@GhislaineDel You will be very pleased with a Woods' KD coop!
You will note in my build article that I used a traditional method of construction that has very few structural members; that style depends on the wall boards for wall integrity. If you use that method using T1-11 will not work unless significant modification is made to the framing described in the book. I suggest that attempting to modify is NOT the way to go.
The common method used by others on BYC uses current standards for wall construction which is vertical studs with horizontal plates on the bottom and double plates for the top. Given that approach, even with the studs 24" on centre, attaching T1-11 sheets to the frame will provide adequate strength to support the roof.
You do not need to use 4x4 posts; 2x4s, 1 stud with attached jack post (a shorter stud attached to a full height stud) is sufficient. However, the majority of snow load depends on the upper monitor frame NOT only the vertical posts. You will need to ensure that frame is beefy with multiple horizontal 2x4s at the top and bottom as all of the snow load is carried by these horizontals. In your shoes I would diagram your design and post it herein, you will get good feed back as to suitability from others who have build this way.
Further, the
walls do support snow loads as they are resting points for the roof sheeting on the outer edges. However, if you do a modern stud and plate on 24" OC the walls will be strong enough to carry the weight.
A few other points:
- The KD nomenclature signifies "Knock Down". You will note in my build article that the coop is built in panels that are then screwed together. Very useful if one wants to get rid of the coop or move it as it avoids a complete tear down. Using stud and plate negates this ability. Of course, for many this detail is irrelevant.
- If you have the room I suggest a 10'x16' coop. The only real difference is a marginal increase in materials cost; labour differences are immaterial. If you proceed with an 8'x12' USE THE WALL HEIGHT MEASUREMENTS USED BY THE 10'X12' as headroom matters when one is inside. Even using these heights the 4' difference in coop length considerably shortens the back section where one stands/works when inside. Also, the larger size provides greater side wall space which can be important if you start to place nest boxes on the side walls rather than under the drop boards.
- Chicken math is real, the extra size provides greater flexibility.
Feel free to reach out with questions as you proceed. Good luck!