1 BUILDING DYNAMICS: BUILDING DYNAMICS: Moisture, Airflows and Moisture, Airflows and Construction Technology Construction Technology James Biddle, Mansel Nelson James Biddle, Mansel Nelson Northern Arizona University Northern Arizona University Presentation Credit to: Joseph T. Ponessa, Ph.D. Presentation Credit to: Joseph T. Ponessa, Ph.D. Professor Emeritus Housing, Indoor Environments Professor Emeritus Housing, Indoor Environments and Health and Health
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1 BUILDING DYNAMICS: Moisture, Airflows and Construction Technology James Biddle, Mansel Nelson Northern Arizona University Presentation Credit to: Joseph.
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BUILDING DYNAMICS:BUILDING DYNAMICS:Moisture, Airflows and Moisture, Airflows and
Construction TechnologyConstruction Technology
James Biddle, Mansel Nelson James Biddle, Mansel Nelson
Northern Arizona UniversityNorthern Arizona University
Presentation Credit to: Joseph T. Ponessa, Ph.D.Presentation Credit to: Joseph T. Ponessa, Ph.D.
Professor Emeritus Housing, Indoor Environments and Professor Emeritus Housing, Indoor Environments and HealthHealth
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GoalsGoals Review basic dynamics of moisture Review basic dynamics of moisture
movement, control in buildingsmovement, control in buildings Review basic dynamics of airflows in Review basic dynamics of airflows in
buildingsbuildings Proper management of moisture and Proper management of moisture and
airflows provides better buildings and airflows provides better buildings and reduces callbacksreduces callbacks
-------------------------------------------------------------------------------------------------------- Understanding of these mechanisms Understanding of these mechanisms
is essential for diagnosticsis essential for diagnostics
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Objective: How does this fit with Objective: How does this fit with weatherization?weatherization?
Weatherization can improve comfort and Weatherization can improve comfort and save money. Downside is ‘inadequate’ save money. Downside is ‘inadequate’ ventilationventilation
When is ventilation inadequate?When is ventilation inadequate? When it is less than prescribed When it is less than prescribed
ventilationventilation When it is inadequate to take care of When it is inadequate to take care of
building excessesbuilding excesses– Too much moistureToo much moisture– Excessive pollution sourcesExcessive pollution sources
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Overview of Today’s Overview of Today’s PresentationPresentation
Building ScienceBuilding Science Moisture dynamics; applications in Moisture dynamics; applications in
buildingsbuildings
Airflow mechanisms; applications in Airflow mechanisms; applications in buildingsbuildings
Basic moisture science: Vapor & Basic moisture science: Vapor & Liquid Liquid – Air – vapor – temperature relationshipsAir – vapor – temperature relationships– Relative HumidityRelative Humidity– Putting it all together – Psychrometric Putting it all together – Psychrometric
chart chart Vapor movementVapor movement
DiffusionDiffusion Bulk transfer – air flowsBulk transfer – air flows
Vapor-Vapor-Temperature Temperature relationshipsrelationships (At (At saturation)saturation)
The amount of moisture that air can hold increases directly with temperature.
Moisture content of air (GMS/m3) at various
temperatures
0
5
10
15
20
25
30
Deg F 20 40 60 80
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Moisture DynamicsMoisture Dynamics VaporVapor
Dew point: Dew point: SaturationSaturation
Air cooled to the limit Air cooled to the limit of its moisture of its moisture carrying capacity carrying capacity releases vapor as releases vapor as droplets droplets condensation (or condensation (or rain) rain)
This is the This is the Dew point Dew point temperaturetemperature
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Moisture DynamicsMoisture Dynamics VaporVapor
So what does it all mean?So what does it all mean?
Moist air that is cooled downMoist air that is cooled down
OR…OR…
Moist air that meets a cool surface Moist air that meets a cool surface will will condense!condense!
Wet surfaces that don’t/can’t dry Wet surfaces that don’t/can’t dry rapidly will produce moldrapidly will produce mold
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Moisture DynamicsMoisture Dynamics Vapor TransportVapor Transport
Vapor transport: how does vapor get Vapor transport: how does vapor get from point A to point B?from point A to point B?
POSSIBLE MECHANISMSPOSSIBLE MECHANISMS DiffusionDiffusion Bulk transport: AirflowBulk transport: Airflow
Which is more important?Which is more important?
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Moisture DynamicsMoisture Dynamics Vapor Transport viaVapor Transport via AirflowAirflow
Moisture carried into wall via air flow / leakage Moisture carried into wall via air flow / leakage through openings. through openings. What is the driving force?What is the driving force?
Source: USDOE
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Moisture DynamicsMoisture Dynamics
Which mechanism is most important?Which mechanism is most important?
Diffusion?Diffusion?
Air transport?Air transport?
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Moisture DynamicsMoisture Dynamics
Diffusion vs. air transportDiffusion vs. air transport
While air transport accounts for bulk While air transport accounts for bulk of moisture migration in most of moisture migration in most buildings, there are circumstances buildings, there are circumstances when diffusion is most important when diffusion is most important factorfactor
Cellulose insulationCellulose insulationBuilding America Best Practices Series: Volume 4 –
…..Mixed-Humid Climate Version 1, 9/2005 • Design-
p13
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PERMABILITYPERMABILITY
An important note about building An important note about building materials and watermaterials and water
Permability of many materials changes Permability of many materials changes when they are wet. Ppermeability of wet when they are wet. Ppermeability of wet plywood, for example, changes from plywood, for example, changes from 0.75 (dry) to 3.0 when wet0.75 (dry) to 3.0 when wet
Questions about Questions about vapor vapor
transmission/dynamictransmission/dynamics?s?
While vapor migration and While vapor migration and condensation can play an condensation can play an important role in moisture important role in moisture
problems, most problems are problems, most problems are caused by rainwatercaused by rainwater
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Moisture DynamicsMoisture DynamicsLiquidLiquid
Liquid water can flow viaLiquid water can flow via Gravity (or wind pressure)Gravity (or wind pressure) Capillary action (wicking)Capillary action (wicking)
= against gravity= against gravity
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Moisture DynamicsMoisture DynamicsLiquidLiquid
GravityGravity
““It flows downhill”It flows downhill”
Source: Builder Magazine
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Moisture DynamicsMoisture Dynamics
Capillary actionCapillary action
Water can flow Water can flow against gravity against gravity when moving in a when moving in a tight space…tight space…
…and, by the same process, can wick through porous materials
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Moisture DynamicsMoisture Dynamics
Practical applicationsPractical applications Water can travel up and behind Water can travel up and behind
flashing that is not properly flashing that is not properly dimensioneddimensioned
Water can diffuse/wick through Water can diffuse/wick through masonry, adding humidity to spaces masonry, adding humidity to spaces and wetting components (e.g. sill and wetting components (e.g. sill plates)plates)
Some builders, at least, have known about Some builders, at least, have known about capillary action for a long time…capillary action for a long time…
XXX barnAbbey grange,Great Coxwell, England
Photo: Barn. Houghton Mifflin, 1992.
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Moisture dynamicsMoisture dynamics
Barn interior, Barn interior, showing posts set showing posts set on stone pierson stone piers
This barn, built in This barn, built in mid- 13mid- 13thth century, century, in use until 1966, in use until 1966, when deeded to when deeded to National trustNational trust
Note detail on top of Note detail on top of pierpier
A sacrificial wood slab A sacrificial wood slab has been placed has been placed here. Moisture here. Moisture migrating through migrating through pier will enter slab pier will enter slab instead of end grain instead of end grain of post; slab is easily of post; slab is easily replacedreplaced
Outline for this sectionOutline for this section Plumbing leaksPlumbing leaks RainwaterRainwater GroundwaterGroundwater Humid air (Including embodied Humid air (Including embodied
Plumbing leaks should be obvious Plumbing leaks should be obvious but can be in concealed spaces, and but can be in concealed spaces, and may involve supply or drain linesmay involve supply or drain lines
Sweating may sometimes be Sweating may sometimes be significantsignificant
Case study: Things Gone WrongCase study: Things Gone Wrong
Photo: Joe Lstiburek Photo: Nathan Yost, BSC
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Anatomy of a DisasterAnatomy of a Disaster
4040
Photo: Mark LaLiberte, Building Knowledge.
Flashing is Key: e.g., WindowsFlashing is Key: e.g., Windows
4141
Photo: Mark LaLiberte, Building Knowledge.
4242
Photo: Mark LaLiberte, Building Knowledge
Reverse Flashing: A Common Reverse Flashing: A Common MistakeMistake
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Building Moisture: Take-Building Moisture: Take-away Messagesaway Messages
Building components that get wet Building components that get wet must be able to dry out quickly. must be able to dry out quickly. Assemblies must be able to dry!Assemblies must be able to dry!
If they don’t, mold and other If they don’t, mold and other organisms will grow, creating health organisms will grow, creating health hazard for occupants and ultimately hazard for occupants and ultimately destroying the buildingdestroying the building
A moisture problem is like a fire: it will A moisture problem is like a fire: it will not get better with time. It cannot not get better with time. It cannot be ignored. be ignored. Respond promptly!Respond promptly!
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Section II:Section II: AIRFLOWS AIRFLOWS
OUTLINEOUTLINE Air moves according to Air moves according to pressure pressure
differencesdifferences; These can be created ; These can be created byby– Temperature differencesTemperature differences– WindWind– Mechanical equipmentMechanical equipment
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• For air to move (leak) into or out of building, you need a hole and a pressure difference
• Air in must equal air out–same for moisture, but on a different time frame
• Pathways can be direct or indirect, natural or mechanical
EEBA BFG
AirflowAirflow
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Airflows: Driving forces:Airflows: Driving forces: Temperature DifferencesTemperature Differences
Airflows can also be influenced byAirflows can also be influenced by Ventilation fansVentilation fans Furnaces / boilersFurnaces / boilers Ductwork (leaking)Ductwork (leaking) Major Appliances (dryer, water heater)Major Appliances (dryer, water heater)
All of the above can remove air from All of the above can remove air from the conditioned space. the conditioned space. What about What about makeup air?makeup air?
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Providing Fresh AirProviding Fresh Air
Best practiceBest practice to control moisture, to control moisture, pollutants and to save energypollutants and to save energy
Build a tight buildingBuild a tight building Tightly seal ductsTightly seal ducts (anything (anything butbut duct duct
tape)tape) Ventilate by design!Ventilate by design!
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Building Ventilation by Building Ventilation by AccidentAccident
Typical Typical ducts ducts can lose can lose 25% of 25% of airflow airflow through through joint joint leakageleakage
Daylight!
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……and some ducts lose more than and some ducts lose more than 25% of 25% of
Building Ventilation by Building Ventilation by DesignDesign
Various choicesVarious choices Passive vent open to buildingPassive vent open to building Outside air ducted to air return; Outside air ducted to air return;
Source controlSource control Some sources addressedSome sources addressed
--------------------------------------------------------------------------------------------------------Backdraft testing required in some Backdraft testing required in some
casescasesSome secondary requirementsSome secondary requirementsSome flexibilitySome flexibilityLots of controversyLots of controversy
Why be concerned about airflows into & Why be concerned about airflows into & out of buildings?out of buildings?
1)1) Energy transfers (losses)Energy transfers (losses)
2)2) Moisture transport (into bldg or into walls)Moisture transport (into bldg or into walls)
3)3) Pollutant transport (eg radon, ozone, Pollutant transport (eg radon, ozone, fireplace smoke, particulates, etc.)fireplace smoke, particulates, etc.)
And on the plus side, airflows provideAnd on the plus side, airflows provide
1)1) Fresh airFresh air
2)2) Replacement/ makeup airReplacement/ makeup air
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Airflow Dynamics Airflow Dynamics SummarySummary
““Nature abhors a vacuum”Nature abhors a vacuum”
The law that gases (and other materials) The law that gases (and other materials) move from a region of high pressure move from a region of high pressure to low pressure is analogous to, and as to low pressure is analogous to, and as immutable as the law of gravityimmutable as the law of gravity
Pressures will equilibrate whenever Pressures will equilibrate whenever there is a pathway, no matter how there is a pathway, no matter how small or indirect small or indirect
Amount of air entering (or leaving) Amount of air entering (or leaving) through various openings (such as through various openings (such as envelope leaks) vs. flue openings envelope leaks) vs. flue openings depends on relative sizes of openingsdepends on relative sizes of openings
ORORIf total envelope leaks are small relative If total envelope leaks are small relative
to flue opening(s), some flues may to flue opening(s), some flues may become main sources of makeup air–a become main sources of makeup air–a problem if flue is active!problem if flue is active!
Direct vent or sealed combustion betterDirect vent or sealed combustion better
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Airflows Airflows SummarySummary
Take Home Message
If building airflow is not balanced
– inflow and exhaust not equal - the building
will become pressurized or depressurized
and bad things can happen.
Likewise, pressure differentials can happen
within the building.
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References & Resources References & Resources for this Sectionfor this Section
Building Science Corporation Building Science Corporation wwww.buildingscience.comwwww.buildingscience.com
BFG: BFG: Builders Guide: Mixed Humid Builders Guide: Mixed Humid ClimatesClimates. Energy and Environmental . Energy and Environmental Building Association (EEBA): Building Association (EEBA): www.eeba.orgwww.eeba.org
Lstiburek, J. Lstiburek, J. Water Management Guide. Water Management Guide. Energy and Environmental Building Energy and Environmental Building Association (EEBA): 2004. www.eeba.orgAssociation (EEBA): 2004. www.eeba.org
Building America Best Practices Series: Building America Best Practices Series: Volume 4. USDOE Building America Volume 4. USDOE Building America program: program: www.buildingamerica.gov
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References (cont.)References (cont.)
Lstiburek, J. Moisture Control for Lstiburek, J. Moisture Control for Buildings. Buildings. ASHRAE Journal, ASHRAE Journal, Feb 02, Feb 02, pp36-41. pp36-41.
HUD HUD Moisture Resistant Homes. March Moisture Resistant Homes. March 2006. 125 pp. 2006. 125 pp. Available atAvailable at