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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 Air Bypass Leaks, Thermal Tracking More Information InspectAPedia TM Home & Site Map Air Conditioning InspectAPedia Bookstore Electrical Environment Exteriors Heating Home Inspection Insulate Ventilate Interiors Mold Inspect/Test Plumbing Water Septic Roofing Structure More Information Accuracy & Bias Pledge Contact Us |
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This is 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.
Home inspectors and building owners should be especially concerned about insulation placed directly under the roof sheathing such as between the rafters. This can trap heat and moisture and damage sub-roofing as well as roofing shingles.
Also, cathedral ceilings without vents in the soffit and up at the ridge or without adequate air path between the roof insulation and the underside of the roof sheathing can lead to major condensation problems, rot, insect damage, and severe structural damage in just a few years.
Do look for those dark rafter lines and don't underestimate the damage that can exist.
The best "fix" for cathedral ceilings and un vented roof cavities is to assure that there is an air path into the attic up the under side of the roof along the building eaves.
If insulation blocks this opening, it is corrected simply by installing soffit vent baffles at the house eaves between every rafter pair (cardboard or Styrofoam pieces made for that purpose and sold at most lumber yards) and adding vents if not in place.
Beware 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.
Installing only a ridge vent and no or inadequate soffit venting is likely to result in unnecessary heat loss from the building as convection currents of rising warm air in the attic, unable to easily draw
in air from outside, will "suck" warm air from the building, thus increasing unnecessary heat loss and increasing the risk of ice damming. Providing a lot of easy air intake at the building eaves avoids this problem.
Installing only soffit venting and no ridge vent works better than a ridge-only vent and this design was used on many residential buildings. But it's not nearly as effective as a ridge and soffit vent combination, first because air moves through the attic space only when wind is blowing in the right direction, towards one of the walls of the Building which has a vented roof overhang, and second, because there is no high exit point to permit warmer air to exit by natural convection.
To be scrupulously fair, on a few 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.
The popular plastic mesh type ridge vent shown in this photograph is popular where ridge vents are installed on new homes or as retrofits. Builders and owners like the ability to nail roof shingles over the easily-stored, transported, and installed roll-out plastic mesh that is simply laid across an opening cut along the building's ridge.
But we have observed that this ridge vent design passes much less air than the older, uglier aluminum ridge vent shown in our sketch above. We prefer the older product which moves air.
As we show in this pair of photos, continuous soffit intake venting will provide optimum intake air flow between every rafter pair.
Here are examples of inadequate intake ventilation: vents at the soffits are intermittent or "spot vents" or are simply too small.
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.
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.
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.
Venting needs to be provided between every rafter pair at the eaves and ridge.
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.
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.
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
Air Bypass Leaks, Thermal Tracking
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:
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.
Contact Daniel Friedman for website content suggestions or for fee-paid consulting
05/12/2008 - 06/02/1990 - www.inspect-ny.com/atticcond7.htm - Web page design & content © 2007 Daniel Friedman All Rights Reserved
