Metsl Versus Fabric Structures

While pressure washing a vehicle inside a Quonset, I noticed that moisture was dripping from the curved roof, yet none of the spray was reaching higher than a few feet above the truck. It was cool outside, and I was using warm water. The vapour was rising, condensing on the upper reaches of the steel ribbing and falling like rain.

That was not the problem that I saw, however. What I saw was that the condensation that remained on the bolts and nut ends was evaporating, and over only a few years of this type of incident reoccurring, rust was evident everywhere. Yes, galvanized metal is supposed to be rust resistant, and it largely is. However, at key stress points such as bolt holes, rust inevitably takes hold and soon those rust spots turn to holes and leakage occurs, exacerbating the problem. This metal building leaked everywhere.

Leakage is one of the problems common to older metal buildings. Cycles of heat and cold, sun and wind and differences between the internal and external conditions lead to warping of the metal so that rivets pop or moistures accumulations lead to rust penetration at key points.

Metal is a great conductor, too, not only of electricity, making steel and aluminum buildings risky for a handyman to wire on his own, but of heat and cold, making them quite uncomfortable in which to work during extremes of temperature.

Once wind gets hold of a loosened panel, it makes short work of the metal, stripping it from its moorings., One of the most common scenes in hurricane season is the flapping of aluminum panels on buildings, or sheets of the metal flying by like a kite in the air.

Metal is rigid. This limitation restricts the design of metal buildings and forces engineers to construct smaller spans than can be created with fabric buildings. The unwieldy configuration of metal buildings reduces options for expansion, development and usage of the interiors. Cuts and bends form stress points or weakened spots in the material, making them prone to breakdown.

Manufacturers of steel clad, steel roofed or aluminum buildings claim that their buildings have lifespans exceeding 50 years, yet simple observation of older steel buildings across the rural landscape shows that many of these supposedly durable buildings already are falling into disrepair, after as little as 20 years. Why? Simply put, manufacturer’s claims of longevity apply to the thickest gauge, most expensive products. These buildings may well be out of the economic reach of most consumers.

On the other hand, fabric buildings, like metal ones, come with a wide range of material options. The differences are many, but the two most salient  are initial cost and replacement cost. Fabric building skins can be replaced as needed, and very often repaired quickly and easily. Yet, even moderate- or budget-level fabric is designed to last twenty years or more. With almost no maintenance, these stretched fabric buildings last a similar length to steel buildings but do so at a fraction of the cost.

Trusses and base plates of fabric buildings generally are coated and designed to last virtually forever, making them less likely to age like many of the swayback and buckling metal building counterparts.

Because of the inherent tensile strength of fabric buildings, they resist wind, rain and snow load easily, deflecting the elements while metal build design encourages blunt resistance against the wind, with roof lines often allowing snow to accumulate and compress roof infrastructure.

Poly-fabric, unlike metal, is resistant to rot, corrosion and even the impact of chemicals and fuels. This makes these buildings much more suitable for use as machine shops, hazardous chemical storage buildings and other high-risk uses. While steel and aluminum served their purpose decades ago, the new fabric, poly-fabric or tension-fabric buildings would serve the majority of applications much better and much more economically, even as a place where I can wash my truck without carrying an umbrella to protect against the falling raindrops from roof rivets.

Genghis Kan Would Have Been Proud

A quick look at today’s polymerfabric buildings – from air-reinforced inflated recreation centres to monstrous stretched canopies covering stadiums – tells us that this is new, innovative technology that only is possible because of recent inventions in specialty fabrics. “Space-age,” we think. Wrong. Tension-fabric buildings actually pre-date the iron age. It is only the substantial engineering advances that are modern. The idea is ancient, proven and reliable. Oddly, it is reliability that most often comes into question when we look at and consider buying our own fabric-covered structures.

Think of the yurt, or ger, that has found a huge following in North American parks and campgrounds over the past three decades. Many of us see it in connection with the Mongols of Genghis Khan, from 1162. Yet, gers were common around the Black Sea around 600 BC and earlier, withstanding extremes of cold and wind without failing. These were the original, true stretched-skin tension buildings, with furs or felt wrapped tightly around a frame of branches. Their design called for a minimum of material while offering great strength and durability. The North American First Nations teepees are excellent examples of tension-fabric structures, and could withstand extreme environmental conditions while being sufficiently versatile to allow for frequent dismantling and re-erection over numerous years.

The doors that opened for modern tension-fabric buildings came during World War II, with the introduction of quanset steel or aluminum buildings used as utility, storage or housing buildings. Shortly afterward, advances in use of natural gas, or off-products from the petroleum industry, along with development of plastisizers, enabled the use of PVC in such applications.

Even the common, inobtrusive tent is a form of tension-fabric building with limited applications.

Because of the supposed novelty of polymer-fabric buildings, many jurisdictions only reluctantly embraced the qualities and advantages of these creations. They have proven to be popular farm buildings, primarily because the building codes for farm building is more relaxed than for urban housing and commercial buildings. Yet, these fabric structures have received exceptional scrutiny by engineers, and have been proven in some of the most advanced and unique architecture around the world.

East Street Project at Westfield Shopping Centre (London, UK),  Grand Pavilion (Melbourne, Au) and the Santa Fe Opera House (USA) are just a few examples. The Qatar inflatable fabric dome is a great example of a habitable tension-fabric structure, as is the Vectorfields Frank Kim residence. These are more artworks than traditional building, however.

It is in the huge gap between these true works of art and the basic Quonset in which the most efficient and practical applications of polymer-fabric buildings occur. Airport hangars, storage buildings for large equipment and supplies, temporary bulk housing and even machine or workshops all become more cost-efficient when  fabric buildings are involved.

In a strange way, tensioned fabric buildings have evolved in a circular manner, originating with available raw materials such as skins and poles, through free-standing polymer structures relying entirely on internal tension to allow for artistic expression, to minimalist designs that offer greater strength, durability, weather and chemical resistance and lower cost than conventional wood, steel or concrete buildings. These new, simple yet solid designs reflect and integrate more of the basic principles of their ancestors –yurts and teepees – than the modernistic creations that immediately preceded them. Low cost now becomes one of their key advantages, while also allowing for installation in almost any extreme of environment on earth, and in harsh conditions where chemicals, weathering and structural stress weaken other buildings much more rapidly than the polymer-fabric designs.

However, unlike their Mongol ancestors, these new buildings are virtually unlimited in size, and fit almost any need. With proper engineering oversight, fewer and fewer jurisdictions impose onerous restrictions on their installation, since, unlike temporary garages, party tents or other budget- and low-quality products, a decent polymer-fabric tension structure often exceeds standards of any comparable house or commercial building. They are a far cry from the old canvas over pole army camp building, and now can be found on even the most sophisticated and technologically advanced armed forces base – thus proving that they are recognized as a high-quality, high-reliability structure. Much like the old Genghis Khan yurt.

Advantages of Tension Fabric Buildings

In the 1970s, rural North America began seeing a proliferation of sway-back barns – the old hip roof barns that had reached their 30-50-year lifespan and the trusses had given way, sagging in the middle like a saddle. In the 1990s, we saw the invasion of sagging Quonsets, with the same swayback saddle appearance, as the steel and aluminum corroded and the rivets began to pop. In the 1990s, a new design emerged to replace these antiquated utility buildings: the tension-fabric or polymer-fabric structure.

Fabric buildings offer a number of advantages over steel or wood construction, not the least of which are cost and versatility.

In Canada, weather presents a huge challenge. In summer, extreme heat and abundant sunlight curl asphalt shingles, dry and crack timber, warp steel. The metals transmit both the heat and the cold, making for significant problems in controlling internal temperature and humidity. Wood rots in high moisture environment and is often scarce in remote areas, including the north and arid areas of southwest USA. Wind wreaks havoc with the blunt-wall, solid steel or vertical wood wall and pitched-roof designs. Winter means extreme cold, and, again, steel and asphalt suffer, while concrete cracks and heaves. Poly-fabric and pvc fabric, on the other hand, withstand great extremes of temperature, moisture and other environmental conditions.

Each of the other cited materials used in construction suffer from either corrosion or deterioration in the presence of chemicals, while polymers withstand corrosive materials much better, making the building perfect for applications where salts and other harsh chemicals (including fuels) are present.

The open, curved design of many of the fabric buildings make them easier to heat, easier to insulate and less costly to light. Their design, lacking the beams and posts commonly required in large-span metal or wood buildings, is so open that equipment and storage space is maximized.

Lightweight materials allow for less costly transportation to remote sites, reducing far-north or even rural remote construction expenses. These lightweight materials also reduce need for support infrastructure, which further reduces cost.

One of the inherent advantages of a simple design is simple construction and minimal labour. Fabric buildings rise in a fraction of the time it takes to build metal or wood buildings. This further reduces construction costs.

Maintenance costs of fabric buildings fall when factoring in the need for fewer windows, less ventilation requirements, no painting, no replacement of roofing materials, less vulnerability to leaking, and lifespans that exceed wood and asphalt construction, approaches, equals and often exceeds that of even the best quality and thickest gauge of steel.

One of the occasional “knocks” against poly-fabric buildings is that they are made from petroleum products and therefore are less environmentally friendly than wood or metal. That claim is false, however. Polymers used are made from natural gas and waste gas emanating from oil wells, and use, by weight, many times less raw material than any other conventional construction form. While wood may be more “natural” (an odd claim), it deteriorates much more quickly than polymers and therefore multiplies the amount of material consumed versus fabric buildings. Almost always, wood buildings use metal or asphalt roofing. Asphalt, of course, is made directly from crude oil and is far less eco-friendly than the pvc products. Steel and aluminum, both mined metals, are far more malignant in environmental issues than pvc, and are far less eco-friendly. After factoring in the huge savings in actual materials of any sort used in poly-fabric buildings, these structures easily become the environmental choice over metal, and generally are more benign than wood buildings, per square foot.

Cost, versatility, durability and even environmental friendliness all weigh in favour of the very lightweight fabric structure, and make it the ideal choice for a multitude of commercial, industrial, agricultural and other applications.

The Basics of Tension-Fabric Buildings

Each building design and structural concept offers unique advantages and obstacles that consumers should consider prior to purchase. Poly-fabric and tension-fabric buildings are no exception. These buildings provide versatility and considerable advantages over conventional construction, yet it is important that you look at the basics of these buildings and design concepts so that you can more clearly see those advantages.

Fabric structures are as varied as wood frame or post and frame conventional buildings. Yet, tension-fabric buildings involve common “building blocks,” and the terminology used in describing these components requires clarification so that consumers may more easily decide upon their specific application preferences.

There are three primary sections to a standard fabric structure: the base or foundation, the skeleton and the coverings.  The base or foundation anchors the building to the ground and provides a solid base for the unit. The skeleton can consist of timber, steel, plastic or aluminum, or, in some instances, fiberglass or graphite (in smaller, more portable units and mobius-ball type units). The fabric may be actual fabric, mesh or films, usually with a poly, vinyl, teflon or pvc coating. The uniqueness of these structures comes primarily from the lightweight yet durable fabric, stretched and providing tension to the entire building. Wood structures, on the other hand, are compression-type construction units.

The footing need not anchor the building to the ground, some of these buildings are truly portable, consisting of a steel or aluminum platform frame on wheels, allowing them to be moved about. Commonly, the skeleton is anchored into concrete footings or pads, enabling installation of a complete flooring system. Less common is the use of pressure-treated timber foundations and even metal screw piles, particularly in soils that shift due to moisture or that are prone to frost heaving.

Today’s fabric buildings usually rely on an aluminum structure that acts like ribbing to hold the fabric tightly. In corrosive environments, the aluminum is often treated with a plastic or vinyl coating to further resist rusting and deterioration. These ribs, trusses and base plates form the skeleton of tension-fabric (also known as poly-fabric) buildings, and require rigid adherence to high engineering standards.

Often, the skin or fabric is made so that the ribs and trusses are pocketing into the design, making them stronger, longer-lived and aesthetically satisfying.

This canopy generally sees the greatest variation in quality. To be able to choose the best material for your application, it is imperative to understand the basics of the most common materials used.

Many of the pvc or polymer skins consist of a woven fabric treated with various topcoats. Canvas structures commonly are used for event venues, equipment shelters and so on. They generally can be deconstructed and reassembled more easily than the poly-fabrics, yet are waterproof and fire-retardant. PVC-laminated polyesters involve a weave of fabric coated and strengthened with vinyl films. Their strength comes from the denier, or size of filament used in the weave, as well as the number of these filaments. Much like a twisted cable versus single cable system used in suspended bridges, the weave provides strength and support for the fabric, while the layer or topcoating provides additional strength, UV protection and protection against moisture, mildew and chemicals. The quality of the poly-fabric can vary as readily as the gauge of steel or aluminum used in construction of other buildings or asphalt in roofing applications.  Nonetheless this tension-fabric design, with the proper skeleton and fabric combination, can span several hundred feet, where conventional construction would require substantially more materials and structural design.

Intuitively, fabric structures might seem more prone to destruction by storms, high wind and harsh weather than conventional buildings, but, due to their design, this is untrue. The tension imparts immense  internal strength, while the flowing design like that of an eggshell, provides consistent integrity that sheds wind, snow and rain. Consider the original tension-fabric building – the Mongolian yurt – which withstands the most violent winds of the Himalayas, because of its curved design. Most fabric structures provide that same advantage.

The three components of the tension-fabric building – foundation, skeleton and fabric – all combine to provide a uniquely cost efficient and utilitarian building, readily adaptable to a multitude of uses.