GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

How to calculate Floor Insulation Effective R-Value

RMGheHhbJx | Posted in Energy Efficiency and Durability on

I have a 2×12 floor system with R-19 supported by spring wires every three feet or so. The insulation is 5″ from being in substancial contact with the floor. What is the effective R-value and what publication can I point to for substantiation.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. GBA Editor
    Martin Holladay | | #1

    Since you don't have an air barrier on the underside of your fiberglass batts, the effective R-value of your insulation is (I'm just guessing here) somewhere between R-0 and R-a very low number.

    If you want to point to a publication, how about Fine Homebuilding? Here's an article, How to Insulate a Cold Floor, that states, "If the batts aren’t thick enough to fill the joist bays, they may fall away from the subfloor and rest on the OSB below. At that point, the floor assembly has an R-value of 0."

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |