I plan to install a bath fan duct thru a dropped ceiling space between the first and second floors. I shot some digi cam pics to see what was up there. It's a three foot distance to the exterior wall from the fan's hole. At the wall, I can see what I believe to be the top plate and the rim joist on top of that. What is the least impactful method to make sure I am opening the right spot (thru the middle of the rim joist)? I will have to do it from the stucco outside. I was thinking of measuring as best I could and then drill a small hole like 3/8 or so (big enough for light to shine thru), then sight it from inside the space inside the house. If I'm off, I figure a hole like that can be easily caulked and patched. Thoughts? Also, what is the best way to get thru the stucco and the rim joist for the 4.5 inch hole needed (4-inch duct)? Hammer/chisel then recip saw, or ? Thanks! Here's a pic of the site: The rim joist is the second joist in back (you can barely see its bottom edge), the question marked wood is the top plate, sound right?