Building Membrane
Document Version: 1.0 Date: November 2025
Weather Resistive Barriers & Vapor Retarders
Weather Resistive Barrier (sd=0.1m)
Weather resistive barriers with sd=0.1m provide water resistance while allowing moderate vapor transmission. These membranes are designed for exterior wall assemblies where both water barrier and vapor management are critical. Typical applications include behind cladding systems and as secondary weather protection. Material must be installed with 1mm thickness in building models. Effective for climates requiring moisture control without restricting vapor drive.
Basic Information
Type
Non-Woven Membrane
Thickness (m)
0.001
Thickness (mm)
1.0
Thickness (inches)
0.039"
Colour
Orange/White
Primary Applications
Weather barrier, secondary water protection, breathable wrap
Thermal Properties
Thermal Conductivity
2.3 W/(m·K)
13.27 BTU·in/(h·ft²·°F)
Specific Heat Capacity
2300 J/(kg·K)
0.55 BTU/(lb·°F)
Density
130 kg/m³
8.12 lb/ft³
Thermal Resistance (R-value)
0.00 m²·K/W
0.00 ft²·°F·h/BTU
Vapour Properties
Water Vapour Diffusion Resistance Factor (µ)
100
sd-value
0.1000 m
Vapor Resistivity
500.00 MNs/gm
Vapor Resistance
0.50 MN.s/g
Perm Rating
0.59 perms
Weather Resistive Barrier (sd=0.2m)
Weather resistive barriers with sd=0.2m provide increased vapor resistance while maintaining breathability. These membranes are intermediate performance vapor barriers suitable for climate zones requiring enhanced moisture control. Allows slower vapor transmission compared to 0.1m equivalent but still permits drying. Used in moderate to cold climates where bulk water protection must balance with vapor management. Material must be installed with 1mm thickness in building models.
Basic Information
Type
Non-Woven Membrane
Thickness (m)
0.001
Thickness (mm)
1.0
Thickness (inches)
0.039"
Colour
Orange/White
Primary Applications
Weather barrier, moderate vapor control, cold climate protection
Thermal Properties
Thermal Conductivity
2.3 W/(m·K)
13.27 BTU·in/(h·ft²·°F)
Specific Heat Capacity
2300 J/(kg·K)
0.55 BTU/(lb·°F)
Density
130 kg/m³
8.12 lb/ft³
Thermal Resistance (R-value)
0.00 m²·K/W
0.00 ft²·°F·h/BTU
Vapour Properties
Water Vapour Diffusion Resistance Factor (µ)
200
sd-value
0.2000 m
Vapor Resistivity
1000.00 MNs/gm
Vapor Resistance
1.00 MN.s/g
Perm Rating
0.30 perms
Weather Resistive Barrier (sd=0.5m)
Weather resistive barriers with sd=0.5m provide substantial vapor resistance while maintaining vapor-open classification. These membranes serve as enhanced water barriers with moderate vapor transmission control. Suitable for warm and humid climates where condensation control is essential. Prevents bulk water infiltration while allowing the building envelope to dry. Material must be installed with 1mm thickness in building models. Bridges between vapor-open and Class III retarder performance.
Basic Information
Type
Non-Woven Membrane
Thickness (m)
0.001
Thickness (mm)
1.0
Thickness (inches)
0.039"
Colour
Orange/White
Primary Applications
Weather barrier, humid climate protection, water control with breathability
Thermal Properties
Thermal Conductivity
2.3 W/(m·K)
13.27 BTU·in/(h·ft²·°F)
Specific Heat Capacity
2300 J/(kg·K)
0.55 BTU/(lb·°F)
Density
130 kg/m³
8.12 lb/ft³
Thermal Resistance (R-value)
0.00 m²·K/W
0.00 ft²·°F·h/BTU
Vapour Properties
Water Vapour Diffusion Resistance Factor (µ)
500
sd-value
0.5000 m
Vapor Resistivity
2500.00 MNs/gm
Vapor Resistance
2.50 MN.s/g
Perm Rating
0.12 perms
Vapor Retarders
Class I Vapor Retarder (≤0.1 perms)
Class I vapor retarders provide the highest level of vapor resistance with µ-values exceeding 10,000. These impermeable or nearly impermeable barriers are designed for applications requiring maximum condensation prevention. Typically used on warm-side (interior) of wall assemblies in cold climates or on vapor-open structures. Installation in conditioned spaces prevents warm, moist interior air from reaching cold surfaces where condensation occurs. Material must be installed with 1mm thickness in building models. Requires careful design to ensure building envelope remains vapor-open to exterior.
Basic Information
Type
Polyethylene/Foil Barrier
Thickness (m)
0.001
Thickness (mm)
1.0
Thickness (inches)
0.039"
Colour
Grey/Clear
Primary Applications
Interior vapor barrier, cold climate protection, condensation prevention
Thermal Properties
Thermal Conductivity
2.3 W/(m·K)
13.27 BTU·in/(h·ft²·°F)
Specific Heat Capacity
2300 J/(kg·K)
0.55 BTU/(lb·°F)
Density
130 kg/m³
8.12 lb/ft³
Thermal Resistance (R-value)
0.00 m²·K/W
0.00 ft²·°F·h/BTU
Vapour Properties
Water Vapour Diffusion Resistance Factor (µ)
32800
sd-value
32.8000 m
Vapor Resistivity
164000.00 MNs/gm
Vapor Resistance
164.00 MN.s/g
Perm Rating
≤0.1 perms
Class II Vapor Retarder (0.1-1.0 perms)
Class II vapor retarders provide moderate vapor resistance with µ-values between 3,000 and 10,000. These semi-permeable barriers are designed for applications where vapor control is necessary but some vapor transmission is acceptable. Positioned typically between insulation and interior finishes. Used in mixed climates where both condensation prevention and potential emergency drying are important. Material must be installed with 1mm thickness in building models. Allows slow vapor movement while restricting bulk vapor drive.
Basic Information
Type
Kraft Paper/Polyethylene Blend
Thickness (m)
0.001
Thickness (mm)
1.0
Thickness (inches)
0.039"
Colour
Kraft/Tan
Primary Applications
Vapor retarder, mixed climate protection, insulation facing
Thermal Properties
Thermal Conductivity
2.3 W/(m·K)
13.27 BTU·in/(h·ft²·°F)
Specific Heat Capacity
2300 J/(kg·K)
0.55 BTU/(lb·°F)
Density
130 kg/m³
8.12 lb/ft³
Thermal Resistance (R-value)
0.00 m²·K/W
0.00 ft²·°F·h/BTU
Vapour Properties
Water Vapour Diffusion Resistance Factor (µ)
3280
sd-value
3.2800 m
Vapor Resistivity
16400.00 MNs/gm
Vapor Resistance
16.40 MN.s/g
Perm Rating
0.1-1.0 perms
Class III Vapor Retarder (1.0-10 perms)
Class III vapor retarders provide light to moderate vapor resistance with µ-values between 300 and 3,000. These highly permeable barriers allow significant vapor transmission while still providing some condensation control. Used in climates where building envelopes must remain relatively vapor-open. Positioned typically on exterior side of insulation to allow drying. Material must be installed with 1mm thickness in building models. Allows emergency drying while providing minimal vapor barrier function.
Basic Information
Type
Latex/Vapor-Retarding Paint
Thickness (m)
0.001
Thickness (mm)
1.0
Thickness (inches)
0.039"
Colour
Various
Primary Applications
Interior paint, vapor retarder, drying capability
Thermal Properties
Thermal Conductivity
2.3 W/(m·K)
13.27 BTU·in/(h·ft²·°F)
Specific Heat Capacity
2300 J/(kg·K)
0.55 BTU/(lb·°F)
Density
130 kg/m³
8.12 lb/ft³
Thermal Resistance (R-value)
0.00 m²·K/W
0.00 ft²·°F·h/BTU
Vapour Properties
Water Vapour Diffusion Resistance Factor (µ)
328
sd-value
0.3280 m
Vapor Resistivity
1640.00 MNs/gm
Vapor Resistance
1.64 MN.s/g
Perm Rating
1.0-10 perms
Vapor Permeance Classification Reference
Classification Standards
Class I
≤ 0.1
µ ≥ 10,000
Polyethylene sheet, aluminum foil
Class II
0.1-1.0
300 < µ < 10,000
Kraft paper, polyethylene blend
Class III
1.0-10
30 < µ < 300
Latex paint, vapor-retarding paint
Vapor-Open
> 10
µ < 30
Non-woven membranes, weather barriers
Conversion Formulas
Perm Rating to µ-value:
µ = 59 ÷ Perm Rating
Example: 0.5 perms = 59 ÷ 0.5 = 118 µ-value
µ-value to Perm Rating:
Perm Rating = 59 ÷ µ
Example: µ=100 = 59 ÷ 100 = 0.59 perms
sd-value Calculation:
sd = thickness (m) × µ-value
Example: 1mm membrane with µ=500 = 0.001 × 500 = 0.5 m sd-value
Thermal Resistance (R-value):
R-value = thickness / thermal conductivity
Example: 1mm, 2.3 W/(m·K) = 0.001 / 2.3 = 0.0004 m²·K/W
SI Unit Conversions
Perm to SI (ng/Pa·s·m²):
1 perm = 57.2 × 10⁻⁹ kg/(Pa·s·m²)
1 perm = 57.2 ng/(Pa·s·m²)
µ-value to Vapor Resistance (MN.s/g):
Vapor Resistance = (sd × 1000) / 21.6
Example: sd=0.1m = (0.1 × 1000) / 21.6 = 4.63 MN.s/g (approximate)
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