BUILDING DYNAMICS: Moisture, Airflows and Construction Technology ITEP Level 2 WX Training

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BUILDING DYNAMICS:BUILDING DYNAMICS:Moisture, Airflows and Moisture, Airflows and

Construction TechnologyConstruction TechnologyITEP Level 2 WX TrainingITEP Level 2 WX Training

Joseph T. Ponessa, Joseph T. Ponessa, Ph.D.Ph.D.

Professor Emeritus Professor Emeritus Housing, Indoor Housing, Indoor

Environments and 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 callbacks.reduces callbacks.

-------------------------------------------------------------------------------------------------------- Understanding of these mechanisms Understanding of these mechanisms

is essential for diagnosticsis essential for diagnostics

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

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Building ScienceBuilding ScienceMoisture Dynamics, sources & Moisture Dynamics, sources &

remedies; Air flowsremedies; Air flows

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Section I:Section I: Moisture Dynamics Moisture DynamicsOutlineOutline

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

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Moisture Dynamics Moisture Dynamics Outline (cont’d)Outline (cont’d)

Basic moisture scienceBasic moisture science (cont.) (cont.) Water movementWater movement

Gravity; windGravity; wind Capillary actionCapillary action

Moisture sourcesMoisture sources Moisture MeasurementMoisture Measurement

AirAir Surfaces / solidsSurfaces / solids

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Moisture DynamicsMoisture DynamicsWater can exist in three statesWater can exist in three states VaporVapor LiquidLiquid SolidSolid

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Moisture DynamicsMoisture DynamicsVaporVapor

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 Vapor (cont.)Vapor (cont.)

Relative Relative humidityhumidity Because air’s Because air’s

moisture-holding moisture-holding capacity increases capacity increases with temperature…with temperature…

……for a given amount for a given amount of moisture in airof moisture in air

RH as Temp RH as Temp

……and vice versaand vice versa

RH is the amount of moistureIn the air compared to the total Moisture capacity of airAt a given temperature.Expressed as %.

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Moisture DynamicsMoisture Dynamics VaporVapor

Dew point: Dew point: SaturationSaturation

Air that is cooled to the Air that is cooled to the limit of its moisture limit of its moisture carrying capacity carrying capacity releases the vapor releases the vapor as droplets: as droplets: condensation (or condensation (or rain) rain)

This is the This is the Dew point Dew point temperaturetemperature

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Moisture DynamicsMoisture DynamicsPutting it all together: The Putting it all together: The

Psychrometric ChartPsychrometric Chart

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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 Vapor Transport viaVapor Transport via DiffusionDiffusion

Moisture transport by diffusion: Molecules Moisture transport by diffusion: Molecules penetrate through drywall. penetrate through drywall. What is the What is the driving force?driving force?

Source: USDOE

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Moisture DynamicsMoisture DynamicsWhich mechanism is most important?Which mechanism is most important?

Diffusion?Diffusion?

Air transport?Air transport?

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Moisture DynamicsMoisture Dynamics Vapor Transfer – cold climateVapor Transfer – cold climate

Seasonal Moisture transfer: 4'x8' gypboard:Int RH: 40% @ 70 deg F

010203040

Diffusion Air leakage 1" sq

Diffusion vs Air leakage

Wat

er (Q

uarts

)

Adapted from Lstiburek 2001 p 290

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Moisture DynamicsMoisture DynamicsDiffusion 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

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Permeability- Bldg Permeability- Bldg MaterialsMaterials

Four classes of Four classes of vapor vapor retarders have retarders have been identifiedbeen identified

Vapor Imperm P Vapor Imperm P <0.1<0.1 * *PE FilmPE FilmGlassGlassAluminum foilAluminum foilFoil faced insul (non Foil faced insul (non perf)perf)Semi-imperm. P 0.1-1Semi-imperm. P 0.1-1

Kraft –backed fiberglass Kraft –backed fiberglass insulinsulOil based paintOil based paintVinyl wallpaper (most)Vinyl wallpaper (most)Extr polystr >1” (unfaced)Extr polystr >1” (unfaced)

P = Perm

* Vapor Barrier

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Permeability- Bldg. Permeability- Bldg. MaterialsMaterials

Vapor semi-perm Vapor semi-perm P1-10P1-10PlywoodPlywoodBitumen impreg kraftBitumen impreg kraftOSBOSBUnfaced Exp Unfaced Exp polystyrenepolystyreneUnfaced Extr poly <1”Unfaced Extr poly <1”Building paperBuilding paperLatex paint (Most)Latex paint (Most)

Vapor perm P Vapor perm P >10>10Fiberglass insulFiberglass insulUnpainted gyp Unpainted gyp board, plasterboard, plasterMasonry, Masonry, Fiberboard,Fiberboard,Dimens. lumberDimens. lumber15# felt, 15# felt, HousewrapHousewrapCellulose insul.Cellulose insul.

Building America Best Practices Series: Volume 4 –

…..Mixed-Humid Climate Version 1, 9/2005 • Design-

p13

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Vapor Barriers and Vapor Barriers and RetardersRetarders

Class I vapor retarder = 0.1 perm or Class I vapor retarder = 0.1 perm or lessless

Class II vapor retarder = 0.1 perm to Class II vapor retarder = 0.1 perm to less than 1.0 permless than 1.0 perm

Class III vapor retarder = 1.0 perm to Class III vapor retarder = 1.0 perm to 10 perm 10 perm

------------------------------------------------------------------------------------------------------A class I retarder is a vapor A class I retarder is a vapor barrier.barrier.A class II retarder is a vapor retarder per A class II retarder is a vapor retarder per

IBCIBCSource: BFG MH p108

PERMABILITYPERMABILITYAn 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

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Hydric Buffer Capacity:Hydric Buffer Capacity:2000 sf Home2000 sf Home

Steel frame with Steel frame with gyp.sheathinggyp.sheathing

Approx 5 gallonsApprox 5 gallons

Wood frame with Wood frame with wood sheathingwood sheathing

Approx 50 gallonsApprox 50 gallons

Masonry wallMasonry wall

Source: Lstiburek, J. ASHRAE Source: Lstiburek, J. ASHRAE Journal 2-03Journal 2-03

Approx 500 gallonsApprox 500 gallons

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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 DynamicsCapillary 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 DynamicsPractical 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)

3131

Moisture DynamicsMoisture DynamicsCapillary actionCapillary action

Source: USDOE

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Moisture dynamicsMoisture dynamics

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 dynamicsBarn 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

Photo: Photo: Barn. Barn. Houghton Houghton Mifflin, 1992Mifflin, 1992

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Moisture dynamicsMoisture dynamicsNote detail on top of Note detail on top of

pierpierA 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

Photo: Photo: Barn. Barn. Houghton Mifflin, Houghton Mifflin, 19921992

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Moisture DynamicsMoisture Dynamics ““Capillary breakCapillary break” ”

can interrupt capillary can interrupt capillary flow of moistureflow of moisture

Use capillary break Use capillary break wherever one porous wherever one porous component (eg., component (eg., wood) meets another wood) meets another (eg., masonry)(eg., masonry)

(Examples later)(Examples later)

Examples of Examples of capillary breakscapillary breaks

Space; drip edgeSpace; drip edge Closed cell sill sealerClosed cell sill sealer Gravel bed beneath Gravel bed beneath

slabslab Poly, other Poly, other

membranesmembranes Sprayed sealantsSprayed sealants

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Moisture SourcesMoisture SourcesOutline for this sectionOutline for this section Plumbing leaksPlumbing leaks RainwaterRainwater GroundwaterGroundwater Humid air (Including embodied Humid air (Including embodied

water)water) Mechanical equipment (Including Mechanical equipment (Including

Combustion equipmentCombustion equipment)) Occupant practicesOccupant practices

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Moisture Sources:Moisture Sources:Plumbing leaksPlumbing leaks

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

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Moisture SourcesMoisture SourcesRainwaterRainwater

Gutters & Gutters & downspoutsdownspouts

Water discharged next Water discharged next to foundation and /or to foundation and /or against building is against building is almost certain to enter almost certain to enter

Most basement Most basement moisture problems moisture problems are due to are due to rainwaterrainwater

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Moisture SourcesMoisture SourcesRainwaterRainwater

Discharge against Discharge against building may also building may also penetrate- penetrate- masonry masonry is not waterproofis not waterproof

(Consider masonry as (Consider masonry as a “Hard sponge”)a “Hard sponge”)

------------------------------------Low spots, backslope Low spots, backslope

next to building also next to building also cause problemscause problems

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Moisture Sources:Moisture Sources:Rainwater and gradingRainwater and grading

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Moisture Sources:Humid air (Summer)

Basement ventilation may add moisture / RH

Also consider air

conditioned interior

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Moisture sources:Moisture sources:Mechanical equipmentMechanical equipment

Combustion Combustion produces a LOT produces a LOT of moistureof moisture

2O2O22 + CH + CH44 = CO = CO2 2 + 2H+ 2H22OO

1 lb of nat gas 1 lb of nat gas 2.25 lb (1.125 2.25 lb (1.125

Q) water!Q) water! Gas furnace, blocked

flu, condensation

soaks brick in & out

Further discussion under

Airflows

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Moisture SourcesMoisture SourcesEmbodied moistureEmbodied moisture – New – New

construction; Several hundred pounds construction; Several hundred pounds of moisture in concrete, lumber, of moisture in concrete, lumber, drywall compound, paint, etc. New drywall compound, paint, etc. New building may exhibit moisture building may exhibit moisture problems for months after constructionproblems for months after construction

Cold weather constructionCold weather construction – –SalamanderSalamander (100 k BTU/h) produces (100 k BTU/h) produces about 1 gal combustion water per hourabout 1 gal combustion water per hour

Occupant practicesOccupant practices -Add moisture, too -Add moisture, too

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Moisture MeasurementMoisture MeasurementAir Air measuremenmeasurementt

Sling Sling psychrometepsychrometerr

Hygrometer Hygrometer (electronic)(electronic)

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Moisture Measurement Moisture Measurement (cont.)(cont.)

Surface / Surface / material material measurementmeasurement

Electronic deviceElectronic device (eg Protimeter)(eg Protimeter)Measures moisture Measures moisture

content- wood, content- wood, drywall, masonrydrywall, masonry

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Moisture Content in Moisture Content in Building MaterialsBuilding Materials

Mold growth can begin…Mold growth can begin… In lumber @16% moisture content In lumber @16% moisture content

(this represents equilibrium (this represents equilibrium @80%RH)@80%RH)

In gypsum sheathing @1% moisture In gypsum sheathing @1% moisture content content

Source: Lstiburek, ASHRAE Journal, 2/02Source: Lstiburek, ASHRAE Journal, 2/02

4747EEBA WMG

Keep Water Out: Drain the Building

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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

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Photo: Mark LaLiberte, Building Knowledge.

Flashing is Key: e.g., WindowsFlashing is Key: e.g., Windows

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Photo: Mark LaLiberte, Building Knowledge.

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Photo: Mark LaLiberte, Building Knowledge.

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Photo: Mark LaLiberte, Building Knowledge.

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Photo: Mark LaLiberte, Building Knowledge.

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Photo: Mark LaLiberte, Building Knowledge.

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Photo: EcoVillage Cleveland townhomes, BSC BA project, 2003.

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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 be not get better with time. It cannot be ignored. ignored. Respond promptly!Respond promptly!

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Section II:Section II: AIRFLOWS AIRFLOWSOUTLINEOUTLINE 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

Heating Season:

Source: USDOE

Aka THERMOSIPHONING

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Airflows: Driving Forces:Airflows: Driving Forces: WindWind

Source: USDOE

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Combustion Products:Combustion Products:BackdraftingBackdrafting

What factors can cause low What factors can cause low (negative) pressure at the (negative) pressure at the furnace and lack of makeup air?furnace and lack of makeup air?

Competition from other Competition from other mechanical equipment:mechanical equipment:– Exhaust fans; Other combustion Exhaust fans; Other combustion

equipmentequipment Duct leakage e.g. return ducts in Duct leakage e.g. return ducts in

exterior walls exterior walls

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Airflows: Driving forces:Airflows: Driving forces: Mechanical EquipmentMechanical Equipment

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 the All of the above can remove air from the

conditioned space. conditioned space. What about What about makeup air?makeup air?

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Airflows:Airflows: Mechanical Mechanical EquipmentEquipmentExamplesExamples

Leaking ductsLeaking ducts-Can lose as much -Can lose as much

as 25% of airflow if as 25% of airflow if joints not properly joints not properly sealed: Energy sealed: Energy loss & poss. loss & poss. moisture problem moisture problem in unconditioned in unconditioned spacespace

FurnaceFurnace-Oil burner draws -Oil burner draws

about 1600 cf of air about 1600 cf of air per per hourhour @ firing @ firing rate of 1 GPHrate of 1 GPH

Downdraft range Downdraft range ventvent pulls 400 CFM pulls 400 CFM

Who’s gonna win this Who’s gonna win this one?one?

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AirflowsAirflows: : Mechanical Mechanical EquipmentEquipment

Backdrafting SummarBackdrafting Summaryy Can affect “atmospheric” equipment Can affect “atmospheric” equipment

(conventional gas furnaces, hot water (conventional gas furnaces, hot water heaters, dryers, etc.) heaters, dryers, etc.)

Inadequate air supply or negative Inadequate air supply or negative pressures in furnace area can introduce pressures in furnace area can introduce combustion gases combustion gases including moistureincluding moisture into building via reverse flow in into building via reverse flow in “weakest” appliance(s) “weakest” appliance(s)

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Providing Fresh AirProviding Fresh AirBest 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

their airflow!their airflow!

“Needs repair”

Typical Ventilation RatesTypical Ventilation Rates 100-year-old house: Two ACH100-year-old house: Two ACH Energy-conserving house (1970’s)”: Energy-conserving house (1970’s)”:

0.1 ACH)0.1 ACH) Estimated optimum, 1980’s: 0.5 ACHEstimated optimum, 1980’s: 0.5 ACH Present day: ASHRAE’s engineering Present day: ASHRAE’s engineering

standardstandard

7070

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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;

dampers, controllersdampers, controllers Sealed combustion equipment Sealed combustion equipment

reduces need for makeup airreduces need for makeup air

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Ventilation by Design Ventilation by Design (cont.) (cont.)

Heat recovery Heat recovery VentilatorsVentilators (aka Air-to-air (aka Air-to-air heat heat exchangers or exchangers or HRV’s) HRV’s)

(NJ economics (NJ economics werewere marginal, marginal, not now)not now)

(c) Natural Resources Canada. Used by permission

HRV’s only make sense in a

tight house

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ASHRAE Residential ASHRAE Residential Ventilation Standard 62.2Ventilation Standard 62.2

Goal: Reduce indoor pollutantsGoal: Reduce indoor pollutantsApproach Approach Whole-house ventilationWhole-house ventilation

50 CFM (typical house)50 CFM (typical house) Vent system rated @ 7.5 CF PP + Vent system rated @ 7.5 CF PP +

1CFM / 100SF (Some exceptions)1CFM / 100SF (Some exceptions) Local exhaustLocal exhaust

Mech exhaust, Kitchens & baths (Not Mech exhaust, Kitchens & baths (Not toilets, utility rooms) toilets, utility rooms)

Source: M. Sherman, Lawrence Berkeley Labs

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ASHRAE Residential Ventilation ASHRAE Residential Ventilation Standard 62.2 (cont.)Standard 62.2 (cont.)

Source controlSource control Some sources addressedSome sources addressed

--------------------------------------------------------------------------------------------------------Backdraft testing required in some casesBackdraft testing required in some casesSome secondary requirementsSome secondary requirementsSome flexibilitySome flexibilityLots of controversyLots of controversy

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ASHRAE Residential Ventilation ASHRAE Residential Ventilation Standard 62.2 (cont’d.)Standard 62.2 (cont’d.)

About whole house ventilationAbout whole house ventilationCalculation: Calculation: House, 3 BR, 1500 House, 3 BR, 1500

sq ftsq ft7.5 CFM/ BR+1 + 1CFM/100 sq ft7.5 CFM/ BR+1 + 1CFM/100 sq ft7.5X4 + 100X15 = 30 + 15 = 7.5X4 + 100X15 = 30 + 15 = 45 45

CFMCFM

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Airflows: Airflows: SummarySummary 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 provide1)1) Fresh airFresh air2)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 to move from a region of high pressure to low pressure is analogous to, and as 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

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Airflow Dynamics Airflow Dynamics Summary (cont.)Summary (cont.)

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–become main sources of makeup air–a problem if flue is active!a 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): www.eeba.orgBuilding Association (EEBA): www.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: www.buildingamerica.govprogram: 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

http://www.huduser.org/publications/http://www.huduser.org/publications/destech/moisturehomes.htmldestech/moisturehomes.html

Or call 1-800 245 2691, option 1 for hard Or call 1-800 245 2691, option 1 for hard copy ($5.00)copy ($5.00)