Expert: Bruce E. Johnson - 8/23/2009

Question
Hi Bruce,
The situation is a 12 x 12 addition that was put on about 30 years ago in the White Mountains of New Hampshire and in my opinion not very well. I say new Hampshire because we endure cold winters and harsh storms.
We’ve been getting this musty smell. So we removed and trashed the carpet. I cut out a section of subfloor and it’s a material I’ve never seen before. The best way I can describe it is it looks like compressed-glued sawdust. It’s a half inch thick and they put 2 layers on creating a 1 inch thick subfloor.
They used 2 x 10 joist and they are 16-inchs on center. Instead of a concrete cellar or a slab they used concrete footings.
The floor joist bays are open, no insulation, and the ground (earth) varies, but a good average is about a foot from the joist. No one I know is skinny enough to crawl under the addition.
I took a piece of subfloor and wet it and smelled it. To me it smelled like the musty smell we have been smelling. My wife smells something, but disagrees that is the musty smell.

My original plan was to use ¾ pt plywood, seal it with Red Guard, have a vapor barrier padding and a new carpet.

Now I’m thinking could I lay down some thick plastic like a drop cloth over the earth, somehow insulate between the joists, subfloor ¾ PT plywood, and seal it with Red Guard, then the vapor barrier padding and a new carpet.

What do you think?
In your opinion, what would you do or recommend?

Thank you,
Randy


Answer
Hi Randy, you took the words out of my mouth..first you need a vapor barrier on the ground, 6 mil visqueen or thicker and tape the joints.  You can insulate your floor best by using a paper or foil backed insulation that can be stapled to the joists prior to the subflooring going on.  Finish with your plywood, red guard, padding and carpet as planned.  I hope this information helps, please feel free to write again regarding this or other matters,sincerely bruce e johnson..bejohnsonconsulting.com