First of all thank you for any advice. We built a home back in 2009. We recently checked out the crawlspace and found water damage from rain around the base of our chimney on the rim board and floor joists. The chimney is made of osb and houses a ventless gas log fireplace. The copper tubing going to the fireplace has started to corrode from the rain water. We have brick veneer around the entire chimney. What could be causing this issue? Thanks!