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