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Here we discuss attic ventilation defects in the soffits or building eaves, as visible from the attic or building interior. This discussion is part of "How to Correct Improper or Inadequate Attic or Under-Roof Ventilation in Buildings", our discussion of "Attic Condensation". This article describes inspection methods and clues to detect roof venting deficiencies, insulation defects, and attic condensation problems in buildings. It describes proper roof ventilation placement, amounts, and other details.

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Inspecting the Soffit or Eaves Vent System from the Attic - look for blockage

Inspecting in the building attic, we check to be sure that there is good air flow at the lower roof edges or "eaves". Even when we see apparent vents installed outside, such as soffit vent strips or perforated soffit covering material, the venting may be blocked or otherwise inadequate.

The cost to heat and cool a building is increased and the risk of an under-roof rot or mold problem is increased as well if the roof is not properly designed and vented.

For example, installing exit venting a the ridge without installing adequate intake venting at the building eaves will increase heat loss from the building during winter months. Warm air leaking into the attic or roof cavity from the building creates a convection current of rising air in the building.

When the convection current of warm moist air leaving at the ridge vent is unable to draw dry cool outdoor air into the under-roof space at the building eaves or lower roof edges, it tends to draw more heated air out of the living space.

Look for these insulation and ventilation defects a the building eaves or lower roof edges:

• Inadequate or incomplete insulation in the attic floor or knee walls.
  
  
• Insulation up tight against the roof decking - blocking air flow there, no air path along roof sheathing or decking
  
  
• Intake venting at the roof eaves blocked by insulation - See Blocked Soffit Intake Vents
  
  
• Intake venting at the roof eaves is only between some rafter pairs, not all rafter pairs - See Continuous Soffit Intake Venting Needed
  
  
• Moisture stains from ice dam leaks or roof leaks, found on rafters and roof sheathing, particularly at the lower roof edges over a poorly-insulated or poorly-vented attic or cathedral ceiling
  
  
• Bath vents or kitchen vents that spill moist air into the attic rather than directing it outdoors; vent fan ducts that are not insulated and that slope so that their interior condensate leaks back into the building.
  
  
• Mold stains on roof sheathing or rafters in areas of inadequate ventilation and high moisture. See Inspect Attics for Moisture or Mold for more indications of attic moisture

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• Alan Carson Carson Dunlop Associates, Toronto, Ontario. Mr. Carson is a home inspection professional, educator, researcher, writer, and a principal of Carson Dunlop Associates, a Toronto home inspection and education firm. Mr. Carson is a past president of ASHI, the American Society of Home Inspectors Some great illustrations of the proper under-roof ventilation pathways are offered by Carson Dunlop.
• Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. (727) 595-4211 mark@BestTampaInspector.com 11/06 & 12/08
• John Annunziata, P.E. - NY Metro ASHI during informal chapter discussions about roof and attic ventilation options (1986-1996).
• Technical reviewers are invited to comment or ask questions - contact us

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INTERIORS of BUILDINGS
AIR BYPASS LEAKS
AIR LEAK DETECTION TOOLS
AIR LEAK MINIMIZATION
AIR SEALING STRATEGIES
BATHROOM VENTILATION
FREEZE-PROOF A BUILDING
ATTIC CONDENSATION CAUSE & CURE
Air Bypass Leaks, Thermal Tracking
Blocked Soffit Intake Vents
CATHEDRAL CEILING INSULATION
Comparing Two Houses
Heat Tapes: Use on Roofs for Ice
HEAT LOSS: How to Calculate Heat Loss in a Building
HOUSEWRAP AIR & VAPOR BARRIERS
HUMIDITY LEVEL TARGET
ICE DAM PREVENTION
INSULATION INSPECTION & IMPROVEMENT
Inspect Attics for Moisture or Mold
Inspect Basements for Moisture or Mold
Inspect Building Exterior
Inspect the Ridge Vent System from the Attic
Inspect the Soffit Vent System from the Attic
ROOF VENTILATION SPECIFICATIONS
Roof Venting: Intake - Outlet Area Ratios
Roof Venting: Proper Locations
Roof Venting: Both Ridge & Eaves Venting Needed
Roof Venting: Eaves Intake if no Overhang
Roof Venting: Soffit Intake Vent-Continuous
Roof Venting: Un-Vented Roof Solutions
ROOF VENTING ENERGY SAVING DETAILS
HEAT LOSS: How to Calculate Heat Loss in a Building
HOUSEWRAP AIR & VAPOR BARRIERS
HUMIDITY LEVEL TARGET
ICE DAM PREVENTION
INSULATION INSPECTION & IMPROVEMENT
THERMAL TRACKING & HEAT LOSS

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More Reading about Dealing with Attic Mold, Identifying, Removing, and Preventing Mold in Attics

Be sure to review HOW TO FIND MOLD: How to Inspect Homes and Other Buildings for Mold - the Basics of How to Find Problem Mold Indoors in our Mold Action Guide. Here are other articles that will be helpful in evaluating attic mold presence, causes, and cures:

• What Mold and Allergens Look Like: mold identification photos to help identify mold - choosing what to sample in buildings
• How to Clean Moldy Wood Framing & Sheathing How to clean/seal mold from/on exposed lumber or plywood subfloor or roof sheathing indoors - some suggestions based on our field and laboratory research
• Lighting, proper use of: proper aiming of a good flashlight can disclose hard to see but toxic light or white mold colonies on walls.
• Mold spores in the Home - a Photo ID Library for detection and identification of mold allergens.
• How to Find and Test For Mold in Buildings A "how to" photo and text primer on finding and choosing the right spots to test for mold in buildings
• Stuff that is not mold but is often mistaken for it - things you may not want to test. Also, not all "black mold" is toxic - here are examples of harmless black mold.
• Simple Adhesive Tape Sampling of Moldy Surfaces - how to send a mold sample to our lab
• Mold Sampling Methods in the Indoor Environment - In-depth article: detailed critique of popular mold testing methods - Is your mold test kit worth the bother?
• Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
• Mold-Resistant Building Practices, advice from an expert on how to prevent mold after a building flood and how to prevent mold growth in buildings by selection of building materials and by anti-mold construction details.

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The Mold Information Center: What to Do About Mold in Buildings, When and How to Inspect for Mold, Clean Up Mold, or Avoid Mold Problems

Use this simple, economical mold test kit by following our instructions on how to collect and mail mold samples to our lab

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