“Picture Framing” Roof Shingles on Insulated Panel Systems
The term “picture framing” was coined to describe the way roof shingles appear to bulge in a a pattern of “frames” around panels when using insulated roofing panels. When sunlight washes across the roof, it is easy to see the outline of every insulated panel. Most clients are not happy with the appearance of their new roof. Something appears to be wrong, and even though there are no leaks or other failures, the new roof simply looks terrible. Understandably, many Owners want the problem fixed before the end of the first year warranty period.
In fact, appearance may be the only problem. Properly installed insulated roofing systems with shingles regularly “picture frame.” The manufacturers of the individual components and the installers generally state that they will stand behind their products and installation for the full term of the warranty. In practice, this is no consolation to the Owner who has a new roof that looks flawed and a nervous feeling that the joints will fail (leak) by cracking before the warranty is up.
Should an Owner want to try to use the warranty to repair or replace the roof, numerous trades could become involved:
• The specifier of the roof
• The general contractor who oversaw the job
• The insulated panel supplier
• The panel installer
• The manufacturers of related roofing parts: eave vents, ridge vents, vapor barriers, ice and water barriers, saturated felts, and roofing shingles
• Roofing installers
The number of trades involved make it simple to lay blame for failures at someone else’s feet. It is difficult to convince one or more of the trades that they are solely responsible for the repair or replacement of a roof system due to a failure. An experienced owner knows that if they accept a “picture framed” roof, it will not be easy to collect on the warranty. What is worse, the Owner feels they paid for a beautiful new roof and they are being asked to accept a poor installation.
To make matters worse, some manufacturers carefully word their warranties to exclude any practical application of their products. One manufacturer of polyisocyanurate roofing products, in their Limitations and Disclaimer of Warranties and Liabilities uses the following language:
“______ makes no implied warranties of any type, including, without limitation, any warranty of merchantability or fitness for purpose.” (Back page of the product literature, 2000)
Clauses like this do not instill confidence in Owners that they are buying a product that the manufacturer will stand behind.
There are several ways to reduce the likelihood of “picture framing.” These solutions differ from the manufacturer’s recommendations for product installation found in some published product literature. A few proposed details are listed at the end of the article. Some background information is important to cover first.
Manufacturers of fiberglass and/or organic mat roofing shingles have cautioned that installation over standard non-vented polyisocyanurate roofing panels can shorten the warranty life of their products. The heat build-up tends to accelerate the aging process of the shingles. The recommended solution by the shingle industry is to use vented systems.
Vented Panel Construction
The usual vented panel construction consists of a layer of plywood or OSB (Oriented Strand Board), ¾ inch or 1 ½ inch clear vertically aligned airspace (depending on the distance between the eave and the ridge) on polyisocyanurate insulation. The manufacturing process usually includes a fiber-reinforced facer (moisture retarding) on both sides of the insulation for protection during shipping and installation and to provide a glue surface to attach the blocking and nail board.
Polyisocyanurate insulation is a generic description of an open-cell expanded rigid foam insulation product available in a wide variety of thicknesses. It has the highest initial insulating resistance per inch of standard foam insulating products, though its resistance can diminish with age and moisture content. Being an open-cell foam, it must be protected from water and humidity as it has the ability to retain and release moisture. For this reason, it must be well protected from the factory through the final installation. It must also be protected from ultraviolet light as this breaks down the foam. Once properly installed under other building products, like roof shingles, it is theoretically well protected.
Use of asphalt saturated roofing felt as shingle underlayment is the industry standard. These organic felts are currently available by ASTM standard D-226, Type I and Type II (commercial) and ASTM 4869 Type I & Type II (residential shingle underlayment). Type II felts are heavier:
Historically, felts were available by weight: 15lb and 30lb. As the title implies, there was 15 or 30lbs of asphaltic material per square of felts. The greater saturation improved the water resistance but increased the weight per roll and made them harder to handle. To reduce roll weight and make the products easier to handle and install; #15 and #30 felts were developed. They had less asphalt, were less expensive to manufacture, were lighter, easier to install, and are prone to buckling with moisture. The organic felts are asphalt impregnated to make them water-resistant. They are, however, only water-resistant. They can absorb water and expand. They have very little structural or tensile integrity and once they have moved, tend not to return to their original shape.
In practice, roofing felts allow the builder to cover a newly installed wood roof deck quickly, protecting it from moisture until the shingles can be installed. Installed dry, the felts lie flat on the decking in direct sun or shade. If they’re exposed to moisture or it rains, they absorb some of the moisture and buckle in “waves.” Once water has been absorbed, they do not appear to go flat, even after drying out.
Major manufacturers like CertainTeed and GAF have developed fiberglass reinforced roofing felts to help stabilize buckling due to moisture absorption. (GAF: Shingle-Mate, CertainTeed: Roofers’ Select, and there are others). These may, if properly installed, discourage “picture framing.” This type of product is described by CertainTeed as: “...an asphalt-impregnated fiberglass reinforced organic felt underlayment designed for use on roof decks…It is more dimensionally stable than standard underlayment when wet. Its resistance to “hygro-expansion” significantly reduces the wrinkles that can result when the felt picks up moisture, thereby reducing the occurrence of visually objectionable wrinkles that can telegraph through to the shingles applied over it.” (Excerpt from CertainTeed Roofers’ Select product cut sheet released in 2001.)
Typical Details for Insulated Panel Roofing Systems
Typical roofing details for insulated panel systems call for: a roof deck (plywood or metal decking) a poly vapor barrier (in Northern climates), rigid insulation panels, air space, roof sheathing/nail board, roofing felt, asphalt/fiberglass shingles. Continuous eave vents and ridge vents are necessary to allow free airflow through the insulated panel system.
The insulating panel systems have to be carefully fastened to the roof deck to help assure no lateral movement and to keep the nail board level between panels. If the panels are out-of-plane, the change will be visible through the shingles.
The vented insulated panel system manufacturers generally hold the nail boards 1/16 inch back from the edge of the insulation panels to allow for nail board expansion after installation. A properly installed panel system maintains 1/8 inch, therefore, between installed panels.
Possible Explanations for “Picture Framing”
If you experience “picture framing” on a new installation and determine that it is not related to panel movement, the most likely cause of the shingles lifting at the insulation panel joints is expansion of the felt underlayment. This generally occurs only at the joints between insulated panels. The 1/8 inch gap between nail boards on properly installed vented insulation panels allows moisture in the vent space under the nail board to rise to the felts and be absorbed. The roofing felts can only expand by bulging upward and lifting the shingles. Once deformed, they appear to retain the new shape even when dry. The result is “Picture Framing.”
There will be moisture in the vented air space below the nail board. Outdoor air and moisture is drawn through the eave vents and circulated up through the system to the ridge vents. Outdoor moisture is present in the form of humidity, mist, fog, rain, and condensation. Remember that the temperature swing in the air space of a typical roof can vary from 140 to 30 degrees F. on a normal Northern spring or autumn day. The dew point is certain to be reached somewhere in that differential. To make matters worse:
1) The polyisocyanurate insulation edges are right below the joints. The unprotected edges are capable of absorbing and slowly releasing moisture. They are a natural sponge.
2) Some heat can escape from the building between the insulating panels. Warmer air can hold more moisture and rises between the panels through the 1/8 inch nail board gaps to be absorbed by the felts.
We have not been able to find any industry information that directly addresses “picture framing” due to the expansion of saturated roofing felts. In fact, some of the general information supplied by industry organizations may contribute to the problem.
The information we have gathered suggests that if shingles buckle, it can be viewed as deck movement. (Plain Facts About Buckled Shingles, Technical Bulletin, Asphalt Roofing Manufacturers Association, ARMA Form #207-RR-85, revised March 1993.)
In the roofs exhibiting “picture framing” that we have examined there is no evidence that the plywood or OSB nail boards have expanded or shifted out-of-level. In addition, the shingles we have removed at the panel joints lie flat when placed on a flat surface. The single component that is deformed is the roofing felt.
Another technical bulletin from the Asphalt Roofing Manufacturers Association: Use of Asphalt Shingle Underlayment (ARMA form #219-RR-89, revised March 1993) recommends: “Installing asphalt-saturated felt helps minimize “picture framing,” which is the visible outline of deck panels, caused by irregularities in roof decking thickness.” Though use of heavy felts clearly will help obscure decking irregularities, Insulated Panel manufacturers appear to have very good control over the uniformity of their product’s thickness during manufacturing. Decking irregularities in vented insulating roofing panels (when properly installed) do not appear to be a problem.
Vapor barriers are a recommendation, but not a requirement, by a number of roofing panel system manufacturers. In theory, if a building houses a moisture producing activity, such as a kitchen or locker rooms, then a vapor barrier is essential to slow moisture from escaping into the roofing system. For buildings that produce less moisture, the need for a vapor barrier is determined by the judgment of the professionals detailing the building. Insulation panel manufacturers like Apache and NRG write: “The need for and location of a vapor retarder system varies depending on the location, climate conditions, and the intended use of the structure beneath it.” Where practical, vapor barriers should be used to slow the transfer of moisture from a warm environment towards a cooler environment. This avoids condensation inside building materials that can rot, degrade, or support mold.
In practical terms, it is difficult to install a poly vapor barrier over roofing deck, especially over metal deck, as it cannot be walked on without damage to the film and danger of slipping to the installer. Even in the best of applications, the roof fasteners are going to penetrate and possibly deform the vapor barrier. For projects requiring vapor barriers with wood decks, consider sealant between panels. On projects with metal decks, consider sealant at panel overlaps. After all, the perm rating of the decking material is very small.
Ice and Water Barriers
Roofs installed over ice and water barriers do not “picture frame.” Only the areas over saturated felts exhibit “picture framing.” Ice and water barriers do not expand when exposed to moisture. However, placement of ice and water barriers over non-vented systems has the potential of trapping moisture or condensation between the insulation and nail board. This would be likely to rot the nail board and support mold. Use of a vented system allows the vent space and the nail board to dry out.
Possible Solutions to avoid “Picture Framing”
1) Always use appropriately vented panel systems or create a built-up vented space above the insulated panels and include eave and ridge venting.
2) Wherever practical: use a vapor barrier under the insulation panels.
3) Increase the number of panel fasteners, particularly along the edges.
4) Do not install asphalt saturated roofing felts unless they are reinforced to prevent bulging, buckling, and lifting shingles.
5) If the area of roofing is small, consider using an ice and water barrier over the entire roof (under the shingles). This should only be done over vented insulation/nail board panel systems and can make roof replacement in the future considerably more difficult.
© 2001, Leonard Wyeth AIA
All rights reserved