Adding Drywall to Part of an Exterior Wall

Reference Number: KB-00370
Last Modified: July 19, 2021

The information in this article applies to:



My latest project involves converting an attached garage into a living area with cathedral ceiling, and part of an existing exterior wall is showing siding in the interior of the addition area rather than sheetrock.

How can I create a single wall that has sheetrock where it is serves as an interior wall, and siding where it serves as an exterior wall?


In some situations, a single wall may need to serve as both an exterior wall with sheathing and siding materials and also an interior wall with sheetrock.

A classic example of this is where a bump-out or addition meets the gable wall of a taller structure. The roof over the addition will butt against the taller gable wall, and the gable wall will require siding above the roof and sheetrock below it.

This condition can be easily achieved using the Lower Wall Type if Split by Butting Roof option in the Wall Specification dialog.

To use lower wall type if split by butting roof

  1. Open the plan in which you need a wall that is partially interior and partially exterior.

  • In this example, a simple rectangular structure with a small addition is used.

  • The wall that needs to be partly interior and partly exterior is shown in brown.

  • Select 3D> Create Orthographic View> Backclipped Cross Section from the menu, then click in front of the wall that you need to edit and drag a short camera arrow beginning in the one-story area and ending on the other side of the wall, in the two-story area.

  • In the cross section view, click the Select Objects tool, then click on the wall that has siding where it is not needed.

  • Look at the lower left corner of the program window, in the Status Bar. 

    • If it says "Exterior Room", click the Select Next Object edit button or press the Tab key on your keyboard.

    • It should now say "Polyline produced by 3D wall editor".

  • With the wall now selected, click the Open Object edit button. On the Roof panel of the Wall Specification dialog:

    • Check the box beside Lower wall type if split by butting roof.

    • Select an appropriate wall type for the lower wall type from the drop-down list. In this example, "Interior-6" is used.

    • Click OK close the dialog and apply your change.

  • The wall will now have two parts - an upper part with siding and a lower part with sheetrock.

    • You can use the wall's edit handles to modify its shape if need be.

    • If you click the wall's Open Object edit button and go to the Wall Types panel in the Wall Specification dialog, you will find that the wall has been automatically specified as a Pony Wall.

  • If there is a wall above the selected wall with this same condition, simply select it and repeat the same steps.