VAPOR BARRIERS MOISTURE CONTROL IN BUILDINGS

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VAPOR BARRIERSMOISTURE CONTROLINBUILDINGS
ASHRAE TECH SESSION APRIL 8, 2004 PRESENTED BY
GARY PETERS GREENTECH
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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 .
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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
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Permeability 0.000 Water vapor transmission of
Zero Perm in a flat condition is 0.000 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 0.0134 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 0.000 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.
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 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.
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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
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• 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.

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TRANSMISSION RATES FOR TYPICAL BUILDING
MATERIALS MATERIAL TRANSMISSION RATE (
grams/hr./sq. meter)

Perms Concrete Block 2.40 Gypsum Board
50.00 Plywood 1.90 Plaster
15.00 Glazed Tile 0.12 Vapor Retarder
Paint 0.45 Semi-Gloss Acrylic
6.61 Polyethylene, 6mil 0.06 Polyethylene,
10 mil 0.03 Mylar/Aluminum 0.00
(Zero-Perm)
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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
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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.
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HYDRIC BUFFER CAPACITY FOR 2000 SQ. FT HOUSE
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• 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

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• 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

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• 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.

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• 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.

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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 Comp
laint 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
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• 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!

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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
Temperature Controlled Vapor Pressure Controlled Air Pressure Controlled
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ENVIRONMENTALLY CONTROLLED SPACES VAPOR BARRIER
IMPACT ON EQUIPMENT SIZING AND OPERATING COST
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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 0.000 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
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FLOW DIAGRAM (No Vapor Barrier)
Electric Re-activation 12.7 kw
DEHUMIDIFIER
Approximate Full Connected Load 22.6kW
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FLOW DIAGRAM With Vapor Barrier
Electric Re-activation 6.3 kw
DEHUMIDIFIER
Approximate Full Connected Load 12.2kW
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EFFECT OF VAPOR BARRIER ON DEHUMIDFICATION
COSTS   Room size 50 x 50 x 9 Room design
64F DB / 35 RH Surrounding conditions 80F 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 7x3
door and moderate work done by 5 occupants in the
space. This equates to a total internal latent
load of 1330 BTUH (excluding infiltration).   Assu
ming 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.
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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.
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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.
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CONTROLLED ENVIRONMENTAL SPACE VAPOR BARRIER
PAYBACK NO CORRECT ITEM VAPOR
BARRIER VAPOR BARRIER SAVINGS Equipment
Costs 20,000 13,000
7,000 Operating Costs 9,944
5,368 4,576 Cost to properly vapor treat the
space..1,200
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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
0.000 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
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HUMIDIFIER SELECTION and OPERATING
COST Calculated humidifier load with perfect
vapor barrier9 / 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
space1,200.00 Use available
manufacturers software to calculate the load
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• 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

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• 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

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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