Understanding the variables is the key to determining the cost of building a fabric structure.
By Samuel J. Armijos, AIA
The hardest part of designing and building a fabric structure is determining its cost. There are three major components to a fabric structure—steel, fabric and cables. Other factors, which we may or may not see—such as location, site access and labor rates—can affect cost, too. In general, the more complex the project is, and the more steel there is in it, the more it will cost to design, fabricate and install. Also, there are two basic ways to proceed: design/build or plans and specifications. Putting it together in a way that makes sense requires expertise in tensioned fabric structures.
Design and engineering
Fabric structures are mostly used as a cost-effective solution for providing shade and shelter. The added bonus is that they are festive in nature and can be used for temporary or permanent applications. The beauty and cost of these structures is in material choices and the details. Architects, designers, consulting engineers and clients all have different ideas about how a fabric structure and its details should look, but may not know their subsequent cost. Consulting with a design professional can save thousands of dollars. Decisions can be made at the beginning to determine if it makes sense to do a project as a negotiated design/build or as a formal public bid.
The current trend in the industry is to work in close collaboration with the designer, engineer, manufacturer and contractor to create the most cost-effective solution, getting people informed and involved as soon as possible. Unfortunately, many clients want to rush to the finish line and look at the bottom line too quickly, choosing the lowest price only to learn too late that the contractor hired was not right for the job. Early collaboration equals success.
Steel. Steel plays a major role in costing. Selecting the method by which primary components are made can greatly influence the overall cost of a structure. A minimum number of elements is usually desirable, and a mast-supported structure is more cost effective than a frame-supported structure. With the price of steel as volatile as it has been, the time frame from conception to build-out can also play havoc on a project’s steel budget.
Beyond the price and type of the material, there are a number of other
Beyond the price and type of the material, there are a number of other factors which can affect the price to contractors. Project timing, completeness of design, finish coatings, project scope, market price, and commonality of materials used all have a major impact on how the steel gets quoted out.
Cables. There is a difference in quality and price between custom parts—cast and stainless steel fittings versus standard and galvanized parts (bolts, nuts, shackles), for example. According to Peter Katcha of Ronstan International, which makes architectural stainless steel fittings, galvanized cables will typically not meet the fabric’s life expectancy and can be the first material requiring replacement on the structure.
“Stainless steel cable systems and hardware will equal and surpass the fabric’s lifespan. Galvanized cables will lower the initial installation cost, but will increase the cost over time to maintain the structure,” Katcha says. There is a common practice in the industry to mix galvanized cables and stainless steel fittings, but that might not be the best plan. Galvanized cables are much cheaper than stainless, but over the last two years the price of stainless has dropped 10 percent, making it a worthy investment.
The cost of the membrane on fabric structures can vary significantly as it is based on the complexity of the design and how much or little steel there is in the project. However, fabric structures are usually chosen for a project to perform a function, such as shade, signage or shelter.
From an overall performance standpoint membranes play the most important role, and many times physical or aesthetic priorities do not take cost into consideration at all. The chosen material is selected for specific reasons, such as light translucency and durability, and there is no further discussion or alternative. Social benefits could also limit or narrow a material choice but rely more on the performance of the end product in action to determine its success. Environmental benefits may dictate one material over another due to a client’s interests in sustainability or a material’s attributes.
All membranes are not created equal and all have different costs. The life span of the membranes should be based on the life span of the application. For example, a structure needed for two years does not need a membrane that can last 30. (However, sometimes codes or material properties require a specific material regardless of its life span or cost.) Membranes also come with different coatings which provide different forms of protection. The two most common materials chosen in the market are PTFE and PVC.
Structures that move. One PTFE material that is quite desirable in the architectural community is Sefar’s Architectural Tenara PTFE, which is 100 percent fluoropolymer made of PTFE yarn. It is free of chlorine, plasticizers, stabilizers and catalysts. It has a 15-year warranty and very high light transmission (20-40 percent). Compared to coated glass fiber fabrics, this material is more pliable and can be used for retractable structures, a growing trend in the industry.
According to Ingo Thalhammer, strategic architecture business unit manager at Sefar AG, Heiden, Switzerland, “PTFE fabrics are often misunderstood. Most fabrics in this market are often described as PTFE fabrics, but their major material is glass. Our fabrics are 100 percent based on fluoropolymers, and that’s why they can offer the true flexibility that one looks for in fabric structures.” Due to its long life expectancy of 25-plus years, sustainable projects can be realized with these fabrics. The material itself is also recyclable.
“Convertible and foldable roof construction is a growing trend in architecture. Folding cycles (the number of times it opens and closes) do not destroy the surface of the material. The surface material does not lose its properties if it is vandalized, and since no chemicals can evaporate from it, it does not get brittle. It is also now available as a material which can be welded with RF equipment,” Thalhammer says. The material is on the high end of the price range for architectural fabrics, but it offers unique advantages.
Textile facades. Occasionally, the structural elements play a minimal role in the overall cost of a fabric structure, in particular in the case of textile facades. The membranes used in a vertical application are more cost effective than woven metals and traditional hard shading devices, says Steve Frederickson of Ferrari Textiles, Pompano Beach, Fla. “Certainly with the increase in the number of fabric structures on the market, there is increased acceptance and understanding of the benefits of textile facades in architecture. From mesh fabrics that provide a significant reduction in energy costs when used in façade applications, to textile roofs with a 20-year track record, PVC textiles are not the 5-7 year product that some have branded them. In addition PVC is 100 percent recyclable, which not everyone can claim.”
Textile facades are usually designed with a metal clamping system attached to the building with a variety of devices to tension the membrane. They have social attributes that are hard to calculate, such as improved worker performance and more use of public shaded spaces, but they also have environmental attributes that can contribute to hard number savings in utility and energy costs.
Topcoats.The hidden cost in fabric is in the operational cost. Most clients want to know how you keep fabric clean and maintenance free. The answer is simple: get the best fabric and get the best topcoat.
“Overall, the demand for architectural fabric structures has been robust, with many owners tending to prefer the higher end materials,” says Brad Hochberger, Western regional sales manager for Seaman Corp., a manufacturer of vinyl-coated polyester located in Cleveland, Ohio. “Architectural fabrics performance has improved with the long-lasting top finishes extending the life and ‘cleanability’ of the membrane … Consideration of the source and type of membrane, the company’s history and warranty is research well worth making. To assure proper performance and long life of these structures, quality performance criteria must be established and specified by the architect, engineer or procurement agency.”
Read the fine print and ask for samples from the manufacturer. Some fabrics require additional prep work and cost in order to be joined, while others may be hard to handle in the field. For membrane fabrication, symmetry and optimization of cutting patterns is important. The fewer the number of cutting patterns, the more cost effective the production will be.
Installations: check the site twice
Installation, which includes shipping and equipment, is the hardest part in cost estimating a fabric structure. Equipment rates and availability can change dramatically, access can play a big role in the install, and shipping rates change as trucking costs and gas go up. As in real estate, fabric structure installers play close attention to location, which can have a dramatic effect on cost. Projects requiring union wages can increase the price, and work in major cities where crane access and street closure permits are required will definitely increase costs.
The ability to transport components to the job site must be considered as well. Many times, projects require “multiple mobilizations” because the membrane cannot be installed right after the steel has been placed. The best way to check the pricing is to make sure your contractor has a ‘means and method’ statement in the proposal, or a written procedure on how they intend to erect their structure. A construction schedule for all to see prior to proceeding is highly desirable.
In short, the key to building a cost-effective fabric structure is to design the lightest structure possible. Less is more. Light is more. Fabric is even better.