ASHRAE Journal - July 2020 - 53

COLUMN BUILDING SCIENCES

FIGURE 1 (TOP) Hygrothermal Regions. Regions. Based on Herbertson's Thermal Regions

and Koeppen climate types (Lstiburek, J.W. 2000 Environmental Loads, Eight Canadian
Building Science Technology Conference, CSCE. Adapted by PNNL to become the IECC
Climate Zone Map and, subsequently, the ASHRAE Climate Zone Map).
FIGURE 2 (BOTTOM) Rain Exposure Zones. Based on annual precipitation from the U.S.

Department of Agriculture and Environment Canada (Lstiburek, J.W. 2000. Environmental
Loads, Eight Canadian Building Science Technology Conference, CSCE).

TABLE 1 Interior climate classes.

Class I

Temperature Moderated
Vapor Pressure (Relative Humidity) Uncontrolled
Air Pressure Uncontrolled (Warehouses, Garages, Storage Rooms)

Class II Temperature Controlled
Vapor Pressure (Relative Humidity) Moderated
Air Pressure Moderated (Houses, Apartments, Offices, Schools, Commercial
and Retail Spaces)
Class III Temperature Controlled
Vapor Pressure (Relative Humidity) Controlled
Air Pressure Controlled (Hospitals, Museums, Swimming Pool Enclosures
and Computer Facilities)
Lstiburek, J.W. 2000. "Environmental Loads." Eighth Canadian Building Science Technology Conference,
CSCE.
TABLE 2 Classes of vapor control layers defined.

Class I

Vapor Control Layer: 0.1 perm or less

Class II Vapor Control Layer: 1.0 perm or less and greater than 0.1 perm
Class III Vapor Control Layer: 10.0 perm or less and greater than 1.0 perm
Lstiburek, J.W. 2004. "Understanding Vapor Barriers." ASHRAE Journal, August.
FIGURE 3 Control Layers. Optimum configuration is to place the control layers on the outside

of the structure. ("The Perfect Wall," ASHRAE Journal, May 2007).

TABLE 3 Insulation for condensation control.
CLIMATE
ZONE

RIGID BOARD
OR AIRIMPERMEABLE
INSULATION

TOTAL
CAVITY
INSULATION

TOTAL WALL
ASSEMBLY
INSULATION

RATIO OF RIGID BOARD
INSULATION OR AIR
IMPERMEABLE R-VALUE TO
TOTAL INSULATION R-VALUE

4C

R-2.5

R-13

R-15.5

15%

R-3.75

R-20

R-23.75

15%

R-5

R-13

R-18

30%

R-7.5

R-20

R-27.5

30%

5
6

Exposure
Over 60 in.
Extreme
40 in. to 60 in.
High
20 in. to 40 in.
Moderate
Under 20 in.
Low

R-7.5

R-13

R-20.5

35%

R-11.25

R-20

R-31.25

35%

7

R-10

R-13

R-28

45%

R-15

R-20

R-35

45%

8

R-15

R-13

R-28

50%

R-20

R-20

R-40

50%

Adapted from Table R 702.1 2015 International Residential Code.

J U LY 2 0 2 0

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ASHRAE Journal - July 2020

Table of Contents for the Digital Edition of ASHRAE Journal - July 2020

Contents
ASHRAE Journal - July 2020 - Intro
ASHRAE Journal - July 2020 - Cover1
ASHRAE Journal - July 2020 - Cover2
ASHRAE Journal - July 2020 - 1
ASHRAE Journal - July 2020 - Contents
ASHRAE Journal - July 2020 - 3
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