Replies

1. 
   Malcolm_Taylor | May 11, 2021 08:00pm | #1

   Douglas,

   The rigid insulation is much more effective placed continuously on the underside of the joists where it can reduce thermal bridging. It should be taped and sealed as an air-barrier, and covered with something like plywood to protect it. The open area underneath would benefit from a layer of poly to stop moisture rising from the soil below.

1. 
   user-1020504 | May 11, 2021 09:49pm | #2

   Thanks, unfortunately the rockwool insulation is already in place. I would prefer not to have to remove it to install the rigid installation adjacent to the underside of the T&G flooring. Just wondering if there is another option.

1. 
   Malcolm_Taylor | May 11, 2021 11:03pm | #4

   Douglas,

   You can leave the rock wool where it is, or pull it down to the bottom of the joist cavities. The rigid foam isn't in the cavities at all, it's on the bottom of the joists as a continuous layer.

2. 
   user-2310254 | May 11, 2021 10:24pm | #3

   Douglas,

   Malcolm is suggesting this sort of solution: https://www.greenbuildingadvisor.com/article/insulating-a-wood-framed-floor-assembly.

   The foam is nailed to the bottom of the floor joists and then covered with a plywood protective layer.

3. 
   DCContrarian | May 12, 2021 12:00am | #5

   This is a good article by Joe Lstiburek: https://www.buildingscience.com/documents/insights/bsi-009-new-light-in-crawlspaces

   You are geographically close to the house with the "icky crawlspace" that he profiles.

   He also recommends continuous foam below the joists.