Roof Venting Defects seen from Outside How to inspect the building exterior to find roof & attic ventilation defects & damage caused by poor venting
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Roof ventilation defects & mistakes:
What are the common mistakes found in roof ventilation systems? What are the effects of inadequate roof venting? What happens if there is too much roof venting? What happens if ridge vent outlet area is greater than roof intake vent areas at a building eaves? What happens when we leave open gable end vents on a building with ridge and soffit venting?
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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Inspection Tips for Roof Venting & Ice Dam Problems
The first signs of a probable attic condensation problem may there for observation before even entering a building.
Look at the roof. If you're in a cold climate during winter months you may see areas of snow-melt showing where there is an insulation defect.
Or you may see actual severe ice dams at the roof eaves.
If the shingles are exposed look for signs of attic moisture in their condition: if there is a high level of attic moisture, unless the roof is quite young,
you might see puckered shingles in the classic "fishmouth" pattern.
This shingle curling is quite obvious. If you inspect the exterior roof surface first, on an old roof you'll note shingles which are brittle and which may crack or break. (Don't walk on such surfaces.) If the roof sheathing is plywood, you may sense
surface deflection which could simply be thin 3/8" plywood (no longer permitted in most jurisdictions) or it could be damaged from heat or moisture. (Beware of falling through).
Look at the ridge. If there is no ridge vent there is no good outlet for an under-roof attic venting system and this roof will be difficult to ventilate.
When you make your inside inspection you will also inspect the roof below any "apparent" ridge vents seen outside, as sometimes we find that a faux ridge vent was installed with no openings cut into the roof cavity.
Look at the eaves or soffits. If there are no continuous intake vents at the soffits, this roof will be difficult to ventilate. And when you make your inside inspection you will look for light or other indications that the eave or soffit vents you found are real, not faux.
Look at the roof lines. If the building has no roof overhang, flat roofs, low-slope roofs, roofs abutting Building walls, or complex roof lines, these roofs will be difficult to ventilate.
The photograph shown at the top of this page offers compelling evidence of roof leaks into the soffit of this older home.
A Photo Guide for Inspecting the Building Exterior for Wet Site, Sources of Attic Condensation, & Roof Venting Problems
Here we provide a series of photographs taken of the exterior of buildings, demonstrating visual clues that can predict a problem with ice dam leaks into these homes.
No Soffit Intake Vents on a Roof Means Ice Dams
In freezing climates, as in our photograph at page top, given the age of construction (pre 1900), the brown color of the stains (oils from roof sheathing boards that have been wet),
and the shape of the roof edge (probably there was a built-in eaves trough gutter), it is likely that when we inspect the attic
interior we'll see that despite the perforated soffit covers, the roof has no intake venting and there has been a long
history of ice dam leaks on this building.
Inadequate soffit or ridge venting risks attic moisture, mold, ice dams, as show by these photos
In both heating and cooling climates, insufficient roof ventilation risks attic or roof cavity condensation, mold, rot, and in some cases increased heating or cooling costs for the building. And as we show just below, do not assume that your building has working roof ventilation even if you see perforated panels covering the building soffit underside
Fake Soffit Vents?
Too often building exterior renovations include covering an existing, solid, un-vented
building soffit or eaves with perforated panels, forming a "faux vent" system since the perforations are not really passing
any air into the building attic.
It's easy to spot this condition both by visual inspection and, where accessible, by
pressing on the perforated panels - if they are over an open space they will move easily.
In our photograph at left, although perforated panels are installed on soffits of this older home, we see extensive leak stains on that material.
From outside we posit that either the perforated panels were installed over solid wood - there is no actual soffit intake venting for the attic, or the building simply has little or no attic insulation, resulting in lots of heat loss into the attic during winter months, combined with freezing of melting snow at the colder roof edges.
No Soffits so No Soffit Vents Means Ice Dams and Wall Leaks are Likely
The home shown in our photograph at left was built with no roof overhang whatsoever - or no roof soffits or eaves extension past the building walls. Not only does roof runoff too often run down the exterior wall surface, inviting rot or insect damage or wall leaks, but also this construction makes it tricky to obtain any roof cavity intake venting.
Special products such as the Hicks (TM) starter vent can be used at roof eaves in this location, but an air path must also be provided inside under the roof decking.
The window at the building right corner tells us that cathedral ceilings were probably installed inside this home - under-roof venting would still be a good step to avoid roof cavity condensation, leaks, mold, or related damage.
Tiny Gable End Vents can Predict Ice Dams and Inadequate Attic Ventilation on buildings
The photograph shown at left demonstrates a tiny gable-end vent in an older building.
This home combines stone construction, multiple shingle layers, shaded site with (unseen) no other attic intake or outlet ventilation, to make attic condensation problems and seasonal ice dam leaks likely.
Photographs of Building Siding Stains Can Indicate Ice Dam Leaks
This photo shows siding stains caused by roof ice dam leaks into the wall cavity.
Notice that the soffit is un-vented on this older home. Roof leaks into the wall cavity have run down the walls and exited between clapboards, leaving stains and peeling paint.
Roof leaks in this area from any cause, ice dams or work, leaky roofing materials will all produce this effect.
Photos of Use of Heating Tapes on Roof Edges Tells the Ice Dam Story
This photo shows roof edge heating tapes installed by an owner to attempt to melt channels through ice that may accumulate at the roof eaves in winter.
This is an inexpensive band-aid that may be sufficient if ice dam formation on a roof is rare and/or it is difficult to install good under-roof venting.
This roof has eaves and a ridge that could have been vented.
If a roof shape prevents easy installation of under-roof venting, or if a home is located where building custom excludes under-roof venting, use of an ice-and-water shield product under the shingles at roof edges, or use of metal covering the lower roof slopes are other measures taken to prevent ice dam leaks into the building interior.
for details about the use of heating cables on roofs to prevent ice dam leak damage.
Signs of Roof Ice Dam Problems Can Be Seen in Any Season
In addition to our photos showing missing roof intake or outlet venting, roof leak stains, and similar clues, you may be able to spot evidence of attempts to remove roof ice dams by chopping at the ice itself.
Usually attempts to remove roof ice by chopping at it results in damaged roof shingles and sometimes holes in nearby flashing or gutters as shown in this photo.
You'll also spot chop or cut marks in roof shingles at the lower roof edges when this procedure has been attempted.
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Citations & References
In addition to any citations in the article above, a full list is available on request.
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).
The Smart Vent™ by DCI roof intake venting provides an intake at the lower edge of roof decking for difficult cases. See www.dciproducts.com/html/smartvent.htm
The AccuVent™ attic ventilation roof baffle produced by Berger permits insulation to extend over the top plate as far forward as possible. See www.bergerbuildingproducts.com/pdfs/AccuVentAtticVent.pdf
GAF Cobra® and other GAF roof ventilation products: see www.gaf.com/Content/GAF/RES1/roof/RS_whyuse_ventchart.asp?viewer=&module=
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.
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. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
"Unvented Roofs, Hot-
Humid Climates, and
Asphalt Roofing Shingles
Research Report - 0306
Feb-2003
Building Science Corporation", Building Science Corporation, 30 Forest Street,
Somerville, MA 02143 Quoting from the article abstract:
"When constructing unvented roofs with asphalt shingles in hot-humid climates, a vapor barrier must be
installed between the asphalt shingles and the roof deck." - Web Search 5/21/2010
Thanks to reader - Mike Martino
for discussing attic ventilation retrofit ideas - August 2010
[1] Air Vent, Inc., Tel: 1-800-247-8368, Email: ventilation@gibraltar1.com, web search 08/11/11,
[4] Steven Bliss served as editorial director and co-publisher of The Journal of Light Construction for 16 years and previously as building technology editor for Progressive Builder and Solar Age magazines. He worked in the building trades as a carpenter and design/build contractor for more than ten years and holds a masters degree from the Harvard Graduate School of Education.
Excerpts from his recent book, Best Practices Guide to Residential Construction, Wiley (November 18, 2005) ISBN-10: 0471648361, ISBN-13: 978-0471648369, appear throughout this website, with permission and courtesy of Wiley & Sons. Best Practices Guide is available from the publisher, J. Wiley & Sons, and also at Amazon.com .
ASHRAE resource on dew point and wall condensation - see the ASHRAE Fundamentals Handbook, available in many libraries.
2005 ASHRAE Handbook : Fundamentals: Inch-Pound Edition (2005 ASHRAE HANDBOOK : Fundamentals : I-P Edition) (Hardcover), Thomas H. Kuehn (Contributor), R. J. Couvillion (Contributor), John W. Coleman (Contributor), Narasipur Suryanarayana (Contributor), Zahid Ayub (Contributor), Robert Parsons (Author), ISBN-10: 1931862702 or ISBN-13: 978-1931862707
2004 ASHRAE Handbook : Heating, Ventilating, and Air-Conditioning: Systems and Equipment : Inch-Pound Edition (2004 ASHRAE Handbook : HVAC Systems and Equipment : I-P Edition) (Hardcover) by American Society of Heating, ISBN-10: 1931862478 or ISBN-13: 978-1931862479 "2004 ASHRAE Handbook - HVAC Systems and Equipment The 2004 ASHRAE HandbookHVAC Systems and Equipment discusses various common systems and the equipment (components or assemblies) that comprise them, and describes features and differences. This information helps system designers and operators in selecting and using equipment. Major sections include Air-Conditioning and Heating Systems (chapters on system analysis and selection, air distribution, in-room terminal systems, centralized and decentralized systems, heat pumps, panel heating and cooling, cogeneration and engine-driven systems, heat recovery, steam and hydronic systems, district systems, small forced-air systems, infrared radiant heating, and water heating); Air-Handling Equipment (chapters on duct construction, air distribution, fans, coils, evaporative air-coolers, humidifiers, mechanical and desiccant dehumidification, air cleaners, industrial gas cleaning and air pollution control); Heating Equipment (chapters on automatic fuel-burning equipment, boilers, furnaces, in-space heaters, chimneys and flue vent systems, unit heaters, makeup air units, radiators, and solar equipment); General Components (chapters on compressors, condensers, cooling towers, liquid coolers, liquid-chilling systems, centrifugal pumps, motors and drives, pipes and fittings, valves, heat exchangers, and energy recovery equipment); and Unitary Equipment (chapters on air conditioners and heat pumps, room air conditioners and packaged terminal equipment, and a new chapter on mechanical dehumidifiers and heat pipes)."
1996 Ashrae Handbook Heating, Ventilating, and Air-Conditioning Systems and Equipment: Inch-Pound Edition (Hardcover), ISBN-10: 1883413346 or ISBN-13: 978-1883413347 , "The 1996 HVAC Systems and Equipment Handbook is the result of ASHRAE's continuing effort to update, expand and reorganize the Handbook Series. Over a third of the book has been revised and augmented with new chapters on hydronic heating and cooling systems design; fans; unit ventilator; unit heaters; and makeup air units. Extensive changes have been added to chapters on panel heating and cooling; cogeneration systems and engine and turbine drives; applied heat pump and heat recovery systems; humidifiers; desiccant dehumidification and pressure drying equipment, air-heating coils; chimney, gas vent, fireplace systems; cooling towers; centrifugal pumps; and air-to-air energy recovery. Separate I-P and SI editions."
Principles of Heating, Ventilating, And Air Conditioning: A textbook with Design Data Based on 2005 AShrae Handbook - Fundamentals (Hardcover), Harry J., Jr. Sauer (Author), Ronald H. Howell, ISBN-10: 1931862923 or ISBN-13: 978-1931862929
1993 ASHRAE Handbook Fundamentals (Hardcover), ISBN-10: 0910110964 or ISBN-13: 978-091011096
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.
In addition to citations & references found in this article, see the research citations given at the end of the related articles found at our suggested
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. Tel: (416) 964-9415 1-800-268-7070 Email: info@carsondunlop.com. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Carson Dunlop Associates provides extensive home inspection education and report writing material. In gratitude we provide links to tsome Carson Dunlop Associates products and services.