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Here we explain how Proper location of roof intake and outlet venting prevents Attic Condensation, Ice Dam Leaks, Attic Mold, & Roof Structure Damage.

This is a section of ROOF VENTILATION SPECIFICATIONS and also ATTIC CONDENSATION CAUSE & CURE. 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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Proper Roof Vent Location for Air Intake and Outlet

Intake venting needs to be at the eaves or lower roof edges. Otherwise these roof areas will not be dry and cool, and we'll find water damage, condensation damage, ice dams, and often mold in these areas.

Some people install the ridge vent (the easy part) and leave older gable end vents as "intake." This does not work very well. Simply pulling in the needed makeup air from typical gable end wall vents will not move air under the lower and center areas of roof sheathing, thus inadvertently encouraging moisture and mold to form in these areas.

In buildings where this vent design has been used we see pretty clean roof sheathing near the ridge and near the building gable walls, but at the lower roof center and looking down to the eaves, the sheathing will often be wet, moldy, damaged.

The sketch at page top is not quite right. It shows the soffit opening along the house wall where wind-blown rain may enter the soffit and wall. A better location for this opening would be at the outer edge of the soffit, just behind the fascia!

Outlet Venting needs to be along the length of the ridge. On some complex roof designs and on pyramid roofs there is no ridge.

The sketch at left is an example of the insulation placement and air flow pathway for homes that combine an attic knee wall space with a partial cathedral ceiling space. We recommend closing the gable-end vent on older homes that have one, installing a continuous ridge vent to assure air flow between every rafter pair.

On some hip roof designs the length of ridge is very short compared with the total roof length. In these cases there may be no option but to add multiple individual exit vent openings across the roof field. In this case they should be placed near the ridge so that the upper attic will be vented.

Putting them at mid roof or lower is ineffective. Usually such vents are placed on just one slope of the roof so that they are not visible from the front of the building. This is ok, provided the vents are near the ridge. Otherwise the un-vented roof slope simply won't be treated.

On lower single-plane shed roofs that abut an upper story building wall, venting can be provided by installing a half-ridge at the upper roof slope. Spot vents and gable end vents are a distant second choice for these designs for the reasons I outlined above.

For cathedral ceilings that have minimal vent space see our suggestions at CATHEDRAL CEILING INSULATION

For roofs that have no soffit or eaves overhang to provide an intake opening, see Roof Venting: Eaves Intake if no Overhang.

For roofs that cannot be vented, roofs whose structure, shape, or choice of insulation (such as sprayed foam insulation under the roof deck, or the "hot roof" design, see Roof Venting: Un-Vented Hot Roof Solutions.

For irregular or hard-to-vent roof shapes, condensation (winter) or summer heat build-up can be relieved by a thermostatically operated attic fan - with a cutout switch to turn off the fan in case of a building fire. (Otherwise the fan spreads and speeds the fire.) But such fans do not run in cold winter weather, so you're only solving the heat problem not the winter condensation and ice dam problem.

Optimum roof ventilation design: provides continuous ridge venting, continuous soffit venting, and then, close off those old gable-end vents to force the intake air to come where you want it to flow. Otherwise the exiting air at the ridge will usually pull its makeup air from the closer gable end vents and not from the soffit or eaves vents.

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Questions & answers about placement of roof vents on buildings

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Technical Reviewers & References

• InspectAPedia.com^® - Daniel Friedman - Publisher & Editor.
• Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
• 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

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.

ATTIC LEAKS, CONDENSATION & ATTIC MOLD
  Air Bypass Leaks, Thermal Tracking
  Blocked Soffit Intake Vents
  CATHEDRAL CEILING INSULATION
  CATHEDRAL CEILING VENTILATION
  Comparing Two Houses
  Heat Tapes: Use on Roofs for Ice
  HEAT TAPES & CABLES on Roofs for Ice Dams
  HOT ROOF DESIGNS: Un-Vented Roof Solutions
  HOUSEWRAP AIR & VAPOR BARRIERS
  HUMIDITY LEVEL TARGET
  ICE DAM PREVENTION
  ICE DAM CURE: Comparing Two Houses
  Inspect Attics for Moisture or Mold
  Inspect Attics for Blocked Soffit Intake Vents
  Inspect Basements for Moisture or Mold
  Cold Pour Joint Leaks
  Form Tie Leaks
  Wall Crack Leaks
  Floor-Wall Joint Leaks
  Inspect Building Exterior - Roof Venting
  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 Hot Roof Solutions
  ROOF VENTING ENERGY SAVING DETAILS
  ROOF VENTING NEEDED?
  SKYLIGHT VENTILATION DETAILS
  Soffit Ventilation

ATTIC VENTILATION

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 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)
• America's Favorite Homes, mail-order catalogues as a guide to popular early 20th-century houses, Robert Schweitzer, Michael W.R. Davis, 1990, Wayne State University Press ISBN 0814320066 (may be available from Wayne State University Press)
• 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: How to find and recognize asbestos in buildings - visual inspection methods, list of common asbestos-containing materials
• Asbestos HVAC Ducts and Flues field identification photos and guide
• 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).
• Asbestos Identification and Testing References
• Asbestos Identification, Walter C.McCrone, McCrone Research Institute, Chicago, IL.1987 ISBN 0-904962-11-3. Dr. McCrone literally "wrote the book" on asbestos identification procedures which formed the basis for current work by asbestos identification laboratories.
• Stanton, .F., et al., National Bureau of Standards Special Publication 506: 143-151
• Pott, F., Staub-Reinhalf Luft 38, 486-490 (1978) cited by McCrone
• 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.
• Dust from the World Trade Center collapse following the 9/11/01 attack: the lower floors of this building contained spray-on fire-proofing asbestos materials.
• "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. "
• Fiberglass: Indoor Air Quality Investigations: Health Concerns About Airborne Fiberglass: Fiberglass in Indoor Air from HVAC ducts, and Building Insulation
• Humidity: What indoor humidity should we maintain in order to avoid a mold problem?
• Lighting, proper use of: proper aiming of a good flashlight can disclose hard to see but toxic light or white mold colonies on walls.
• 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 ] -
• 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.
• 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.
• 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?
• 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 Staircase, Ann Rinaldi
  
• Common Sense Stairbuilding and Handrailing, Fred T. Hodgson
• The Art of Staircases, Pilar Chueca
• Building Stairs, by pros for pros, Andy Engel
• A Simplified Guide to Custom Stairbuilding, George R. Christina
• Basic Stairbuilding, Scott Schuttner
  
• The Staircase (two volumes), John Templar, Cambridge: the MIT Press, 1992
• The Staircase: History and Theories, John Templar, MIT Press 1995
• 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.
• What Style Is It?: A Guide to American Architecture, Rev., John C. Poppeliers, S. Allen Chambers, Wiley; Rev Sub edition (October 6, 2003), ISBN-10: 0471250368, ISBN-13: 978-0471250364
• ...