Coordinating Roof Insulation with Metal Building Construction

Energy codes and increasing energy costs have prompted the installation of more roof insulation into metal buildings in recent years to make them more energy efficient. That is fundamentally a good thing and metal building manufacturers have developed ways to accommodate a variety of building enclosure packages that increase energy performance while still being engineered to meet the structural requirements of the building. This allows the whole building envelope to be designed and fabricated so it works as a complete, coordinated system.

Metal Building
Insulation helps maintain a comfortable interior temperature in your metal building during the winter and summer months. 

The metal roofing or metal building suppliers typically don’t design the insulation systems. However, it is important to include them in the discussions or make them aware of what type of system is to be installed. It is not uncommon for a metal building to be ordered with the design stipulation of “insulation by others.” In that case, coordination is needed between the person ordering/designing the insulation system and the metal building manufacturer or roofing supplier. Since there are a great many variables in the way that insulation can be provided, it is not appropriate to think that the design of structural systems (purlins and roof bracing) and cladding systems (clips, fasteners, and metal roofing profiles) will necessarily accommodate all the same insulation in all conditions. Rather, unless the specific details of the insulation system being used in the building are communicated effectively at the time of the order, the manufacturer can not assure compatibility of the systems used with the insulation system that is to be installed.

In order to understand some of the variability in the options, let’s look at some of the common ways that metal buildings are or are not insulated.

Uninsulated Roofs:

Buildings that do not have any heat or air conditioning in them may not need for an insulated roof. This could be true for outdoor shelters, some agricultural buildings, or vehicle storage buildings. However, uninsulated metal roofs have the potential for “roof rumble” as they move due to thermal expansion and contraction, wind, or weather as there is no insulation to mask or deaden this noise. Absence of insulation can also lead to condensation during certain times of the year if temporary heat is added to the building. This condensation builds up and can drop or fall onto whatever is below. Many times condensation issues are mistaken for roof leaks when in fact it’s a mechanical design issue of the building envelope that’s not been properly addressed. If neither sound nor potential condensation are a concern, then there’s no problem. But if either or both need to be avoided, then some basic level of insulation may be prudent.

Over the Purlin Systems:

One of the most common insulation systems for metal buildings and/or open framing systems is to simply install rolls of blanket insulation. In this case, fiberglass insulation with a reinforced liner is draped over structural beams and purlins. The rolls are supplied to length by the insulation supplier based upon the roof structural layout and the required “R” value necessary for the building envelope in thicknesses that can vary from 3″ to 12″. Is is this thickness to be installed over open framing that the metal building/roofing supplier must be made aware of. Based on this thickness, the panel profile can be verified to determine if it can be used as well as confirmation of the correct clip heights and screw lengths for installation. Keep in mind that the supplier will offer a guide to the installer based upon insulation thickness. As insulation can vary by manufacturer, it will be up to the installer to make adjustments as needed in the field to ensure proper placement and hold modularity of the steel system. (See Respect the Module: Metal Roofing Panels are Modular for Good Reason)

Cavity Fill Insulation Systems:

When higher “R” values are required for roof insulation, a single layer over the open framing system may not be sufficient. When that occurs, the designers of the building envelope may need to employ the framing cavity to add more insulation. There are also variation on the cavity fill approach.

One means is to simply introduce a second layer of unfaced blanket on top of the faced insulation. Sometimes referred to as a “sag and bag” approach, here the first layer of insulation over the purlins is ordered to accommodate larger amounts of drape between the roof structure to permit another layer of unfaced insulation to be added on top. This increases the insulation thickness between the purlins but keeps it thin enough to be compressed to accommodate the roof panel installation. For coordination purposes, the thickness of this upper insulation over the purlins needs to be known by the building manufacturer so the clips and fasteners can be properly sized. Likewise, the amount of insulation draping between the purlins needs to be known to determine if purling bracing or other accessories may potentially interfere with the insulation installation.

Other types of cavity fill system may include a faced batt or face roll insulation with long tabs, which are secured to the tops of roof purlins and nest fully into the purlin cavity to fill the space more effectively. This helps in eliminating greater compression of multiple layers of insulation on top of the purlins and permits an additional layer of unfaced insulation on top of the roof structures and/or a thermal spacer block. This system may also require some intermediate banding to support the insulation between the primary supports.

A liner system may be installed that employs a continuous vapor retardent material. This liner is secured to the bottom of the roof structure and additionally supported with metal banding allowing the cavity to then be filled with unfaced insulation between the purlins. More unfaced insulation can also be added on top of the purlins as well. In all of the cases where cavity fill systems are used, it is important to advise the building manufacturer/roof supplier which type is being used to ensure proper panel clip heights and screw lengths. This is important because these systems can and will interfere with the roof structural bracing making them more difficult to install. The metal building supplier may be able to offer bracing alternatives or remedies to eliminate some or all of the bracing that would otherwise be in the way when installing the roof insulation. There may also be suggestions on how to avoid impeding or penetrating the vapor barriers which could lead to condensation issues. Overall, it is best to discuss and coordinate all of these items ahead of time.

Rigid Board/ Composite Systems:

In this insulation approach, rigid foam insulation board is used to achieve the sought after energy performance. Commonly, these use metal deck panels over the roof structure thus supporting the insulation and a vapor retardant material on top of the deck. The insulation and the metal roofing can then be secured to the framing substructure or to the metal deck itself, which means the details of attachment need to be reviewed and engineered to avoid adverse affects on the roofing system.

Metal Building
Minimum decking gauge, clips spacing and clip screw lengths should be considered as well as associated adjustments to labor costs.

Spray-on Insulation:

All of the above systems typically require attention to providing additional air and vapor barriers and proper cutting and fitting during installation so as not to cause unwanted infiltration or to prevent condensation from occurring. For these reasons and more, some people will consider the use of closed cell spray-on foam insulation, which can continuously provide all of these features in one product. It can also be installed after the roof is completed and structure is weathertight.

Metal Building
Any corrosion of the panel due to adhesion of the insulation is not covered by the panel.

In the case of metal buildings, spray-on insulation is typically applied in the field onto the inside face of installed roof panels and sometimes wall panels too. There are, however, a few concerns with this approach in metal buildings. First, if conditions are not right and the panels are not properly prepared, then the spray foam can, in fact, trap moisture between the insulation and the metal components it is sprayed onto. That can lead to corrosion of the metal or deterioration of the insulation. Secondly, not all spray foams on the market are intended for this type of use so they don’t always adhere well to some metal panels, meaning it could become loose and fall away. Finally, continuous spray foam in this application will not always be able to expand and contract at the same rate that metal does. In some cases, that could mean that the foam suffers from differential movement causing it to break or lose adhesion.

For all of these reasons, be certain to research all options before considering or selecting a foam spray-on insulation that will not negatively impact your roof performance. If a foam insulation is preferred, it may be worth considering the use of insulated metal panels (IMPs) that are designed, engineered, and fabricated to be compatible with metal building construction.

Recognizing all of the above variations and options, the key point to remember about insulating metal buildings is the importance of communication between those designing and ordering an insulated metal building and those who are manufacturing and fabricating it. To find out more about the best ways to do that, contact your local MBCI representative.

Five Retrofit Choices Using Metal Roofing Systems

Buildings usually need new or replacement roofing installed at some point during their service lives. New metal roofing is an ideal roofing retrofit option due to its longevity and durability, which can extend the life of the roofing and require fewer replacements over time. The aesthetic appearance of a new metal roof can also make a notable visual impact to upgrade the building itself.

When considering such a metal roof retrofit on an existing building, the first thing to realize is that there are a number of choices available. Here is a quick look at five of the most common ones that can be selected from and tailored to suit a particular building. Note that since all of them will add some structural loading to the roof, all the retrofit solutions should be reviewed by a professional structural engineer to be sure the existing building can accommodate the changes.

1. Double-Lok® Clip System

When an existing building has an existing PBR roof panel or similar, a Double-Lok® clip and panel system can be installed directly over the existing roof with minimal alterations. In this case, 2″ standoff clips are run from eave to ridge and fastened through the existing roofing panels down into the existing purlins. Then new standing seam metal roofing panels are installed along these clips so they are held 2″ above the purlins and 3/4″ above the major ribs of the existing panel roof. Because of these clearances, the cavity between the old and new roofs can either be vented or additional insulation can be added. Venting the cavity can be a good option when the existing roof slope is 3:12 or greater, as this allows for convective air flow during the summer and can help reduce the chance of ice damming in the winter. For any slopes of 1/2: 12 or greater, adding insulation can improve the overall thermal performance of the building. Generally, this system allows for considerable versatility, even if it takes more parts and labor than some other solutions.

2. Retrofit Roof Panels Over Existing

For cases where a standoff isn’t sought, new, non-structural metal roof panels with a specifically retrofit profile can be installed directly over existing roof panels on roof slopes of 1/2: 12 and greater. That means there is no need to tear out the old roof, since the new panels are through-fastened into the old ones and the purlins below, all in a pattern that avoids the original fasteners. Such retrofit panels are available in 29 and 26 gauge in full range of colors and come with a factory-applied vapor barrier on the underside. Even light-transmitting panels are available for this retrofit panel system.

Retrofit
5 most common choices for retrofit metal roofing systems

3. Notched Sub-Purlins

A variation on the metal-over-metal roofing approach is to use specifically designed z-purlins with notch-outs that are screwed down to the existing purlins. Unlike other systems that run retrofit support members from the eave to the ridge, the notched purlins run parallel to both (in line with existing purlins) with the notches spaced to clear the ribs or corrugations in the existing metal roofing. Profiles are available to match virtually any metal roof produced in the last 50 years. That means they can be installed over existing roofing and, in the process, provide enhanced structural capabilities because of the added sub-purlins.

4. Grid System

When an existing purlin spacing doesn’t meet current code requirements, then the use of crisscrossing hat sections in a grid pattern can provide the additional support needed. Such grid systems are designed to go directly over existing sloped roof systems but many require the use of specific metal roofing panels to work properly.

5. New Framed Roof System

In some cases, a full, steep-sloped roof (greater than 4:12) is sought to be installed over a low-slope roof (1/4:12 – 4:12). In this case, a full metal framing system is available that will create the desired roof slope and transfer the new roof weight to the existing roof deck above the existing roof structural members. As such, the coordination of the new system with the existing roofing, insulation and structure needs to be addressed by licensed engineers. Once designed and installed, an “attic space” will be created by the new retrofit roof system, which should include proper venting in accordance with applicable codes, allowing trapped moisture to escape. It is also recommended that such “attic space” be reviewed by other building, fire, or insurance-related officials for possible sprinkling or extension of existing fire walls to the bottom of the “new” roof system. Regardless, a minimum of 3″ vinyl-faced roll insulation between the retrofit panels and the retrofit purlins will help prevent condensation and roof noise in addition to improving energy efficiency.

To find out more about which retrofit options, or options, are best suited to a particular building that you are involved with, contact your local MBCI representative.

Using Wind Clamps to Improve Wind Uplift on Standing Seam Metal Roofs

Among the most important factors to account for when specifying a standing seam metal roof are wind control and wind uplift. It is imperative to take the necessary measures to ensure the safety and efficacy of the metal roof. The wind clamp—an extruded piece of aluminum that is placed on the panel seams at clip locations—is one accessory that can be used to improve wind uplift characteristics on metal roofs, delivering substantial time and cost savings as these devices help mitigate risk of wind uplift and improve overall wind design.

Panel Deflection
Standing Seam Panel Deflection as a Result of Wind Uplift

Why Use a Wind Clamp

A typical failure mode of a standing seam metal roof panel is the clip top pulling out of the panel seam when the panels are subjected to high winds.  With a standard install of a standing seam panel, the seams just fold into each other. With enough pressure, wind will force seams to come apart—be it a vertical failure, horizontal movement of the seam or from clip disengagement. The clip top can then pull out of the panel seam.

The wind clamp resists the panel seam being opened, allowing for higher uplift loads. The purpose of wind clamps, in fact, is to prevent Windclamprszdfailures at the seam openings due to any deflection of the panel. The wind clamps provide more strength, thereby dramatically improving wind uplift performance.

The clamp is installed over the panel seam at clip locations, in the edge and corner zones of the roof.  This allows the roof to resist the higher wind pressures in these zones, usually eliminating the need for additional purlins or joists. On large roofs, the savings can be substantial.

Another benefit is shorter installation time. Since additional purlins or joists are typically not required at the edge or corner zones of the roof, the building can be erected faster.

Choosing Wind Clamps

When choosing the type of wind clamp, it is important to consider the type of panel and the special features of the clamps. MBCI, for example, uses S-5!’s patented wind clamps, which work for two panel types—Ultra-Dek® and Double-Lok®. The S-5! wind clamps do not penetrate the steel, thereby eliminating the risks of corrosion and water leakage that can be introduced by a hole in the steel. Since the screws are hidden from the weather elements, it helps to maintain waterproofing.

Quantitative Difference with Wind Clamps

One of the biggest benefits of using wind clamps in the edge and corner zones is that usage minimizes the quantity of purlins needed, resulting in substantial cost savings. For example, let’s look at a comparison using MBCI’s Double-Lok 24” – 24 ga. panels with and without wind clamps.Chart for blog image

In this example:

  1. The use of wind clamps in the edge and corner zones eliminated 3,800 linear feet of purlins.
  2. Assuming 8” x 2-1/2” Zee 14 ga. purlins were used, there would be a cost savings of $10,400.

Conclusion

Utilizing wind clamps to protect the investment of a standing seam metal roof can increase strength, make installation faster and lower overall cost.

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