Steel Building Covering Systems
Performance of Covering Systems
The basic structural system of a building is designed to resist forces imposed on it, such as live, dead, and wind loads. In addition, the covering system of roof and walls provide a skin, which protects the building and its contents against the elements: rain, snow, ice, wind, heat, and cold.
Although the resistant and protective features of these two systems are of vital importance, the casual observer obtains his/her first and most lasting impression of the building from its appearance, and appearance is an important function of any building’s complete covering system of roof and walls. (The term “walls” includes both endwalls and sidewalls.)
When evaluating a completed building, we tend to consider the roof primarily in terms of protection, and the walls in terms of appearance. However, a successful covering system must possess other, less obvious, but equally important features.
10 Important Features of a Covering System
Attractive in APPEARANCE
Offers PROTECTION from the elements
Possesses STRUCTURAL STABILITY
Controls MOISTURE condensation
Offers resistance to SOUND transmission
Protects against FIRE
ECONOMICAL to own and maintain
Allows EASY INSTALLATION of accessories
Remember that most customers place a high value on the appearance of a covering system. While they usually direct most of their attention to the walls, some take a critical look at the roof as well.
Appearance is particularly important in commercial and community installations, where the covering system becomes the face of the building shown to the public and the image that the occupant projects.
Water is potentially the source of more maintenance and repair problems than any other single cause.
Whether in the form of snow, ice or wind-driven rain, water can find and penetrate the smallest openings in a roof or wall. Result: damage to a building’s contents, discomfort for its inhabitants and eventual deterioration of the building itself as a result of rot, corrosion or saturated insulation.
The entire covering system – panels, fasteners, sealants, flashings, and other components – must work together to offer effective protection against the elements.
All components of a covering system must have adequate strength and structural properties, since they are the first to offer resistance to loads and forces imposed on the building.
The roof must be able to support its own weight, plus live loads, such as snow and ice, and be designed to resist wind. The wall system, on the other hand, must be strong enough to resist predicted wind loads, wind uplift, and abuse.
A good covering system is designed to allow for expansion and contraction of its components as a reaction to temperature changes. In many parts of the United States, surface temperatures of building components can range from 10 degrees below zero to 140 degrees or more above it. Since cold causes materials to contract, and heat causes them to expand, good building designs must take these factors into consideration. Concrete highways and steel bridges provide for movement caused by expansion and contraction by means of movable joints at regular intervals. The joints act as safety valves and allow controlled movement in the structure.
Well-designed masonry walls contain control joints for the same reason. However, if too few of them are used, or if they are improperly spaced, the wall will invariably crack as a result of temperature changes. Such expansion and contraction cannot be eliminated; it can only be provided for in the building design with control joints and spandrel beams.
Thermal transmission is the technical term generally used to describe heat flow. Roof and wall systems must be able to effectively resist the flow of heat through them by possessing good insulating characteristics.
To put it quite simply, a successful covering system must do two things:
A. Keep natural heat inside the building during winter, and
B. Keep natural heat outside the building during the summer.
The total insulating value of the complete covering system must be known in order to calculate heating and air conditioning requirements.
Moisture condensation in a building can damage both the structure and its contents by encouraging rot, mildew and rusting. Condensation can even blister outside paints if the roof or wall does not contain a barrier (such as a metal sheet) to prevent moisture penetration.
You are familiar, of course, with the formation of condensation on a glass of cold water or on a cold windowpane. The same condition can occur on the inside of a building under similar conditions if it is not well designed with respect to insulation, heating and ventilation.
The use to which a building is put may tend to encourage or discourage condensation. For example, a laundry establishment represents high moisture occupancy, while a hardware or machinery warehouse usually has much lower moisture content in the air. But the important thing to remember is – water vapor is present in all buildings therefore we only provide the 2% penetration facing on our insulation.
Sound waves that strike a surface are partially reflected, partially absorbed and partially transmitted through its mass, depending upon the type of surface and the properties of the materials.
Obviously, a desirable quality in a covering system is its ability to prevent either the start or the spread of a fire. Its properties in this respect can have an important bearing on insurance rates for the building. In addition, fire resistance of materials generally must comply with local building codes and zoning laws. The fire protection classification of construction materials is based on many factors, and the best source of information within your territory is that provided by local zoning and code authorities.
A good covering system can be economically evaluated in terms of a building’s use and the value placed on it by the owner. Total cost of any system, however, must include both the initial cost and the long range or ultimate costs involved in maintenance, repairs, heating and cooling.
The relative adaptability and workability of a covering system for easy installation of such accessories as doors, windows and ventilators is often an important consideration from the customer’s point of view. A good covering system must possess enough flexibility to permit rapid installation of accessories, as well as easy relocation if the operations or use of the building should change.
The Components of a Covering System
You may have wondered why we refer to the covering as a system rather than simply walls and a roof. It is natural to identify a particular wall or roof by naming the basic material used in it. For example: a CMU, tilt-up wall, or metal roof.
However, such a description is not complete, since most walls and roofs must consist of insulation, fasteners, sealants, trim and finish, in addition to the basic material. Generally, the elements of a complete system, exclusive of accessories such as doors and windows, will include some or all of the following components:
Structural Framing and Support
A covering system obtains its support and strength from either or both of two sources:
- The Structural Frame
- Its own Stability and Rigidity
The roof is supported by, and attached to, purlins and eave struts. The walls either hang on the structural framework or rest on the foundation, or both, and attach to base angles, rake angles, girts and eave struts.
The role of structural framing is absolutely necessary, but the strength of the covering material itself is equally important. A properly designed covering system must have sufficient strength and rigidity to resist forces and transmit applied loads to the structural system. Light gauge metal covering materials are often fabricated with corrugations or ribs or breaks in a specific form or shape which will increase the strength, and also enhance the appearance of the panel.
The resulting form or shape of the metal sheet’s cross-section is called configuration or panel profile. Shown below are three examples of the Manufacturer’s most common wall panels, which are “PBR” panel, “PBA” panel, and “PBU” panel. We offer “PBR” panel with our building system.
The configuration of a metal panel, when properly designed and fabricated can provide substantial increases in structural strength. Strong configuration of a metal panel is one of the major design factors employed in metal buildings. The Manufacturer achieves many panel profiles or configuration by roll-forming the panel from pre-painted coils.
Roll-forming is a continuous process performed on a machine consisting of a series of graduated metal rolls arranged in pairs, (one on the top and one on the bottom) called stands. Instead of inserting single sheets of stock, metal may be fed through the rolls directly from coil stock, which may consist of hundreds of feet of continuous materials. As it progresses through the series of rolls, each succeeding roll takes a comparatively deeper bite to form the panel.
The roll-forming machine shown above has a number of stands, which enable gradual stages of forming. Each forming stage should take only a slightly greater bite than the preceding stage in order to produce panels with precise tolerances and to avoid surface damage. The machine illustrated roll-forms the standard “PBR” panel. The panel is rolled from coil stock material that is Galvalume Plus® or has already been color coated. The coil stock material is also illustrated below.
Thickness of material may be expressed in either inches or the decimal equivalent. Most of the time, thickness is referred to as a gauge, which is a standard numbering system to designate the thickness of materials. 29 gauge material is our lightest or thinnest gauge used only for liner. Most of our standard panels are rolled with 26 or 24 gauge material, where all standing seam panels are at a minimum of 24 gauge. The lower the gauge is the thicker the material. 26 gauge “PBR” panel is provided with our Value Building System.
The Manufacturer’s panels are available in three different finishes.
- Galvalume Plus®
- Royal K-70®
Recently a new development has introduced a product called Galvalume Plus®. Galvalume Plus® is the trade name for a patented sheet steel product having a highly corrosion resistant coating of 55% aluminum – 44% zinc alloy followed by a state-of-the-art polymeric passivation system. This newly developed passivation system is a two component package consisting of an acrylic-based polymer resin system and an inorganic corrosion inhibitor.
Galvalume Plus® is excellent where corrosion resistance is required and can be used in high profile application like architectural panels and residential roofing. Galvalume Plus® is also perfectly suited for standing seam roofing applications.
The base metal is 26 or 24 gauge Galvalume Plus® steel. The base metal is pretreated and then primed with a primer for superior adhesion and superior resistance to corrosion. The painted panels are available in two finishes: The Manufacturer’s standard Dura-20® or The Manufacturer’s premium finish Royal K-70®.
Dura-20® and Royal K-70®
Appearance is one of the most important features of a covering system, particularly the walls. Nothing enhances the appearance of a wall more than the color finish. In addition, the color finish of a building will often provide added protection against normal weathering. After early metal buildings were established as good utility buildings, people began to consider them for other uses. Galvanized steel was often painted to provide a more pleasing appearance. This is certainly understandable, since color plays such an important role in our lives. Even bare wood or concrete block is not a particularly attractive material unless it has been given a good color finish. In any event, the first painted metal buildings were coated by a standard procedure of applying a good primer and then a good grade of commercial paint. Generally, paint consist of three basic ingredients:
- Pigment – this gives the paint its color.
- The vehicle or carrier – this provides paint with flexibility and offers protection of the pigment.
- Solvent – this assures a compatible joining of the pigment and vehicle and proper curing.
The wide selection and proportions possible with each of these basic ingredients are reasons why you see such a great number of paints available for so many different purposes.
Typical color finishes do not bond very well to metals, especially Galvalume Plus® steel is limited because of the corrosion resistance. Therefore, it is necessary to apply a primer to insure adequate adhesion of the system to the metal substrate and to obtain optimum corrosion resistance.
Coil stock goes through an exacting pre-cleaning and pretreatment process to insure proper adhesion of the Dura-20® or Royal K-70® finish, uniformity of thickness, and flexibility for forming purposes. The following is a typical process:
- Coil stock starts by receiving a hot alkaline detergent wash, under pressure, to remove oil and other residues.
- Material is rinsed thoroughly.
- A pretreatment coating system is applied.
- The primer is roller coated on both sides.
- Polymer coat is oven-baked.
- Final color finish is applied by roller coating to assure a uniform film of finish to the exterior surface and polyester baked to the interior surface.
- Finishes are oven-baked.
Almost as important as the warranty itself is the exacting means of judging whether or not the finish falls within the limitations of the warranty. A standard 20-year finish warranty is available on all of our panels against peeling, blistering, cracking, fading, and chalking. This warranty covers cost of labor and material to repair, replace, or repaint material proved to be defective under the terms of the warranty.
Dura-20® is the Manufacturer’s standard modified siliconized polyester paint system. Most of the Manufacturer’s panels are available in the standard color offerings. Dura-20® offers optimum exterior protection and resistance to chemical corrosion and ultraviolet radiation. This coating also offers excellent chalk, fade and mar resistance. The Dura-20® is the finish provided with the Value Building System online pricing system.
Royal K-70® is the Manufacturer’s premium fluorocarbon paint system. Royal K-70® coating is formulated with Kynar 500® /Hylar 5000® polyvinyulidene fluoride resin and modified with a proprietary resin for toughness. This long-life finish offers the ultimate in color retention, film flexibility and durability.
Light Panels (Roof or Walls)
The light transmitting panel is a high strength translucent glass fiber reinforced polyester. The light transmitting panels match the standard panel profiles and are 1/16 ” thick, weigh 8 ounces per square foot, and are white with a granitized top surface. The Manufacturer’s light transmitting panels are available in both insulated and uninsulated panels with a UL 90 Wind Uplift rating. Insulated light transmitting panels are available in “PBR” panel and Standing Seam Panel profiles only. We only offer roof panels with or Value Building System.
The benefits of the use of light transmitting panels are obvious:
- As light transmitting panels, the need for artificial light is reduced and electrical cost lowered.
- As decorative panels, the appearance of a building is enhanced.
Mentioned earlier was that one of the most important jobs a covering system must perform is to retain heat inside a building during winter, and keep heat outside in the summer. Heat flow cannot be stopped but it can be slowed considerably by using heat-reflective materials or colors, materials that are poor heat conductors, or by trapping still air. Therefore, a good insulation may have a reflective surface exposed to heat, plus many small cells or pockets to trap and hold air as still as possible. This explains why most good insulating materials are made of light, fluffy substances like fiberglass, organic fibers, cotton, cork or foamed plastics.
Joining and Fastening
All the elements or parts that go together to make up a complete wall or roof system must join and fasten together in such a manner to assure pleasing appearance, good protection, and low maintenance.
Laps and Joints
Lapping, tongue and groove, or snap down or mechanical seaming can be used to join the panel edges of two panels that are set side by side.
When two panels are to be joined together end to end, the intersection is identified as an endlap or end-joint condition.The following illustration shows how the panels should be installed with back-up plates. Also shown is the sequence of installing the fasteners for endlap panels.
Joining is particularly important when weather protection is being considered. Roof panels must always be joined so that the upper panel laps over the lower panel an adequate distance, which is a 3″ minimum overlap. Wall panels may also be lapped with the upper panel over the lower, although this is not a common practice. Wall panels are cut to run continuously from floor to roofline. The standard maximum length panel is 50′. However, longer panels are available upon request.
Since sidelap and end-lap conditions occur in most covering systems, they deserve a substantial amount of attention both in design and in selection of materials to do a specific job. It is important to note that the fewer the joints in any covering system, the less chance for problems of weather tightness to arise. Thus, the wider the panel, the fewer the sidelap conditions and the longer the panel, the fewer the end-lap conditions. The Manufacturer’s standard practice of roll forming from coil sheet stock has made it possible to reduce substantially the number of endlaps and sidelaps in the total covering system.
Regardless of the joining and fastening method used in a covering system, a sealer, or sealant, is invariably used to provide added protection and weather tightness. Three basic types of sealants are:
Tube Sealant: such as mastic from a caulking gun.
Tape Sealant: Tri-Bead – often referred to as mastic tape. It is used at the eave, outside closures, endlaps, and trim connections.
Minor Rib – used to fill voids at minor ribs of the panel at the eave.
Factory Applied Sealant: a foam sealant that consists of a glue and gas mixture that is factory injected into the female leg of the standing seam panels.
The fastening or attaching of panels to structural members and to neighboring panels is of such prime importance that they are emphasized frequently in selling situations. As the design and material of the covering panels have improved throughout the years, so have the methods of fastening.
Standard fasteners come in two (2) types and groups, various lengths and colors, and three (3) different grades. Using the correct fastener for the right job is vital. It is important to take into account the location, application, and circumstances when choosing the fastener that is best for the particular job.
The two (2) types of fasteners are self-tapping and self-drilling. The self-tapping screws require pre-drilling the panel/trim prior to applying the fasteners. This step is not necessary for the self-drilling. The self-drilling fastener combines a unique non-walking point with a drill bit shaped tip to provide quick, positive penetration of both metal panels and steel framing. The threads are engineered to maximize strip out and pull out values while avoiding over driving torque.
Self-drilling fasteners should be used with unpunched panels and framing structural members. The self-drillers are now available in various sizes. Keep in mind that panel fasteners are used for two different purposes. One is for fastening the covering panel to the intermediate structural members. The second purpose is for attaching panels to one another, such as side-to-side or end-to-end.
Panel screws are used for two (2) purposes. Depending on the use of the fastener, all fasteners will fall into one (1) of two (2) groups — member screws and stitch screws.
Fasteners used in panel-to-steel, trim-to-steel, and steel-to-steel applications are member screws.
Fasteners being used in panel-to-panel and trim-to-panel applications are stitch screws. The length of the member screws is primarily dependent on the thickness of insulation used. Stitch screws are a standard length (3/4″ for self-tapping and 7/8″ for self-drilling.) Fasteners being used on colored panels or trim will match the color of the material, plain fasteners will be used on Galvalume® panels.
The Manufacturer’s mechanically seamed standing seam roof panel requires the use of an electric seamer. The seamer is only used with the standing seam roofing. The Value Building System does not offer Standing seam roofing.
Unlike the other fastening systems, this system secures the panels side-by-side by seaming the panel edges together. A portable self-powered roll-forming machine called the electric seamer does this seaming.
The electric seamer works at close tolerances and folds the panel edges over twice creating a double standing seam, which is weather tight. This mechanically formed standing seam fastening system is a revolution in the metal roof industry. With the electric seamer, the cost of the standing seam roof has been cut while its features have been saved.
Trim and Flashing
The final element of a good covering system is the method of handling its edges. For example, there must be some method of joining and finishing so that the transitions from wall panels to roof panels offer both weather protection and good appearance.
Flashing is a word used to describe a material for joining two components together to provide proper weather tightness.
Trim on the other hand, generally refers to a material or part used to finish out and cover a joint or juncture to improve appearance.
Gutter refers to a channel member installed at the eave of the roof for the purpose of carrying water from the roof to the drains or downspouts.