I found a deal on engineered click-lock hardwood that's tough to pass up. I have old carpet in a room on top of old solid hardwood. I've sanded/refinished this flooring before in a similar house, but it took a lot of work, and I can put new engineered hardwood on top for about what it would cost just to rent the sander. It's a small room, only about 10x10 that doesn't see heavy traffic.

1. I've read some people say that 3/8" is borderline for floating, and that nailing may be necessary. Could I float it over the hardwood, or would it need to be nailed?

2. If I did this, should there be any special type of vapor barrier/felt/whatever on top of the old hardwood?

Here is a pic, thanks for any input.

https://i.imgur.com/S7LXwUb.jpg

I contacted the manufacturer (Heritage Mill), and they said it was ok to float, and to just use an underlayment pad. This was their email:

Yes, the click flooring can be floated over any flat, structurally sound substrate including existing solid hardwood. You would not need 15# felt, only an underlay pad for floating floors.