Hi, new beekeeper here. I have a flow hybrid, installed bees in the brood box about 3 weeks ago. Things are going great and the box is about 50% built out, so I’m preparing for the next phase. Since I started preparing, I’ve decided I need a second brood box because it’s frigid here in the winter. I bought an 8 frame box that will fit nicely with the flow setup.
My question, can I add the second brood box below the first rather than on top?
I want to keep the flow brood box and super together, the only reason being we decorated the outside and it looks awesome, a box between just wouldn’t be the same.
I’ve read some things that say naturally bees build our top to bottom. But I don’t want to make things more complicated when I add the super to the top in a month or so.
Any advice is much appreciated!
Yes you can. No problem at all. Wait until the first box is over 80% full before you do it though. 
Correct, but they also consume their stores from the bottom to the top. While wintering they will eat up everything in the bottom brood box and move to the upper one. While the weather is not warm enough in springtime, the queen will continue to lay eggs in the upper box. It is warmer there. Eventually, she will move down, but at the first stage of the spring colony growth, it will limit the quantity of brood a colony may produce. And this limits the amount of honey they may collect. This becomes particularly important in areas where nectar flow happens early and it is short. To mitigate the issue, beekeepers rotate brood boxes in spring. The empty bottom brood box goes up, becomes a warmer place and the queen moves up to continue to lay there.
Another thing that may happen to the empty bottom brood box is to become pollen-bound. If the colony has not moved down yet and there is plenty of pollen available, they may stuff the whole box with it. On it is own it is not a bad thing, but it limits room for brood rearing again with the same consequence. An additional problem is when a colony does not have enough room to expand, it provokes swarming instinct.
Is it possible to decorate boxes a way it does not matter which brood is on top?