empty coop /treating it

[the girls club]

All my chickens are gone now. Want to prepare the coop or new ones. Had 10 chickens were pecked each other in the backside area
and all died. Never figured t which on was doing it.. I felt really bad for them. Checked them for bugs. Could not find any. All I thought I saw was dirt.
I want to treat the coop before I put the new chickens in it.
Questions
1.How do I clean it and prepare it?
I will get ALL cobwebs out.
Plan on putting in new roost and nest and any walks they use to enter the coop ones outside and inside to the floor.
I have a concrete floor and about 6 inch concrete sides then wood for walls. The rest of the coop is all wood. it's a converted milk shed. The first time I had 6 chickens had NO problems. I cleaned the coop out before I got my second batch of 10 chickens. These last 10 chickens were peace full in the brooder. They were golden buffs and suppose to be docile. I put them in the coop at the proper age. As they grew older they began picking each other backside drawing blood. So I don't want that happening to the new ones I will get.
I don't know if the coop was to small for the 10. the coop is 10 by 14. So I want to clean the coop extreamly well this time. So what do I use between the cracks and crevises to kill anything that might be in the coop. I plan on getting 8 females this time. Any information will be greatly appreciated.

 

[JJSS89]

Treating with Sevin powder will kill the bugs.

That coop is up to industry standards but for backyard lifetime purposes, that coop is small. I wouldn't go with more than 4-6 hens

 

[the girls club]

Will Sevin powder hurt the chickens? Can I dust the chickens with it?If I'm correct the sevin powder gets into the skeleton of the bugs. So will it get into the chickens skeleton of the chicken? As you can tell I'm new to this dusting thing. Basically will Sevin powder hurt the chickens?
I plan on replacing All the wood that a chicken lands it's feet on. I plan on dusting everything. How do you put the powder between the top cracks of the inside roof and walls. I don't want to waste the powder. I would like to do a really good job of dusting.

 

[aart]

If you never had a confirmed insect pest problem, I wouldn't cover the coop in poison for no good reason.
Sevin will kill all insects (including bees and other pollinators) which is not necessarily a good thing.