-roof as our current layer.

And this is the only geometry that needs to go on the A-roof outline. In this case, I don't need to see A-wall anymore. Again, I was using it as the example for where the no-plot line was representing.

And for now, I don't need the no-plot layer either. So I'll turn both of those back off. And this is, believe it or not, the only geometry we're going to need as we draw our roof plan.

The first thing we want to see on the handout is that we have a typical overhang for this building. And that typical overhang is two feet. So right away, I know a lot of my lines are going to be two feet away from this wall.

And we could explode this like we did for our other geometry, our wall offsets at the beginning. But in this case, I want to offset it two feet and then explode it and do some cleanup. A different workflow for us to see a slightly different order of operations.

So let's go explode. So let's go offset. Two feet.

Enter. I'll pick this line and go to the outside. Click.

And we know it's going to the outside because we can see the fireplace, for instance, get much wider. If you went in, you wouldn't see that fireplace at all. Let's select that outer line and migrate it to a roof.

Now, we can see that there are a lot of incorrect pieces of geometry. Here on the back, we have a covered porch. And here at the front walkway, we see that this roof actually aligns with this roof.

So to start, let's select this and hit X, Enter, to explode our geometry. All we need to do here is fillet this line and this line. And we can get rid of all of the rest of this geometry.

So I'll go fillet, R, Enter, 0, Enter. This line and this line. And I can use a selection window.

I'll get above the geometry here on the left. Come across. And I'll only pick this geometry.

Hit Delete. And also down here at the front, we need to stretch this geometry down to align with this geometry. So I'm going to use the Stretch tool.

S, Enter for stretch. I'm going to select all of these lines. Enter.

And I'll pick this endpoint to start. Now, you can do a couple of things here. You can use TRA tracking.

You can use a – you can see I have my running object snaps on, my running tracking so I can track across. In this case, I want to use another tool on the right-click pop filter menu. So I'm going to shift-right-click and select my point filter of the dot Y. Now, what this means is it's going to match the Y value of the next point I click, the Y value, of course, being up and down.

So I'm going to go shift-right-click, point filter dot Y. I'm going to pick this endpoint here. And then you can see I'm limited to going in this exact Y direction. So all I need to show is a vertical, either up or down, because the Y coordinate is locked.

And click. And that will place this line and this line perfectly in alignment, collinear. I'll hit Escape, Escape.

Zoom extends and Control-S to save. Before we go any further, we can join this geometry back together. So I'll use my selection window, select both of these lines, J, Enter.

And similar to the last time we tried this, you'll see 14 objects have been converted into one polyline, one object discarded. This was the object that was discarded. It was already a polyline.

But our other lines that create the outside of our roof, with that two-foot offset typical, has been created as a single polyline. So once again, Zoom Extends, Control-S to save. You'll notice that our Zoom Extends is no longer getting close to the geometry.

And that's because the A no-plot layer is hidden but not frozen. Hidden geometry still is rendered in AutoCAD's brain. So things like Zoom Extends and other operations will include A no-plot.

If we freeze A no-plot and Zoom Extends, you will see we zoom in a little bit more. We're still not going all the way. There's other layers on, like the A dims layer, for instance, the dimensions layer.

So there's other objects in geometry that are still loaded in the background. But just understand that there's a slight difference between a frozen layer and a hidden layer when it comes to especially zooming in how AutoCAD is rendering that geometry in the background. So I'll unfreeze A no-plot.

Zoom Extends will zoom out just a bit. This doesn't bother me, but it might bother you once we eventually bring in the no-plot for this roof plan geometry. This roof plan is representing a gable roof, which is fairly easy to draw but much harder to conceptualize.

So let's take a look at our roof plan handout and see what these diagonal lines mean. I think the easiest side to visualize is actually either the front of the garage or this wall and this portion of the roof. You can see that a 45-degree angle is coming out from this corner and a 45-degree angle is coming out from this corner.

That means that where the two roof slopes meet, they are the same slope. By just looking at a 2D roof plan, you would never be able to tell what the slope is as long as the two roof slopes are identical. The roof could be at a 5-12, which we can see on our handout.

The slope arrows are telling us, but it could also be at a 6-12 or even a 12-12, which is a 45-degree slope. In this case, the 45-degree lines simply represent that two sloped faces are meeting. And when two sloped faces of the same slope meet, they generate a line that in this case is 45 degrees because it's in between a 90-degree angle.

When you see a horizontal line, like at the top of those two 45-degree lines, or you see a vertical line running here above the garage, those lines represent where two roof slopes meet, but at their tops. So this creates that classic roof shape, either gable or hip roofs. At the top, you have your peak.

So the 45-degree lines are where any two roof slopes meet, which is at every 90-degree angle in our roof. And the horizontal line or vertical lines are where two of the opposing slopes, sloping down to the right, sloping down to the left, they meet at the top. So in this case, what I want to do is check my polar tracking.

Make sure it's set to 45 degrees and that it's turned on. And we're going to use the line tool. And I'm going to start in this corner, click, and I don't want to bring this all the way down.

I'll go right about here, click, enter to say I'm done. And again, I'll choose the line tool and I'll do the same. The line lengths don't need to meet.

They don't need to be the same. I just want to visualize where these are going to go. So I'll select this line first, hit copy.

And anywhere there's a 90-degree angle that is facing in this direction, I'll paste. It's these three to start. And I'll do the same down here.

I'll click this, copy. This is here, here, here, and here. Enter to say I'm done.

Now I can actually use the same line. I'll just use this endpoint as my copy to represent any geometry drawn in the other direction. Here, here, here.

Enter to say I'm done. I can do the same thing with this line. I'll use this top endpoint, copy.

This is this one all the way over here, here, and here. There will be some additional lines we need to draw. But we won't be able to draw them until we start to trim or fillet these lines together.

So I'm going to go fillet, starting with this triangle, 1 and 2. And we can see those come to a nice point. Now I can't fillet to this line yet because I need to draw a horizontal line. So I'll go line, out to the right.

Click enter to say I'm done. And again, I don't need the distance because I'm about to use fillet. So here I'll go fillet, here to here.

And now I can either copy this 45-degree line or simply draw a new one. I'll do that. L, enter for line.

Enter to say I'm done. Once again, I'll fillet, here to here. And I'll draw a new horizontal line.

L, enter. Enter to say I'm done. This one is going to come all the way down, so I'll go fillet, here to here.

Coming down with a diagonal line this time, click enter to say I'm done. Fillet, here to here. You can see on the handout that this one is going to come down and then meet up with this line.

So I'll go line, here to here. Enter to say I'm done. Fillet.

And then these two meet at the front. Let's see where they meet up. I'll go fillet.

And let's see what happens when we try to extend this line. I'm going to hit the dropdown, choose extend, and click here. This line and this line miss by about an inch.

And so in this case, I'll hit Control-Z to undo. And we need the shortest little vertical line here. Enter to say I'm done.

In practice, this will probably not even be built. The framers will put it all together. But this is accurate.

There's a tiny vertical line here of about an inch. I can fillet that together. And then draw my diagonal line.

And these two should meet up exactly. So I'm going to start by drawing this diagonal and extend to see where it goes. And it does meet up right at the top of that very small vertical line.

This would be a great opportunity for value engineering if you were working on this plan in the office. We are done with the majority of this roof. We just have this little bump out.

And we can see that this one is going to need a vertical line between this intersection. Shift-right-click intersection. And the shift-right-click intersection here.

Enter to say I'm done. And in this case, I can use trim with this line as my cutting edges. T, Enter for cutting edges.

Enter to say I'm done. One, two, three, four. Enter to say I'm done.

Zoom extents and Control-S to save. Drawing a roof plan like this is fairly simple in practice. Even if you don't know what the shape of the roof is going to be when you're done.

Start with 45-degree lines. Start with 45-degree lines wherever there are two slopes that meet at a right angle. And then draw a horizontal or vertical line when two slopes meet on opposing sides of the roof.

This shape would have been impossible for me to figure out with the actual lengths of each of these roof segments. I needed to use the logic of drawing that roof plan to find the exact shape of this roof. So zoom extents, Control-S to save.

And I'll see you in the next video.