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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. - PowerPoint PPT Presentation
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ARCH-432
Vapor Retarders and Air Barriers
Attendance
In what modern day country was the first cavity wall developed and used? For what purpose?
A. SpainB. RomeC. GreeceD. TurkeyE. Macedonia
Add Infiltration Through Open Door
Determine Door Usage Number of People per Minute = ת
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
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!
LEED Points Available
Environmental Quality (EQ) “Ventilation” Credit 1 – Install permanent CO2 monitoring
system with feedback to ventilation system Credit 2 – Ventilation system 30% above
ASHRAE Standard 62.1
Infiltration Variables
Wind velocity and directionStack effectsCorner roomsExhaust fans on or offPressure zoningFrequency of useMaintenance
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 ceilingProperly place an air barrier in a wallProperly place a vapor retarder in a wall, if one is needed
Terms
Temperature gradientVapor barrierVapor retarderAir barrier
Design Goals
Keep water from getting inLet 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…
North Side
Siding warps
Siding pulled away
You see…
North Side Windows
You note that the snow extends into the closet
Check for condensation within walls
-20o
10o
0o
-10o
20o
30o
40o
50o
60o
70o
80oF
Temperature Heat Transmission and Exfiltration (ventilation)
Infiltration
IA: DB=75oF WB = 56oF
OA: DB=-5oF
DP: 39oF
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 spacesAn 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 indoor air can condense inside a cold wall
In hot and humid climates (summer) humid outdoor air can condense inside a cold wall
Air Barrier RulesIn hot and humid climates, place the air barrier/vapor retarder on the outdoor side of the insulation or wall sheathingIn 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 workAvoid 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, humid1B – Very hot, dry2A – Hot, humid2B – Hot, dry3A – Warm, humid3B – Warm, dry3c – Warm, marine4A – Mixed, humid4B – Mixed, dry4C – Mixed, marine5A – Cool, humid5B – Cool, dry5C – Cool, marine6A – Cold, humid6B – Cold, dry7 – Very cold8 - Sub arctic
Vapor Barriers
Where would you put a vapor retarder in the proposed assembly?
6" Batt insulation
5/8" gypboard
8" Face Brick
1" air gap
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