1. VAPOR BARRIERS MOISTURE CONTROL IN BUILDINGS
ASHRAE
TECH SESSION
APRIL 8, 2004
PRESENTED BY
GARY PETERS
GREENTECH

2. VAPOR BARRIERS versus AIR BARRIERS
Air Barriers prevent air movement while allowing moisture to pass through. Air barriers must be carefully sealed at all penetrations.
Vapor Barriers are used to control the flow of moisture through the building envelope’ .

3. Classes of Vapor Barriers and Vapor Retarders
The unit of measurement for water vapor permeability is the “perm”.
Three general classes of materials, based on permeability.
Vapor Impermeable – “Vapor Barriers”
0.1 perms or less: Class I
1.0 perms or less: Class II
Typical Materials: Rubber membranes; polyethylene film; glass; aluminum foil; sheet metal; some vinyl wall covering; foil- faced insulating sheathings
Vapor Semi-permeable – “Vapor Retarders”
10 perms or less: Class III
Typical Materials: Plywood; unfaced expanded polystyrene (EPS); asphalt impregnated building paper; many latex based paints; paper and bitumen facing on fiberglass batt insulation
Vapor Permeable – “Breathable”
More than 10 perms
Typical Materials: Unpainted gypsum board; unfaced fiberglass insulation; lightweight asphaltimpregnated building paper; exterior gypsum sheathing; “housewraps”

4. Permeability
0.000
Water vapor transmission of Zero Perm in a flat condition is grams per hour per square meter. After sharp creasing under 25-lb. pressure at 3/4'' intervals with creases at right angles forming crease intersections at 3/4'' intervals permeance is only grams per 100 sq. in. per 24 hrs. Joints sealed with 1 1/2'' Zero Perm Pressure Sensitive Tape and joints overlapped 1 1/2'' and sealed with Alumiseal Zero Perm Adhesives also exhibit a permeance of grams per lineal inch per 24 hrs. Test sources available on request.
UL Listing
An important feature of Zero Perm is its performance in Underwriters Laboratories (UL) Surface Burning Characteristics Test (UL 723). Zero Perm is UL listed as follows:
 Flame spread 5 Fuel contributed 0 Smoke developed 5Note: The numerical flame spread ratings are not intended to reflect hazards presented by this or any other material under actual fire conditions.
Flex Life
Zero Perm's outer mylar layer can endure over 20,000 cycles of flexing without failure.

5.  Thermal Stability
Zero Perm remains flexible and stable over a temperature range from -100° F to +300° F
 Tensile Strength
Has a tensile strength of over 25,000 psi, a bursting strength of 96.6 psi. It requires a 23,500 psi stress at 130% strain to cause an elongation break in the mylar outer laminate
Inertness
Zero Perm exhibits excellent inertness to water, salt spray, wet mortar, caustics plus chemical solvents, oils, greases and can be safely applied to masonry walls.
 Resistance to Abrasion
Zero Perm has extremely high resistance to abrasion.

6. Vapor Transportation Mechanisms
Capillary Action: Wetted surfaces
Air transported moisture – Air transported moisture can be more significant than vapor diffusion.
Vapor Diffusion: Second law of thermodynamics. Moisture will flow by diffusion because of a concentration gradient as well as a temperature gradient. “More to less” “Warm to cold”
Moisture control generally requires both an air barrier and a vapor barrier.
Uncontrolled air infiltration into walls because of inadequate air barriers can cause catastrophic problems

7. LOCATION of VAPOR BARRIERS and AIR BARRIERS
COLD CLIMATES
Goal is to make it as difficult as possible for the building assemblies to get wet from the interior.
Install air barriers and vapor barriers on the interior building assemblies. Let the building assemblies dry to the exterior by installing the vapor permeable materials toward the exterior.
HOT and HUMID CLIMATES
Goal is to make it as difficult as possible for the building assemblies to get wet from the exterior.
Install air barriers and vapor barriers on the exterior of the building assemblies. Let the building assemblies dry to the interior. Impermeable interior wall coverings must be avoided. The interior space must be maintained at a slight positive pressure with conditioned/dehumidified air to limit infiltration
MIXED CLIMATES COMPLICATED!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
Flow through approach: Use permeable materials on both interior and exterior. This requires both air pressure control and interior moisture control.
Install the vapor barrier in the approximate thermal “middle” of the wall with insulating sheathing on the exterior. The air barrier can be toward the interior or the exterior. Air pressure control and interior moisture control must be utilized.

18. TYPICAL BUILDING MATERIALS
TRANSMISSION RATES
FOR
TYPICAL BUILDING MATERIALS
MATERIAL TRANSMISSION RATE
( grams/hr./sq. meter)
Perms
Concrete Block
Gypsum Board
Plywood
Plaster
Glazed Tile
Vapor Retarder Paint
Semi-Gloss Acrylic
Polyethylene, 6mil
Polyethylene, 10 mil
Mylar/Aluminum
(Zero-Perm)

19. VAPOR BARRIERS and MOLD
Moisture accumulates in the building envelope when the rate of moisture entry exceeds the rate of moisture removal.
When moisture accumulation exceeds the ability of the materials to store the moisture, moisture problems result.
Moisture storage capacity of materials depends on
Time – Dwell time, or drying time
Temperature
Material Properties

20. EXAMPLES:
In a house the average 2000 square foot house, the wood based sheathing and wood framing have an equilibrium moisture content of 5% to 6%. The walls have a hygric buffer capacity of 10% which equals approximately 50 gallons of water for the 4,000 to 5,000 pounds of wood product in the exterior walls. When the moisture content exceeds 16% by weight, mold will develop.
That same house with steel framing and gypsum sheathing has a hygric buffer capacity of 5 gallons of water. A highly insulated wall has a high dwell time and poor drying characteristics. Very small amounts of water will cause problems because of the low hygric buffer capacity and the slow drying times.
A house with masonry exterior walls and masonry cladding has a hygric buffer capacity of 500 gallons.

21. Wood Frame with Wood Sheathing Steel Frame with Gypsum Sheathing
HYDRIC BUFFER CAPACITY FOR 2000 SQ. FT HOUSE
Approx. 500 gallons (1892L)
Masonry Wall
Approx. 50 gallons (189L)
Wood Frame with Wood Sheathing
Approx. 5 gallons (19L)
Steel Frame with Gypsum Sheathing

22. MOISTURE CONTROL IN BUILDINGS
TO MINIMIZE THE RISK OF
MOISTURE DAMAGE
I. Control Moisture Entry
Repair roof leaks, flashing, floors, foundations
Prevent wind driven rain fro entering the wall assembly
Direct rain and ground water away from building
Airflow retarder must resist pressure from wind, stack effect, and mechanical ventilation

23. Control Water Vapor Migration
Limit water entry into building envelope with proper airflow retarders and vapor retarders
6 to 22% of air leakage at windows and doors
18 to 50% of air leakage occurs through walls
3 to 30% of air leakage occurs through ceilings

24. Control Moisture Accumulation
Control dominate direction of air flow
In climates requiring cooling, maintain the building at light positive pressure to prevent unconditioned, humid air from entering the envelope.
In climates requiring heating, maintain a neutral building pressure.

25. Control the Removal of Moisture
Provide envelope system that allows assembly to dry to either the exterior or the interior, depending on climate.
Provide dedicated, conditioned low moisture content make up air systems
Maintain slight positive pressure
Leakage of saturated air from building AC system can migrate into building envelope assemblies.

26. Classic Example of a Connecticut Wall System
Building: Upper range hotel
Walls: Vinyl Wall Covering, Gypboard, Vapor Barrier,Fiberglass Insulation, Sheathing,EIFES and Brick
Flashing: Poorly installed
Guest Room AC: PTAC Thru the wall, exhaust fan in Bathroom
Corridor AC: Standard split system air conditioning units delivering conditioned outside at saturated conditions
Complaint: Employee complaints, very high rate of sick days, some customers complained odors
Findings: Rooms were some times positively pressured, sometimes negative. Air leakage into building envelope around PTACS. The gyp board and sheathing facing the interior of the wall cavity were 100% covered with black and green mold

27. The Brick Veneer Wall Problem
Rain wetted followed by solar radiation
The sun drives the moisture inward. Ideally, the vapor barrier would be behind the brick veneer to stop the inward flow. That does not work in a cold climate.
In a cold climate, the vapor barrier is typically on the “warm” side. Moisture can get trapped in the wall cavity for extended periods of time.
Possible Solutions
Vapor Barrier behind the bricks and a vapor retarder on the inside
Semi-vapor permeable insulating sheathing on the outside wall, insulation to provide sufficient thermal resistance to elevate the temperature of the condensing surface during the heating season and a vapor permeable interior finish to allow drying to the interior
There are no easy answers!
There is no one correct solution!

28. Interior Climate Classes
Class I
Temperature Moderated
Vapor Pressure Uncontrolled
Air Pressure Uncontrolled
Class II
Temperature Controlled
Vapor Pressure Moderated
Air Pressure Moderated
Class III
Vapor Pressure Controlled
Air Pressure Controlled

29. ENVIRONMENTALLY CONTROLLED SPACES
VAPOR BARRIER IMPACT ON
EQUIPMENT SIZING
AND
OPERATING
COST

30. TECHNICAL SESSION PRESENTATION
ASHRAE
TECHNICAL SESSION PRESENTATION
“VAPOR BARRIERS”
DEHUMIDIFICATION
Select and size a dehumidification system for a site constructed with and without a vapor barrier.
Project the equipment (first) cost and the operating cost for the dehumidification system with each construction method.
ASSUMPTIONS:
Hours/per year of dehumidification: 4,000
Electric Utility Rate: $0.11/Kwhr.
Space Dimensions: 50’ x 50’ x 9’ high, all interior surrounded by conditioned space, 24” ceiling plenum and roof above.
Room conditions to be maintained: 64 degrees db/35% RH
Room Load – Constant:
375,000 Btu/hr Sensible
225,000 Btu/hr Latent
600,000 Btu/hr Total
Room surrounding conditioned space: 80 degrees db / 50% RH
CONDITION “A”
Walls constructed with 5/8” sheetrock on both sides, no insulation and no vapor barrier
Ceiling, standard acoustical tiles
Roof, insulated with no vapor barrier
CONDITION “B”
Walls constructed with 5/8” sheetrock on both sides, no insulation, and with a vapor barrier with a transmission rate of grams/hr/sq. meter. The vapor barrier is installed under the sheetrock on the conditioned space side of the wall.
Ceiling, acoustical tiles with a vapor barrier with a transmission rate of 0.04 grams/hr/sq. meter

32. DX AFTER-COOLING 29.2 MBH 3 TR desiccant dehumidification
RETURN AIR CFM 64°FDB 31 GR/LB
200 CFM
284°FDB
REACT
EXHAUST
600 CFM
97°FDB
7.9 GR/LB
56°FDB GR/LB
30%
FILTER
DEH
64°FDB
31 GR/LB
84°FDB
PROCESS
FAN
CONDITIONED SPACE
22,500 FT.3
35% RH 31 GR/LB
BRY-AIR, INC.
ROUTE 37-W
SUNBURY, OH 43074
TEL (740)
FAX (740)
The choice for
desiccant dehumidification
FLOW DIAGRAM
(No Vapor Barrier)
Electric
Re-activation
12.7 kw
DEHUMIDIFIER
Approximate Full Connected Load: 22.6kW

34. DX AFTER-COOLING 29.2 MBH 3 TR desiccant dehumidification
RETURN AIR CFM 64°FDB 31 GR/LB
100 CFM
284°FDB
REACT
EXHAUST
300 CFM
97°FDB
7.9 GR/LB
49°FDB GR/LB
30%
FILTER
DEH
64°FDB
31 GR/LB
84°FDB
PROCESS
FAN
CONDITIONED SPACE
22,500 FT.3
35% RH 31 GR/LB
BRY-AIR, INC.
ROUTE 37-W
SUNBURY, OH 43074
TEL (740)
FAX (740)
The choice for
desiccant dehumidification
FLOW DIAGRAM
With Vapor Barrier
DEHUMIDIFIER
Electric
Re-activation
6.3 kw
Approximate Full Connected Load: 12.2kW

35. EFFECT OF VAPOR BARRIER ON DEHUMIDFICATION COSTS
Room size: 50’ x 50’ x 9’
Room design: 64°F DB / 35% RH
Surrounding conditions: 80°F DB / 50% RH
Hours/per year of operation: 4,000
Electric Utility Rate: $0.11/Kwhr
Assuming a constant latent load in the space of 8,840 gr/hr from the 5 door openings/hour of a 7’x3’ door and moderate work done by 5 occupants in the space. This equates to a total internal latent load of 1330 BTUH (excluding infiltration).
Assuming a constant sensible load in the space of 2 BTUH per square foot, over 2500 sq ft of the space the total internal sensible load will be 5000 BTUH.

36. CONDITION “A” (NO VAPOR BARRIER)
Using 0.9 as the F4 factor in the dehumidification calculation sheet for no vapor barrier, the infiltration load is 48,566 gr/hr.
The total latent load is 57,406 gr/hr and the required airflow is 600 scfm.
Reactivation energy required is 43,200 BTUH or 12.7 KW.
Cooling (3 TR condensing unit) energy required is 5.9 KW.
Total energy required (including motors) is 22.6 KW.
First cost of equipment is approximately $20,000 USD.
Operating cost of equipment is $9,944 USD yearly.

37. CONDITION “B” (WITH VAPOR BARRIER)
Using 0.35 as the F4 factor in the dehumidification calculation sheet for room with vapor barrier, the infiltration load is 18,887 gr/hr.
The total latent load is 27,727 gr/hr and the required airflow is 300 scfm.
Reactivation energy required is 21,600 BTUH or 6.3 KW.
Cooling (2 TR condensing unit) energy required is 2.9 KW.
Total energy required (including motors) is 12.2 KW.
First cost of equipment is approximately $13,000 USD.
Operating cost of equipment is $5,368 USD yearly.

38. CONTROLLED ENVIRONMENTAL SPACE
VAPOR BARRIER PAYBACK
NO CORRECT
ITEM VAPOR BARRIER VAPOR BARRIER SAVINGS
Equipment Costs $20, $13, $7,000
Operating Costs $ 9, $ 5,368 $4,576
Cost to properly vapor treat the space……………..$1,200

39. TECHNICAL SESSION PRESENTATION
ASHRAE
TECHNICAL SESSION PRESENTATION
“VAPOR BARRIERS”
HUMIDIFICATION
Select and size a humidifier system for a site constructed with and without a vapor barrier.
Project the equipment (first) cost and the operating cost for the humidification system with each construction method.
ASSUMPTIONS:
Hours / year for humidification: 4,000
Electric Utility Rate: $0.11/Kwhr
Space Dimensions: 50’ x 50’ x 9’ high, all interior surrounded by conditioned space, 24” ceiling plenum and roof above.
Room Conditions to be maintained: 72 degrees db/ 50% R.H.
Room Load - Constant:
672,000 Btu/hr Sensible
50,000 Btu/hr Latent
722,000 Btu/hr Total
Room surrounding conditioned space: 76 degrees db / 30% RH
CONDITION “A”:
Walls constructed with 5/8” sheetrock on both sides, no insulation and no vapor barrier
Ceiling, standard acoustical tiles
Roof, insulated with no Vapor Barrier
CONDITION B:
Walls constructed with 5/8” sheetrock on both sides, no insulation, and with a vapor barrier with a transmission rate of grams/hr/sq. meter. The vapor barrier is installed under the sheetrock on the conditioned space side of the wall.
Ceiling, acoustical tiles with a vapor barrier with a transmission rate of: 0.04 grams/hr/sq. meter
Roof, insulated with no vapor barrier

40. HUMIDIFIER SELECTION and OPERATING COST
Calculated humidifier load with “perfect” vapor barrier………9# / hr; 3.0 kW
Load with no vapor barrier – many variable – Probably…… 22# / hr; 7.3kW
Rule of thumb: 3# / hr / kw
Savings with vapor barrier………………………………………….4.0kW / hr
4.0kW / hr x 3500 hrs x $0.11 / kwhr = $1,540.00
Cost to vapor treat the space………………………………………$1,200.00
Use available manufacturer’s software to calculate the load

41. Neptronic Humidisoft Humidification Software is an indispensable tool for anyone who is involved in the design, selection or installation of humidification systems. Consulting Engineers are able to quickly calculate humidification loads, select humidifiers, select steam dispersion systems, generate calculation reports, produce exportable product schedules and wiring diagrams. Contractors can quickly obtain dimensional data, installation information and much more. Humidisoft Humidification Design Software Features:
General:
English or French language
Metric (SI) or English (US) units
Easy to use, visual help
Auto-update feature to ensure latest version is easily available
All reports are exportable to rich text and PDF formats for easy transfer of information

42. Technical:
Design criteria (temperature, humidity and altitude) for most major cities already in the software
Load calculations can be done based on infiltration, mechanical or economizer fresh air exchange
Best-cost humidifier selection based on calculated load
Dispersion distance calculation
Dispersion manifold selection
Calculation report
Detailed option selection chart
Integrated product schedule
Complete submittal drawings including PROJECT AND PRODUCT SPECIFIC information, installation, dimensions and wiring information

43. RESOURCES
Alumiseal Corporation
ASHRAE FUNDAMENTALS HANDBOOK
Bry-Air Corporation
Building Science Corporation, Joseph Lstiburek, PhD
Lincoln Electric System
Louisiana State University, Dept of Natural Resources
University of Wisconsin – Cooperative Education