Why Both Ridge & Soffit Venting are Needed under Building Roofs InspectAPedia® -
Adding a ridge vent alone can increase building heating costs
Adding soffit venting alone is ineffective
How to Correct Inadequate Attic Venting to Stop Attic Condensation, Ice Dam Leaks, Attic Mold, & Roof Structure Damage
Questions & answers about attic moisture, condensation & ventilation: why are both soffit intake and ridge outlet needed?
Here we explain why a functional roof venting system needs both intake venting at the eaves or soffits and outlet venting at the roof peak or ridge.
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This article series explains How to Correct Inadequate Attic Venting to Stop Attic Condensation, Ice Dam Leaks, Attic Mold, & Roof Structure Damage. Our photo at page top shows a modern synthetic mesh type ridge vent (with modest airflow capacity) and our photo at left shows a typical installation of continuous soffit or eaves intake venting at the lower roof edges of a building.
Both Ridge and Eaves or Soffit Ventilation are Needed in buildings. 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. This article is part of the series ROOF VENTILATION SPECIFICATIONS and also ATTIC CONDENSATION CAUSE & CURE.
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.
A High-Capacity Ridge Vent Moves More Air than a Low-Profile Good-looking Vent
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.
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.
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.
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. Not what is shown in our photo (left).
Where we 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. In these attics of buildings in climates where moisture is often a concern, we find moisture stains in the attic at the building eaves, sometimes moldy building insulation, and on occasion serious attic moisture and condensation problems.
Where we inspect attics where even larger vent openings are provided in the soffits or eaves, if the openings are intermittent, we see wet and often moldy roof sheathing on those roof sections where no venting is provided (the "in-between-vent" roof sections), even though at other roof sections where vents are present
the sheathing often looks clean and dry.
This is compelling visual evidence that air is not moving up the under-side of the sections of roofing where no intake vents are
present at the building eaves.
Venting needs to be provided between every rafter pair at the eaves and ridge.
Just as we want continuous intake venting along the building eaves, 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.
Questions & Answers regarding this article
Questions & answers about attic moisture, condensation & ventilation: why are both soffit intake and ridge outlet needed?
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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 and 12/08
Daniel Friedman -edited and added to comments from John Annunziata, P.E. - NY Metro ASHI during informal chapter discussions about roof and attic ventilation options (1986-1996).
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
"The Elimination of Unsafe Guardrails, a Progress Report," Elliott O. Stephenson, Building Standards, March-April 1993
"Are Functional Handrails Within Our Grasp" Jake Pauls, Building Standards, January-February 1991
Access Ramp building codes:
UBC 1003.3.4.3
BOCA 1016.3
ADA 4.8.2
IBC 1010.2
Access Ramp Standards:
ADA (Americans with Disabilities Act), Public Law 101-336. 7/26/90 is very often cited by other sources for good design of stairs and ramps etc. even where disabled individuals are not the design target.
ANSI A117.4 Accessible and Usable buildings and Facilities (earlier version was incorporated into the ADA)
ASTM F 1637, Standard Practice for Safe Walking Surfaces, (Similar to the above standards)
American Plywood Association, APA, "Portland Manufacturing Company, No. 1, a series of monographs on the history of plywood manufacturing",Plywood Pioneers Association, 31 March, 1967, www.apawood.org
Asbestos products and their history and use in various building materials such as asphalt and vinyl flooring includes discussion which draws on Asbestos, Its Industrial Applications, D.V. Rosato, engineering consultant, Newton, MA, Reinhold Publishing, 1959 Library of Congress Catalog Card No.: 59-12535 (out of print).
Building Research Council, BRC, nee Small Homes Council, SHC, School of Architecture, University of Illinois at Urbana-Champaign, brc.arch.uiuc.edu. "The Small Homes Council (our original name) was organized in 1944 during the war at the request of the President of the University of Illinois to consider the role of the university in meeting the demand for housing in the United States. Soldiers would be coming home after the war and would be needing good low-cost housing. ... In 1993, the Council became part of the School of Architecture, and since then has been known as the School of Architecture-Building Research Council. ... The Council's researchers answered many critical questions that would affect the quality of the nation's housing stock.
How could homes be designed and built more efficiently?
What kinds of construction and production techniques worked well and which did not?
How did people use different kinds of spaces in their homes?
What roles did community planning, zoning, and interior design play in how neighborhoods worked
"An Example of Colonial Paneling", Norman Morrison Isham, The Metropolitan Museum of Art Bulletin, Vol. 6, No. 5 (May, 1911), pp. 112-116, available by JSTOR.
"Energy Savers: Whole-House Supply Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Supply_Vent.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11880?print
"Energy Savers: Whole-House Exhaust Ventilation Systems [copy on file as /interiors/Energy_Savers_Whole-House_Exhaust.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11870
"Energy Savers: Ventilation [copy on file as /interiors/Energy_Savers_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Natural Ventilation [copy on file as /interiors/Energy_Savers_Natural_Ventilation.pdf ] - ", U.S. Department of Energy
"Energy Savers: Energy Recovery Ventilation Systems [copy on file as /interiors/Energy_Savers_Energy_Recovery_Venting.pdf ] - ", U.S. Department of Energy energysavers.gov/your_home/insulation_airsealing/index.cfm/mytopic=11900
"Energy Savers: Detecting Air Leaks [copy on file as /interiors/Energy_Savers_Detect_Air_Leaks.pdf ] - ", U.S. Department of Energy
"Energy Savers: Air Sealing [copy on file as /interiors/Energy_Savers_Air_Sealing_1.pdf ] - ", U.S. Department of Energy
Falls and Related Injuries: Slips, Trips, Missteps, and Their Consequences, Lawyers & Judges Publishing, (June 2002), ISBN-10: 0913875430 ISBN-13: 978-0913875438 "Falls in the home and public places are the second leading cause of unintentional injury deaths in the United States, but are overlooked in most literature. This book is unique in that it is entirely devoted to falls. Of use to primary care physicians, nurses, insurance adjusters, architects, writers of building codes, attorneys, or anyone who cares for the elderly, this book will tell you how, why, and when people will likely fall, what most likely will be injured, and how such injuries come about. "
Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
Pergo AB, division of Perstorp AB, is a Swedish manufacturer or modern laminate flooring products. Information about the U.S. company can be found at http://www.pergo.com where we obtained historical data used in our discussion of the age of flooring materials in buildings.
Plank House Construction: weblog from plankhouse.wordpress.com/2009/01/25/plank-house-construction/ and where plank houses were built by native Americans, see
Large 1:6 Scale Plank House Construction / P8094228,
Photographer: Mike Meuser
06/12/2007 documented at yurokplankhouse.com where scale model Museum quality Yurok Plank Houses are being sold to raise money for the Blue Creek - Ah Pah Traditional Yurok Village project.
Re-Bath, tub lining products is a bath tub relining manufacturer and distributor located in Tempe, Arizona - see rebath.com
Slips, Trips, Missteps and Their Consequences, Second Edition, Gary M. Bakken, H. Harvey Cohen,A. S. Hyde, Jon R. Abele, ISBN-13: 978-1-933264-01-1 or
ISBN 10: 1-933264-01-2,
available from the publisher, Lawyers ^ Judges Publishing Company,Inc., www.lawyersandjudges.com sales@lawyersandjudges.com and also from the InspectAPedia Bookstore (Amazon.com)
The Stairway Manufacturers' Association, (877) 500-5759, provides a pictorial guide to the stair and railing portion of the International Residential Code. [copy on file as http://www.stairways.org/pdf/2006%20Stair%20IRC%20SCREEN.pdf ] -
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.
Manufactured & Modular Homes: Modular Building Systems Association, MBSA, modularhousing.com, is a trade association promoting and providing links to contact modular builders in North America. Also see the Manufactured Home Owners Association, MHOAA, at www.mhoaa.us. The Manufactured Home Owners Association of America is a National Organization dedicated to the protection of the rights of all people living in Manufactured Housing in the United States.
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.
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.
Slips, Trips, Missteps and Their Consequences, Gary M. Bakken, H. Harvey Cohen, Jon R. Abele, Alvin S. Hyde, Cindy A. LaRue, Lawyers and Judges Publishing; 2 edition (April 2006), ISBN-10: 1933264012 ISBN-13: 978-1933264011
Steps and Stairways, Cleo Baldon & Ib Melchior, Rizzoli, 1989.
"The Dimensions of Stairs", J. M. Fitch et al., Scientific American, October 1974.
"Weather-Resistive Barriers [copy on file as /interiors/Weather_Resistant_Barriers_DOE.pdf ] - ", how to select and install housewrap and other types of weather resistive barriers, U.S. DOE
Weaver: Beaver Board and Upson Board:
Beaver Board and Upson Board: History and Conservation of Early Wallboard, Shelby Weaver,
APT Bulletin, Vol. 28, No. 2/3 (1997), pp. 71-78, Association for Preservation Technology International (APT), available online at JSTOR.
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