My house was built in 1837 and for the most part in great shape. We are going through the usual repairs but the one that has me stumped is a small section of the douglas fir flooring that is giving way. The strips are about 1x3 and give way when you step on them. This problem only exist in the master bedroom and at the front entrance to the house. It is as if the supports under the house have failed at these locations allowing the finish floor to move. As we only have a small crawl space under the house I am unable to make this repair from below. Any suggestions.