I have a free standing, mostly enclosed 12x12 run in shed. We plan to attach an additional 12x12 on the side so both horses can have their own space without any drama. Currently, there is a small, open window on the side that will be sharing a wall with the other shed enclosure. The window is just big enough for a horse to comfortably fit his head through to look out.
My question: what is the best plan for the walls that divide the two enclosures? I have a fear of leaving the only window between them...I can just see scraped heads from jerking back when they mess with each other through it. I can remove the wall down to the kick boards, which would leave a dividing wall about 4 1/2 feet high (give or take a few inches). Is that tall enough? Just not sure how to give them space to socialize safely. I don't want to completely separate the two sides with a solid wall, because if I do, I'll have one standing inside comfortably and the other standing out in front rather than going inside like he's supposed to!
I have a 4 1/2 foot wall with a grill above separating my horses individual run-in areas. Similar to a regular stall wall design. Works well, good ventilation and socialization ability. My grills have bars 2.5" apart as I have foals as well.
I would just put a grate (like a piece of cattle panel) or even a piece of screen over the window. Open it would allow ventilation in the summer, closed, it would make the stalls cozier in the winter. I would not leave it uncovered with the chance of a head getting stuck in a quick retreat.
I would try a small opening metal screen (like deer fencing) in the window first to see if that's enough interaction for them. If one still stands outside then I would cut the wall as you described. My horses would still probably try to squeeze into one side together anyway. <sigh>
Oh just make it a half wall. It's not like the horses are in separate paddocks. They live in one paddock with each other. Just have a half wall between the two sides and keep it simple.
I also suggest you add shade tarps over the open sides to darken the interiors. It makes all the difference in the world for keeping flies out of the sheds. flies do not like DARK. I have shade tarps across all the barn doorways and the horses can sand in the shade nearly fly free. Well, one door has the tarp ties back a little as the Phoebes always build a nest inside the bar and need the ability to fly in and out. Love my Phoebes.
This is the type that I use now. You want maximum shade or sun blocking. This type is heavy duty and UV resistive so they last for years. Air however will move thru the mesh so the interior of the shelter doesn't heat up.
An interesting thing about stable flies is that after sunset they will be found on walls and ceilings. This is why you find fly "spots" which I suppose is fly excrement. Anyway, a great way to kill flies is to spray the walls of stalls and barns with a pesticide during the day. Flies will go to the walls as it is getting dark and pick up the pesticide and die. It really works!