1 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Attic VentilationWEATHERIZATION ENERGY AUDITOR SINGLE FAMILY

WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012

2 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Learning Objectives

By attending this session, participants will be able to:• Explain the purpose and principles of attic ventilation.

• Summarize misconceptions about attic ventilation.

• Determine ventilation needs by code and practical alternatives.

• List ventilation options.

• Propose specific attic ventilation.

• Describe safeguards for ensuring that attic ventilation does not cause problems.

ATTIC VENTILATION

3 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

• Removes solar heat during hot weather

• Removes moisture vapor during cold weather

Purpose of Attic Ventilation

Photo courtesy of US Department of Energy

ATTIC VENTILATION

4 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Common Misconceptions

• Attic ventilation always removes moisture vapor during cold weather.

• Attic ventilation will cure an attic moisture problem.

• The more attic ventilation, the better.

• Attic ventilation is not necessary.

ATTIC VENTILATION

5 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Post Wx Attic Moisture Problems

Mold on Sheathing Frost on Sheathing

Both conditions occurred after attics were insulated and vented, not before.

ATTIC VENTILATION

Photo courtesy of US Department of Energy

6 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Passive Attic Venting: Convection

How does it work?

Natural Convection• Hot air rises,

escapes high vents• Cooler air pulled

through soffit vents• Heat rises,

escapes ridge vents

Inlet(Cool Air)

Outlet(Heated Air)

Ridge vent

ATTIC VENTILATION

Graphic developed for the US Department of Energy

7 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Passive Attic Venting: Wind

How does it work?

• Bernoulli Principle• Positive pressure on

windward side• Negative pressure

on leeward (protected) side

• Air sucked out leeward vents

WIND

ATTIC VENTILATION

Graphic developed for the US Department of Energy

8 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Power Venting

• Attic fan mounted in central hallway used in non-air conditioned homes.

• Roof vent (pictured) used in air conditioned homes.

Neither is recommended as weatherization measure.

Potential for moisture condensation is high.

How does it work? Fan-powered

roof vent

ATTIC VENTILATION

Graphic developed for the US Department of Energy

9 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Code Issues

Requirements are based on presence of ceiling vapor retarder, climate zone, and vent location.Options:1/150

One square foot of net free vent area per 150 square feet of attic

1/300

One square foot of net free vent area per 300 square feet of attic

Thermal boundary - Ceiling

ATTIC VENTILATION

Graphic developed for the US Department of Energy

10 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Code Issues

Attic ventilation not required when the roof assembly is the thermal and pressure boundary.

Thermal boundary – Roof deck

ATTIC VENTILATION

Graphic developed for the US Department of Energy

11 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Applied Ventilation Formula

• Calculate the number of roof vents required.

• Climate is Zone 7.

• Ceiling is air sealed and insulated.

• Ceiling has vapor retarder.

• Ceiling area is 60’ x 30’.

• Each vent has a net free area of 60 square inches.

How many roof vents does it take?

Photo courtesy of the US Department of Energy

ATTIC VENTILATION

12 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Applied Ventilation Formula

• Ceiling = 60’ x 30’ = 1,800 square feet.

• Formula for attic with vapor retarder = 1/300

• 1,800 ÷ 300 = 6 sq. ft. required NFA ventilation

Convert to inches:

• 6 sq. ft. x 144 sq. in./sq. ft. = 864 square inches

• 864 ÷ 60 square inches NFA/vent = 14.4

15 vents!

ATTIC VENTILATION

13 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Ground Rules and Specifications

Vented attics should not communicate with the conditioned space.• The ceiling air barrier must be continuous with no leakage.

• Specify appropriate attic sealing as part of the work scope.

• Specify that vents be placed low and high on roof.

• Specify eave chutes when soffit vents are present and loose fill insulation is needed.

• Specify that all mechanical ventilation ducts and plumbing stacks are vented directly to the outside.

ATTIC VENTILATION

14 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Venting Configurations

In a perfect world...Continuous ridge vent

Continuous eave vent (soffit vents)

ATTIC VENTILATION

Graphic developed for the US Department of Energy

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Vent Types

Gable vent

Eave vent

Roof vent

Images courtesy of J&R Products Inc.

ATTIC VENTILATION

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Vent Types

Turbine vent R-144 mushroom roof vent

ATTIC VENTILATION

Images courtesy of J&R Products Inc.

17 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Vent Placement

Roof vents placed high on roof

Photo courtesy of PA WTC

Continuous soffit vent

ATTIC VENTILATION

18 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

• Cut hole to fit; test fit vent.

• Caulk edges of hole where flange will sit.

• Slide vent into place under shingles.

• Seal and nail.

Vent InstallationATTIC VENTILATION

Photo courtesy of the US Department of Energy

19 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Vent Placement

Gable vents are attached similarly to roof vents.

Photos courtesy of the U.S. Department of Energy

ATTIC VENTILATION

20 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Attic Window Vent

Photo courtesy of the US Department of Energy

ATTIC VENTILATION

21 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Eave Chutes

Eave Chute

Photo courtesy of PA WTC; Product photo by J&R Products, Inc.

ATTIC VENTILATION

22 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Mechanical Vent TerminationsATTIC VENTILATION

Photo courtesy of PA WTC

23 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – December 2012 eere.energy.gov

Summary

• Vent attics where possible and practical.

• Follow 1/150 and 1/300 code guidelines.

• Don’t specify vents to solve an attic moisture problem.

• Keep moisture out of the attic by air sealing.

• Use the right vent for the job.

• Place vents high and low.

• Avoid turbine or power vents.

ATTIC VENTILATION