Hello

My house was built in 1964 and had hardwood flooring installed in the family room. I pulled out the old flooring and to my shock the subfloor is only 1/2" of plywood. It bends under my foot when I walk on some sections (and i'm only 154!!). Pulling out the subfloor is out of the question. So only option is to add another layer. What's the minimum that I can add? Would 1/4" plywood (using nails and liquid nail) be enough? I will be installing either 1/2" engineered wood or 3/4 solid wood.

Thanks,
-h

I don't think a 1/4" would help you much and the 1/2" CDX is not a T&G either. Bare Minimum for me would be 3/8" under a solid. Under a 1/2" engineered I would look at using 1/2" underlayment.

I thought I read some specs for this double layer type construction of subfloor. However, I couldn't find anything last night. I remembered basically what Jerry stated.

I agree with Jerry. 3/8" minimum for a 3/4" nailed down run 90 degrees to the joists which should be spaced no greater than 16" OC. If using 1/2" engineered, you'd need to go up to 1/2" at least, which is really 15/32 and only slightly thicker than 3/8". I'm running into this right now. I'm using both 3/8" and 15/32". And the 15/32" really isn't much thicker. Too bad they do not make a true 1/2" or 9/16" plywood in a utility grade, like CDX.

The other thing that needs to be said it the additional layer of subfloor needs to be spaced at a minimum of 1/8" apart.