I like the stand alone dehumidifers better than ones incorprated in to hvac system. When you place the dehumidiferes in the conditioned space they sense the RH in that space, many central dehumidifiers sense the RH in the area they are located in and do not dehumidify the conditioned space as well. Where are you located? Where are central units located? Have you talked to hvac company about adjusting dip switch settings? Many times they are installed with factory settings and need to be adjusted for your climate. ERV's are usually not for cold climates..that would be an HRV, so I wonder about your location. Also ERV's are for 'tight' houses..with less than .25 air changes per hour. If your house is not at this level of air tightness the ERV can bring in moisture adding to the dehumidification load of hvac. Was the house tested for air tightness with a blower door? To 'see' what is happening behind the walls and between floors of your home would require a thermal scan of your home. This will show you moisture intrustion sites and moisture in walls, ceilings and floors. IMO this will be the way to go to actually KNOW what is happening. Then whatever the IR scan shows will be on you to address. Around here (Louisiana) thermal scan (InfraRed) scans are used often when home owners and builders are seeking solutions. I've even seen them used in court cases. But hopefully...it won't come to that! best of luck.

@worthy I guess I'm speaking to my experience within the same part of the world as you, so it may differ from others experience where foundations don't need to be as deep below grade (which causes them to become basements more often than not). My answer to the OP took into consideration that he's not doing a full basement and he doesn't care to have the gold standard, an acceptable, lower-cost option would do. Therefore I agree that CMU will be just fine. Certainly poor installation could be done just as crappily on CMU foundation as it could on a poured foundation.When both are installed correctly, I would judge a poured foundation to be able to do a better job of resisting lateral pressure causing cracks which cause foundation leaks. Maybe I'm wrong, but my experience tells me CMU foundations crack more often and the Building Code tables would seem to infer they can withstand less unsupported lateral height (ie: they're weaker)

When we bought the house 11 years ago we had the plumbing updated by a reputable plumber. I’d have to ask my husband for the specific answers to these questions. We have the cleanup guys under there today and hoping for insight as to where the failure is. It all appears to be under the addition completed 4 yrs ago.

Above all, the lot needs to be sloped in such a way as to direct water away from the foundation. Your gutter downspouts need to be extended in order channel water away from the edge of the structure or buried drainage pipes need to be installed. The thinking about crawlspaces has changed in the last few years. It used to be that crawl spaces were ventilated. Now, crawlspaces are encapsulated as closed conditioned spaces. Often this is an additional item after you build a home involving a specialty contactor. If this were an entirely custom home, you would consult with your general contractor and get them to order it. My guess is this a production home. You need to discuss your options with the salesmen and construction supervisor and determine the plan for this space. It can involve HVAC elements. You definitely want pay attention to this. It's easy to forget until you have a problem with mold, mildew and air quality in the home. Better to take care of it before it becomes a problem.