Instructions / Assembly
8
OVERVIEW
Drivers of Continuous Insulation
Paths to Code Compliance
There are three typical paths to compliance. Perhaps the most commonly known path is the prescriptive method. In this method, the
chart previously illustrated is used to select the construction type and climate zone, which will prescribe the R-value with continuous
insulation required as well as overall assembly R-value.
Another path is the performance method, often used if the assembly is particularly complicated or requires further analysis. You’ll also
see this used on curtain walls and in WUFI analysis. Finally, the last method uses software and web tool calculators developed by the
U.S. Department of Energy to compare a structure to a basis of design.
1. Prescriptive R-Value
• Considers R-value of insulation only.
• Compliance is achieved by installing insulation with code-prescribed R-value.
2. Performance (overall assembly)
• Considers:
– U-factors: U-value of assembly (above grade).
– C-factors: Thermal conductance (below grade).
– F-factors: Slab edge factors.
• Compliance is achieved when assembly meets minimum U-value.
•
3. Envelope Tradeoff
•
• Allows for tradeoff between various parts of the building envelope.
• ASHRAE Standard 90.1-2007/2010 provides the basic rules.
Tradeoff is implemented in the COMcheck™ software.
Designing Beyond Codes
Many owners, designers, and contractors feel that the insulation requirements set out in state-adopted codes are not robust enough
to truly save energy and reduce greenhouse gas emissions. These owners, designers, and contractors look beyond code initiatives to
USGBC’s LEED
®
rating system, ASHRAE Standard 189.1, Architecture 2030, Passive House, Title 24, Declare, or LL 97.
Including increased insulation levels in the building envelope can help reach these goals with a negative marginal cost, generating a
positive economic return over the building’s lifecycle.
Assembly Insulation Methods
Exterior Insulated Split Insulated Stud Cavity Insulated