Two Faces should be just one - Best way to fix this?

I inherited a home design file from a designer who had first made the room ceiling heights all 9 feet tall. He later moved the ceiling up another 4 feet, so all the walls are now 13 foot tall. Whatever method he used to increase the height, caused the walls to be made up from two distinct Faces. A 9 foot Face below with a 4 foot Face above it.

My goal is to convert all walls to be single Faces. When I try to merge them, I get an error of course, because they are not Solids. I’m hoping I can do this without having to punch new holes and rebuild the windows. Can anyone suggest the best way to accomplish this?

I also have a second issue. For the specific wall in this screenshot, the upper Face portion has a Material Front called ‘Fir Framing 2’, while the lower portion has a Material Front called ‘Drywall’. At some point I may have accidentally deleted the Drywall Face. How can I get it back so that the entire wall has a Drywall Face Material?

Without seeing your model, as a guess if the faces are coplaner then you should be able to simply delete the edge joining them. But the construction of the model may be very different.

Thank you for the suggestion. I just attempted to delete an edge from the upper face, but the two faces did not become one. Instead, the Drywall material was deleted from the upper face. (Which explains how I must have inadvertently lost it from the one wall at some earlier point).

I’ve now uploaded the model and do very much appreciate your advice. (Just by the way, this model was initially sent to me as a Chief Architect .3ds file).

Thank you.

House Model.skp (13.4 MB)