PROTECTING THE BUILDING ENVELOPE

1
PROTECTING THE BUILDING ENVELOPE

• Barriers to Air, Vapour,
• Weather and Moisture

2
TYPES OF BARRIERS

• The building envelope is protected by four types
  of barrier systems
• Moisture barrier below grade
• Weather barrier above grade
• Vapour barrier warm side
• Air barrier - continuous
• barrier system refers to all of the components
  membranes, building components and / or
  sealants.

3
Types of Moisture Flows

• Gravity bulk water
• Capillarity rising damp
• Air Transport
• Diffusion

4
COMPARING DIFFUSION AND AIR TRANSPORTED MOISTURE
5
VAPOUR PERMEANCE

• VAPOUR PERMEANCE Measurement of a materials
  resistance to vapour diffusion
• Lower perm rating more effective vapour barrier

6
VAPOUR BARRIER SYSTEM MATERIALS

• Polyethylene
• Aluminum foil
• Oil-based paints
• Vapour barrier paints
• Some foam insulation materials
• Some plywoods

7
VAPOUR BARRIER CRITERIA

• Installed on the warm side of the insulation
• Stops vapour diffusion
• Must cover as much surface area as possible
• Durable during construction and over the expected
  life of the building

8
AIR PERMEANCE

• AIR PERMEANCE Measurement of a materials
  resistance to air flow when subjected to a
  pressure difference

9
THE AIR BARRIER SYSTEM

• The primary function of the air barrier is to
  enhance building durability.
• To stop inside air from exfiltrating out
  through the envelope
• That is to say - to stop warm moist air from
  being transported into the assemblies by air
  leakage.
• To stop outside air from infiltrating in
  through the envelope

10
AIR BARRIER CRITERIA

• Must be CONTINUOUS - sealing all seams, edges,
  gaps, holes and tears
• IMPERMEABLE to air flow
• Not necessarily impermeable to moisture flow
• Rigid and strong enough to withstand wind
  pressures
• DURABLE during construction and for the expected
  life of building
• Can be installed anywhere in building envelope
  assembly

11
ENVELOPE BARRIER LOCATION CHOICES

• There are 3 above grade barrier systems

• Vapour barrier

• Air barrier

• Weather barrier

12
FUNCTION OF THE WEATHER BARRIER SYSTEM

• To protect the wall assembly from the effects of
  wind, rain, snow and sun
• Improve envelope thermal performance by keeping
  wind out

13
WEATHER BARRIER CRITERIA

• Installed towards the exterior
• Resistant to air flow
• Able to shed rain or snow
• Able to withstand the forces that may act upon it
• Durable during construction and over the expected
  life of the building
• Can become the primary air barrier

14
HOUSE WRAP MATERIALS

• Examples spun bonded polyolefin and woven
  polypropylene house wraps asphalt-impregnated
  building paper

15
AIR BARRIER SYSTEM CHOICES

• Membrane barrier system
• Flexible membranes and compatible sealants create
  the air barrier system
• The addition of a vapour barrier will only be
  required with the exterior membrane system
• Rigid barrier systems
• Rigid components such as drywall, wood
  components, sheathing and certain board stock
  insulation, are combined with gaskets and
  sealants to form the air barrier system
• A vapour barrier will be required in addition to
  the air barrier system

16
INTERIOR MEMBRANE BARRIER SYSTEM

• Example Polyethylene air vapour barrier system
• In this system, the membrane serves as both the
  air and the vapour barrier.

17
EXTERIOR MEMBRANE BARRIER SYSTEM

• Example house wrap air barrier system
• This system has 2 membranes the air barrier on
  the exterior and the vapour barrier on the
  interior

18
EXTERIOR RIGID BARRIER SYSTEM

• Example Exterior insulation air barrier system
• In this system, the air and vapour barriers are
  separated

19
INTERIOR RIGID BARRIER SYSTEM

• Example Airtight Drywall Approach (ADA)
• Both the air and vapour barriers will be towards
  the inside of the house