I have clapboard covered with asphalt. There's a big debate whether to remove the outer layer or not. Some people say I should leave it for insulation purposes, but that means the trim will stick out around the windows, ect.-even without putting on additional insulation. Plus there's furring under the asphalt and I'm worried about nailing through that much thickness and having it hold up. On the otherhand, removing the asphalt is a big job for me. If I put insulation board up-do I need a vapor barrier?