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?