ABC’s

In 2004 most states and municipalities adopted the new “International Building Code” (IBC). This code differs dramatically from the previous building codes in many ways. The most important to you and your project is how it looks at the design load for wind uplift pressures subjected to the roof. Different from years past, the roof is now divided into three zones: The “Field” or central areas of the roof, the “Edge or Perimeter” and the “Corner” zones of the roof. The loads for each “Zone” as shown in the below illustration must now be calculated separately to determine attachment points of the new roof panel system to the Roof Hugger framing system. Essentially, these locations are the same as “Panel Clip” spacing in the case of standing seam metal roofs or fastener placement for thru-fastened metal roofs. It is very important to understand that the required locations of new Roof Huggers on the existing roof will be governed by the new metal roof system’s ASTM E-1592 tested values.

The new roof must withstand the full forces calculated for each of these “Zones” on a per project basis. It is important to understand that code based reductions allowed in the past are usually no longer permitted. Since no two buildings are exactly alike, the size and shape of these “Zones” vary from building to building and depends on numerous factors. Included in these factors are height above ground, roof geometry, exposure of the roof to surrounding obstructions, distance from coastal areas, etc. Each building must be considered individually and engineered based on the existing conditions and proposed changes. The basic steps in the evaluation process are as follows:

  • STEP 1: Collect the basic information needed as requested in our Project Questionnaire.
  • STEP 2: An engineer should calculate the design pressures for each zone of the roof. This can be completed by Metl-Span when you request a “Clip Analysis” for the new Retro-Seam metal roof.
  • STEP 3: Once the design analysis is completed, the next step is to determine what is required in the Roof Hugger sub-framing system. This is done by comparing the new CFR IMP maximum allowed pressures (uplift capacity) with the existing building’s purlin spacing. If the existing purlin spacing is 5′ (typical in older buildings) you would compare the capacity of the new panel on 5′ purlin spacing. If the new panel cannot meet the required uplift pressures (PSF) for a 5′ purlin spacing, then an additional Roof Hugger will be necessary between the existing building’s purlins. This needed framing can be achieved by adding additional purlins from under the old roof or by adding additional framing on top of the existing roof.
  • STEP 4: If additional framing is needed to reduce the purlin spacing, it must be determined what that framing consists of. Roof Hugger, Inc. has designed a number of above roof options for reducing the purlin spacing in the corner and edge zones when needed. The specific design will depend on the existing panel type and rib spacing. If the existing roof is a 12″ o.c., “PBR” type panel, Roof Hugger, Inc. has several FLORIDA PRODUCT APPROVED Systems that may work in this case. Other existing panels may require special grid designs consisting of Hats, Cee’s or Zee’s or a combination of all.
  • STEP 5: Once the new roof’s sub-framing has been determined and the overall height of the framing is established, the Roof Huggers can be estimated.

If you need assistance with the above process please feel free to call Metl-Span Estimating: 877-585-9969 to discuss your specific project.