1 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.energy.gov Attic Ventilation WEATHERIZATION ENERGY AUDITOR SINGLE FAMILY WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010

2 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.energy.gov Learning Objectives By attending this session, participants will: Understand the purpose and principles of attic ventilation. Become aware of misconceptions about attic ventilation. Know how to determine ventilation needs by code and practical alternatives. Become aware of ventilation options. Know how to specify attic ventilation. Understand safeguards for ensuring that attic ventilation does not cause problems. ATTIC VENTILATION

3 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.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 – August 2010eere.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 – August 2010eere.energy.gov Post Wx Attic Moisture Problems Mold on SheathingFrost 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 – August 2010eere.energy.gov Passive Attic Venting: Convection How does it work? Natural Convection Hot air rises, escapes high vents. Cooler air is pulled through soffit vents. Heats, rises, escapes ridge vents. Inlet (Cool Air) Outlet (Heated Air) Ridge Vent ATTIC VENTILATION

7 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.energy.gov Passive Attic Venting: Wind How does it work? Bernoulli Principle. Positive pressure on windward side. Negative pressure on leeward (protected) side. Air is sucked out leeward vents. WIND ATTIC VENTILATION

8 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.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

9 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.energy.gov Code Issues Based on presence of ceiling vapor retarder. No vapor barrier: 1/150 One square foot of net free vent area per 150 square feet of attic. Vapor barrier: 1/300 One square foot of net free vent area per 300 square feet of attic. Thermal Boundary - Ceiling ATTIC VENTILATION

10 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.energy.gov Code Issues Attic ventilation not required when the roof assembly is the thermal and pressure boundary. Thermal Boundary – Roof Deck ATTIC VENTILATION

11 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.energy.gov Applied Ventilation Formula Calculate the number of roof vents required for this ranch home with a gable roof. Ceiling is air sealed and insulated. Ceiling has vapor retarder. 60’ x 30’ ceiling area. 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 – August 2010eere.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 = Vents! ATTIC VENTILATION

13 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.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 called for. Specify that all mechanical ventilation ducts and plumbing stacks are vented directly to the outside. ATTIC VENTILATION

14 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.energy.gov Venting Configurations In a perfect world…. Continuous Ridge Vent Continuous Eave Vent (Soffit Vents) ATTIC VENTILATION

15 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.energy.gov Vent Types Gable Vent Eave Vent Roof Vent Images courtesy of J&R Products Inc. ATTIC VENTILATION

16 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.energy.gov Vent Types Turbine VentR-144 Mushroom Roof Vent ATTIC VENTILATION Images courtesy of J&R Products Inc.

17 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.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 – August 2010eere.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 Installation ATTIC VENTILATION Photo courtesy of the US Department of Energy

19 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.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 – August 2010eere.energy.gov Attic Window Vent Photo courtesy of the US Department of Energy ATTIC VENTILATION

21 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.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 – August 2010eere.energy.gov Mechanical Vent Terminations ATTIC VENTILATION Photo courtesy of PA WTC

23 | WEATHERIZATION ASSISTANCE PROGRAM STANDARDIZED CURRICULUM – August 2010eere.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