As a retired owner of garage door company, I offer this advice.
Put a 14' tall by at least 12' wide door in any pole barn you in which you will store an RV. If you ever move up to a bigger unit the cost to do that now will be considerably less than it will be later.
Travel safe
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2019 Ford F-350 Super Duty CC Dually 6.7 Diesel
2011 Cedar Creek 36CKTS Touring Edition
If our MH is 11 feet 3inches according to specs, how tall should an opening be for a slight incline going onto the slab?
I built a pole barn for my 13' fiver. I built it with 14 feet of clearance to bottom of joists. Mine is 16 feet wide and 55 feet long. I should have built it 18 feet wide so the slides could all be fully opened. If i'm careful and park it dead center i can just barely open all three slides. But i usually miss center by a few inches.
My pole barn has 15' high and 16' wide doors. I have absolutely no regrets going that big
I don't have a problem as to how wide barn is because it's 86' X 60'.
like someone above stated make it wide enough to put slides out .
IMHO I would mot go less than 20' Wide building W/ 16' wide door.