Sealing Air Leaks during new home construction

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Sealing Air Leaks during new home construction
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Why Seal Air Leaks?
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What is whole house air infiltration

• Air movement between conditioned and
  unconditioned spaces.
• Whole house Infiltration includes both air
  getting in (infiltration) and air getting out
  (exfiltration)
• This infiltration compromises the building
  envelope and reduces comfort and increases energy
  use.

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The building envelope

• The boundary between the conditioned space inside
  and an unconditioned attic, crawlspace, garage,
  or outside (ambient).
• Typically the building envelope is defined by
  where the insulation has been installed.
• Sheetrock, framing, sheathing, subflooring, and
  foundations are all part of the envelope.
• Joints, cracks, and holes in these materials are
  sources of air leakage.

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Heat seeks cold

• In Winter, warm air wants to get out
• In Summer, hot air wants to get in

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Air movement

• In order to have air movement the following needs
  to exist
• Hole Driving Force Air Movement
• Common driving forced
• Wind
• Temperature Difference
• Pressure Difference

We are addressing the hole part of the equation.
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Major contributors to air leakage

• Sealing air leaks should begin with these major
  contributors

Homes Without fireplaces
Homes with Fireplaces
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Leaky House
In a poorly sealed house, inside air may be
completely replaced by outside air one or more
times per hour. This is referred to as one air
change.
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Duct Leakage
In many homes, the largest single contributor to
air leakage is the duct system. Joints in the
duct work should be sealed with mastic sealants
instead of duct tape to remedy this situation.
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Air Infiltration
Check for the presence of interior holes, gaps,
and cracks.
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Around the attic hatch. Around the light
fixtures. Around the plumbing stacks. Where the
chimney comes through the ceiling.
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Attic Bypass
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In the walls
Around windows, doors and their trim. Where vents
penetrate exterior walls. Where different
materials meet (such as where the chimney meets
the wall).
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In the basement

• Where the wood plate meets the foundation
• In gaps between fieldstones in the foundation
• In holes leading to the heated living space above
  a cold basement or crawl space.

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Vented crawl spaces

• The places to look for sources of leakage
  include
• Plumbing penetrations through subfloor.
• Joint between exhaust duct and subfloor.
• Interior chase wall gaps in the subfloor.
• Joint between register boot and subfloor.
• Access door edges.

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Basements

• The places to look for sources of air leakage
  include
• Framing joint between subfloor and band joist
• Cantilever floor framing joints
• Joint between foundation and sill plate
• Utility entry through the band joist or
  foundation
• Framing joint between band joist and sill plate
• Around window and door units and foundation
• Joint between exhaust vent and sheathing

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Materials for sealing
Any flexible caulking that adheres to most
construction materials, withstanding minor
movement, and remains flexible for at least 10
years.
Polymeric Foams Adheres to most construction
materials, fills the volume or crack of space
(interior use only).
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Sealing materials
Housewraps Sheet of material applied to the
exterior of a wall assembly. It seals most
construction joints against air
leakage. Gasketing Not permeable to air movement
that are compressible, but will return to their
original shape. Placed into joints or openings
during construction, and expecting the joint to
be closed against air leakage, even when framing
materials shrink or move.
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Tapes Mastics
Tapes Joints in sheathing, housewraps, or vapor
retarders may be closed with tapes, when the
correct tape is used. Mastics Joints in duct
systems should also be sealed with mastic
sealants reinforced with a membrane.
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Weather stripping blocking
Weather stripping Joints around moveable parts
of the building envelope need to be sealed. Field
fabricated doors and windows must have the edges
of the unit fitted with a flexible material, that
will not block air leakage. Blocking Solid
blocking, such as wood framing, plywood, duct
board or drywall must be installed and secured to
seal large openings. Fire Stopping Penetrations
around hot objects, such as flues or metal
chimneys, shall be sealed to prevent the passage
of fire and smoke. Fiber glass and rockwool batts
are fire stop materials, however, will need to be
sealed.