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

1
BUILDING DYNAMICSMoisture, Airflows and
Construction TechnologyITEP Level 2 WX Training

• Joseph T. Ponessa, Ph.D.
• Professor Emeritus Housing, Indoor Environments
  and Health

2
(No Transcript)
3
Goals

• Review basic dynamics of moisture movement,
  control in buildings
• Review basic dynamics of airflows in buildings
• Proper management of moisture and airflows
  provides better buildings and reduces callbacks.
• --------------------------------------------------
  --
• Understanding of these mechanisms is essential
  for diagnostics

4
Objective how does this fit with weatherization?

• Weatherization can improve comfort and save
  money. Downside is inadequate ventilation
• When is ventilation inadequate?
• When it is less than prescribed ventilation
• When it is inadequate to take care of building
  excesses
• Too much moisture
• Excessive pollution sources

5
Overview of Todays Presentation

• Building Science
• Moisture dynamics applications in buildings
• Airflow mechanisms applications in buildings

6
Building ScienceMoisture Dynamics, sources
remedies Air flows
7
Section I Moisture DynamicsOutline

• Basic moisture science Vapor Liquid
• Air vapor temperature relationships
• Relative Humidity
• Putting it all together Psychrometric chart
• Vapor movement
• Diffusion
• Bulk transfer air flows

8
Moisture Dynamics Outline (contd)

• Basic moisture science (cont.)
• Water movement
• Gravity wind
• Capillary action
• Moisture sources
• Moisture Measurement
• Air
• Surfaces / solids

9
Moisture Dynamics

• Water can exist in three states
• Vapor
• Liquid
• Solid

10
Moisture DynamicsVapor

• Vapor-Temperature relationships (At saturation)

The amount of moisture that air can hold
increases directly with temperature.
11
Moisture Dynamics Vapor (cont.)

• Relative humidity

• Because airs moisture-holding capacity increases
  with temperature
• for a given amount of moisture in air
• RH as Temp
• and vice versa

RH is the amount of moisture In the air compared
to the total Moisture capacity of air At a given
temperature. Expressed as .
12
Moisture Dynamics Vapor

• Dew point Saturation
• Air that is cooled to the limit of its moisture
  carrying capacity releases the vapor as droplets
  condensation (or rain)
• This is the Dew point temperature

13
Moisture DynamicsPutting it all together The
Psychrometric Chart
14
Moisture Dynamics Vapor

• So what does it all mean?
• Moist air that is cooled down
• OR
• Moist air that meets a cool surface will
  condense!
• Wet surfaces that dont/cant dry rapidly will
  produce mold

15
Moisture Dynamics Vapor Transport

• Vapor transport how does vapor get from point A
  to point B?
• POSSIBLE MECHANISMS
• Diffusion
• Bulk transport Airflow
• Which is more important?

16
Moisture Dynamics Vapor Transport via Airflow
Source USDOE

• Moisture carried into wall via air flow / leakage
  through openings. What is the driving force?

17
Moisture Dynamics Vapor Transport via Diffusion
Source USDOE

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

18
Moisture Dynamics

• Which mechanism is most important?
• Diffusion?
• Air transport?

19
Moisture Dynamics Vapor Transfer cold climate
Adapted from Lstiburek 2001 p 290
20
Moisture Dynamics

• Diffusion vs. air transport
• While air transport accounts for bulk of
  moisture migration in most buildings, there are
  circumstances when diffusion is most important
  factor

21
Permeability- Bldg Materials
Vapor Imperm P lt0.1
PE Film
Glass
Aluminum foil
Foil faced insul (non perf)

• Four classes of vapor retarders have been
  identified

Semi-imperm. P 0.1-1
Kraft backed fiberglass insul
Oil based paint
Vinyl wallpaper (most)
Extr polystr gt1 (unfaced)
P Perm
Vapor Barrier
22
Permeability- Bldg. Materials
Vapor semi-perm P1-10
Plywood
Bitumen impreg kraft
OSB
Unfaced Exp polystyrene
Unfaced Extr poly lt1
Building paper
Latex paint (Most)
Vapor perm P gt10
Fiberglass insul
Unpainted gyp board, plaster
Masonry, Fiberboard, Dimens. lumber
15 felt, Housewrap
Cellulose insul.
Building America Best Practices Series Volume 4
..Mixed-Humid Climate Version 1, 9/2005
Design-p13
23
Vapor Barriers and Retarders

• Class I vapor retarder 0.1 perm or less
• Class II vapor retarder 0.1 perm to less than
  1.0 perm
• Class III vapor retarder 1.0 perm to 10 perm
• --------------------------------------------------
  -
• A class I retarder is a vapor barrier.
• A class II retarder is a vapor retarder per IBC

Source BFG MH p108
24
PERMABILITY

• An important note about building materials and
  water

• Permability of many materials changes when they
  are wet. Ppermeability of wet plywood, for
  example, changes from 0.75 (dry) to 3.0 when wet

25
Hydric Buffer Capacity2000 sf Home
Steel frame with gyp.sheathing Approx 5 gallons
Wood frame with wood sheathing Approx 50 gallons
Masonry wall Source Lstiburek, J. ASHRAE Journal 2-03 Approx 500 gallons
26
Questions about vapor transmission/dynamics?

• While vapor migration and condensation can play
  an important role in moisture problems, most
  problems are caused by rainwater

27
Moisture DynamicsLiquid

• Liquid water can flow via
• Gravity (or wind pressure)
• Capillary action (wicking)
• against gravity

28
Moisture DynamicsLiquid

• Gravity
• It flows downhill

Source Builder Magazine
29
Moisture Dynamics

• Capillary action
• Water can flow against gravity when moving in a
  tight space

and, by the same process, can wick through
porous materials
30
Moisture Dynamics

• Practical applications
• Water can travel up and behind flashing that is
  not properly dimensioned
• Water can diffuse/wick through masonry, adding
  humidity to spaces and wetting components (e.g.
  sill plates)

31
Moisture DynamicsCapillary action
Source USDOE
32
Moisture dynamics
Abbey grange, Great Coxwell, England
XXX barn
Photo Barn. Houghton Mifflin, 1992.

• Some builders, at least, have known about
  capillary action for a long time

33
Moisture dynamics

• Barn interior, showing posts set on stone piers
• This barn, built in mid- 13th century, in use
  until 1966, when deeded to National trust
• Photo Barn. Houghton Mifflin, 1992

34
Moisture dynamics

• Note detail on top of pier
• A sacrificial wood slab has been placed here.
  Moisture migrating through pier will enter slab
  instead of end grain of post slab is easily
  replaced
• Photo Barn. Houghton Mifflin, 1992

35
Moisture Dynamics

• Examples of capillary breaks
• Space drip edge
• Closed cell sill sealer
• Gravel bed beneath slab
• Poly, other membranes
• Sprayed sealants

• Capillary break can interrupt capillary flow of
  moisture
• Use capillary break wherever one porous component
  (eg., wood) meets another (eg., masonry)
• (Examples later)

36
Moisture Sources

• Outline for this section
• Plumbing leaks
• Rainwater
• Groundwater
• Humid air (Including embodied water)
• Mechanical equipment (Including Combustion
  equipment)
• Occupant practices

37
Moisture SourcesPlumbing leaks

• Plumbing leaks should be obvious but can be in
  concealed spaces, and may involve supply or drain
  lines
• Sweating may sometimes be significant

38
Moisture SourcesRainwater

• Gutters downspouts
• Water discharged next to foundation and /or
  against building is almost certain to enter
• Most basement moisture problems are due to
  rainwater

39
Moisture SourcesRainwater

• Discharge against building may also penetrate-
  masonry is not waterproof
• (Consider masonry as a Hard sponge)
• ------------------
• Low spots, backslope next to building also cause
  problems

40
Moisture SourcesRainwater and grading
41
Moisture Sources Humid air (Summer) Basement
ventilation may add moisture / RH
Also consider air conditioned interior
42
Moisture sourcesMechanical equipment

• Combustion produces a LOT of moisture
• 2O2 CH4 CO2 2H2O
• 1 lb of nat gas
• 2.25 lb (1.125 Q) water!

Gas furnace, blocked flu, condensation soaks
brick in out
Further discussion under Airflows
43
Moisture Sources

• Embodied moisture New construction Several
  hundred pounds of moisture in concrete, lumber,
  drywall compound, paint, etc. New building may
  exhibit moisture problems for months after
  construction
• Cold weather construction Salamander (100 k
  BTU/h) produces about 1 gal combustion water per
  hour
• Occupant practices -Add moisture, too

44
Moisture Measurement

• Air measurement
• Sling psychrometer
• Hygrometer (electronic)

45
Moisture Measurement (cont.)

• Surface / material measurement
• Electronic device
• (eg Protimeter)
• Measures moisture content- wood, drywall, masonry

46
Moisture Content in Building Materials

• Mold growth can begin
• In lumber _at_16 moisture content (this represents
  equilibrium _at_80RH)
• In gypsum sheathing _at_1 moisture content
• Source Lstiburek, ASHRAE Journal, 2/02

47
Keep Water Out Drain the Building
EEBA WMG
48
Case study Things Gone Wrong
Photo Nathan Yost, BSC
Photo Joe Lstiburek
49
Anatomy of a Disaster
50
Flashing is Key e.g., Windows
Photo Mark LaLiberte, Building Knowledge.
51
Photo Mark LaLiberte, Building Knowledge.
52
Photo Mark LaLiberte, Building Knowledge.
53
Photo Mark LaLiberte, Building Knowledge.
54
Photo Mark LaLiberte, Building Knowledge.
55
Photo Mark LaLiberte, Building Knowledge.
56
Photo EcoVillage Cleveland townhomes, BSC BA
project, 2003.
57
Reverse Flashing A Common Mistake
Photo Mark LaLiberte, Building Knowledge
58
Building moisture Take-away messages

• Building components that get wet must be able to
  dry out quickly. Assemblies must be able to dry!
• If they dont, mold and other organisms will
  grow, creating health hazard for occupants and
  ultimately destroying the building
• A moisture problem is like a fire it will not
  get better with time. It cannot be ignored.
  Respond promptly!

59
Section II AIRFLOWS

• OUTLINE
• Air moves according to pressure differences
  These can be created by
• Temperature differences
• Wind
• Mechanical equipment

60
Airflow

• For air to move (leak) into or out of building,
  you need a hole and a pressure difference
• Air in must equal air outsame for moisture, but
  on a different time frame
• Pathways can be direct or indirect, natural or
  mechanical

EEBA BFG
61
Airflows Driving forces Temperature Differences
Heating Season
Aka THERMOSIPHONING
Source USDOE
62
Airflows Driving Forces Wind
Source USDOE
63
Combustion ProductsBackdrafting

• What factors can cause low (negative) pressure at
  the furnace and lack of makeup air?
• Competition from other mechanical equipment
• Exhaust fans Other combustion equipment
• Duct leakage e.g. return ducts in exterior walls

64
Airflows Driving forces Mechanical Equipment

• Airflows can also be influenced by
• Ventilation fans
• Furnaces / boilers
• Ductwork (leaking)
• Major Appliances (dryer, water heater)
• All of the above can remove air from the
  conditioned space. What about makeup air?

65
Airflows Mechanical EquipmentExamples

• Furnace
• -Oil burner draws about 1600 cf of air per hour _at_
  firing rate of 1 GPH
• Downdraft range vent pulls 400 CFM
• Whos gonna win this one?

• Leaking ducts
• -Can lose as much as 25 of airflow if joints not
  properly sealed Energy loss poss. moisture
  problem in unconditioned space

66
Airflows Mechanical EquipmentBackdrafting
Summary

• Can affect atmospheric equipment (conventional
  gas furnaces, hot water heaters, dryers, etc.)
• Inadequate air supply or negative pressures in
  furnace area can introduce combustion gases
  including moisture into building via reverse flow
  in weakest appliance(s)

67
Providing Fresh Air

• Best practice to control moisture, pollutants and
  to save energy
• Build a tight building
• Tightly seal ducts (anything but duct tape)
• Ventilate by design!

68
Building Ventilation by Accident
Daylight!

• Typical ducts can lose 25 of airflow through
  joint leakage

69
and some ducts lose more than 25 of their
airflow!
Needs repair
70
Typical Ventilation Rates

• 100-year-old house Two ACH
• Energy-conserving house (1970s) 0.1 ACH)
• Estimated optimum, 1980s 0.5 ACH
• Present day ASHRAEs engineering standard

71
Building Ventilation by Design

• Various choices
• Passive vent open to building
• Outside air ducted to air return dampers,
  controllers
• Sealed combustion equipment reduces need for
  makeup air

72
Ventilation by Design (cont.)

• Heat recovery Ventilators (aka Air-to-air heat
  exchangers or HRVs)
• (NJ economics were marginal, not now)

(c) Natural Resources Canada. Used by permission
HRVs only make sense in a tight house
73
ASHRAE Residential Ventilation Standard
62.2Goal Reduce indoor pollutants

• Approach
• Whole-house ventilation
• 50 CFM (typical house)
• Vent system rated _at_ 7.5 CF PP 1CFM / 100SF
  (Some exceptions)
• Local exhaust
• Mech exhaust, Kitchens baths (Not toilets,
  utility rooms)

Source M. Sherman, Lawrence Berkeley Labs
74
ASHRAE Residential Ventilation Standard 62.2
(cont.)

• Source control
• Some sources addressed
• --------------------------------------------------
  --
• Backdraft testing required in some cases
• Some secondary requirements
• Some flexibility
• Lots of controversy

75
ASHRAE Residential Ventilation Standard 62.2
(contd.)

• About whole house ventilation
• Calculation House, 3 BR, 1500 sq ft
• 7.5 CFM/ BR1 1CFM/100 sq ft
• 7.5X4 100X15 30 15 45 CFM

76
Airflows Summary

• Why be concerned about airflows into out of
  buildings?
• Energy transfers (losses)
• Moisture transport (into bldg or into walls)
• Pollutant transport (eg radon, ozone, fireplace
  smoke, particulates, etc.)
• And on the plus side, airflows provide
• Fresh air
• Replacement/ makeup air

77
Airflow Dynamics Summary

• Nature abhors a vacuum
• The law that gases (and other materials) move
  from a region of high pressure to low pressure is
  analogous to, and as immutable as the law of
  gravity
• Pressures will equilibrate whenever there is a
  pathway, no matter how small or indirect

78
Airflow Dynamics Summary (cont.)

• Amount of air entering (or leaving) through
  various openings (such as envelope leaks) vs.
  flue openings depends on relative sizes of
  openings
• OR
• If total envelope leaks are small relative to
  flue opening(s), some flues may become main
  sources of makeup aira problem if flue is
  active!
• Direct vent or sealed combustion better

79
Airflows Summary
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.
80
References Resources for this Section

• Building Science Corporation wwww.buildingscience
  .com
• BFG Builders Guide Mixed Humid Climates. Energy
  and Environmental Building Association (EEBA)
  www.eeba.org
• Lstiburek, J. Water Management Guide. Energy and
  Environmental Building Association (EEBA) 2004.
  www.eeba.org
• Building America Best Practices Series Volume
  4. USDOE Building America program
  www.buildingamerica.gov

81
References (cont.)

• Lstiburek, J. Moisture Control for Buildings.
  ASHRAE Journal, Feb 02, pp36-41.
• HUD Moisture Resistant Homes. March 2006. 125 pp.
  Available at
• http//www.huduser.org/publications/destech/moistu
  rehomes.html
• Or call 1-800 245 2691, option 1 for hard copy
  (5.00)