Our 1920 home has the original skirting. It is in bad shape and has way too many vents (imagine a wind tunnel in our basement). We want to replace with cement board and then cover with faux stone to take the house back to its craftsman bungalow look. How deep do I need to bury the cement board in the ground to keep animals from burrowing under? How many vents do I need to keep approx 240 square feet of crawlspace adequately ventilated?