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 Barrier Wall Construction vs Cavity Wall Building Construction Methods
- Two approaches to constructing building exterior walls to resist water entry: barrier wall construction is compared with cavity wall or rain/screen wall construction
- Definition of cavity / rain-screen wall construction and barrier wall construction approaches to building wall water or moisture resistance
- What is the difference between the cavity approach and the rain screen approach?
- What are the design objectives of barrier wall construction
- What are the design objectives of cavity wall construction
- What are the vulnerabilities of barrier walls and cavity walls: where do leaks and problems occur?
- Questions & Answers about barrier wall vs. cavity wall and rain/screen wall construction methods
- References
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Barrier wall and cavity wall construction methods: this article describes the two design approaches to keeping water and moisture out of building exterior walls: designing barrier walls (the exterior skin is waterproof) and designing cavity / rain-screen walls (the wall is designed to get rid of water that penetrates it). Here we define and describe these approaches and we illustrate what can go wrong with each of them, leading to building leaks and mold or structural damage. Page top illustration courtesy Carson Dunlop Associates.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Barrier Wall Construction vs Cavity Wall Building Construction Methods
Definitions of Barrier Wall Construction and Cavity Wall Construction
 To diagnose a building water entry or moisture problem originating at its exterior walls we must first understand the construction concepts that were used to build that wall: two very different concepts apply, though they often appear mixed or even confused in buildings. Williams & Williams stated these definitions most clearly: [1]
Definition of barrier wall construction
A barrier wall is designed and constructed to shed all water, thereby preventing any moisture from penetrating beyond the outermost surface and into the wall itself. Barrier walls are essentially moisture-tight constructions. Beneath the barrier's outer skin, the underlying materials and building interior are kept dry. [1]
Our photo (left) illustrates a barrier wall constructed building - Bard College South Hall, Annandale NY, photographed in 2005. The wall was intended to shed all water but our inspection found vulnerabilities and leaks traced to original construction errors and to mechanical damage. A common example: installation of exterior wall lighting fixtures after construction punches and leaves un-sealed holes in the exterior wall face.
Examples of barrier wall constructions are architectural pre-cast concrete, most EIFS (Exterior Insulation & Finish Systems - STUCCO EIFS DRAINAGE SYSTEMS), and single-wythe masonry walls.
The vulnerability of a barrier wall construction system to leaks and water entry is that because the wall does not make any provision whatsoever for handling water that penetrates the wall (due to a construction error, mechanical damage, wear and tear, etc.), once any water has leaked into the wall damage will follow, occurring as mold contamination, rot (rot is caused by wood destroying fungi), or an invitation for insect attack.
Readers can compare air and water barrier concepts at WATER BARRIERS, EXTERIOR BUILDING and AIR SEALING STRATEGIES. In addition to VAPOR BARRIERS & HOUSEWRAP, readers should see HOUSEWRAP INSTALLATION DETAILS and HOUSEWRAP at SILLS, SOLES, TOP PLATES for details. Also see VAPOR BARRIERS & CONDENSATION in buildings. Additional remarks about the requirement for weather barriers behind vinyl siding specifically, are found at SIDING VINYL.Also see FLASHING MEMBRANES PEEL & STICK and FLASHING WALL DETAILS.
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Definition of cavity wall construction: difference between the cavity approach and the rain screen approach
Cavity / rain screen walls also shed water at the outer face; however, this wall concept anticipates some degree of water intrusion by including internal drainage provisions. Specifically, an air space situated between the inner and outer wall components forms a "cavity". The dimension of this air space depends on the version of the cavity / rain screen concept implemented in the wall. [1]
 Our photo (left) illustrates a cavity-wall construction - Eula Hall on the Vassar College Campus.
In 2009 when we took this photo, decades of water running down the wall face (from a gutter leak) had led to extensive frost damage to the wall. We left that brick turned on-end as a clue for site maintenance staff but in fact the facilities management crew were well aware of the conditions here.
By 2012 the college had the wall rebuilt. There are two approaches to cavity wall construction: cavity and rain screen. Continuing with help from Williams and Williams:
In the cavity wall version, the air space, detailed with flashing and drainage features, returns water to the building exterior. In its most basic form the air space relies on the force of gravity to collect and redirect water to the building exterior.
To function properly, the space must be unobstructed. Any blockage or obstacle within the space hinders the collection and proper discharge of water. [1]
 The Carson Dunlop Associates sketch at page top also illustrates the cavity wall approach to construction. The sketch at left, courtesy of Steven Bliss & J Wiley & Sons, illustrates use of the rain-screen approach on a clapboard-sided structure. The rain-screen system in this sketch has four components: an exterior
cladding, an air space, a drainage plane, and weep holes. [14]
In the rain screen version, the air space serves as a means of wall drainage as well as a means of equalizing air pressure in the space. An air-tight barrier is placed within the inner layer of the wall construction. The air barrier and specialized vents equalize pressure differences between air inside the cavity and outside the building. [1]
The air space between the inner wall structure and the outer wall veneer is designed wider in the cavity wall approach than in the rain screen approach. In fact the rain screen approach
... necessitates a narrower, compartmentalized air space. This reduces the volume of air in the space and increases the rate of pressure equalization.[1]
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 In the field, a very common instance of blockage of the wall cavity drainage system begins at the time of construction. In constructing a brick masonry veneer, the mason, working to place bricks from the exterior side of the wall, places excess mortar atop each brick in each course. On the wall exterior face the mason cuts away any excessive mortar from the joint before the joint is then tooled.
An example of what happens when water is trapped in a structural brick wall cavity is illustrated at left. The author repaired this wall in the 1980's. Leaks into the wood frame wall from above ran through the brick foundation wall cavity below.
The same brick foundation wall cavity that was attempting to drain that large volume of water also provided an inviting highway for carpenter ants to enter and attack the wall structure from below. We had to re-frame the wall corner, replace wall sheathing and insulation, and of course fix the yankee gutter leaks at an inside corner roof structure above.
During construction, on the wall interior, in the cavity side, excess mortar can block the wall cavity in-situ, or more commonly, much of this mortar actually falls down inside the brick veneer cavity where it blocks the weep holes at the wall bottom. If the space between the outer veneer and inner wall is wide enough, the blockage of falling mortar is minimized. How wide is that? It depends.
Any renovation contractor (such as the author, DF) who has disassembled a brick veneer wall or a structural brick wall built with a wall cavity, has found substantial blockage in at least a good part of the wall cavity. W&W continue:
At below left we show a brick wall (a veneer in this case) with weep openings at regular intervals at two heights above ground level. Below right is a closeup of one of the drainage openings. Veneer wall weep openings are placed at least at the very bottom of the brick veneer wall cavity. We suspect that the wall cavity does not extend lower than the weep holes in our photo - why? The lower brick courses were probably laid tight, with no cavity at all, against a solid concrete or masonry block foundation wall.
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Many Brick or Stone Veneer Walls are Barrier Walls not Cavity / Rain Screen Walls
The brick walls of the New York home in our photo at below left contain no weep openings. Bricks were laid tight against a solid masonry block wall with "faux" bond courses to the left of the chimney and all stretcher brick courses to the right of the chimney. Walls both left and right of the chimney were constructed with no drainage. Bricks were mortared against the masonry block structural walls of the home with no air space and no drainage provision.
This is a brick veneer on block structure approximately 30 years old. While the mason omitted weep openings, we did not find any evidence of water or frost damage to the brick veneer except at another wall where splash-up from roof spillage had worn mortar joints. This is a barrier wall design, not a cavity / rain-screen wall designed structure.
Traditional structural brick walls such as at the building shown at above right are comprised of two or more wythes [defined below] of brick laid in parallel and reinforced by bond courses at regular intervals. Such walls typically include an air gap between the exterior wythes of brick - the wall outside surface, and the wall interior.
That space allowed water that leaked into the wall to run down the wall interior and drain at the wall bottom - provided that the wall bottom included weep openings or drainage. At BRICK FOUNDATIONS & WALLS we describe the collapse of the structural brick walled building shown at above right.
Frequently Asked Questions (FAQs) about barrier wall or cavity wall construction
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
- [1] Williams, M.F., Williams B.L., "Water Intrusion in Barrier and Cavity / Rain Screen Walls", Water in Exterior Building Walls: Problems and Solutions, ASTM STP 1107, Thomas A. Schwartz, Eds., American Society for Testing and Materials, ASHRAE, Philadelphia, 1991, retrieved 8/10/12, Abstract:
Exterior walls are designed and constructed using barrier or cavity / rain screen wall principles. Exterior Insulation and Finish Systems (EIFS) are typically constructed as barrier walls; masonry is often constructed as a cavity wall. These wall systems are discussed along with common deficiencies that allow water intrusion to occur.
[Mark F. Williams and Barbara Lamp Williams are president and vice president respectively of Kenny/Williams/Williams, Inc., a building diagnostics firm at 945 Tennis Ave., Maple Glen PA 19002.]
- [2] Airolite BVC Brick Vents (extruded aluminum), The Airolite Company, LLC, PO Box 410, Schofield WI 54476, TelP 715-841-8757.
- [3] Brick Development Association, The Building Centre, 26 Store Street, London, WC1E 7BT, England, U.K., Tel: 020 7323 7030, Email: brick@brick.org.uk
- [4] Brick Industry Association, 1850 Centennial Park Drive, Suite 301, Reston, VA 20191
Phone: 703.620.0010 Fax: 703.620.3928.
- [5] Brickvent™, Masonry Innovations, Masonry Innovations, 36 Woodview Drive, Pittsboro, IN 46167, Tel: 317.341.0882 or 317.695.0509, Email: info@masonryinnovations.com - the company provides this BrickVent™ moisture control system instruction sheet. Web Search 02/16/2011, original source: http://masonryinnovations.com/Instruction_Sheet.pdf
- [6] Canada Masonry Centre, 360 Superior Blvd., Mississauga ON Canada L5T 2N7. Tel: (905) 564-6622. Offers the CMCA Textbook of Canadian Masonry.
 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.
- [8] Canada Masonry Centre, 360 Superior Blvd., Mississauga ON Canada L5T 2N7. Tel: (905) 564-6622. Offers the CMCA Textbook of Canadian Masonry.
- [9] Masonry Design Manual, James E. Amrhein & Walter L. Dickey, Civil & Structural Engineers, Masonry Industry Advancement Committee, Masonry Institute of America, ASIN B0006XMFZE
- [10] Tamlyn building products, Tom Tamlyn, President, 13623 Pike Rd., Stafford TX 77477, Tel: 800-334-1676.
- "Concrete Slab Finishes and the Use of the F-number System", Matthew Stuart, P.E., S.E., F.ASCE, online course at www.pdhonline.org/courses/s130/s130.htm
- [12] Dave Wickersheimer, P.E. R.A. - IL, professor, school of structures division, UIUC - University of Illinois at Urbana-Champaign School of Architecture. Professor Wickersheimer specializes in structural failure investigation and repair for wood and masonry construction. * Mr. Wickersheimer's engineering consulting service can be contacted at HDC Wickersheimer Engineering Services. (3/2010)
- [13] A HREF="http://astore.amazon.com/inspectapedia-20?_encoding=UTF8&node=13">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.
- [14] 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.
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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- Avongard foundation crack progress chart for structural crack monitoring
- Basement Moisture Control, U.S. Department of Energy
- Building Failures, Diagnosis & Avoidance, 2d Ed., W.H. Ransom, E.& F. Spon, New York, 1987 ISBN 0-419-14270-3
- Building Pathology, Deterioration, Diagnostics, and Intervention, Samuel Y. Harris, P.E., AIA, Esq., ISBN 0-471-33172-4, John Wiley & Sons, 2001 [General building science-DF] ISBN-10: 0471331724
ISBN-13: 978-0471331728
- Building Pathology: Principles and Practice, David Watt, Wiley-Blackwell; 2 edition (March 7, 2008) ISBN-10: 1405161035 ISBN-13: 978-1405161039
- Construction Drawings and Details, Rosemary Kilmer
- Crawl Space Moisture Control, U.S. Department of Energy
- Diagnosing & Repairing House Structure Problems, Edgar O. Seaquist, McGraw Hill, 1980 ISBN 0-07-056013-7 (obsolete, incomplete, missing most diagnosis steps, but very good reading; out of print but used copies are available at Amazon.com, and reprints are available from some inspection tool suppliers). Ed Seaquist was among the first speakers invited to a series of educational conferences organized by D Friedman for ASHI, the American Society of Home Inspectors, where the topic of inspecting the in-service condition of building structures was first addressed.
- Domestic Building Surveys, Andrew R. Williams, Kindle book, Amazon.com
- Defects and Deterioration in Buildings: A Practical Guide to the Science and Technology of Material Failure, Barry Richardson, Spon Press; 2d Ed (2001), ISBN-10: 041925210X, ISBN-13: 978-0419252108. Quoting:
A professional reference designed to assist surveyors, engineers, architects and contractors in diagnosing existing problems and avoiding them in new buildings. Fully revised and updated, this edition, in new clearer format, covers developments in building defects, and problems such as sick building syndrome. Well liked for its mixture of theory and practice the new edition will complement Hinks and Cook's student textbook on defects at the practitioner level.
- Guide to Domestic Building Surveys, Jack Bower, Butterworth Architecture, London, 1988, ISBN 0-408-50000 X
- "Avoiding Foundation Failures," Robert Marshall, Journal of Light Construction, July, 1996 (Highly recommend this article-DF)
- "A Foundation for Unstable Soils," Harris Hyman, P.E., Journal of Light Construction, May 1995
- "Backfilling Basics," Buck Bartley, Journal of Light Construction, October 1994
- "Inspecting Block Foundations," Donald V. Cohen, P.E., ASHI Reporter, December 1998. This article in turn cites the Fine Homebuilding article noted below.
- "When Block Foundations go Bad," Fine Homebuilding, June/July 1998
- Historic Preservation Technology: A Primer, Robert A. Young, Wiley (March 21, 2008)
ISBN-10: 0471788368 ISBN-13: 978-0471788362
- Masonry structures: The Masonry House, Home Inspection of a Masonry Building & Systems, Stephen Showalter (director, actor), DVD, Quoting:
Movie Guide Experienced home inspectors and new home inspectors alike are sure to learn invaluable tips in this release designed to take viewers step-by-step through the home inspection process. In addition to being the former president of the National Association of Home Inspectors (NAHI), a longstanding member of the NAHI, the American Society of Home Inspectors (ASHI), and the Environmental Standard Organization (IESO), host Stephen Showalter has performed over 8000 building inspections - including environmental assessments. Now, the founder of a national home inspection school and inspection training curriculum shares his extensive experience in the inspection industry with everyday viewers looking to learn more about the process of evaluating homes. Topics covered in this release include: evaluation of masonry walls; detection of spalling from rebar failure; inspection of air conditioning systems; grounds and landscaping; electric systems and panel; plumbing supply and distribution; plumbing fixtures; electric furnaces; appliances; evaluation of electric water heaters; and safety techniques. Jason Buchanan --Jason Buchanan, All Movie Review
- Masonry Design for Engineers and Architects, M. Hatzinikolas, Y. Korany, Canadian Masonry (2005), ISBN-10: 0978006100, ISBN-13: 978-0978006105
- Masonry Structures: Behavior and Design, Robert G. Drysdale, Ahmid A. Hamid, Lawrie R. Baker, The Masonry Society; 2nd edition (1999), ISBN-10: 1929081014, ISBN-13: 978-1929081011
- Masonry, Engineered: Using the Canadian Code, J. I. Gainville, Cantext publications (1983), ASIN: B0007C37PG
- Masonry, Non-reinforced masonry design tables, Hans J. Schultz, National Concrete Producers Association and the Canadian Masonry Contractors Association (1976), ASIN: B0007C2LQM
- Moisture Control in Buildings, U.S. Department of Energy
- Moisture Control in Walls, U.S. Department of Energy
- "Vapor Barriers or Vapor Diffusion Retarders", U.S. DOE: how vapor barriers work, types of vapor diffusion barriers, installing vapor barrier
- Ventilation for energy efficient buildings, Purpose, Strategies, etc.,
- ...
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