Thermal Barrier

R-Values Explained

One of the more noteworthy characteristics of Foard Panel SIPs is how well they perform thermally. The tables below compare SIPs with their most common competitor; stick construction with fiberglass (or any batt) insulation.

Stick frame construction leaves gaps in the insulation for every stud

Stick frame construction leaves gaps in the insulation for every stud

In order to appreciate these tables, however, the concepts of “Center of Cavity” and “Whole Wall” R-values need to be understood. Center of Cavity refers to the R-value of the insulation only. Whole Wall, as the term implies, takes into consideration the thermal properties of all the components of a finished wall system.

SIPs Give Insulation Throughout

SIPs feature uninterrupted insulation throughout the structure

Naturally, Whole Wall R-values are lower than Center of Cavity R-values. Conventionally framed, fiberglass, systems typically perform at only 65% of the stated Center of Cavity R-value. Once thermal bridging, convection within the bay and air infiltration are taken into account, an R-19 (center of cavity) wall, for example, will perform at only R-13 (whole wall). Here is the good news! Foard Panel SIPs perform at 96% of the stated Center of Cavity R-value. This is because the SIPs that form the building envelope are super-tight. They don’t experience air infiltration, thermal bridging, or bay convection. Because Whole Wall performance for these two methods of insulating are so different, it has been difficult for many people to make accurate comparisons and to choose appropriate SIPs for their projects. These tables were designed to help with that process.

R-Value Comparison Table Foard Panel SIP vs. Conventional Stick Built

Wall Thickness Fiberglass Cellulose EPS SIP NEO SIP XPS SIP PIR SIP
4.5" Center of Cavity R-11 R-13 R-15 R-18 R-19 R-23
Whole Wall R-9 R-11 R-14 R-17 R-18 R-19
6.5" Center of Cavity R-17 R-20 R-23 R-26 R-29 R-34
Whole Wall R-15 R-17 R-22 R-25 R-27 R-32
8.25" Center of Cavity R-23 R-26 R-29 R-36 R-37 R-44
Whole Wall R-20 R-22 R-27 R-34 R-36 R-41
10.25" Center of Cavity R-29 R-33 R-37 R-45 R-47 R-56
Whole Wall R-24 R-28 R-35 R-42 R-45 R-52
12.25" Center of Cavity R-35 R-40 R-45 R-54 R-57 R-67
Whole Wall R-30 R-34 R-42 R-51 R-54 R-63
These are only suggestions, based on our understanding of building codes and actual thermal performance, all final assessments are made by local building code officials. For more information on how we got these numbers see the following technical bulletin.Whole Surface vs Cavity R-Values_180730