Power washing is like hand scrubbing, only without the elbow grease. In fact, it might even work better! It will easily get into all the nooks and crannies and decorative details of your coop, blasting out dirt and those nasty green moss particles that grow on the roof. Power washers come in all shapes and sizes, but lets assume you're going to use a typical home power washer (not one of those industrial things...it'll blow holes right in your coop!) You're going to want to start with a warm dry day. It'll take forever to dry out if it's a rainy day and then you'll be putting the chickens back into a wet coop at night...bad idea.
First step is to remove everything from inside the coop, and I mean everything! Take the roosts out if you can. Remove the nest boxes, feed tubs, even hanging feeders if you have them. Clean out the bedding and sweep the floor. If you have electric you'll want to remove as much as you can and cover everything else with plastic bags secured by duct tape. UNPLUG YOUR COOP! Flip the breaker if you have to. Whatever you do don't spray it with water if it's on! I cannot stress that enough.....(quit laughing....you know somebody, somewhere did it!) While everything is outside this is the perfect time to scrub nest boxes. These I scrub by hand because I like to clean them with dish soap and Oxine. You can use bleach if you need to, but make sure to rinse thoroughly. Set them in the sun to dry and start on the outside of the coop.
Most plastic structures aren't airtight. So what happens is, when you're spraying from the outside water is gushing inwards through the cracks and when you're spraying inside it's going outwards. The dirt moves with it, which makes for just a tad bit more work. Start at the top and work down. Always work down! Poop is at the bottom and you don't want to push this up. Roof first, then work each side top to bottom. Don't hold the sprayer on one spot for very long, you don't want to damage the plastic. Several passes back and forth are better then holding it in the same spot.
Do the porch, floor or base last. We have a wood base and it gets slightly green from algae or moss or whatever it is that grows in this shady location. That gets blasted off too. Once the outside is 'done' move inside and take a minute to look around. See where water came in through cracks and crevices? Those are your winter draft holes. Make a mental note on which ones you want to plug up (chicken level) and which ones you want to leave open (ceiling level). The loose rule on this is is if the draft is on the chicken, then it's a draft and if it's above roost level then it's ventilation. You can work on these later now that you know where they are. Now you can start your power washer back up and get spraying. Ceiling first, then each side working top to bottom once again. Be careful around any electric even though you taped it off. It's better to have to scrub a few spots by hand then to ruin anything. Finish with the floor and your ready to start outside again!Oh wait...did you think you were done? lol
You can actually just switch to your regular hose for this part. Remember how water and dirt blasted into the coop? Well, it blasted back out in the same spots and your clean outside now looks dirty again. This will hose right off though. A quick spray and you can call it done! You might want to squeegee the floor inside if you don't have good drainage, but a few hours in the heat should dry the coop right out.
Once it's dry add fresh bedding and put everything back in. Wasn't that easy?