Membrane Roofing Materials, EPDM, PVC, or Rubber Roof Choices, Membrane Roof Costs, Flat Roof Covering Life Expectancy, Flat Roof or Membrane Roof Characteristics
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"Membrane roofs" is a general term that may be applied to a low slope or flat roof covered by any means that is intended to produce a continuous waterproof barrier.
Our photo (left) shows roof penetrations and flashing on an EPDM roof in New York. [That chimney may be too short, violating code and safety if it extends less than 2 feet above the roof surface.] Look closely and you can see the marks left by round anchors that tied rooftop insulation to the roof deck below. This telegraphing of insulation fasteners is not a roof defect - it's normal.
Asphalt shingles, in contrast to the EPDM roof shown here, , are not a "waterproof membrane" and depend on the drainage offered by the roof slope to function effectively.
That's why without special measures (discussed at LOW SLOPE ROOFING) we don't expect to find shingles installed on roofs of pitch lower than 4" of rise in 12" of run.
While a variety of single-ply roofing membranes are used
on commercial jobs, only EPDM has become widely used
on residential sites. EPDM, a form of synthetic rubber,
owes its popularity to its relative ease of installation combined
with exceptional durability. If installed correctly,
roofs often exceed 20 years of service and callbacks are
exceedingly rare.
While some commercial EPDM systems are loose-laid
or ballasted, residential applications are typically fully
adhered. Rolls typically vary from 10 to 50 feet in width
and from 50 to 200 feet in length, but many distributors
will cut a piece to size for smaller jobs. If possible, use a
single piece with no seams for the field of the roof. EPDM
membranes are available in two thicknesses: .045 inch and
.060 inch.
For fully adhered applications or any application
where foot traffic or decking is planned, the thicker
membrane is recommended.
Substrates for EPDM Roofs
EPDM can be bonded to a wide variety of
substrates, including plywood, OSB, fiberboard, and urethane
insulation board. The substrate should be smooth,
even, and free of debris. Fasteners should be driven flush
except in the case of insulation fastening caps, which
project their shape though the membrane. If the surface is
uneven or deteriorated, a layer of fiberboard or thin
plywood should be installed first.
Installation Details for EPDM Roofs
After cutting the material to fit, installers
use a roller to apply a proprietary contact cement to both
the membrane and the substrate. Typically, a length of
roofing is set in place and folded in half lengthwise so onehalf
can be glued at a time. The adhesive should be fully
dry on both surfaces before bonding, or bubbles may develop.
Also, care must be taken to smooth out wrinkles and
air pockets as the two surfaces are mated. Where seams
are required, the material is lapped 4 to 6 inches and sealed
with either double-faced seam tape or a special adhesive
used for bonding rubber to rubber.
At openings, inside corners, outside corners, and other
irregular shapes where the EPDM roof membrane has been cut, patches
of uncured EPDM are applied using the rubber-to-rubber
adhesive. The uncured form of EPDM is highly elastic and
can be stretched to conform to irregular shapes.
The material is lapped up abutting walls and serves as
its own flashing. Other terminations are usually sealed
with an aluminum termination bar or an aluminum flashing
covered with a strip of EPDM. Finally all exposed
edges of EPDM at laps, patches, and terminations are
sealed with a bead of proprietary caulking that protects the
edge and acts as an extra water stop.
Self-Adhesive.
For small EPDM roof jobs, a few manufacturers
offer a peel-and-stick version of EPDM. Installation is
similar to standard EPDM but may require a primer on plywood
and OSB substrates. Seams generally require a proprietary
adhesive with special caulking on exposed edges.
Although the square foot cost is greater than with siteglued
EPDM, on small jobs labor savings offset the higher
material costs.
Pros and Cons of EPDM Roofing
While not intended as a walkway,
EPDM works well as a substrate under rooftop decks. Leftover
strips of membrane should be used to cushion the
roofing from wood sleepers. Leaks are rare and usually can
be traced to sloppy sealing of joints. Leaks are also relatively
easy to identify and fix. One caution is that EPDM
can be damaged by grease and petroleum-based products,
a potential problem with outdoor grills and spillage of
oil-base finishes used on siding or wood decking.
Common Problems in PVC or EPDM Membrane or "rubber" Roofs
As Carson Dunlop's sketch (below) illustrates, wrinkling and failure at seams are problems to watch for where membrane roofs of EPDM, PVC, or similar materials are installed. A wrinkle in an EPDM roof is also shown at the top of this page.
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Additional technical contributors & reference sources for this article are listed below.
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"Choosing Roofing," Jefferson Kolle, January 1995, No. 92, Fine Homebuilding, Taunton Press, 63 S. Main St., PO Box 5506, Newton CT 06470 - 800-888-8286 - see http://www.taunton.com/FineHomebuilding/ for the magazine's website and for subscription information.
Problems in Roofing Design, B. Harrison McCampbell, Butterworth Heineman, 1991 ISBN 0-7506-9162-X (available used)
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.
Green Roof Plants: A Resource and Planting Guide, Edmund C. Snodgrass, Lucie L. Snodgrass, Timber Press, Incorporated, 2006, ISBN-10: 0881927872, ISBN-13: 978-0881927870. The text covers moisture needs, heat tolerance, hardiness, bloom color, foliage characteristics, and height of 350 species and cultivars.
Green Roof Construction and Maintenance, Kelley Luckett, McGraw-Hill Professional, 2009, ISBN-10: 007160880X, ISBN-13: 978-0071608800, quoting: Key questions to ask at each stage of the green building process Tested tips and techniques for successful structural design
Construction methods for new and existing buildings
Information on insulation, drainage, detailing, irrigation, and plant selection
Details on optimal soil formulation
Illustrations featuring various stages of construction
Best practices for green roof maintenance
A survey of environmental benefits, including evapo-transpiration, storm-water management, habitat restoration, and improvement of air quality
Tips on the LEED design and certification process
Considerations for assessing return on investment
Color photographs of successfully installed green roofs
Useful checklists, tables, and charts
Roof failure causes in depth (and specific methods for avoiding them)
Roof design fundamentals and flourishes, based on voluminous industry research and experience
New technologies and materials -- using them safely and correctly
Comprehensive coverage of all major roofing systems
pecifications, inspection, and maintenance tools for roofing work
Problems in Roofing Design, B. Harrison McCampbell, Butterworth Heineman, 1991 ISBN 0-7506-9162-X (available used)
Roofing The Right Way, Steven Bolt, McGraw-Hill Professional; 3rd Ed (1996), ISBN-10: 0070066507, ISBN-13: 978-0070066502
Slate Roofs, National Slate Association, 1926, reprinted 1977
by Vermont Structural Slate Co., Inc., Fair Haven, VT 05743, 802-265-4933/34. (We recommend this book if you can find it. It
has gone in and out of print on occasion.)
The Slate Roof Bible, Joseph Jenkins, www.jenkinsslate.com,
143 Forest Lane, PO Box 607, Grove City, PA 16127 - 866-641-7141 (We recommend this book).
"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
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