Expert: Dan Griffin - 5/6/2008

Question
I have a cabin (60+ yrs old) built on concrete piers. The existing floor is 2 x 6 joists 16 oc with 3/4 floor boards and oak floors on top. The section I have a question about is 14ft x 16ft.

I would like to build a 2 x 4 floor over the top of existing floor, level this and install plumbing between these two floors in this section.

This new floor would not carry any load. It is next to impossible to level the existing floor from underneath, no access room for jacking. We'll both assume the existing wood perimeter on piers is sound.

What do you think? Thanks.

Answer
Scribed 2x is a very common solution to floor flattening in old buildings.  2x6 make floor joists less than 10 feet long, it sounds as if yours have settled with time. Here is the calculation using Southern Yellow Pine / #2 grade / 40#perSF loading:
http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?species=Southern+Pi...

The concern would be whether they are finished or will continue to deform.

You are losing the existing floor anyway, have you considered cutting access through the floor  and working from above to reduce the span on those joists?