ARCH-432 Vapor Retarders and Air Barriers

Attendance A.

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In what modern day country was the first cavity wall developed and used? For what purpose?

Spain Rome Greece Turkey Macedonia

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

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

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

Mitigation Strategies Pressurization Q S = 1.1 x CFM x (T 2 – T 1 ) Vs.

You own the variables!

Q S = 1.1 x (CFH/ft of crack x ft of crack)/60 x ΔT

LEED Points Available Environmental Quality (EQ) “Ventilation”  Credit 1 – Install permanent CO 2 monitoring system with feedback to ventilation system  Credit 2 – Ventilation system 30% above ASHRAE Standard 62.1

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

Stack Effect

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

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

Terms Temperature gradient Vapor barrier Vapor retarder Air barrier

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

Temperature Gradients The temperature differential between two separate surfaces as heat transmits across them.

  A Proportional calculation   Uses Indoor/outdoor DB Temperatures R values Purpose  Determine surface temperatures   MRT Dew Point

Thermal Breaks Significantly reduce the Resistance of the wall assembly

Concrete Wall

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

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

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

Check for condensation within walls

Temperature 80 o F 70 o 60 o 50 o 40 o 30 o 20 o 10 o 0 o -10 o -20 o

Heat Transmission and Exfiltration (ventilation) Infiltration IA: DB=75 o F WB = 56 o F OA: DB=-5 o F DP: 39 o F

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

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)

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 condense inside a cold wall indoor air can  In hot and humid climates (summer) humid outdoor air can condense inside a cold wall

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

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

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

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

Placing Vapor Retarders 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

Goal Keep high humidity out of the walls

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

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

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

8" Face Brick 1" air gap 6" Batt insulation 5/8" gypboard

Cold and Very Cold Climates Open cell

Drainage Planes Weep holes and slots  They allow the wall to drain  From leaks  From condensation

What about Concrete Floors