Even walk out basements are considered "basements". Any time a concrete slab is even 1" below grade in 1ft of the basement, the WHOLE THING is considered "below grade". The reason: subterranean water floor. Water in the ground is forced AROUND and under the slab.

Below grade is below grade is below grade. No matter how much or how little of the slab is technically "below" the level of the ground. It is all painted with the same brush.

Even "slab on grade" hardwood gets tricky. Very tricky. Your installer needs to be good and technically well trained in moisture mitigation (both testing for and treating moisture issues). Hardwood on concrete is always risky. Hardwood "below grade" must be an engineered product. Even then it can get very technical very quickly. A "Chuck in a Truck" handyman doesn't have the skills to handle hardwood over concrete. Many "Joe flooring installers" can't handle hardwood over concrete.

NWFA Certified HARDWOOD flooring installers should be able to handle hardwood over concrete. Engineered hardwood in a basement still needs all the testing done and the right mitigation and the right installation technique.

That is a lot of ducks that MUST BE in a row to get engineered hardwood into a basement. Any duck out of place and this is going to end in tears.

This type of install will carry a heavy price tag. The lowest bid should be thrown out with the bathwater....they obviously don't grasp the scope of work needed. Another $1-$2 more per square foot just for labour should show up on a bid (when compared to hardwood install over above grade plywood).

I suggest vinyl...but moisture mitigation is still needed. Good luck.