John, Next time Bill Kibbel teaches a class on Inspecting old houses, you need to attend. Or read everything he has written on the "Old House Web". When things, like you posted, come up on my Inspections and I don't want to write a long explanation in the Inspection Report, I direct the reader to Bill's site (I know it is not his site, but he seems to have the most articles posted). TIJ should put together a 2 day class on wall systems with Bill leading the Experts in teaching the great unwashed. Chicago would be a good location , Kurt could host it and suggest the best places to eat.