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Moisture Assessment. WEATHERIZATION ENERGY AUDITOR SINGLE FAMILY. WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012. Learning Objectives. Moisture Assessment. By attending this session, participants will be able to:

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moisture assessment

Moisture Assessment

WEATHERIZATION ENERGY AUDITOR SINGLE FAMILY

WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012

learning objectives
Learning Objectives

Moisture Assessment

By attending this session, participants will be able to:

  • Analyze the symptoms of moisture problems in houses.
  • Identify moisture sources.
  • Explain moisture terms and concepts.
  • Demonstrate how to measure relative humidity.
  • Demonstrate how to use a psychrometric chart.
  • Apply moisture control strategies.
  • Use moisture assessment tools.
symptoms 1
Symptoms #1

Moisture Assessment

Excessive window condensation

Photo courtesy of PA WTC

symptoms 2
Symptoms #2

Moisture Assessment

Frost on underside of roof sheathing

Photo courtesy of PA WTC

symptoms 3
Symptoms #3

Moisture Assessment

Mold on interior surfaces

Photo source: PA WTC Photo

Photo courtesy of PA WTC

symptoms 4
Symptoms #4

Moisture Assessment

Peeling Exterior Paint

Photo courtesy of PA WTC

symptom 5
Symptom #5

Moisture Assessment

Standing Water in Basements

Photo courtesy of PA WTC

moisture sources
Moisture Sources

Moisture Assessment

  • Foundations
  • Unvented space heaters
  • Unvented dryers
  • Disconnected ventilation fans
  • Drying wood indoors
  • Excessive mechanical or passive humidification

Photo courtesy of PA WTC

These water stains are a result of fan venting into the attic.

slide9

Sources of Water Vapor

Moisture Assessment

important terms and concepts
Important Terms and Concepts

Moisture Assessment

  • Condensation: water vapor transformed to liquid water
  • Evaporation: liquid water transformed to water vapor
  • Absolute humidity (vapor pressure): the ratio of water vapor to a given volume of air
  • Relative humidity (RH): the ratio of the amount of moisture in the air compared to amount of moisture that the air can hold
  • Dew point: the temperature at which condensation occurs
measuring relative humidity
Measuring Relative Humidity

Moisture Assessment

  • Sling Psychrometers
  • Two thermometers side by side
  • One is wrapped in wet wick (wet bulb), the other is dry (dry bulb)
  • Spinning it around speeds temperature stabilization
  • Plot wet bulb and dry bulb temperature on psychrometric chart to determine dew point and RH

Photos courtesy of Bacharach

psychrometric chart 1
Psychrometric Chart #1

Moisture Assessment

Dry bulb = 80°

Wet bulb = 66°

Dew point = 60°

RH = 50%

Grains of water per pound of dry air

slide13

Psychrometric Chart #2

Moisture Assessment

156

78

Grains of water per pound of dry air

psychrometric chart 3
Psychrometric Chart #3

Moisture Assessment

Grains of water per pound of dry air

psychrometric chart 4
Psychrometric Chart #4

Moisture Assessment

Grains of water per pound of dry air

psychrometric chart 5
Psychrometric Chart #5

Moisture Assessment

Grains of water per pound of dry air

rh things to remember
RH: Things to Remember

Moisture Assessment

  • Warm, wet air contacting cold surfaces creates condensation instantly.
  • Cold winter air typically contains very little moisture and therefore has a low RH. When that air is heated, the RH drops even lower.
  • RH below 15% can lead to respiratory problems, failure of furniture glue and other problems.
attic case study

Floored Attic and First Condensing Surface

Attic Case Study

Moisture Assessment

Photo courtesy of PA WTC

attic case causes solutions
Attic Case – Causes & Solutions

Moisture Assessment

Possible Causes

  • Moderate to high interior moisture source
  • Attic surface temps are below the dew point of the indoor air
  • Air leaks to attic

Control Strategies

  • Source control
  • Air seal the attic
basement case study
Basement Case Study

Moisture Assessment

  • Symptom
  • Condensation evident on basement walls
  • Reason
  • Light to moderate interior moisture source
  • Basement walls are below the dew point of the indoor air

Mold on cool interior corner

Photo courtesy of PA WTC

basement case study solutions
Basement Case Study Solutions

Moisture Assessment

Control moisture sources.

Remove susceptible materials.

Educate occupants to:

  • Mechanically dehumidify.
  • Increase air flow in basement (fans).
  • Close basement openings during hot humid periods.
crawl space case study
Crawl Space Case Study

Moisture Assessment

Symptoms

  • Wet wood
  • Condensation on foundation surfaces

Possible Reasons

  • High ground moisture source
  • Warm humid air entering vents from outside
  • Crawl space surfaces are below the dew point of the outside air

Photo courtesy of PA WTC

Water droplets of condensation on AC ducts.

crawl space case study solutions
Crawl Space Case Study Solutions

Moisture Assessment

  • Install a ground vapor retarder.
  • Control moisture sources and remove susceptible materials.
  • Consider converting to a conditioned crawl space.

Photo courtesy of INCAP

Conditioned crawlspace with air sealed and insulated walls.

tools of the trade
Tools of the Trade

Moisture Assessment

Clear understanding of moisture management principles.

  • Senses - Visual inspection
    • Evidence of condensation
    • Evidence of mold
  • Communication Skills
    • Know what questions to ask
    • Documentation is vital
  • Wood Moisture Meter
    • To make quantitative assessments on wood moisture content
  • Psychrometer
    • To determine real time RH levels
  • Digital Camera
moisture meters
Moisture Meters

Moisture Assessment

Photos courtesy of PA WTC

PhotoSource: PA WTC

summary
Summary

Moisture Assessment

  • The first step in doing a moisture assessment is to look for visible signs of moisture and moisture sources in the house.
  • Plotting the wet bulb and dry bulb temperatures on a psychrometric chart gives dew point and relative humidity.
  • Understanding the effects of temperature and vapor pressure on RH can help identify solutions.
  • Source control, air sealing, ventilation, and thermal improvements are important moisture mitigation strategies.
  • Photos and diagnostic equipment help document existing conditions.