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. 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!

SIPs Give Insulation Throughout

SIPs feature uninterrupted insulation throughout the structure

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-17 R-19 R-23
Whole Wall R-9 R-9 R-13 R-15 R-16 R-18
6.5" Center of Cavity R-17 R-20 R-23 R-26 R-29 R-34
Whole Wall R-13 R-14 R-20 R-22 R-24 R-27
8.25" Center of Cavity R-23 R-26 R-29 R-34 R-37 R-44
Whole Wall R-17 R-18 R-25 R-28 R-31 R-35
10.25" Center of Cavity R-29 R-33 R-37 R-43 R-47 R-56
Whole Wall R-21 R-23 R-32 R-36 R-38 R-44
12.25" Center of Cavity R-35 R-40 R-45 R-52 R-57 R-67
Whole Wall R-26 R-28 R-38 R-43 R-46 R-53

 

Standard Wall Thickness Comparison Table Foard Panel SIPs vs. Conventional Stick Built
Center of Cavity or Code R-value Fiberglass Cellulose EPS SIP NEO SIP XPS SIP PIR SIP
R-14 4.5" 4.5" 4.5" 4.5" 4.5" 4.5"
R-19 6.5" 6.5" 6.5" 6.5" 4.5" 4.5"
R-22 8.25" 8.25" 6.5" 6.5" 6.5" 4.5"
R-30 10.5" 10.25" 8.25" 6.5" 6.5" 6.5"
R-35 12.25" 12.25" 10.25" 8.25" 8.25" 6.5"
R-38 15" 12.25" 10.25" 8.25" 8.25" 8.25"
R-40 15" 12.25" 10.25" 10.25" 8.25" 8.25"
R-49 17" 15" 12.25" 10.25" 10.25" 8.25"
R-60 21" 19" 15" 15" 12.25" 10.25"
R-70 25" 21" 17" 15" 15" 12.25"

Note: This table provides the wall thicknesses required to meet the same whole wall R-values as a conventional wall with the given center of cavity number. The thicknesses listed are the standard SIP sizes not the stud or insulation thickness. 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_1501016