WHY VINYL WINDOWS ARE GROWING RAPIDLY IN NEW CONSTRUCTION

Over and over, architects, builders, and home buyers specify the same requirements: design versatility, energy efficiency, and long-term durability. With a long history in replacement windows, vinyl has demonstrated its endurance.  Now advances in materials, designs, and manufacturing enable it to meet stringent demand for windows in new homes.

 

THE BUILDERS OF tomorrow's houses demand more from windows, and vinyl is meeting the challenge. Windows now must save energy even while creating spaciousness. They must withstand the elements for decades yet be economical.  What enables vinyl to meet these and other requirements of the new-construction market is its unique combination of durability and versatility.

The durability of vinyl has been proven in more than 35 years of service in replacement windows, where vinyl units recently surpassed aluminum in annual shipments and are expected to catch up with wood by 1996. Now vinyl is also growing rapidly in new construction. From only 200,000 windows sold to home builders in 1987, vinyl will reach an annual total of 4.3 million - 19% of new construction - in 1996, according to the American Architectural Manufacturers Assn. (AAMA), Palatine, IL. This does not include millions of units of vinyl-clad wood, a major factor in new construction.

This market differs in many ways from replacement, and it places an even greater demand on versatility. At one and the same time, today's new-construction windows must be thermally efficient, cost-competitive, maintenance-free, architecturally innovative, available in many styles and colors, and conserving of resources - all this while not compromising durability!

To meet these needs, companies are taking advantage of the remarkable adaptability of vinyl as a material system. Here are some key developments:

• Advanced raw-material compounds tailored for window components with especially rigorous performance requirements.
• Injection-moldable compounds and processing technology that bring to windows a manufacturing technique for expanding design freedom, consolidating parts, and reducing assembly steps.
• High-performance color systems, ranging from pigmented formulations with high weatherability and low heat buildup to ultra-weatherable, vinyl alloy-based capstocks.
• Design and fabrication innovations that enhance the dimensional stability of window lineals, relieve stresses caused by temperature changes, and permit easy production of curved window sections.
• Waste-reduction technique that cut back on scrap from fabrication, recycle such scrap, and reclaim whole windows after a lifetime of service (see article below).

Much of the work on new technology is taking place at The Geon Company, the largest supplier of vinyl raw materials to the window industry. Based in the Cleveland, OH, area, Geon has developed the concept of a systems approach to vinyl windows. "Our mission is to give designers, fabricators, and builders as many choices as possible while still benefitting from the proven performance advantages of vinyl," says Joseph H. Muhs, Manager of Sales and Market Development.

Materials technology extends performance of window components.

The systems approach enables window manufacturers to build on the existing base of vinyl technology to meet the special performance needs of specific components.

Consider the requirement of dimensional stability. This involves retaining part shape and dimensions in spite of the expansion and contraction that materials undergo with changes in temperature. After years of use in windows, vinyl has demonstrated levels of stability suitable for all types of window components, but for some parts manufacturers may seek to build in even greater margins of safety. Temperature shifts are greatest, for example, in horizontal profiles like sills, which may gain 20% more heat than vertical profiles under exposure to sunlight.

For such components, Geon now offers a choice of materials ranging from conventional vinyl to Fiberloc^® composites, which are vinyl compounds reinforced with short glass fibers. The reinforcement is enhanced by a proprietary "coupling" formulation that chemically binds the fibers to the polymer matrix.  Geon recently introduced weatherable extrusion grades of Fiberloc composites for profiles exposed to the outdoors.

Compared with unreinforced vinyl, Fiberloc composites exhibit considerably higher strength and stiffness, along with a 45 to 70% lower coefficient of thermal expansion (CTE).

Other reinforced compounds developed by Geon show not only higher stiffness and lower CTE than unreinforced vinyl but also a smooth surface for interior window faces.

CTE is an important factor affecting dimensional stability because the extent to which heated material actually moves and changes part dimension is proportional to CTE. Another thermal parameter is heat distortion temperature (HDT), which indicates the temperature at which, under a specified load on a test sample, deflection may begin to occur.

While HDT is not a major factor in performance of large profiles, such as main frames or sashes, it is the prime factor for a few parts like glazing beads, the thin narrow strips that hold the glazing in the frame. Geon has developed two extrudable, weatherable grades in its HTX™ series of high-HDT vinyl alloys. Their HDTs are rated at 79 °C and 86 °C; by comparison, conventional rigid vinyl ranges from 70 to 73 °C.

These advanced materials join a range of vinyl window products that includes rigid formulations for structural profiles and cladding, flexible compounds for parts like weatherstripping, and foamable compounds for insulation in dual-glazed windows.

Drive to save energy is transforming windows.

By helping to keep windows dimensionally stable, the new materials improve weather-tightness, a property that is increasingly critical because of stringent new requirements for energy efficiency.

Although glazing is the biggest factor in such efficiency, frame and sash profiles account for at least a fifth of window area. As insulators, vinyl and wood windows have similar ratings, and (assuming that glazing stays the same) both have substantially lower U-values than aluminum. 

"Because of superior thermal performance, there has been a major material substitution going on, with vinyl replacing aluminum," says Bill Uhl, Director of Marketing at vinyl window profile extruder Dayton extruded Plastics, Springboro, OH.

Versatility of vinyl is reflected in window designs such as the half-round pictured right. Photo: Dayton Extruded Plastics.

Throughout the rest of this decade, energy will be a major growth driver for vinyl in new construction. This is because of regulations that were first implemented in the western states but are spreading through the rest of the country. The regulations make it possible for home buyers to compare windows for thermal performance in the same way that they compare refrigerators for energy efficiency.

Appearing on all windows will be labels bearing U-values determined in tests standardized by the National Fenestration Council (NFRC), Silver Spring, MD. The labels have been mandated by the U.S. Dept. of Energy, working through the state and local building codes. New code provisions are already on the books in six states, California's being the strictest.

That state's Title 24 legislation sets energy standards for many products and systems used in home building - from windows to wall panels to hot water systems to lighting and appliances. In effect the builder is given an energy budget for a house, and if one component uses too much energy or insulates poorly, then that loss must be offset with an improvement elsewhere.

Design freedom shifts from a plus to a must

"One result is that builders and architects have more incentive for using vinyl windows," says Richard Walker, Technical Director for the Vinyl Window and Door Institute (VWDI) of the Society of the Plastics Industry, Washington, DC. "For example, by using energy-efficient vinyl windows you can provide more glazing area in the house while still meeting your energy budget."

Of course, home buyers also have reason to prefer vinyl for its thermal efficiency, and this will be brought home to them more forcefully in the near future. Work is under way to add annual savings in utility costs to the labels on windows. Software for calculating such costs, called RESFEN, is in the development stage and is available through the NFRC.

New easy-flow vinyl compounds make possible injection molding of windows like the doorlites produced by RSL Inc., on either side of the doorway at right.  The closeup below shows the detail and surface finish provided by injection molding, which also eliminates need for corner welding.

Extruders of lineals can further enhance the thermal efficiency of vinyl windows by designing profiles that are multi-chambered. The dead air spaces enclosed in the chambers cut back on heat transfer between the interior and exterior faces of the window frame.

"Energy legislation will completely transform the window industry by the end of the decade," says Geoff Card, vice president of lineal designer/extruder Spectus Systems, Winnebago, IL. Writing in Fenestration magazine, Card maintains that multi-chamber profiles "are essential for energy savings."

One of the most cost-effective ways for architects and builders to add homeowner value is to do something interesting or innovative with windows. In low-cost homes, windows play an important role in differentiating builder products and adding the all-important element of charms. In upscale homes, architects use windows to create a sense of spaciousness or achieve other dramatic effects.  Either way, the key word is choice - in window types, sizes, shapes, decorative motifs, and colors.

Once limited in some of these offerings, vinyl now embodies them. "This increasing diversity," says a recent report in Shelter magazine, "is the most significant change in the vinyl window industry over the last ten years."

In the past three years, U.S. window companies have purchased European-made systems for reheating and bending vinyl lineals to make curved sections, and today almost every supplier to the new-construction market offers shapes beyond the traditional rectangle. "Even in modest housing developments you'll see many half-rounds," says Uhl of Dayton Extruded Plastics. "These would be very expensive to produce in wood."

Breakthroughs in the production of vinyl components with innovative shapes and other new design features are just arriving.  The key technology is injecting molding. The extrusion that is limited to continuous cross-section parts. Molding can overcome this, but vinyl was previously difficult to injection mold into the large, complex parts that are needed in windows. Now Geon has introduced easy-flow compounds that retain weathering and other key window properties while making large, complex parts possible.

Molded windows are just beginning to emerge.

One of the first applications of these compounds is in doorlites, the windows in entry doors. Novatech Glass Inc., Ste. Julie, Quebec, has taken advantage of the design freedom of molding to produce a completely new type of venting doorlite, which the company calls Novastar. The company consolidated parts and reduced assembly steps by "molding in" components and features.

Working with Geon engineers, Novatech designed the doorlite to be produced in two halves (exterior and interior) with molded-in screw bosses. The halves are designed to fit together precisely, and the use of fasteners eliminates corner-welding. The screen, which is injection molded in one piece, cannot be removed from the outside, making the window "the most secure venting doorlite on the market," says the company.

A nonventing molded doorlite has been switched from polystyrene to vinyl by RSL Inc., McKee City, NJ. The switch applies to certain sizes in a high-end series of doorlites that house etched or stained glass.

In prime windows, injection molding has wide-ranging possibilities for curved sections, gothic arches, and other complex shapes, but it also can yield specialized functional parts. A case in point is a vinyl-clad window being introduced by East Coast Millwork Distributors, Elkin, NC.

The company snap-fits vinyl cladding (extruded by Intek, Hastings, MN) onto a wooden frame. The cladding "floats" on the frame, says Alan Bridges, Product Development Manager. No tape, caulk, or overlapping of joints is used to seal (or mask) openings between cladding components caused by temperature shifts. Instead, while the cladding at the top two corners of the window is thermally welded, the bottom corners are left free to expand and contract. Acting as expansion joints at these corners are two complex vinyl plugs injection molded by Imperial Plastics, Lakeville, MN.

The plugs are designed to cover the corners, preventing air infiltration and exposure of wood while giving the cladding free play. Each plug has two perpendicular sleeves to receive two frame lineals at the corner. The shape is impossible to produce by extrusion (see schematic above).

Proven technology yields new choices in dark colors.

Design freedom applies to colors as well. It is true that 85% of vinyl windows come in white because it best accommodates the colors of materials used in the rest of the house; another 10% are lighter pastels - beige is popular because it also coordinates with any color and is softer in tone than white. Still, the demand for dark colors is growing, and the number of dark-color options available in vinyl is increasing steadily.

The key to dark colors is capstock, a thin layer of pigmented material permanently fused to the surface of the window profile. With vinyl, capstock is used only for dark colors, and its purpose is to restrict more expensive pigments and additives to a thin layer. In another recently introduced polymer system for windows, that of acrylonitrile-butadiene-styrene (ABS) capped with acrylic-styrene-acrylonitrile (ASA), the capstock Is necessary for all colors, even white. This is because ABS embrittles and discolors upon exposure to sunlight.

 

Source: Two-year outdoor exposure tests conducted by the Geon Company a: Measures discoloration or yellowing upon exposure to sunlight. b: Uncapped test sample processed from conventional white outdoor compound. c: Acrylic-styrene-acrylonitritle (ASA) material typically used as protective weatherable capstock for BAS (acrylonitrile-butadiene-styrene).

 

Since the late 1960s, Geon has maintained a continuous program of capstock development and outdoor testing. It commercialized its line of vinyl-based dark-color capstock compounds, now tradenamed Duracap, in 1972, and it as accumulated ten years of weathering data from outdoor testing in Arizona, Florida, and Ohio.

Applied to lineals by coextrusion or lamination in 0.003 to 0.005 in. layers, Duracap^® compounds show two to ten times the color weatherability of uncapped rigid PVC, depending on color, as measured by standard tests for color change. They can be applied not only to vinyl substrates but also to aluminum, wood, and other polymers, including ABS. In Geon tests the weathering performance of Duracap compounds is on a par with that of acrylic and is better than that of ASA, yet they cost considerably less than both on a cents/sq.ft. basis. Most expensive is ASA, which must be applied to ABS in a minimum capstock thickness two to three times that of Duracap capstock.

In fact, even uncapped, conventional white PVC window compounds outperform ASA/ABS in weatherability, as measured in terms of impact strength retention and resistance to color change (see graph above).

Over many years, Geon has developed a variety of capstock colors formulated not only for weatherability but for minimum heat buildup. Colors include black, green, blue, gray, brown, red, tan, gold, olive, yellow, ivory, and white.

Freedom from maintenance: more valuable than ever.

Regardless of color, vinyl windows offer big advantages by eliminating the need for painting and other maintenance. Builders benefit by saving paint and labor costs. For homeowners, the fact that vinyl is maintenance-free has topped the list of selling points, and today it is even more important. "In any age of dual-earner households, nobody has the time to paint or maintain windows," says Susan Adams, Market Development Specialist at Geon.

Unclad wood not only must be painted (and regularly repainted) but many swell or rot. Aluminum, which must be oven-painted at the factory, is still subject to corrosion, especially in salt-water environments. And the ASA capstock used over ABS has very low resistance to mildew and is badly stained by it, according to a VWDI study.

Vinyl resists attack by all common household cleaners; by salt water, acid rain, and other pollutants; by many other chemicals; and by microbials. It resists dirt pickup. It has a surface lubricity that contributes to smooth operation of moving parts. And it may be formulated for glossy or matte finishes and is easily embossed into a variety of textures.

These advantages are attractive to window fabricators, distributors, architects, specifiers, builders, and other new-construction professionals, but many of these individuals may be more accustomed to wood and aluminum. To them it is important that vinyl has a long record of its own in building products. The record shows that after decades of outdoor service, vinyl continues to perform, maintaining key properties like weatherability, thermal stability, and toughness.,

How many years of service? Weatherable rigid vinyl for building products was first used in the 1950s. Vinyl windows went commercial in Europe during the 1960s and in the U.S. during the 1970s.

The raw-material formulation for these products has been modified over the years, but it has kept its basic identity as "rigid" white exterior compound" - polyvinyl chloride resin with titanium dioxide as pigment and UV screen, impact modifier, heat stabilizer, and processing aids. This is what all vinyl windows and cladding are made of today - as well as storm windows and doors, doorlites, skylights, patio enclosures, rolling shutters, rainwater systems, fencing, and house siding.

In the U.S. alone, these applications consumed a 1993 total of 1.5 billion lb. of vinyl compound, according to consultant Richard H. Roman of R.H. Roman Assoc., Cleveland, OH. Of this, windows accounted for 165 million lb., and the number is expected to grow by 13% this year to 300 million lb.

There are around 50 companies extruding vinyl window lineals in the U.S. and Canada, Roman estimates. In the U.S., 29 extruders have certified over 700 different profile designs in accordance with voluntary specifications promulgated by AAMA and based on ASTM standard tests for weathering and impact strength.

By comparison, profiles for a recently introduced ABS/ASA window system are produced by one extrusion company.

How heat affects windows: more data, better vinyl.

The chief performance claim for ABS/ASA windows is based on the fact that the HDT of ABS is higher than that of vinyl, and that, upon heating, vinyl undergoes a more rapid loss of rigidity. In a systematic study of how dimensional change takes place in vinyl and other samples exposed to heat, Geon's Dr. Elvira B. Rabinovitch concluded that neither of these parameters predicts what really happens in windows: "Dimensional stability problems such as bowing of window parts occur at lower temperatures than either the HDT or the temperature at which the material becomes unacceptably rubbery. The cause of such problems is the thermal stress in the parts due to the temperatures differential caused by the sun's heating."

The stress occurs because materials expand when heated. Polymeric materials like vinyl and ABS expand and contract to greater degrees (have higher coefficients of thermal expansion, or CTEs) than aluminum, wood, and glass. When one section of a window component is exposed to sunlight while the rest of it is not, or when the whole part is heated but constrained from expanding by adjacent parts or by fasteners, thermal stresses develop. In regions of intense sunlight, the stresses may be great enough to warp or crack the part.

The study by Dr. Rabinovitch demonstrates that CTE is a more important consideration than HDT in designing a window for dimensional stability. For most materials, CTE increases directly with temperature. Dr. Rabinovitch concludes: "The designer must consider the maximum temperature that the product will reach and the average CTE in the interval between lowest and highest temperature."

Data for CTE of polymers used in windows actually show vinyl expanding and contracting less than other materials. The CTE range for conventional rigid vinyl is 3.3 to 3.6 in./in./°F. x 10^-5. The range for ABS is 3.6 to 6.1, and ASA is rated at 5.6.

Coextruded capstocks on vinyl substrates permit use of a range of dark-color pigments while saving costs by confining the pigments to a thin layer. Geon has tested weatherable capstocks in a full range of colors for more than 20 years in different parts of the country, with excellent results.

Other Geon research and work by window system designers demonstrate that the thermal performance of a window is far more complicated than HDT or even CTE would suggest. Here are some other major factors in heat buildup and therm stress.

• Compound formulation. Thermal performance varies with the grade of resin used and can also be modified by alloying or by reinforcement, as the new advanced compounds from Geon show. The company's Fiberloc compounds, for example, can be formulated to show expansion and contraction as low as aluminum. The CTE of this material is only 1.7 in./in./°F. x 10^-5.
• Color System. Dark colors absorb more heat than pastels or whites. Two similarly dark colors may differ considerably in the amount of heat buildup that they cause. Geon formulates its dark-color capstocks to minimize this buildup.
• Lineal extrusion. Inappropriate conditions for extruding molten polymer into complex profiles like window lineals can generate thermal stresses that are frozen into the part upon cooling and are activated by solar heating. Factors that can be varied to reduce stress levels include extruder conditions, profile die design, cooling rates, and lineal-takeoff speeds. Annealing - reheating lineals to release stresses - is another useful step in lineal manufacture.
• Profile design. "The data clearly demonstrate," says Dr. Rabinovitch, "that an increase in profile thickness and a decrease in width improves dimensional stability. The effective thickness can easily be increased by introducing ribs and bridges in the hollow profile, rather than increasing thickness throughout. This keeps material cost to a minimum."
• Window design. "Product design, such as thickness and width of the window profile, has a much or more effect on the dimensional stability of the window that the material used," says Dr. Rabinovitch. Other examples of important factors in product design: location of welds or fasteners and the type and placement of adjacent parts. Both affect the thermal stresses in a component.

In addition, window fabrication and installation also affect how windows perform. Work on all of these factors has long since made vinyl windows reliable performers in even the hottest regions of the U.S.

Long term outlook: economy and stability

Without such performance, vinyl could not have made the window-market inroads that it has achieved so far, but it must be added that competitive pricing has helped. Current prices for wood raw materials are such that vinyl is replacing wood in the most price-sensitive segments of the new-construction market. Aluminum faces longer-term difficulties in competing on price because raw material production is so energy-intensive.

By comparison, the outlook for vinyl is continued stability in price and supply. Vinyl windows are specialty products at the front end of a vast commodity industry. For example, fully 55% of the vinyl molecule derives from salt water, not petroleum. Its chlorine content helps mitigate material price inflation. And the petrochemical ingredient is ethylene, the world's largest-volume commodity petrochemical. The two ingredients are reacted to form vinyl feedstock, which in turn is polymerized to form vinyl polymer.

Vinyl too is an abundant, relatively inexpensive polymer, well suited for giant, intensely competitive markets like pipe and siding, as well as for windows. In fact, today's price for PVC resin is only slightly higher than it was ten years ago.

For this and many other reasons, the future is bright for vinyl in new-construction windows. What sets vinyl apart as a polymer for use in building is its long track record and proven durability. At the same time, continuing improvements in materials, design, and manufacturing are providing builders and their customers with the versatility that is so important in today's new homes.

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FROM LINEAL SCRAP TO ENTIRE WINDOWS, RESOURCE CONSERVATION WORKS

Recent work by the vinyl industry has reduced window-lineal waste and developed technology to reuse scrap. The public demands such waste management. At the same time, the practice can save companies raw material, handling, and disposal costs.

The nation's hundreds of window fabricators stand to save the most, because cutting lineals into frame and sash lengths necessarily generates a large fraction of scrap. Rates used to run as high as 12%. In order to reduce scrap, fabricators have employed computerized "lineal optimization" programs that can lower the rate to the 2 or 3% level. Achieving such reductions is not always possible, especially with the mitre-cut lineals often used in new construction.

For recycling that unavoidable minimum of scrap, two companies have commercial programs.

PWPike, Eugene, OR, has begun collecting vinyl scrap and is reusing it in two plants (Seattle and Los Angeles) as the core layer in three layer, pipe (see photo). Technical manager Keith Steinbruck says the company uses various types of non-window vinyl scrap - e.g. siding and bottles - but windows play an important role.

"We have two collection programs for lineals," Steinbruck says. "We will purchase ground profile scrap from a recycler that can supply documentation as to source. Or we go directly tot he fabricators, whom we pay for the scrap."

The company arranges for regular pickup of scrap from the fabricators with which it is working. These companies are concentrated in the West Coast and bordering states. "We hope to encourage other pipe manufacturers to do similar work elsewhere in the country," says Steinbruck. He notes that two ASTM standards are being written to cover use of recycled PVC. Four types of non-pressure vinyl pipe are covered: sanitary sewer, DWV, land drain, and utility conduit.

Breakthrough installations for PWPipe's three-layer product have recently taken place in San Diego and Santa Barbara, CA. The company worked with the Vinyl Institute, Morristown, NJ, to market the pipe to the San Diego County Recycling  Task Force, a consortium of government officials, recycles, consultations, environmental groups, and plastics industry representatives.

Non-pressure pipe represents an enormous potential market for window lineal scrap. Nearly two billion pounds of virgin vinyl compound are used in such pipe each year in the U.S. Another outlet cited by industry observers is substrate for vinyl siding. For both applications, lineal scrap promises to be a preferred material because it is free from contamination and uniform in makeup.

The second company that is putting vinyl lineal scrap to work, Regenex Corp., Farrell, PA, is carrying out closed-loop recycling: from lineals to lineals. "We recycle scrap from window fabricators and extruders high-quality lineals, typically accessory parts, that are really indistinguishable from the products produced with virgin material," says president Daniel Berent.

In Europe, where the vinyl window business is older, recycling has taken on another dimension. Some windows there have been in service long enough that homeowners now want to modernize. What to do with the old windows?

Profile extruder Veka AG, Behringen, Germany, has started up an operation to reclaim vinyl window components. The company crushes the windows and grinds the components; vinyl is separated from other materials, washed, and sorted into "white" and "all other" streams. The company claims it can produce 100% pure PVC for use in new window profiles.

Core layer of this coextruded pipe is vinyl recycled from window lineals.
Photo: PWPipe