Hey guys. I'm installing 3" rift and QSWO. Half the floor will be installed over a "crawl space." The other half will be above a basement with 7' ceilings. This crawl space is around 4 ft tall. The question I have is whenever I read or see photos of crawl spaces, they are dirt. People discuss vapor barriers over the dirt etc. My crawl space has a regular block foundation around it just like the rest of the basement , and has a concrete slab for a floor, just like the rest of the basement. Essentially, it is no different in construction than the rest of the basement, except the joists are 4' above the slab instead of 7' above the slab.. Do I still have all of the concerns associated with a "crawl space?" Or are most crawl spaces we speak of dirt, and thus a different animal in terms of moisture? Thanks!

Treat it as you would the rest of the basement and control its humidity as it relates to the new hardwood flooring and the rest of the house.

Ok. So no need to start covering the space in a vapor barrier then? I currently run a dehumidifier in the rest of the basement and it keeps it around 45 rel humidity. So maybe just take some readings and if it's too high throw a dehumidifier in that space as well? Thanks

From the picture the 4 foot tall basement area appears to be open to the 7 foot tall basement area. The dehumidifier should take care of that area too unless it is a really large area and the dehumidifier continually runs or the areas are closed off from one another. 45 relative humidity is a good number. Your new flooring will be happiest if the relative humidity around it is between 45% and 55% year round.

Ok thanks. Yes, the crawl space is open to the rest of the basement. I was just concerned after all of the reading I've done regarding crawl space mositure and horror stories for the wood flooring. And how I should cover it in a vapor barrier etc etc. it seems strange because it's the same as the rest of the basement just the slab is 3 feet closer to the joists in this area. Crawl space is pretty deep (about 15 feet). But I'll take a reading at the far side in there and hopefully still <55 or so.

The layer of concrete over the dirt is commonly called rat proofing. If you would like to save energy and also help keep moisture away from the flooring you could add kraft faced insulation between the floor joists.

The horror stories are typically about dirt floor basement/crawl space situations and the moisture that comes up through the dirt. It's a lot less work and $ to dig a 4 foot basement rather than a 7 foot basement. If whoever paid for the addition wanted a full height basement it would probably would have been doable.....maybe didn't do it for financial reasons or didn't need the extra full height space. Also, depending on location, crawl spaces are either vented or not vented to the outside air which in some cases would make humidity control difficult. 25+ years ago the building sciences folks determined that all crawl spaces should be ventilated. Over time and with experience they changed their position on this, again depending on geographical location, and determined that crawl spaces should not be ventilated and they should be treated as part of the entire house envelope.

Very good info. Thanks a lot. Appreciate it.