Here’s information on how to make better roof curb choices
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| Photo courtesy of KCC International Inc. |
I’m often asked what thebest roof curb design is for pre-engineered metal roof applications. Everyone has horror stories of curb installations gone wrong. I’ve seen the results of many firsthand. While very few would intentionally purchase and install the wrong product, curbs are often provided by those that don’t fully understand the implications of their choice until it is too late. The most common problems I see are curbs that are not designed for pre-engineered roof systems (i.e., curbs intended for installation on a conventional roof, knock down curbs), curbs that do not properly fit the roof panel profile and improper installation methods. If roof curbs are a source of customer dissatisfaction (leaks in their roof), the following items should help you make better roof curb choices.
Building Manufacturer
Check to see if your building manufacturer has a recommended curb design. Some are very specific and may even require a certain type of curb to satisfy their warranty requirements. If it is available, it is a good idea to take advantage of their engineering expertise. In doing so, you may avoid pitfalls they have already discovered from builder feedback, by design or due to trial and error.
Building Erector
If your erector has had success with a particular type of curb
(and if your building manufacturer does not recommend a specific design), consider his preference. Asking him to install a curb design that he dislikes or is unfamiliar with can lead to a problematic installation.
Roof Panel Type
Roof panels are available in four basic styles; trapezoidal standing seam, vertical leg standing seam, screwdown (‘R’ panel) and architectural standing seam. While one curb design may work perfectly on a given panel type, it may be totally inappropriate for another.
Roof Curb Type
Many differences exist in the specific manner in which curbs can be fabricated and installed but the basic designs fall into three categories.
• Uphill base flanges install under roof, downhill base flanges install over roof.
• Uphill and downhill base flanges install over roof.
• Uphill and downhill base flanges install under roof.
All curb designs offers certain advantages, yet none can be considered the ‘best’ for all aspects of the curb installation. For instance, a curb design that is easy to install may not offer the most natural water-shedding capability. Conversely, a more naturally weathertight design may need to be installed as the roof is installed, therefore impeding installation of the roof system.
Roof Curb Manufacturer
Do your curbs come from a local sheet metal fabricator or from a bona fide roof curb manufacturer experienced in the metal building industry? Local fabricators often lack the knowledge, experience, materials and equipment to properly address the fabrication details crucial to proper curb design. A pre-engineered metal building roof curb manufacturer is aware of typical standards used in the metal building industry for most roof panel types, as well as specific curb recommendations from metal building manufacturers who offer such details.
Roof Curbs Provided by Subcontractors
This is where the most egregious mistakes occur, including the curb type, material of construction (never use galvanized metal!) and the method of installation. Subcontractors often hard bid projects without fully understanding that the curbs used for pre-engineered roof systems are totally different than curbs used on conventional roof systems. I’ve seen many curbs tarred into a metal roof! Disaster! You’ll get the best result if you keep the curbs out of the hands of uninformed subcontractors and in your metal building package. If this can’t be done, work with the subs and direct them to reputable pre-engineered roof curb manufacturers.
If you’ve had recurrent problems with roof curbs, it’s time to examine the curb design, sealants and fasteners, support framing and installation procedures. Each of these aspects of the roof curb system has an impact on the watertightness of the installation. A correctly installed, proper curb design can offer you the same level of watertightness that you have with the rest of your roof system. To properly evaluate your best roof curb solution, factors such as price, ease of installation and water-shedding capability are some of the areas to consider. This evaluation may involve compromise but understanding how these factors affect all aspects of the curb installation will equip you to make your decision based on facts. You can then provide your customer with the best roof curb for their preengineered roof application.
Greg Conrad is the technical sales manager and Midwest business manager for Louisville, Ky.-based KCC International Inc. (formerly known as Kentuckiana Curb Co.) where he has been employed for 28 years. He’s a board member of the Indiana Metal Building Association, conducts roof penetration seminars and is a consultant to industry contractors, dealers and metal building manufacturers. For more information, visit www.kcccurbs.com.
