Structural Penetrations in Standing Seam Metal Roofs

In our prior post on “Pipe Penetrations in Standing Seam Metal Roofs,” we identified important guidelines for when pipe penetrations are made to metal roofing systems, typically after the metal roofing is installed. That means an opening is cut in the metal roofing, it is properly flashed or sealed, and the penetrating member is passed through it. However, some penetrations are already in place before the roofing contractor shows up. These can be things like vertical members resting on the building structure that support a platform for HVAC equipment above the sloped roof. Or, it can be parapet wall with offsets or other conditions that are already in place. In cases like this, a different approach is needed to assure that the roof remains watertight.

Equipment Platforms for Structural Penetrations

Penetrations
Structural Penetrations in Standing Seam Metal Roofs

From the standpoint of a roofer, a structural equipment platform is a pre-existing condition. The metal roofing industry already recognizes the need to address such situations, particularly on existing buildings, by offering retrofit flashing and curb products. The same, proven approach can be used when pre-existing conditions are encountered on new buildings as well. For example, when structural posts for equipment platforms are encountered running up through the roof plane, roof jacks and curbs specifically designed for retrofit applications should be used. The retrofit roof jack, or boot, should be made out of rubber and be designed to install around the penetration, rather than over it. The boot should ideally rest on a two-piece retrofit pipe curb which can span across one or more standing seams and create a smooth, flat surface for the boot to be attached and sealed. The two-piece design allows for the pipe curb to be properly shingled on the up slope and down slope side of the roofing, thus preventing a “backwater lap,” which will leak. Trying to use only products intended for new construction on such conditions will require unwarranted field modifications or an over-reliance on caulking and sealant, all of which can be prone to problems and failure of the watertight abilities of the roofing.

Parapets

The use of parapet walls around some or all of a perimeter of a building is a common condition. However, if the building shape varies, and the parapet along with it, then there may be some rather uncommon conditions in which the roofing meets an offset or irregularly shaped parapet walls. The issue is that water coming down the sloped roof runs into the offset or other obstruction, causing a buildup of water and a potential leak. The typical approach is to provide a cricket, which is flashed into the parapet wall and diverts water away from the corner created by the offset. It is important, in this case, to be aware that standard sheet metal crickets have not proven to be effective. Instead, welded aluminum crickets and fixtures are recommended to create a truly watertight seal. Also, the welded cricket can be “shingled” into the roof to prevent “backwater laps.” The key is to provide a complete seal at the corners by welding the material, which cannot be done with sheet metal crickets.

Design Planning

The best way to address all of the structural roof penetration issues described here is with proper upfront planning. Avoiding any of these conditions would of course be ideal, and perhaps they can be designed out of some projects. However, if they’re unavoidable, then the roofing contractor and the design professionals need to review the conditions together ahead of time. This advance design planning is the best way to assure that the best, most effective detailing is employed and the proper materials are available on site.

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.

 

Details, Details, Details

Water runs downhill.  And, gravity is our friend.  Yet sometimes we forget these basic concepts when installing metal panel roofing.

When it comes to metal roofing details, a contractor should always think about the flow of water.

Roofing contractors are in the business of controlling water, so let’s install details that allow water to run downhill and let’s use gravity to our advantage.  A more precise way to say it: Implement drainage details that don’t buck water!

Details, details, details

Defending Against Water Leaks

Metal roof penetration and edge details should not rely on sealant as the primary defense against water leaks.  Certainly, sealant is and should be used as a secondary measure against water leaks.  Consider this: A transverse panel seam is created by lapping the upper panel over the lower panel, and sealant is used as a secondary seal.  Installers would never reverse the lap of a transverse seam (where the lower panel is on top of the upper panel), bucking water and relying only on sealant to keep water out.  A penetration detail (e.g., a vent stack or roof curb) should use the same logic.  There’s no doubt that bad details are rooted in low cost and speed of installation, but those are not details that are going to have equal service life to the metal panels on a roof.  A penetration detail is as critical to the long-term success of a metal roof as a transverse seam.

Prefabricated Penetration Details

It’s best to use prefabricated penetration details that have welded or soldered weathertight seams.  The prefabricated piece should be the width of a panel and include the male and female seams, and be seamed into the adjacent panels.  And just like a typical transverse seam, the top edge of the prefabricated piece should be under the upper panel, and the bottom edge of the prefabricated piece should be above the lower panel.  Water is not bucked and seams are fully intact.  That is a long-term penetration detail.

Where proper overlap can’t happen, redundancy is necessary.  A small pipe penetration detail should use a rubber roof jack with added levels of redundancy for weatherproofing.  First, the roof jack should only be installed in the flat of the panel; sealant tape should be installed between the panel and the roof jack; and closely spaced, gasketed fasteners should be installed to create compression on the sealant.

Roofing That Lasts

Metal roofs sell themselves because metal is long-lasting.  And construction details need to be developed and installed with that in mind.  Metal panels don’t leak—the joinery and fastener locations can leak.  Remember to design and build details that have equivalent service life to the panels themselves.  Proper laps are critical, and remember, gravity is our friend.

To learn how to design a roof system that prevents possible infiltration and allows for proper water runoff, take MBCI’s AIA-accredited course, The Devil is in the Details.

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