How does roof type affect humidity in the coop?

[Egghead_Jr]

It's physics. With proper slant the air is literally sucked in. The vacuum effect multiplies the rate of flow. You don't need huge vents. With low pitch the first foot or so of air along roof line is mixing opposed to a steep pitch where the fresh air is mostly inches from roof line zipping to the vent without as much mixture of coop moisture.

 

[aart]

It's physics. With proper slant the air is literally sucked in. The vacuum effect multiplies the rate of flow. You don't need huge vents. With low pitch the first foot or so of air along roof line is mixing opposed to a steep pitch where the fresh air is mostly inches from roof line zipping to the vent without as much mixture of coop moisture.

I can visualize this with eave and ridge vents...the differences with just gable vents and a low intake vents could be much different flows?

 

[aart]

@aart, Here in blue is what I would envision the gable roof would look like.

Much lower pitch than I had imagined.
Quick and dirty cross section area.

 

[Ridgerunner]

It can get complicated on how natural (no fans) air flow works. But there are two simple concepts, it's how they work together that gets complicated. If you have two separated vents and a wind is blowing across between them you get a stream of air. The friction between the air in that air stream and the air in the part that is calm will cause turbulence. Gentle turbulence can be good, it allows the good fresh air and the bad stale air to mix without creating a breeze blowing on the birds. That's one reason why I like at least two openings up high, whether they are the same level like the OP's gable vents or under the overhang of a single slanted roof. The energy for this comes from the wind blowing.

In calm weather you don't have wind energy, but you still have gravity. Warm air is lighter than cold air because the molecules are more active and are further apart. So warm air rises as long as there is colder air to replace it. Warm air holds more moisture than colder air. Chickens give off moisture through their warm breath and their warm poop. You might have a heated waterer. If your coop were on the ground the soil could act as a thermal mass in the really cold snaps and warm the air, but yours isn't. The sun can heat up a coop, especially a dark coop, when the sun is shining. For this to work you need a difference in temperatures, which often happens. It doesn't have to be a huge difference in temperatures to get some movement.

In summer I like a vent on the cool side of the coop, preferably low down. If the vent is on the hot (sunny) side of the coop there may not be a good difference in air temperature. It's the temperature difference of the air inside and out that gravity uses to cause air flow. In winter in cold climates you do not want the chickens in the air flow between vents if the wind id blowing so vents higher up can work. Gravity can still work with higher vents in winter because it's the difference in temperature of the air, not its elevation. But typically the more difference in elevation of the low spot and the high spot the more air movement. In your case the low spot is the coop floor.

This is mostly concerned with removing moisture from the coop, moisture being a big factor in frostbite. Another risk is that when poop breaks down it creates ammonia, a poisonous gas. Ammonia is lighter than air so gravity pushes it up. As long as you have an opening above the chickens' heads gravity will remove ammonia from your coop. Most of our coops are not that airtight but I still like an opening up high.

I don't know why your design is working as well as it is, but as long as they are not getting frostbite it seems to be working. If you see frostbite you probably need to cut some more holes in your coop. In my opinion I don't think the area under the roof is that critical, I'd think it is more the elevation of the vents, even if they are both at the same elevation. You are not trying to store moist air, you are trying to get rid of it.

Appearance can be a very important factor in coop design for some people's personal pleasure or to keep neighbors happy. I think we strive to be efficient but I try to not let the pursuit of perfection get in the way of good enough. But that's just me and my opinion, I'm sure others will settle for nothing less than perfection. In my opinion if you are happy with that design you can replicate it. But be aware that if you change anything, even where it is located on your property, you might get different results.

 

[gtaus]

Much lower pitch than I had imagined. Quick and dirty cross section area.
View attachment 1987045

Thanks @aart, the numbers seem to confirm my suspicion that the gambrel roof had more than 3X the volume of the gable roof I was considering. I had not considered the 12/12 pitch as some have mentioned.

 

[gtaus]

@Ridgerunner, many good points to consider. Thanks.

I know that changes in design might affect the performance of the coop's ventilation. I had considered making the gambrel roof into a loft for storage for such things as bags of leaves for the winter. But then I thought lowering the roof to 6 feet high in part of the coop might adversely affect the ventilation and increase the humidity.

 

[aart]

I know that changes in design might affect the performance of the coop's ventilation. I had considered making the gambrel roof into a loft for storage for such things as bags of leaves for the winter. But then I thought lowering the roof to 6 feet high in part of the coop might adversely affect the ventilation and increase the humidity.

Lowering the roof or filling the loft with stored items would more than likely affect current ventilation scenario.

Thinks the height of your coop is helping, have you ever put the hygrometer way up high inside the coop?

I believe gambrel roofs were designed for barns to increase loft storage capacity, probably for hay/straw. They also often had venting in eaves.

 

[Old-clucker-55]

you might be able to get away with using 1/2 of the upper part for storing some leaves.

 

[gtaus]

Thinks the height of your coop is helping, have you ever put the hygrometer way up high inside the coop?

I put my remote temp/humidity sensor at the same height as my chicken roost - so about 5 feet off the floor of the coop.

 

[gtaus]

you might be able to get away with using 1/2 of the upper part for storing some leaves.

That is what I was considering. Putting a loft covering about half the coop on the side opposite of where the chickens roost. That way, the mass of the air volume above their heads is still open.