Replies

1. 
   finefinish | Feb 26, 2016 11:07am | #1

   Hi Woodguy,  

        I would frame the new floor, wait on the subfloor, then have the floor and walls sprayed with closed cell foam.  Ideally the sprayed foam connects to the rigid foam on the walls above the floor while encapsulating the new rim joist,  but I cannot determine from your description if the walls have exterior foam, or rigid foam inside the wall cavities - you did say it was "poorly insulated" so I am not sure.   The closed cell foam will act as the vapor barrier so you don't need poly etc.  You will most likely want more thickness on the walls than on the floor, but definitely check with the inspector about required R-Values for your area.  After insulating, glue and nail the subfloor down and you should be good to go.  

1. 
   woodguy9 | Feb 29, 2016 07:49pm | #2

   Thanks much,

   Let me explain a little more.  The foundation has what looks like 1.5 inch of closed cell on the exterior.  I think the walls are just 2x4 with fiberglass.  The new floor will be about 1.5 ft. above the foundation and the old dirt floor level  (Longer term is to hang more insulation on the exterior).   I could dig down along the wall and add ridged foam board insulation on the interior up to the new header/rim joist.   Do I understand you right that I could spray foam over the dirt floor?  Would this be better than ridged foam over the dirt floor.  Both of these would keep the floor itself on the inside the envelop.   I was thinking about filling the whole cavity with blown-in.   You would recommend against this? 

1. 
   finefinish | Feb 29, 2016 08:16pm | #3

   Hi Woodguy,

          Yes you can spray foam with closed cell over the dirt floor, or maybe better and cleaner for the foam installers, is to leave the brick installed and foam on top of that.  You don't need that much insulation on the ground because it is within the foundation walls and should be a fairly consistent temperature throughout the year.  The foundation walls that are above grade is where more foam on the inside is a good idea to keep the cold from outside the walls from migrating to the interior of the crawlspace.  Sprayed foam is better than ridgid because it is continuous in this application.  With sheets you would be relying on tape and can foam to seal all the seams, which is much more unreliable compared to sprayed foam.  After the foam there is no need for filling the entire space with blown in.  I am not sure of your location so the amount of foam and specific details I can not answer for you.  

1. 
   finefinish | Feb 29, 2016 08:38pm | #4

   Sorry Woodguy,  I missed your first sentence in your original post...   you are in southern Vermont.  I live in work in northeastern MA so I am familiar with your locale.  My advice should work well for your situation but still check on foam thickness requirements/recommendations for your specific area.  

1. 
   woodguy9 | Mar 02, 2016 02:44pm | #5

   Thanks Finefinish

   I will look into this option.  Learning that the spray could go direckly over dirt or th brick is key.  I can work the details with the installer.