Black Spots Inflicting Render

Hey! I’m very new to Blender, I just started learning yesterday from the Noob to Pro book in fact. I’m sorry if the following question seems stupid.

The render that you see above is plagued by those black spots. I have no idea where they came from. Some searches brought up Non Manifold points which are indeed present since I was able to select them. But I have no idea how to fix them. I tried recalculating the normals. Could someone please explain?

Also, how did I manage to do this? Anyway to prevent it from happening again?

Thank you. :slight_smile:


house.blend (579 KB)

You have duplicated faces overlapping each other where you have those dark speck, remove one of them

It worked! Thank you so much. Is there any way to detect that there are multiple duplicate faces anywhere, other than Remove Doubles and manually checking? I see that the face centres is a possible way to detect them.