I am an engineer currently working on repairing the roof of a house on a plantation in Louisiana built around 1800. They want to reuse as much original timber as possible, but some of the members will have to be replaced because of large cracks, splits, rot, etc. The house has relatively long overhangs that have gradually sagged at the corners over the years to the point that temporary braces were built under them to keep the roof from falling apart. I can size the roof members using cypress with today's grades, but I have little knowledge of what kind of stress grades to use on the existing 200+ year old members that still appear to be useable. I realize that this was built well before timber was regulated, but I still need to determine or assume some strength value for them. Any suggestions? Also, some of the existing sizes are overstressed using today's codes. Is there some kind of gray area code wise that applies to historic buildings like this that are only used as a sort of museum or do they have to meet the most recent code standards like any other building?