Poop board as a roost

[feathermaid]

How much head room above the Roosting Board do they need and is the 2 x 4 flat on the 3-1/2" way or on edge the 1-1/2" edge?

A little late answering your question...
Chickens will need at least 12-15" above the bar to fly up to the roost without bonking their head on the ceiling. But you may need even more space above for higher open ventilation because you don't want a cold draft blowing directly on them while they sleep... unless you have the draft-free vents. Not much of a concern in warmer temperatures.
I prefer 2x4 roosts with the wider side facing up, just to give them more walking space to get settled. Also if temperatures are freezing, the flat bar lets their feet stay warm under their bellies instead of being exposed as they would be wrapped around a skinny bar.

 

[Cornbread49]

A little late answering your question...
Chickens will need at least 12-15" above the bar to fly up to the roost without bonking their head on the ceiling. But you may need even more space above for higher open ventilation because you don't want a cold draft blowing directly on them while they sleep... unless you have the draft-free vents. Not much of a concern in warmer temperatures.
I prefer 2x4 roosts with the wider side facing up, just to give them more walking space to get settled. Also if temperatures are freezing, the flat bar lets their feet stay warm under their bellies instead of being exposed as they would be wrapped around a skinny bar.

Thanks