Attic Ventilation
Presented by: Rob Kaethler
Presented in Partnership with:
Builder’s Technical Sessions
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Residential VentilationAgenda
Principles of Ventilation
Types of Ventilation
Building Code
Vented and Un-Vented Attics
Balanced Ventilations
Cold Weather roofing
New products and solutions
Trends
Poor Ventilation
Insufficient Ventilation
Adequate Ventilation
Roofing
Manufactures
Require
Ventilation
9.19.1.2 Vent Requirements 1) Except as provided in sentence (2), the unobstructed vent area shall be not
less than 1/300 of the insulated ceiling area
2) Where the roof slope is less then 1 in 6 or in roofs that are constructed with
roof joists, the unobstructed vent area shall be not less than 1/150 of the
insulated ceiling area
3) required vents may be roof type, eave type, gable-end type or any
combination thereof, and shall be distributed
a) uniformly on opposite sides of the building
b) with not less than 25% of the required openings located at the top of the
space, and
c) with not less than 25% of the required openings located at the bottom of
the space
4) except where each joist is separately vented, roof joists spaces shall be
interconnected by installing purlins not less than 38mm by 38mm on the
top of the roof joists
5) vents shall comply with CAN3-A93-M, “Natural Airflow Ventilators for
Buildings”
Highlights of Building Code
• 1 in 300 rule for normal attics
• 1 in 150 rule for rafter attics
• Uniformly on opposite sides of the roof
• Minimum 25% at or near ridge
• Minimum 25% at or near the bottom
• Meets CSA
Three Strategies for Controlling
Moisture in Roof Assemblies:
• Controlling moisture entry.
• Controlling moisture accumulation.
• Removing moisture that does accumulate by drying.
Un-Vented Roofs
• Un-vented roofs operate on the principle that moisture can be controlled from entering the roof assembly
• The building must have a tight building envelope
• The different parts of a building must be properly pressurized
Un-Vented Roofs
• Building code doesn’t totally allow for it
• Shingle manufactures may not allow for it
• There is no margin of error
• Shingle longevity may be be reduced
Vented Roofs
• Remove moisture from roof cavities
• Control ice damming
• Enhance roofing material life span
• Increase occupant comfort
Vented Roof Assumptions
• The building envelope is tight
• The roof assembly has enough insulation
• Inlet and outlet areas are distributed evenly
• The outside air is able to absorb moisture
Cold Weather Roofing Keys
• Minimize the amount of moisture attic ventilation must deal with
• Use a good vapour retarder
• Reduce air leaks through the ceiling
• Educate home owners about indoor humidity levels during cold weather
The Stack Affect
• Attic air heated by contact with a hot roof on a
warm day tends to rise. This is natural
convection, which pulls cooler air from the soffit
up towards the ridge.
• Natural convection, with a balanced system of
soffit and vents at or near the ridge is the most
effective means of venting the roof.
• The steeper the roof pitch the better the stack
affect works in particularly cold weather
NFA (Net Free Air) or Airflow or
CFM
• NFA is a static measurement;
• Airflow is a dynamic measurement.
• Cubic feet per minute
Balanced Ventilation
• Means for every inch of air exhausted, it must be balanced by providing the same or greater amount of air intake at the eaves or soffits.
Why is balance so important
Balanced Ventilation
Cold Weather Venting
Why Vent an Attic In Cold Weather
• Reduce “ice dams”and “icicle ups”
• Remove moist air from the attic
• Occupant comfort
“Ice Ups” and “The Icing Envelope”
• Snow melts on the roof
• The melt water refreezes
• 22°F or -5.6°C is the magic number
Why We Vent in Cold Weather
“the Icing Envelope”Snow on the roof begins to melt anytime the attic temperatures reaches 30°F(-1.1C), but only refreeze when the outdoor temperature is below 22°F (-5.6C) This is called the “icing envelope” Ice dams could be avoided if attic ventilation could maintain the attic at 30°F or lower when the outdoor temperature was 22°F or lower
Army Core of Engineers
Why we Vent in Cold Weather
Ice Damming
Cold Weather Roofing Keys
The system approach
• Insulation
• Vapour Retarder
• Ventilation
Cold Weather Roofing Keys
Insulation
• A properly insulated home keeps as much of the heat in the house as possible
• Keeps the attic as cold as possible
• Saves money
Cold Weather Roofing Keys
Ventilation
• Balance the ventilation
• What is your air intake?
• What is your air exhaust
• What solution are you using? Why
• Certifications
It is tougher to keep snow out of an attic then rain
Types of Vent Solutions
Potential Vent Options
• Front and back soffit venting
• Gable end vents
• Traditional plastic or metal pot vents
• Ridge vents
• Off peak vents
• Power ventilators
• Wind driven Ventilators
Front and Back Soffit Venting
Slots for Ventilation
Dropped Gabel Truss
Front and Back Soffit Venting
Products and Solutions
• Air intake vents installed low on the roof
Trends
• Solutions to specific application
• Low or no maintenance
• Curb appeal
• Longevity of our roofs
New Products and Solutions
– Off-peak air intake vents
Air Intake Vent
Vents for Special Applications
• Roof meets a wall
New products and solutions
Vents For Hip
New products and solutions
• Vents for specialty applications
– Flexible Vents
Powered Ventilation
Drawbacks of Powered and
Mechanical Ventilators
• If the fan is turned off how much NFA are you getting?
• If it is a mechanical device and it does not function correctly how much NFA are you getting?
• If the air intake doesn’t match the air exhaust where does it get the additional needed air?
Certifications and Standards
• Is it a standard that requires certification or compliance?
• Does the vent have to be modified to meet the standard?
• Is this important?
Miami Dade County• Wind driven rain test 8.8-inches of water at 110 miles per
hour
• Independent NFA Verification
TDI
• Static Pressure Uplift
ICC
Independent NFA Verification
Wind driven snow tests
Dust exposure test
UL and ULC
• Fire Testing
• Code compliance testing
CSA
• CAN3-A93-M
Conclusion
• Reduce the moisture load to the attic from the house
• Make sure you have a balanced system
• Air intake is critical
• Vent for all the weather conditions and all seasons
Questions?