[victory1504]

I agree Mike. You would really have to crowd them to get them to build comb below the brood nest. A good, and widely used trick is to pull frames # 1 & 10 ( or maybe 2 & 9 ) from the full hive body and put them in the 5 & 6 position in the new, empty super above ( or possibly the 4 & 6 position ). This will tend to "bate and bridge" them upward.
Some of us, ( like me ) believe in reversing the brood chamber under certain conditions. This should only be done when the colony is strong and the weather is warm. Over time ( probably several months ) they will fill-out the upper super and gradually move into it as the primary brood nest.
When you check the lower ( old ) super in August chances are it will be mostly empty comb ( ripe for the SHB ). If you reverse the supers the brood nest will move up once again into the partially vacant combs.
Reversing the brood nest is primarily useful for swarm prevention, to reclaim the abandoned comb on the bottom. Swarming usually cannot be prevented by reversing once they begin building swarm cells.

 

[victory1504]

As their brood operation moves up into the upper deep super, they will gradually use the lower hive body less. Chances are you will find lots of empty comb in late summer, especially as brood rearing slows down. In my area August is very slow ( no honeyflow ).
If you put foundation on them when there is no honeyflow, they just "frost" it, chew holes in it, track it up, and generally damage it. THEY WILL NOT DRAW COMB with no honeyflow ! So why waste your foundation !
It makes more sense to make them use that vacant comb in the bottom brood chamber by putting it on top ( reversing ).

By the way, you have my WRITTEN permission to examine the bottom brood chamber as you see fit. Monthly sounds about right.