I am ripping out the carpet on the main floor of my house which was built circa 1900 in Utah. I'm going to be nailing down 800 sq ft of 3/4" solid red oak in its place. The main floor is over a crawl space that is about 8" tall and has no vapor barrier on it and two very small vents to the outside. I measured the moisture of the sub floor to be 15% (+/- 2%). I contacted an installer here and he told me that I could use Quiet Walk underlayment without anything else. He claimed that the moisture would wick to the edges and out under the base boards. I looked up the Quiet Walk and it is not suitable for nailing down and I'm questioning its ability to wick in this scenario.

I'm trying to figure out if I have to do some crawl space excavation (so that I can get in there to lay down a vapor barrier) or if there is another option. i.e. enlarging the vents and installing fans for force ventilation. I don't really want to dig tunnels under my house if it can be avoided.

Thanks

I forgot to add, underneath the carpet is asphalt tile that is on top of 3/4" plywood that is on top of subfloor planks. I plan on leaving the asphalt tile in place.

how are you conducting your moisture testing?

leave the VCT tile as that will work as a moisture barrier..

A pin type moisture meter. I jabbed it into the subfloor planks from inside the crawl space in a few locations.

can you calibrate it to adjust for different materials?..if so, did you adjust it for the correct material as that is important..a house that old will have a a fir or even yellow pine subfloor..

No, it is a really cheap one. I just took the access panel for the crawl space, weighed it, and measured the moisture to be 14% with the meter and placed it in the sun. Tomorrow I will check the moisture and weight again.