Animation Render Result

Blender Cycles, 2.79b

I’m attaching a pic of the animation render result, which is not what I want and has totally baffled me, and what appears in the ‘display render preview mode’, which is what I’m after. It’s like the walls disappear. I’ve done some amateur ! animations before, and never run into this.

The windows are glass and the background is a tall glass tower city HDRI. The floor and window sills are textured. I’ve tried turning up the roughness on the walls to 1.0, but no change. Does anyone have any thoughts on what’s gone wrong?


Here’s the animation rendered result. Somehow it didn’t end up on the original post.

And here’s how it’s suppose to appear