I just spent the better part of my day reading through this thread. haha.
I also have a barn that is 80+ years old, made from what looks like the same wood yours is made from. It seems to be a trend with the poison ivy to LOVE old barns. I have a poison ivy tree growing in mine too, we don't use the barn and it hasn't been used in 15 years or more so no need to kill it yet.
But its amazing how well they withstand anything time throws at them. Last year we had terrible storms and i was really worried that the bard would collapse, but it stayed upright, its like it said to the storms "you'll have to do A LOT better than that to take me out!" Your granny's house looks a lot like ours too, we live in a 100 year old super small and completely uneven farm house. So i know old and love old.
Our barn also has a rock foundation and dirt floor. We've been thinking about clearing everything away from it to fix it up and make it into a chicken coop, since my chickens are living in a dog kennel right now. And i think i'll start that project soon, you've inspired me to get out there and start it.
I think about our house and barns all the time about how old they are, when we first moved in i thought the first big storm would knock everything down and then i realized that they all have minds of their own. When everyone else around us doesn't have power, our house does. They refuse to go down without a fight, so we count ourselves lucky to live in such a strong well built house. Because in a 50 years when the new neighborhoods filled with cheap-cookie-cutter-only-took-a-month-to-build houses come crashing down, our houses and barns will still be standing. That was my ode to old houses.
Great job on the chicken coop, keep up the good work. Your chickens are going to love it!