The way to make this kind of stair in VWA is to re-think the winders—not as treads, but as platforms. Let's start the process with a default straight stair. In a blank VWA document, at an appropriate scale, select the Stair tool. Click in the drawing to insert the stair and click again to set the rotation. Choose the straight stair configuration and click OK:
The Stair Preferences dialog box displays. Set the overall height to 10'0", and then click the "Flights and Platforms" tab:
Click "Add After" and choose a straight flight. Click "Add Before" and choose an L Platform. Click “Add Before” and insert a second L platform. Click "Previous" and set the number of treads in the first flight to 7. Click “Apply.” The preview window in the dialog box displays a stair preview similar to the following:
Now we'll configure the first two winder platforms. Our stairs are 36" wide; so, remembering high school geometry class, we recall that the diagonal of the first platform’s square is 1.4142, so the diagonal side of our riser platform should be 36 * 1.4142, or 50.9112 inches. Armed with this number, we can proceed.
Click “Next” to highlight the first (lowest) of the L platforms and make the following entries:
Start Width: 3'0"
End Width: 50.9112
Length Side 1: 3'6"
Length Side 2: 0.0001"
Click "Apply" and the stair preview looks like this:
Click "Next" to highlight the remaining L platform and make the following entries:
Start Width: 50.9112
End Width: 3'0"
Length Side 1: 0.0001"
Length Side 2: 3'6"
Click “Apply.” Your screen should look like this, and, finally, it should be apparent where we're headed:
With the second platform highlighted, click "Add After" and choose an L platform again. It will have the same settings as the second L-platform. Now, click "Add Before" to add another L platform with the same parameters as the original L platform. What you should end up with looks like this:
Voila, a 45-degree, platform-winder stair that meets IRC code!
Here it is in 3D: