If you use the Place Timber Joists at Spacing tool, the joists are automatically rotated 90 degrees, which is at a flat position for the member. Instead of the joist sitting, e.g., 10" high x 2" wide, it is placed 10" wide x 2" high. The Place Timber Plate tool has an option where you can rotate the beams at placement to 0 degrees. By default, the rotation is set to 90. The problem is that if you use the Place Timber Joists at Spacing tool you can't keep the rotation on 0 degrees because it automatically changes back to 90. Where can you modify the rotation of the timber members?
You can modify the framing member rotation from the Dataset Explorer Part Editor. Open Dataset Explorer Part Editor.Choose the WoodJoists_Floor Part or any Part that you are using under the Framing Family to have a default rotation value. You need to right click on the column header to choose from a list of other hidden Part attributes that will display in the Part Editor. Choose Rotation. In this case you should change the rotation from the default 90 degrees value to 0 degrees. Then Commit the change and use the Place Timber Joists at Spacing tool to place the desired number of joists between a given area. Note that now all the joists will come in rotated.