My wife and I just purchased a 1909 craftsman house with a wrap around porch on three sides. The porch is in very bad shape and will be rebuilt, I was thinking of using a composite material but the porch is over the crawl space and I really don't want to have any water or debris from the porch getting under the house. Should I plan on installing a sub-floor to catch the water and debris? Could the sub-floor be sealed with a membrane and pitched to drains that would lead away from the foundation? Any help would be appreciated.

Thanks
JPennestri