Imported Blender Models Issue

When I import a model I created and saved in Blender into Unity, some of the faces appear invisible. I cannot figure out why, I have created two different models and both seem to have some of their faces appearing invisible. Here’s a few screenshots so you can better understand what I’m trying to explain.

Picture of Model from Behind Showing the Faces

Picture of Model from in-front of the Door Showing the Invisible Faces

You will often see posts about ‘normals’. The backside of the house has only one “side”, and it’s faced outwards, so when viewed from the front one does not see it at all. Go back in Blender and extrude the wall slightly in and use the Blender Flip Normal function on this new face. Search Google for more details if needed.