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How to Install Soffit Intake Vents to Stop Attic Condensation, Ice Dam Leaks, Attic Mold, & Roof Structure Damage
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• How to Correct Inadequate Attic Venting to Stop Attic Condensation, Ice Dam Leaks, Attic Mold, & Roof Structure Damage
• How to detect roof venting deficiencies, attic insulation defects, and attic condensation problems

Here we discuss how to properly inspect, place, and size ventilation air intakes at the lower edges of a building roof - its soffit, or eaves. This is a section of chapter 7, "How to Correct Improper or Inadequate Attic or Under-Roof Ventilation in Buildings", part of 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.

These recommendations are based on 30 years of building inspections, on the observation of the locations of moisture, mold, ice dams, condensation stains, and other clues in buildings, and on the correlation of these clues with the roof venting conditions at those properties.

I have also measured changes in airflow, temperature, and moisture before and after installing roof venting. More in-depth, un-biased, expert information on these topics and on building defect inspection, diagnosis, & repair can be found at "More Information below. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use links at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website.

Continuous High Capacity Eaves or Soffit Intake Venting Provides Adequate Intake Air Under Roofs

As we show in this pair of photos, continuous soffit intake venting will provide optimum intake air flow between every rafter pair.

On buildings with very large gable end vents, lots of insulation in the attic floor, and perhaps lucky house siting, I have seen attics that were perfectly dry and free of condensation, ice dams, and mold.

But these have been the exception, not the rule, at least for inspections in northern climates subject to cold winters and hot humid summers.

Installing Continuous High Capacity Eaves or Soffit Intake Venting Works Best to Avoid Attic Moisture, Mold, & Ice Dams

Here are examples of inadequate intake ventilation: vents at the soffits are intermittent or "spot vents" or are simply too small.

Continuous soffit/eaves intake venting is the proper location for the intake air, in order to assure that the entire under-side of the roof sheathing is vented and kept dry.

Where I inspect attics with "spot vents" in the soffits (those little round louvered vents ranging from about 3/4" diameter to 2" in diameter, are completely ineffective, never moving enough air.

Venting needs to be provided between every rafter pair at the eaves and ridge. You won't achieve this if venting is intermittent along the soffits or eaves of a home.

Don't install intermittent or occasional or faux soffit intake venting or vents with too little opening area such as we show in the photo at left.

Not only are the openings too small to pass enough air (obstructed further by the louvers and insect screens), intermittent soffit intake vents or little round or rectangular soffit spot vents are singularly ineffective in providing good under-roof or attic ventilation.

Where I inspect attics where even larger vent openings are provided in the soffits or eaves, if the openings are intermittent, I see wet and often moldy roof sheathing on those roof sections where no venting is provided, even though at other roof sections where vents are present the sheathing often looks clean and dry.

This is very strong evidence that air is not moving up the under-side of the sections of roofing where no vents are present.

Continuous ridge venting is the optimum exit path for warm rising air in an attic, thus pulling new cooler, drier outside air into the under-roof area from between every rafter pair. (C)Daniel Friedman - copyright protection trap.

But also remember the danger of adding a ridge vent without soffit vents (the worst) or soffit vents without a ridge vent (bad) or only gable-end vents (usually bad).

The up-draft of air from the building (convection current of rising warm air which moves up through most buildings) will be increased and will mean unnecessary heat loss if you have a ridge vent to vent air out without also providing good intake venting at the soffits or eaves.

Technical Reviewers

Particular thanks are due to experts and also consumers who read these articles and suggest corrections, changes, and additions to the material. Content suggestions, technical corrections and content critique are invited for any of the content at our website.

• 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 11/06Daniel Friedman - principal author Daniel Friedman, editing, expanding, adding to comments from John Annunziata, P.E. - NY Metro ASHI informal chapter discussions.
• Technical reviewers are invited to comment or ask questions - contact us

Use links just below or at the left of each page to navigate this document or to view other topics at this website. Green links show where you are in our document or website. If you just "scroll down" you'll miss some important articles. See links at page left.

MOISTURE, MOLD, ICE DAM LEAKS in ATTICS & ROOFS
Attic Condensation
Inspect Building Exterior
Comparing Two Houses
Inspect Basements for Moisture or Mold
Inspect Attics for Moisture or Mold
Inspect the Ridge Vent System from the Attic
Inspect the Soffit Vent System from the Attic
Blocked Soffit Intake Vents
Correcting Roof Ventilation
Ridge and Eaves Venting Both Needed
Continuous Soffit Intake Venting Needed
Proper Roof Vent Location
Roof Vent Area Ratios
Un-Vented Roof Solutions

More Information on Effects of Building Moisture & Building Diagnostic Inspections and Repairs

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.

InspectAPedia ^TM Home & Site Map - Building Inspection, Diagnosis, & Repair, Environmental Inspection & Testing - Research Website

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

Home Inspection Construction Consulting Services & advice for home buyers

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

Environmental Inspection, Testing, & Diagnosis On-Site IAQ, Gas, Air Testing, Mold Investigation, Sick Building Diagnosis, Lab Services, & Remediation Plan Preparation - indoor air quality testing, problem source determination, supporting lab work, written remediation plan addressing removal of environmental and other hazards and prevention of their recurrence.

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