We are getting ready to build a fairly large addition on a house that has a crawl space. We are bumping out the back of the house and the grade rises gradually. In order to maintain a reasonable height in the new crawl,we would need to have the interior elevation lower than the exterior. We would plan on installing a curtain drain in conjunction with a french drain linked to a sump pump. I have suggested to the client to encapsulate both crawl spaces but he is extremely reluctant. He thinks that ground moisture will collect under the vapor barrier on cmu walls and cause mold issues that may migrate through the masonry. I feel that in our climate (coastal Maryland) encapsulation is the best option and want to direct him to some literature that may convince him. Can you suggest a clearly stated article for the lay person?
We also suggested possibly doing a slab for the new addition but then have no way to run the ductwork since the ceilings will be vaulted. Another concern with slabs on grade here is termites. I have made many repairs due to termites entering a home through the seam between the slab and the walls or cracks in the slab.
After reading an article on the site I would say that the reason crawlspaces are popular in our area is because ground water makes basements wet and crawl spaces allow for easy mechanical , plumbing , and electrical upgrades.

Thanks,
Mike Labesky
The Cypress Group Limited