Thank you for the link!I am guessing in the DC area you wouldn't need to worry about cold harming them. The snap would need to get past -10 for any damage to occur. Maybe you could do wind baffling, since that can affect them negatively. Here is a good article for that.
https://www.backyardchickens.com/articles/repecka-illustrates-coop-ventilation.77659/
You basically want air moving around them, but not directly hitting them, especially where they sleep.
What breeds to you have btw? It looks like barred rock and autrolorp from the photo. Those guys shouldn't need any heat, only wind cover.
I have a Barred Rock and a Cream Legbar in one coop and a Welsummer and Delaware in the other.