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Cathedral Ceiling Ventilation Specifications
- CATHEDRAL CEILING VENTILATION - How should I vent a cathedral ceiling?
- Does air movement (wind washing) through a vented cathedral ceiling cause heat loss through the insulation?
- Should I install an air barrier in the cathedral ceiling above the insulation?
- Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices & Best Practices Guide to cathedral ceiling ventilation designs, Steven Bliss
- CATHEDRAL CEILING INSULATION - separate article
- HOT ROOF DESIGNS: Un-Vented Roof Solutions - separate article
- Questions & Answers about the best methods for ventilationg cathedral ceilings and other sloped building ceilings
- References
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This article describes the best methods for ventilation in a cathedral ceiling and the effects on heat loss of air movement through a ventilated attic or cathedral ceiling.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Advice on Venting Cathedral Ceilings
The link to the original Q&A articles in PDF form immediately below is followed by an expanded/updated online version of each article.
Accompanying text is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss. Sketch above showing venting in a steep-slope cathedral ceiling roof is courtesy of Carson Dunlop Associates. Readers should see CATHEDRAL CEILING INSULATION and also our concerns with the "hot roof" un-vented cathedral ceiling design discussed at HOT ROOF DESIGNS: Un-Vented Roof Solutions. Also see Roof Venting: Un-Vented Hot Roof Solutions. At INSULATION LOCATION & QUANTITY for ATTICS we discuss the relative benefit of adding insulation to a cathedral ceiling versus building walls in the same area. And see COOLING LOAD REDUCTION by ROOF VENTS. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
The question-and-answer article below paraphrases, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.
Wind Washing: Does airflow in a vented cathedral ceiling cause unwanted heat loss from the building?
Question about wind washing at building eaves:
Cathedral ceilings are vented at the ridge and eaves to allow airflow through the ceiling. Doesn't this airflow remove heat from the fiberglass insulation during the heating season?
Is it better practice to separate the cathedral ceiling insulation from the air flow with a permeable fireproof material such as drywall, leaving approximately 1/2 inch between the drywall and the bottom of the roof sheathing? -- Larry Gunther, Neola, UT
Sketch (left) showing how wind washing steals heat from fiberglass insulation is courtesy of Carson Dunlop Associates.
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Reply: The Effects on Insulating Value of Airflow Across Fiberglass Insulating Batt Surfaces
Anything that induces (causes) airflow through a fiberglass insulating batt will reduce the effectiveness of that insulation, since fiberglass works by reducing air movement. Air flowing across a fiberglass batt, however, should not seriously reduce the insulation's R-value except with very thin batts and very fast air movement.
In laboratory experiments, a 3-inch fiberglass batt on an attic floor had a 29-percent reduction in R-value caused by air flowing across it at 2 mph.
In another experiment, 6 inches of loose fill fiberglass had a 14 percent reduction at similar airspeeds.
With the thicker fiberglass insulating batts in contemporary use, the reductions in insulating value caused by air movement across the fiberglass surface will be less.
Also it is unlikely that airflows across insulation in a cathedral ceiling will reach this speed, even under extreme conditions.
More details are at COOLING LOAD REDUCTION by ROOF VENTS.
Baffle Designs to Stop Airflow Effects Across Insulating Fiberglass Batts in a Cathedral Ceiling
To be safe, you could build a baffle such as you suggest, or use manufactured baffles,such as ProperVent.
If you are going to the trouble of making your own baffle, use something like perforated foil board (Dennyboard or Thermoply). You will have an effective summertime radiant barrier as well. (See RADIANT BARRIERS). Drywall is probably not an ideal product for an inter-rafter air baffle over the cathedral ceiling insulation since drywall can get soggy if there is excess condensation or a roof leak. Also, unless the drywall were perforated it may trap moisture in the ceiling cavity.
At INSULATION LOCATION for CATHEDRAL CEILINGS we describe a high-labor method that combines providing an air barrier above fiberglass insulation in a cathedral ceiling to avoid heat loss by air movement in the roof, combined with the addition of solid foam insulation to provide a much higher R-value for the completed cathedral ceiling structure. -- DF
But as Bliss points out in the original Q&A on cathedral ceiling ventilation, the risk of forming a vapor barrier sandwich around fiberglass ceiling insulation (foil faced insulation above and poly vapor barrier below) is that any moisture entering the insulation will be trapped, risking future mold or rot problems. The risk of hidden mold and rot due to moisture entering from the building involves two concepts:
- Interior sealing: Be sure that the room side of the cathedral ceiling is sealed meticulously against air leaks, such as by using a 6-mil polyethylene vapor barrier on the warm side of the insulation (in a heating climate) and careful workmanship, gaskets, sealants around any ceiling penetrations for electrical wiring or fixtures.
- Exterior inspection: monitor the condition of the roof from above, with an annual inspection - unattended leaks on any roof structure can lead to costly rot, insect, or mold damage, but on a well-insulated, sealed cathedral ceiling roof, leaks from above can go for quite a while without notice from inside the building.
Another possibility would be to perforate the kraft paper on the insulating batts and face the paper up in the roof cavity. Of course you will have to install a continuous poly vapor barrier below the insulation as well.
Adequate Air Space over Cathedral Ceiling Insulation
It is unlikely that your proposed 1/2" air space between the top of the fiberglass insulation and the underside of the roof sheathing will provide an effective airflow between the building eaves and ridge. As you'll notice in Carson Dunlop's sketch at the top of this article, experienced home inspectors and other building professionals recommend a 3-inch air space.
The question-and-answer article about the effects of airflow on loss of R-value in fiberglass insulating batts, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.
Readers should see COOLING LOAD REDUCTION by ROOF VENTS and see CATHEDRAL CEILING INSULATION and also our concerns with the "hot roof" un-vented cathedral ceiling design discussed at HOT ROOF DESIGNS: Un-Vented Roof Solutions. Also see Roof Venting: Un-Vented Hot Roof Solutions. At INSULATION LOCATION & QUANTITY for ATTICS we discuss the relative benefit of adding insulation to a cathedral ceiling versus building walls in the same area.
Use of Radiant Barrier Foil in a Cathedral Ceiling?
 The link to the original Q&A articles in PDF form immediately below is followed by an expanded/updated online version of each article.
Question: Is the foil-based radiant barrier in my cathedral ceiling in a useful place?
In my proposed cathedral ceiling detail [sketch at left], I want to use a reflective foil between the insulation and the roof sheathing to double as a radiant barrier and a cathedral ceiling ventilation space liner. Is the radiant barrier in a useful place? James French, Suffern, NY.
Reply: Yes but ...
The foil is in the right place to block radiant heat across the air space. But there are some other problems.
First, radiant barriers are not really cost effective in cold climates.
Second, in winter a continuous layer of foil above the insulation in a cathedral ceiling creates a cold-side vapor barrier, vulnerable to condensation on the underside. [Foil has a perm rating of about zero.] In other words, your vapor barrier is in the wrong place and you could end up with trapped moisture, wet insulation, and even rot and mold in the ceiling cavity over time.
Most builders and designers feel that a lining material is not necessary in the airspace of a cathedral ceiling except at the eaves [to avoid wind-wash or moved insulation]. At the eaves a rigid baffle is recommended to keep the insulation in place and to keep wind out of the insulation.
For extra protection from wind, some builders line the space with a housewrap material such as Tyvek.
See RADIANT BARRIERS for details about radiant barriers.
Tight Ceiling - Cathedral Ceiling Advice for Venting & Moisture
As explained in Best Practices Guide to Residential Construction, chapter on BEST ROOFING PRACTICES:
Although the code-mandated ventilation rate has proven
adequate under normal conditions, homes with highmoisture
levels and air leaks in ceilings may still experience
problems such as moldy sheathing. Cathedral ceilings
are at the greatest risk due to the limited ventilation path.
The best defense against problems is to create a continuous
air and vapor barrier between the living space and attic or
roof cavity by carefully sealing all air leaks. The ceiling air
barrier may consist of foam insulation with taped seams,
taped polyethylene sheeting, or finished drywall that is
sealed at corners and top plates with gaskets or sealants.
Penetrations & Roof Ventilation Challenges - Common Air Leak Points in Ceilings
Pay special attention to penetrations in
the ceiling plane, particularly in cathedral ceilings.
Chimneys,
recessed lights, plumbing chases, and holes drilled
through top plates for plumbing or wiring should all be
sealed (Figure 2-53 at left).
Plug holes with durable materials, such as expandable
urethane foam, foam backer rod, EPDM, or sheet metal,
and use long-lasting sealants such as high-quality urethanes,
silicones, and butyls.
With a tightly sealed ceiling, attic moisture is no
longer a significant problem.
Attic ventilation is still recommended
for these other reasons:
Original article - PDF:
-- Adapted with permission from Best Practices Guide to Residential Construction.
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- Solar Age Magazine was the official publication of the American Solar Energy Society. The contemporary solar energy magazine associated with the Society is Solar Today. "Established in 1954, the nonprofit American Solar Energy Society (ASES) is the nation's leading association of solar professionals & advocates. Our mission is to inspire an era of energy innovation and speed the transition to a sustainable energy economy. We advance education, research and policy. Leading for more than 50 years.
ASES leads national efforts to increase the use of solar energy, energy efficiency and other sustainable technologies in the U.S. We publish the award-winning SOLAR TODAY magazine, organize and present the ASES National Solar Conference and lead the ASES National Solar Tour – the largest grassroots solar event in the world."
- Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
- Steve Bliss's Building Advisor at buildingadvisor.com helps homeowners & contractors plan & complete successful building & remodeling projects: buying land, site work, building design, cost estimating, materials & components, & project management through complete construction. Email: info@buildingadvisor.com
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
- 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. Mr. Cramer serves on the ASHI Home Inspection Standards. Contact Mark Cramer at: 727-595-4211 mark@BestTampaInspector.com
- John Cranor is an ASHI member and a home inspector (The House Whisperer) is located in Glen Allen, VA 23060. He is also a contributor to InspectApedia.com in several technical areas such as plumbing and appliances (dryer vents). Contact Mr. Cranor at 804-747-7747 or by Email: johncranor@verizon.net
 Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
- ASHRAE resource on dew point and wall condensation - see the ASHRAE Fundamentals Handbook, available in many libraries. The following three ASHRAE Handbooks are also available at the InspectAPedia bookstore in the third page of our Insulate-Ventilate section:
- 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: 978-0910110969
- Best Practices Guide to Residential Construction, by Steven Bliss. John Wiley & Sons, 2006. ISBN-10: 0471648361, ISBN-13: 978-0471648369, Hardcover: 320 pages, available from Amazon.com and also Wiley.com. See our book review of this publication.
- Decks and Porches, the JLC Guide to, Best Practices for Outdoor Spaces, Steve Bliss (Editor), The Journal of Light Construction, Williston VT, 2010 ISBN 10: 1-928580-42-4, ISBN 13: 978-1-928580-42-3, available from Amazon.com
- "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
- "Insulation: Adding Insulation to an Existing Home," U.S. Department of Energy - tips on how to do your own check for the presence of absence of insulation in a home
- Insulation Types, table of common building insulation properties from U.S. DOE. Readers should see INSULATION R-Values & Properties our own table of insulation properties that includes links to articles describing each insulation material in more detail.
- The National Institute of Standards and Technology, NIST (nee National Bureau of Standards NBS) is a US government agency - see www.nist.gov
- "A Parametric Study of Wall Moisture Contents Using a Revised Variable Indoor Relative Humidity Version of the "Moist" Transient Heat and Moisture Transfer Model [copy on file as/interiors/MOIST_Model_NIST_b95074.pdf ] - ", George Tsongas, Doug Burch, Carolyn Roos, Malcom Cunningham; this paper describes software and the prediction of wall moisture contents. - PDF Document from NIST
- Ice Dam Leaks in building attics and roof cavities, how to inspect for evidence of leaks, identify causes, and correct bad attic ventilation, improper roof venting, and these causes of attic mold or roof structure damage
- Mold Information Center: What to Do About Mold, mold action plan, valid and invalid test methods, mold remediation
- ProperVent, ProperVent Inc., 750 Boone Ave. N., Minneapolis MN 55427 612-544-9776.
- "Radiant Barrier Attic Fact Sheet, Effect of Radiant Barriers on Heating & Cooling Bills", U.S. Department of Energy, - PDF file. Click in the top area of this document to return to this website.
- "Radiant Barrier Attic Fact Sheet, Important Non-Energy Considerations", U.S. Department of Energy, - PDF file. Click in the top area of this document to return to this website.
- "Radiant Barrier Attic Fact Sheet, [Radiant Barrier] Installation Procedures [for Attics]", U.S. Department of Energy, - PDF file. Click in the top area of this document to return to this website.
- "Radiant Barrier Attic Fact Sheet, Appendix: Radiant Barrier Test Results", U.S. Department of Energy, - PDF file. Click in the top area of this document to return to this website.
- "Radiant Barrier Attic Fact Sheet, DATA TABLES: Cost of Radiant Barriers in Locations, Savings of Radiant Barriers by U.S. City, Average Reductions in Ceiling Heat Flow due to Radiant Barrier, Table of Typical Heating Equipment Efficiencies, Table of Cooling Load Factors for Radiant Barriers by U.S. City, Table of Cooling Load Factors for Additional Insulation by U.S. City,", U.S. Department of Energy, - PDF file. Click in the top area of this document to return to this website.
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, 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. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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