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.

5 Tips for Problem Free Pipe & Flue Penetrations in Standing Seam Metal Roofs

Standing seam metal roofs have proven record of longevity and value in providing a very weathertight roofing solution. But the performance of any roof can be compromised by needed penetrations to accommodate other building systems. Done poorly, those penetrations can cause leaks, building damage, and unnecessary expenses. When properly designed and installed however, roof penetrations can be integrated into metal roofing successfully without compromising performance.

Pipe Penetrations

Pipe penetrations, whether for plumbing vents, flues, or other miscellaneous pipes, are probably the most common type of roof penetration in commercial metal roofs. Here are five proven and practical guidelines to help avoid problems.

1. Use Qualified Installers

A qualified roofing installer is the best person to cut and install an appropriately flashed and booted pipe penetration. If that isn’t possible or practical, then any penetration installed by another contractor should be fully coordinated with the architect/owner’s representative and the roofing contractor. This is the only way to be sure that the integrity of the roofing system is maintained.

2. Use Only Commercial Materials

To properly seal around the pipe penetration, use only a rubber roof jack made specifically for use with metal roofs. Do not use residential-type roof jacks or those designed for other roof types – they will not last over time. Further, do not use materials that are dissimilar to the standing seam metal roof, such as copper, lead, or galvanized metal roof jacks, which can corrode the metal roof system, or are an inferior quality with a short service life (less than 20 years). Proper commercial roofing products combine an EPDM rubber boot (or silicone for high heat applications) with a bonded aluminum band to allow a compression seal to be formed at the roof panel.

Penetrations
Pipe and flue penetrations allow for a long-term performance of the roof.

 

  • Standard EPDM roof jacks can withstand temperatures up to 212º and are suitable for most applications.
  • High-heat, silicone-based roof jacks can withstand temperatures up to 437º and are suitable for flues.
  • Retrofit roof jacks are available in both temperature ranges for applications in which the roof jack cannot be slipped over the top of the pipe.
  • Use only tape and caulk sealants approved by the roof manufacturer.
  • Use only long-life fasteners at all exposed fastener applications. Note that zinc-plated fasteners will not last for 20 years and will typically void roof warranties for finish and weathertightness.

3. Penetration Locations

All planned penetrations should be assessed first to be sure they are not inadvertently creating a potential leak or other problem. Rather, they should be located so they can be properly sealed with no immediate obstructions that would make the seal to the roof unnecessarily difficult or compromise long-term performance.

  • Never allow a pipe to penetrate through a standing seam. It is almost impossible to seal around the roof jack and the panel seam in a manner that will be leak free for the life of the roof. Therefore, always locate the roof penetration onto a smooth or flat area of the roof surface.
  • Place the penetration in a location that has the least amount of water draining into the immediate area around it.
  • Similarly, never allow a pipe to block the water flow down a roof panel and create a buildup of water. When a pipe is encountered that is too large to fit in the flat of the panel without blocking the water flow, use an aluminum pipe curb to allow the water to flow around the pipe and to provide a large, flat area in which to seal the roof jack to the roof surface.
  • In Northern areas, vent pipes should be located as high as possible or otherwise protected against sliding ice and snow from above. On roofs with slopes as low as 2:12, sliding snow, impacting an unprotected pipe, can tear the metal roof or shear the pipe off flush with the roof.

4. Allow for Thermal Movement

The penetration must allow for thermal movement of the roof. Pipes or other penetrations that are rigidly attached to the structure below may not be able to move as the roof expands and contracts. In these cases, the hole in the standing seam roof should be large enough to allow for this movement without the roof panels impinging on the penetration.

5. Check Warranties

If the penetrations are to be included in a manufacturer’s weathertightness warranty, the manufacturer must approve in writing beforehand the materials and methods to be used to install the penetrations. Failure to follow this guideline may result in the penetrations being excluded from the weathertightness warranty.

If everyone involved with the roofing penetrations is aware of, and follows these five guidelines, then in the end everyone should be quite happy with the long-term performance of the roof. If not, the potential for roof leaks and other related problems only increases.

 

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