QE Roofing started doing only commercial metal roofing over 17 years ago. We have installed over 1,000,000 square feet of metal roof and we still have a flawless reputation. This should make any potential customer feel comfortable knowing we take pride in our work. We appreciate the opportunity to serve you and will strive to make your roofing project an unforgettable great experience.
Metal panel roof systems can be installed over a large variety of structural substrates. There are two general categories of structural substrates for metal panel roof systems: One is a continuous or closely spaced roof deck, and the other is composed of spaced structural supports, such as purlins, where the metal panels must be fastened to and span between supports.
A structural substrate must be able to safely support dead loads, including the weight of a metal panel roof system, and design live loads, including any additional loads that may be required by the applicable building code. A structural substrate also must be able to provide adequate pull out resistance for fasteners used to attach a roof system. Geographical location and climatic conditions can influence the type, spacing, slope and other structural characteristics appropriate for a structural substrate.
Depending on a roof substrate's slope and exposure conditions of an architectural metal panel roof system, differing underlayment materials and configurations will be appropriate.
In some instances, metal panels will outlive the underlayment over which they were installed. Therefore, if the long-term water-shedding characteristics of an underlayment are necessary to provide the weatherproofing integrity of a finished roof system, designers should carefully consider the type and quality of underlayment to be specified.
There are different underlayment configurations that can be used for architectural metal panel roof systems. Generally, these configurations can be categorized as follows:
- Single layer of underlayment
- Single layer of self-adhering underlayment
Underlayments typically are not used with structural metal panel roof assemblies where spaced supports are used. Structural metal panel roof assemblies installed over steel joists, light-gauge framing or purlins over a continuous substrate should not include underlayment. Underlayments should be used for metal panel roof assemblies where the spaces between purlins over a continuous substrate are filled with a rigid material (Ex., polyisocyanurate insulation).
The primary purpose of roof insulation is to provide thermal resistance. A roof can be one of the largest surface areas of a building envelope through which interior heat escapes. Insulation within a roof assembly will help maintain the inside temperature of a building at a more constant, comfortable level. Building codes have requirements for the minimum amount of thermal insulation required.
Insulation can be a vital part of a structural metal panel roof assembly. A properly insulated building uses less heating and cooling energy to maintain a comfortable interior environment than a poorly insulated building. It should be determined the insulation requirements of a metal roof system as a part of an overall building envelopes thermal insulation requirement.
Blanket Insulation: Blanket insulation, installed with a structural metal panel roof assembly, will typically be installed over open purlins or other spaced structural members. Blanket insulation is typically made from fiberglass insulation and may have a polypropylene, vinyl or aluminum facer. The facer may act as a vapor retarder. It can also provide acoustical benefits by minimize the noise associated with panel movement and rainfall.
When metal roof panels are installed over blanket insulation that is located over purlins or other structural members, the insulation is compressed, particularly at the clips. This compression results in a reduction of R-value at this location. In cold climates, this R-value reduction can cause the dew point, below the vapor retarder, to fall below the air temperature. In these cases, condensation can occur on the inside of a building and drip into the building's interior. The proper selection and installation of vapor retarders and thermal spacer blocks at purlins will reduce the loss of R-value where blanket insulation is used.
Typically, blanket insulation over open purlins or other structural members is installed perpendicular to purlins and runs from eave edge to ridge. However, there are methods used whereby blanket insulation is installed from rake edge to rake edge. When a vapor-retarder film
is used, the side tabs of the film should be lapped then sealed or taped together to ensure the continuity of the vapor retarder and help minimize sagging of the insulation at the side laps. Additionally, the facing tabs of the blanket insulation should be carried over the purlins or other structural members and lapped and then sealed or taped together. This should occur at no vented ridges, hips, valleys and end joints.
Insulation
The primary purpose of roof insulation is to provide thermal resistance. A roof can be one of the largest surface areas of a building envelope through which interior heat escapes. Insulation within a roof assembly will help maintain the inside temperature of a building at a more constant, comfortable level. Building codes have requirements for the minimum amount of thermal insulation required.
Insulation can be a vital part of a structural metal panel roof assembly. A properly insulated building uses less heating and cooling energy to maintain a comfortable interior environment than a poorly insulated building. It should be determined the insulation requirements of a metal roof system as a part of an overall building envelopes thermal insulation requirement.
Blanket Insulation
Blanket insulation, installed with a structural metal panel roof assembly, will typically be installed over open purlins or other spaced structural members. Blanket insulation is typically made from fiberglass insulation and may have a polypropylene, vinyl or aluminum facer. The facer may act as a vapor retarder. It can also provide acoustical benefits by minimize the noise associated with panel movement and rainfall.
When metal roof panels are installed over blanket insulation that is located over purlins or other structural members, the insulation is compressed, particularly at the clips. This compression results in a reduction of R-value at this location. In cold climates, this R-value reduction can cause the dew point, below the vapor retarder, to fall below the air temperature. In these cases, condensation can occur on the inside of a building and drip into the building's interior. The proper selection and installation of vapor retarders and thermal spacer blocks at purlins will reduce the loss of R-value where blanket insulation is used.
Typically, blanket insulation over open purlins or other structural members is installed perpendicular to purlins and runs from eave edge to ridge. However, there are methods used whereby blanket insulation is installed from rake edge to rake edge. When a vapor-retarder film is used, the side tabs of the film should be lapped then sealed or taped together to ensure the continuity of the vapor retarder and help minimize sagging of the insulation at the side laps. Additionally, the facing tabs of the blanket insulation should be carried over the purlins or other structural members and lapped and then sealed or taped together. This should occur at no vented ridges, hips, valleys and end joints.
STRUCTURAL PANEL ROOFS
Structural metal panel roof assemblies have the strength and capability of spanning structural members, such as joists or purlins, without being supported by a continuous or closely spaced roof deck. Structural metal panel roof assemblies are typically weatherproof roof systems. They are designed to resist the passage of water at joints, laps and junctures under minimal hydrostatic pressure. In most configurations, structural metal roof panels do not require an underlayment. It is recommended ½ inch per foot as the minimum slope for structural metal panel roof assemblies. There are manufacturers who allow structural metal panel roof systems to be installed on slopes as low as ¼ inch per foot.
The ½-inch-per-foot recommendation is based on concerns for water tightness at end laps, transverse seams, panel ends, junctions of metal and where deflections may be present at penetrations and curbs. Structural metal panel deflection should be limited to no more than ½ of the span between supports to accommodate the stresses of either concentrated or uniform loading.
Structural metal panels derive their strength from panel and seam configuration and/or the use of heavier gauges of metal. These panels are profiled with high side ribs and stiffening ribs or intermediate ribs or fluting located in the pan.
Structural metal roof panels can also be used in architectural applications--that is, over continuous or closely spaced substrates. Structural metal panel roof assemblies are used in architectural applications, generally for increased wind- uplift resistance. The most common types of continuous or closely spaced substrates for structural metal roof panels used in architectural applications are steel and wood roof decks. Structural panels used in architectural applications typically have flat pans and vertical (i.e., nontrapezoidal) seams to allow for simpler flashing installation. In addition, these types of panels have different seam aesthetics and shadow lines that can be more appealing on roofs that are visible.
Metal panel roofs standard sizes are 29, 26, 24, & 22 gauge.
Panel profiles vary depending on the different methods used for forming the panels. Metal panels can have different physical characteristics and aesthetic appearances. The choice of the profile is often based on performance, as well as aesthetics. Seam height not only affects aesthetics; it also affects performance. Generally, taller seams can accommodate greater amounts of water runoff.
Many structural metal roof panels incorporate striations or longitudinal stiffening ribs in the field of the panel to minimize the effects of oil canning.
There are three general panel profiles common to Structural metal panels:
- Trapezoidal: The trapezoidal profile is a common profile used for structural metal roof panels and is often used for low-slope applications. The rib usually has a triangular or trapezoidal shape from which its name is derived. This type of profile provides rib height and structural strength.
- Intermediate rib: The intermediate rib profile incorporates a center rib, typically of the same profile as that of the end ribs. A panel using this type of profile has a multiple-panel look but is, in fact, a single panel. This profile type allows for the use of larger panel widths because of the increased structural capacity provided by the intermediate rib.
- Vertical leg: The vertical leg profile uses a standing-seam design resembling the typical profile of an architectural metal roof panel with or without stiffening ribs in the pan.
During design of a metal panel roof system, consideration must be given to the fastening requirements. The fastening schedule and substrates should provide adequate anchorage to resist design wind-uplift pressures. Design wind-uplift pressure requirements will vary depending on design wind speed for the area, topography, building height and building importance classification.
With metal roof systems, it is critical that fasteners and clips and their placement densities be designed to meet the wind-uplift requirements for the project. It is important to select correct fasteners for a substrate. Selection criteria should include fastener size, point or tip type, thread type, shank type, length, compatibility and corrosion resistance.
Because metal panel roof systems are frequently interrupted by the intersections of adjoining roof sections, adjacent walls, or penetrations such as curbs and plumbing soil-pipe stacks--all of which create potential locations for leakage-_special provisions for weather protection must be made at these locations. Flashings are used to prevent water entry at these locations. Careful attention to flashing details is essential to successful long-term roof system performance regardless of the type of metal panel roof construction. The number of roof penetrations should be kept to a minimum.
Eaves: Flashings at the eaves used as attachment for panels should be made of equal- or heavier-gauge metal than the roof panels to achieve proper panel securement. When a T-type drip edge metal is used at an eave, it can serve as a securement point for the roof panel. If this type of detail is used, the fixed-point location will be at the ridge or hip. In this detail, the panel is hooked to the T-type drip edge to allow movement and secure the panel edge. This type of eave flashing may be used with a vertical leg structural panel but is not typically used with a trapezoidal rib structural panel.
Eave flashings installed over an L-type metal edge require a continuous bead of sealant between the drip edge and panel. At the seam ends, metal and/or foam closures, set in continuous sealant, are required to seal the open ends of the seams, Structural metal roof panels can be attached at the eaves with clips in the seams or with exposed, gasketed fasteners through the panel and drip edge. Use of through-panel fasteners will fix the panels at the fastener locations.
Rakes: Flashings used at rakes as attachment for panels are made of equal- or heavier-gauge metal than the roof panels to achieve proper panel securement. When a Z-closure is used at the rake, it often serves as a securement point for the roof panel, as well. The rake is hooked to the top of the Z-closure to allow movement. This type of rake flashing may be used with a vertical leg structural panel, as well as a trapezoidal structural panel.
Valleys: When designing a metal panel roof system valley, you should consider several factors, including:
- Angle of adjoining roof slopes and resultant slope of the valley
- Continuous substrate support for valley metal
- Severity of the topography and climate, such as possibilities of debris and snow buildup, ice damming and strong wind-driven rain
- Type and profile of the adjacent metal roof panels that will overlap the valley metal
- Proximity of hips, dormers, chimneys, skylights, penetrations or other valleys
- Size of the roof areas that will contribute runoff into the valley
- Number and type of surrounding trees that will deposit debris onto the roof, which can eventually create buildup or blockage, hampering drainage through the valley
- Total length of the valley
- Type of metal used, expected amount of thermal movement and required dimensions of hem to account for thermal movement
The metal valley design in a structural metal panel roof assembly will vary depending on panel profile, substrate and slope of the adjoining roofs. For all valley designs, the flow of water must be in a positive direction and the panel-to-valley metal junction sealed in a weatherproof manner. Thermal movement also needs to be considered and accounted for.
Ridges and Hips: Ridges and hips occur along the intersection of two adjacent roof slopes. Ridge and hip assemblies use similar detailing techniques. Flashing at the ridges and hips is needed to provide a closure for the top edges of metal panels. Proper flashing and securement of a metal cap and panel assembly at these intersections are essential for a long-term, weathertight detail. Depending on the slope of the roof and type of metal panel roof system, flashing of a ridge or hip may be accomplished by using metal closures, upturned panel ends and sealant.
Reference: National Roofing Contractors Association, The NRCA Roofing Manual: Metal Panel and SPF Roof Systems, National Roofing Contractors Association 10255 W. Higgins Road, Suite 600, Rosemont, IL 60018, 2011