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ARCH-432

ARCH-432. Vapor Retarders and Air Barriers. Groups. Please write down your partner for your groups. Attendance. In what modern day country was the first cavity wall developed and used? For what purpose? Spain Rome Greece Turkey Macedonia. Attendance.

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ARCH-432

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  1. ARCH-432 Vapor Retarders and Air Barriers

  2. Groups • Please write down your partner for your groups.

  3. Attendance • In what modern day country was the first cavity wall developed and used? For what purpose? • Spain • Rome • Greece • Turkey • Macedonia

  4. Attendance • The oldest known cavity wall still in existence is in Western Turkey, in the ancient Greek City of Pergamum. The cavity wall was used to capture moisture, exactly its same function today. • The British “reinvented” the cavity wall, as evidenced by a design guide describing its construction published in 1821. • The building pictured is the Great Temple of Zeus from Pergamum.

  5. Add Infiltration Through Open Door • Determine Door Usage • ת = Number of People per Minute • Determine CFM per person (D) CFM = ת x D

  6. Infiltration by Crack Method • Add CFM from Crack losses to CFM for Open Door losses

  7. Mitigate These Losses • How do you reduce or mitigate these losses?

  8. Mitigate These Losses Question: How do you reduce or mitigate these losses? Answer: Really good weather-stripping Pressurization Vestibules Revolving doors Seal cracks and openings CO2 sensors

  9. Mitigation Strategies • Pressurization QS = 1.1 x CFM x (T2 – T1) Vs. QS = 1.1 x (CFH/ft of crack x ft of crack)/60 x ΔT You own the variables!

  10. Infiltration Variables • Wind velocity and direction • Stack effects • Corner rooms • Exhaust fans on or off • Pressure zoning • Frequency of use • Maintenance

  11. Stack Effect

  12. Stack Effect Question: What type of door was invented because of the stack effect? Answer: The revolving door.

  13. What You Need To Know • The cause and effects of infiltration and exfiltration on moisture migration

  14. What Do You Need To Be Able To Do • Be able to calculate the dew point within a composite wall or ceiling • Properly place an air barrier in a wall • Properly place a vapor retarder in a wall, if one is needed

  15. Terms • Temperature gradient • Vapor barrier • Vapor retarder • Air barrier

  16. Design Goals • Keep water from getting in • Let water out if it gets in • Wetting prevention versus drying • Select materials and locate vapor retarders to allow the assembly to dry • Different for each climate zone

  17. Design Goals • Water is lazy! It always takes the easiest route available. • Be careful in material selection. Many modern materials (such as O.S.B.) can make a great vapor retarder.

  18. Design Goals • Air barriers are really as (if not more) important than vapor retarders. • Air, even a small leak, can carry a lot of moisture into parts of a wall or roof • Vapor can condense where you do not want water vapor to condense.

  19. Thermal Breaks • Significantly reduce the Resistance of the wall assembly

  20. Concrete Wall

  21. Failure Analysis • Prof. Kirk’s one-of-a-kind, surefire process guaranteed to result in a mind-numbing law suit.

  22. At inspection, you see… Siding pulled away North Side Siding warps

  23. You note that the snow extends into the closet You see… North Side Windows

  24. Heat Transmission and Exfiltration (ventilation) Temperature 80oF 70o 60o Infiltration 50o 40o 30o IA: DB=75oF WB = 56oF 20o OA: DB=-5oF 10o 0o -10o -20o DP: 39oF Check for condensation within walls

  25. Definitions • Vapor Retarder – The element that is designed and installed in an assembly to retard the movement of water by vapor diffusion • Class I – .10 perm or less • Class II – .10 perm to 1.0 perm • Class III – 1.0 perm to 10.0 perm • Vapor Barrier – A Class I vapor retarder

  26. Air Barrier • Air barriers are systems of materials designed and constructed to control airflow between conditioned and unconditioned spaces • An air barrier is not necessarily a vapor barrier (i.e., they can be permeable)

  27. Air Barrier Rules • Water vapor moves from the warm side of building assemblies to the cold side • Climate dependant • Season dependant • In cold climates (winter) humid indoor air can condense inside a cold wall • In hot and humid climates (summer) humid outdoor air can condense inside a cold wall

  28. Air Barrier Rules • In hot and humid climates, place the air barrier/vapor retarder on the outdoor side of the insulation or wall sheathing • In very cold climates, place the vapor barrier on the indoor side of the insulation

  29. Placing Air Barriers • For a climate that is both hot/humid and cold, where do you place the air barrier?

  30. Construction and Installation • The air barrier on the outside must be continuous • Individual sheets must be taped together • Entire sheet must be taped to all window and door frames, foundations and roofing

  31. Construction and Installation • Dry all material before interior finish is applied • Problems often occur on accelerated or fast-track projects • Seal all ductwork and its connections

  32. Air barriers are more effective than Vapor Barriers Vapor permeation is minor compared to infiltration Vapor retarders make a wall more fragile Vapor retarders can prevent seasonal drying Vapor retarders can be very important Cold climates Any building with a high indoor moisture level Placing Vapor Retarders

  33. Goal • Keep high humidity out of the walls

  34. Placing Vapor Retarder Guidelines • Locate only on the warm side of the wall (except basement) • Avoid vapor barriers where vapor retarders will work • Avoid vapor retarders on both sides of assemblies • Avoid vinyl wall coverings on the inside of air-conditioned assemblies • Avoid polyethylene vapor barriers, foil faced batt insulation and reflective radiant barrier insulation on the interior of air-conditioned assemblies

  35. R Value Sheet

  36. R Value Sheet

  37. R Value Sheet For: Doors Windows Ceilings - and anything else Example 3 x 7 Insulated Door Inside air film . xx Door x.xx Outside air film .xx Total x.xx

  38. Placing a Vapor Retarder • 1A – Very hot, humid • 1B – Very hot, dry • 2A – Hot, humid • 2B – Hot, dry • 3A – Warm, humid • 3B – Warm, dry • 3c – Warm, marine • 4A – Mixed, humid • 4B – Mixed, dry • 4C – Mixed, marine • 5A – Cool, humid • 5B – Cool, dry • 5C – Cool, marine • 6A – Cold, humid • 6B – Cold, dry • 7 – Very cold • 8 - Sub arctic

  39. Vapor Barriers • Where would you put a vapor retarder in the proposed assembly?

  40. Cold and Very Cold Climates Open cell

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