INSULATION STRATEGIES
Interior Insulation (wall)
• Advantages • easier to install
• Material costs low
• Disadvantages • Allows dewpoint interior to weather barrier
• May require fire separation from habitable space
• Does not protect weather barrier from thermal movements
• Thermal bridging at framing members reduces effective R-value
INSULATION STRATEGIES
Interior Insulation (wall)
• Product Types
• Fiberglass batts (3.1 to 4.3/in)
• Mineral wool (3.7 to 4.5/in)
• Cotton batts (3.5/in)
• Sprayed-in cellulose (3.6 to 3.8/in)
• Sprayed-in fiberglass (3.7 to 4.2/in)
• Closed cell spray foam (6/in)
• Open cell spray foam (3.5/in)
INSULATION STRATEGIES
Exterior Insulation (wall)
• Advantages • Mitigates thermal bridging
• Protects weather barrier from thermal movements
• Pushes dewpoint exterior of weather barrier
• Disadvantages • Installation requires more coordination
• Higher material cost
• Drying time of wall may lengthen depending on material choices
INSULATION STRATEGIES
Exterior Insulation (wall)
• Product Types
• Extruded polystyrene (XPS) (4.5 to 5.0/in)
• Expanded polystyrene (EPS) (3.6 to 4.0/in)
• Polyisocyanurate (5.6/in)
• Closed cell spray foam (6/in)
• Mineral wool (3.7 to 4.5/in)
INSULATION STRATEGIES
Split Insulation (wall) • Advantages
• Mitigates thermal bridging • Protects weather barrier from most thermal
movements • Sometimes cost effective
• Disadvantages • Installation still requires more coordination • Drying time of wall may lengthen depending on
material choices • Weather barrier material choices narrow • Dewpoint will reside in stud cavity….but for how long?
INSULATION STRATEGIES
Interior Insulation (roof)
• Advantages • Easier to install
• Material costs low
• Disadvantages • Allows dewpoint interior to roof membrane
• Does not protect roof membrane from thermal movements and weathering
• Susceptible to moisture during construction
• Thermal bridging at fasteners reduces effective R-value mildly
INSULATION STRATEGIES
Infrared Scan of EPDM Roof
THERM model w/ fasteners thru all insulation
THERM model w/ fasteners thru first layer of insulation
INSULATION STRATEGIES
Exterior Insulation (roof)
• Advantages • Mitigates thermal bridging
• Protects roof membrane from thermal movements
• Pushes dewpoint exterior of roof membrane
• Quicker “dry-in” of building
• Disadvantages • Installation requires more coordination
• Insulation needs to be covered (pavers, ballast, vegetation, etc.) to protect from exposure
Why is CONTINUITY important?
PORTLAND AIR INFILTRATION
WATER VAPOR DIFFUSION
1” SQUARE HOLE
10000 1000 100 10 1 0.1
# GRAINS PER HOUR
INTERIOR 68°F 50%RH
EXTERIOR 41°F 80%RH
SOURCE: WBDG
Why is CONTINUITY important?
MIAMI AIR INFILTRATION
INTERIOR 70°F 50%RH
WATER VAPOR DIFFUSION
1” SQUARE HOLE
EXTERIOR 91°F 56%RH
0.1 1 10 100 1000 10000 # GRAINS PER HOUR
SOURCE: WBDG
Case Study 2 – Interior infiltration
Temperature = 20°F Relative Humidity = 93%
Vapor Pressure Force = 7.2psf
Temperature = 70°F Relative Humidity = 53%
Vapor Pressure Force = 15.7psf