Easy Stairs in SketchUp

As a carpenter, one of the most challenging things to plan out is stairs. Tricky math, figuring out the rise and run of each step and accounting for thicknesses of treads, risers and finished floor height are all opportunities for mistakes. In this tutorial, you’ll learn how to use SketchUp to plan out deck stairs. Watch the video or continue below.

Stair design pitfalls

The hardest part about building stairs is knowing how to plan out the stringers. Stringers are the structural members of the stairs that the treads and risers are fastened to. To build stringers, you need to cut out notches for the treads and risers, typically out of 2×12 pressure treated lumber.

To figure out how big the notches need to be, there are ideal measurements and building codes you can refer to. However, the most common mistake made when cutting stringers is incorrectly accounting for the thickness of the treads, risers or the finished floor thickness.

Ultimately, you want each step to be the same size; from the ground, all the way up to the top of the deck. In order for this to happen, you need to account for the thicknesses of various materials that you’ll be installing on the stringers. So the tricky part is that the dimensions you need to use for cutting the stringers are relative to the finish materials that will be installed on top of the stringers, not the stringers themselves. So this means you need to intentionally account for and subtract the finish material thicknesses to arrive at the stringer dimensions.

These are the most common pitfalls made when laying out stringers: (From personal experience) 😉

• Incorrect total rise – The total rise is the total vertical distance from the bottom landing to the top of the finished deck at the top of the stairs. A lot of times when you’re planning the stringers, you already have the deck framed out, but you might not have the decking installed yet. When measuring the total rise, you need to make sure you add the thickness of the decking material to your measurement. (For interior stairs, you also need to account for finished floor thickness at the top and the bottom of the stairs.)
• Forgetting about overhangs – If you are going to overhang the tread past the riser or stringer, you need to account for that overhang in your calculations so the risers are inset appropriately.
• No riser at top step – If you are installing risers on the stringers, most times you don’t need to install one at the top step because the rim joist acts as the top riser. If that’s the case, the top step run on the stringer should be shorter by one thickness of a riser.
• Bottom step riser height – The bottom riser height should be shorter than all the rest because the landing represents the top/finished surface of the tread. Once the treads are installed on the stringers, the riser height interval should be the same for each step, including the step from the ground/landing up to the first step. This will only happen if the stringer is shorter for the first step.

Easy stringer planning

SketchUp makes the job of planning stringers fool-proof. Instead of doing a bunch of mental math, you can create some very simple reference geometry that can easily scale to the finish dimensions of the stairs. This will allow you to work backward until you arrive at the final stringer dimensions.

The International Building Code requires a maximum 7 3/4″ riser height and minimum 10″ tread depth for each step. The actual riser height will be dictated by the total rise of the stairs, divided by the total number of steps. The tread depth has more flexibility, assuming you are not constrained on space in front of the stairs. When starting your stair layout, you can start with an ideal tread depth, or you can adjust the tread depth once you’ve calculated your riser height. Here are some good rules of thumb for getting an ideal riser and tread combo.

To create reference geometry for the stairs, follow these steps:

Before you begin modeling the stairs, you should have a surface representing the ground, as well as geometry representing the top surface of the deck.

1. To start creating reference geometry for the step, draw a rectangle using the RectangleR tool. (You can tap the left or right arrow key to lock axis if needed). Type in 7 3/4",10" ENTER to set the size. 7 3/4″ is the maximum riser height and 10″ is the minimum tread depth allowed by the International Building Code, so we will use that as a starting point, knowing we can scale as needed.
2. Double-click on the face of the rectangle to select, then press G to make a component. Name the component “Step”.
3. With the Step component selected, activate the MoveM tool. Click on the bottom corner of the step to start the move, tap Ctrl/Option to switch to “copy” mode, then click on the opposite corner of the first step to place a copy.
   Type in the number of copies you need, to make it just past the top of the deck, plus the letter X, then press ENTER. For example, type in 5x ENTER. (If you don’t get it right on the first try, just type in a different interval, and SketchUp will update the number of copies. You can always delete extra copies too if you’d rather do that.) Make sure you include the step that intersects with the top of the deck, even though you aren’t going to include that in the stringer, you still need to account for that step interval for reference.
4. With the Select tool, hold down Ctrl/Option key to add each step component to your selection. Right-click > Make group. This will make it easier for you to manipulate the steps as an assembly.
5. Finally, use the ScaleS tool to scale the step group down until you snap to the top of the finish decking.
6. Use the MoveM tool to align the top corner of the top step to the top front edge of the decking.

You now have an accurate interval for the height of each step. Instead of measuring the total rise then doing the math to figure out what each riser height needed to be, you just used the ScaleS tool to set the interval for you automatically. Easy!

If you want to change the tread depth, you’ll need to calculate the total run, which is the tread depth multiplied by the number of treads. With that number, use the ScaleS tool to stretch the width of the stairs, then type in the total run and press ENTER. For example, if you want an 11 3/4″ tread, and you have 4 treads, type in 47" ENTER. (11 3/4″ x 4 = 47″)

Building the stairs backwards

Now that you know the boundaries of where the finish materials need to be, you can start building the stairs backwards, until you arrive at where the stringers need to be.

You can jump inside of the same step component you’ve already made. You should isolate the guide lines into their own group before you start modeling inside of the component. You’ll likely need to make one or two of the components unique once you’ve got everything in place, but you can just keep everything as the same component definition for now.

TIP: To make it easier to distinguish the reference geometry, you might want to apply a semi-translucent material to the face of the rectangles and assign them to a layer with a dashed style.

Treads

Start by modeling one of the tread boards. You might have a single 2x for each tread, or you might have several boards that make up each tread. Inside of the step component, draw a board at the front edge of the step with the RectangleR tool, then extrude it with the Push/PullP tool. Snap to the dashed lines for reference. Triple-click the board, Right-click > Make Group. Remember, you don’t want to extend past the dashed lines, so extrude downwards to get the thickness of the board. Also, you may decide to use components instead, but I chose to use groups here because some of these tread boards will need to be customized. It’s up to you if you want to use components and Make Unique as needed.

Use the MoveM tool with the Ctrl/Option modifier to make several copies of the board to span the full depth of the tread.

One of the boards will be longer than needed. Don’t worry about that right now. We will go back and modify it after the risers are in place.

Risers

Draw a riser board using the RectangleR tool and Push/PullP tool, snapping to the dashed lines, and using the tread boards as reference.

Since the treads have a small overhang, use the MoveM tool to move the riser back by 1/2″.

To create an overhang on the sides of the stairs, use the Push/PullP tool to shrink the risers by 1/2″ on each side.

If you’ve done everything correctly so far, the very top step should be intersecting perfectly with the top of the deck and the front of the rim joist. If so, you can go ahead and delete that top step component now, since the deck itself will act as the top step.

To fix the rear tread board that is extending too deep past the risers, use the Push/PullP tool to correct its size. (Note: You’ll likely need to make the upper step component unique, since the board sits in front of the rim joist, and not under the riser like in the other steps.)

You’ll also notice in the picture above, moved the tread boards and adjusted them so that I don’t have single, tiny board at the back of each tread. Instead, the front and the back boards are ripped down equally.

Stringers

Now that the treads and risers are in position, confidently placed according to the dashed reference line, we can begin modeling the stringers. The stringer will be created by tracing the edges where the risers and treads attach to the stringer.

1. Draw a rectangle using the RectangleR tool. Type in 11 1/4", 6' ENTER. (The length is not too important since we’ll be “cutting” it to size once in position.) Draw the rectangle along the axes. Don’t try to draw it at an angle. We want to turn it into a component while aligned to the axes, then we’ll rotate it and position it into place, that way the component axes align with the geometry inside the component.
2. Use the Push/PullP tool to extrude the stringer 1 1/2″.
3. Triple-click with the Select tool > press G to Make Component.
4. Move and rotate the component into position so it is aligned to the top front edge of the deck.
5. Activate the RotateQ tool, click and drag from the front edge of the deck, and drag the mouse along the front edge to align the rotation axis with it. Click on the edge of the stringer to start the rotation, then snap to one of the front edge points of one of the treads. Use the MoveM tool to move the stringer into its final position.
6. Double-click into the Stringer component with the Select tool, then use the LineL tool to trace around the treads and risers. Use the Push/PullP tool to remove parts of the board.

You now have a perfect stringer! Copy it however many times you need to. I find this is the best way to plan and execute stringers, as it eliminates so much opportunity for human error. I hope you enjoyed this tutorial! Let me know now in the comments below if you have any questions.