I don't think you should have a problem with them jumping up to get on an 18" high roost, as adults. They can jump from there to the 36" high roost. One of mine continued up, to get in the rafters. When they are younger and smaller, though, they might have a little trouble with that. The idea of giving them a step, or a ramp, is a good suggestion.
Are you going to have a big service door at each end for cleaning and just reach inside? Are there going to be any other openings?
I know that ventilation vs draft can be confusing sometimes. Please don't be offended if I am telling you things you already know. I'm just starting with the basics and going from there. If anything helps you, swell, if not, just ignore it.
Ventilation is when air comes in one opening, flows through the coop and goes out another opening. What you don't want to do, is have a chicken roosting in the path of that air, particularly in the wintertime. That would be placing them in a draft. In the winter, that will chill them even further, when they are already in a cold coop. Just like people can get frostbite faster, when their skin is open to the elements in windier conditions. That's why they talk about wind chill in the winter weather reports. Now, in hot weather, you don't need to worry as much about drafts when they are roosting. Just like with people. A light breeze when it's 95 degrees and humid is a relief for us. When it's -15, not so much.
As far as placement of openings, there are two main ways air moves in a coop. One is to blow in one opening and out another, because of wind. The other is when warmer air rises and cooler air sinks. For roost placement, you want to look at the places air will be coming in, the places it will be going out and not put your chickens in the path of that air flow, to avoid placing them in a draft. Openings at the very tops of the walls do the best job of venting hot air. Also adding an opening at the bottom will allow more of a flow through the entire coop.
As for the right balance in the amount of ventilation, these are the things I think about. Fresh air brings in oxygen and lets carbon dioxide leave. The air flow from ventilation lets out excess humidity. It lets out excess heat. Those are the good things it does in a coop. Not enough ventilation and you can have overheated chickens and mold growing on the walls. Some say you can also have more frostbite in the winter, but our winter air is extremely dry, so I have no experience with that. Too much ventilation in severe winter weather can let too much heat out and make the coop colder than it needs to be. In the winter, a draft can blow on the chickens and chill them more or also add to frostbite. You don't want a winter coop in a severely cold climate to be no better than roosting in a tree.
For my climate, I need some ventilation year round and a lot in the summer, when it's very hot and humid. So, I build coops that are like our houses, with openings that can be closed in the winter and opened in the summer. For a coop, these can be actual glass windows or they can just be openings that are lined with hardware cloth. The air blocking portion can be a piece of plywood, instead of a pane of glass. They can be hinged and work like shutters, hang by a chain or rope and be adjustable or only be used seasonally, like the old storm windows.
One trick I have when designing the openings for a larger coop, is to think about how big I'd want them to be if I had to sit in a chair in there all day, during the hottest days of summer. For a smaller coop, I just scale it down. It seems to help. I think of how hot closed up storage sheds, closed up garages or a parked car with the windows up can be, compared to a house with a light breeze coming in a window or a screened in porch, in hot weather.
I hope this helps a little.
Are you going to have a big service door at each end for cleaning and just reach inside? Are there going to be any other openings?
I know that ventilation vs draft can be confusing sometimes. Please don't be offended if I am telling you things you already know. I'm just starting with the basics and going from there. If anything helps you, swell, if not, just ignore it.
Ventilation is when air comes in one opening, flows through the coop and goes out another opening. What you don't want to do, is have a chicken roosting in the path of that air, particularly in the wintertime. That would be placing them in a draft. In the winter, that will chill them even further, when they are already in a cold coop. Just like people can get frostbite faster, when their skin is open to the elements in windier conditions. That's why they talk about wind chill in the winter weather reports. Now, in hot weather, you don't need to worry as much about drafts when they are roosting. Just like with people. A light breeze when it's 95 degrees and humid is a relief for us. When it's -15, not so much.
As far as placement of openings, there are two main ways air moves in a coop. One is to blow in one opening and out another, because of wind. The other is when warmer air rises and cooler air sinks. For roost placement, you want to look at the places air will be coming in, the places it will be going out and not put your chickens in the path of that air flow, to avoid placing them in a draft. Openings at the very tops of the walls do the best job of venting hot air. Also adding an opening at the bottom will allow more of a flow through the entire coop.
As for the right balance in the amount of ventilation, these are the things I think about. Fresh air brings in oxygen and lets carbon dioxide leave. The air flow from ventilation lets out excess humidity. It lets out excess heat. Those are the good things it does in a coop. Not enough ventilation and you can have overheated chickens and mold growing on the walls. Some say you can also have more frostbite in the winter, but our winter air is extremely dry, so I have no experience with that. Too much ventilation in severe winter weather can let too much heat out and make the coop colder than it needs to be. In the winter, a draft can blow on the chickens and chill them more or also add to frostbite. You don't want a winter coop in a severely cold climate to be no better than roosting in a tree.
For my climate, I need some ventilation year round and a lot in the summer, when it's very hot and humid. So, I build coops that are like our houses, with openings that can be closed in the winter and opened in the summer. For a coop, these can be actual glass windows or they can just be openings that are lined with hardware cloth. The air blocking portion can be a piece of plywood, instead of a pane of glass. They can be hinged and work like shutters, hang by a chain or rope and be adjustable or only be used seasonally, like the old storm windows.
One trick I have when designing the openings for a larger coop, is to think about how big I'd want them to be if I had to sit in a chair in there all day, during the hottest days of summer. For a smaller coop, I just scale it down. It seems to help. I think of how hot closed up storage sheds, closed up garages or a parked car with the windows up can be, compared to a house with a light breeze coming in a window or a screened in porch, in hot weather.
I hope this helps a little.
