Design the building envelope to avoid thermal bridging
Avoid thermal bridgingHeat flow that occurs across more conductive components in an otherwise well-insulated material, resulting in disproportionately significant heat loss. For example, steel studs in an insulated wall dramatically reduce the overall energy performance of the wall, because of thermal bridging through the steel. through careful insulation detailing. This reduces energy loss and moisture damage to wall assemblies. Avoid low R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. materials.
Often, thermal bridges are metallic elements in the roof or wall that pass from inside to outside. One example: structural steel framing with only the exterior skin as insulation from the outdoors. In another example, the exterior wall is insulated, but outdoor air is drawn through exterior envelope leaks–bypassing the insulation and chilling the outermost surface of the steel frame. Sometimes flashing or a termite-barrier creates a thermal bridge.
Avoid thermal bridging by using rigid insulation. Many of Green Building Advisor’s CAD drawings show exterior wall details that employ rigid insulation. This reduces heat loss, lowering the chance that interior wall-cavity temperatures will fall below the due point, creating condensation. This increases the life of the building, reduces maintenance costs, and avoids contamination by mold, fungus, etc.
Keeping a watchful eye on insulation details is the greatest challenge in preventing thermal bridging.
Green Points
LEED for HomesLeadership in Energy and Environmental Design. LEED for Homes is the residential green building program from the United States Green Building Council (USGBC). While this program is primarily designed for and applicable to new home projects, major gut rehabs can qualify. : EA 3.1 reduced envelope leakage is a requirement; EA 3.2 - 2 pts for greatly reduced envelope leakage; EA 3.3 – 3 pts for minimal envelope leakage
NGBSNational Green Building Standard Based on the NAHB Model Green Home Building Guidelines and passed through ANSI. This standard can be applied to both new homes, remodeling projects, and additions. /ICC-700: under Chapter 7, Energy Efficiency: up to 15 pts for third-party verification; up to 3 pts for no verification; insulation and air-sealing includes: spray or rigid foam insulation; ICFInsulated concrete form. Hollow insulated forms, usually made from expanded polystyrene (EPS), used for building walls (foundation and above-ground); after stacking and stabilizing the forms, the aligned cores are filled with concrete, which provides the wall structure. or SIP(SIP) Building panel usually made of oriented strand board (OSB) skins surrounding a core of expanded polystyrene (EPS) foam insulation. SIPs can be erected very quickly with a crane to create an energy-efficient, sturdy home. wall systems; spray foam attached to top, bottom and both sides of cavities; voids are less than 2% of the total; exterior rigid insulation is tightly fitted
Further Resources
Building Science Corp.
A Bridge Too Far
