Perspectives
A Quarterly Information Source from Benchmark, Inc.

Volume 59 September 2007

In July of 2007, bids were received for the replacement of the low-slope roof sections at the ABBE Center for Community Care. This facility is a residential housing complex owned by Linn County and located in rural Marion, Iowa. Originally constructed in 1975, the sprawling complex is primarily a one story building with several connecting "raised" pods. Two roof systems are utilized on the complex: 1. Asphalt shingles on the steep-slope "Dog House" roof sections (replaced in 2000), and 2: Adhered EPDM single-ply on the low-slope sections.

The focus of this article regards the two different roof

systems utilized on the low-slope roof sections.

A - 45-mil EPDM adhered to 1 layer of 1.5" polyisocyanurate insulation; 12 roof sections totaling approximately 47,000 square feet.

B - 45-mil EPDM adhered to 1 layer of 1/2" fiberboard insulation; 23 roof sections totaling approximately 5,000

square feet.

Installed in 1983 as one project, both roof systems were installed over (recover) the original roof system (smooth surfaced, asphalt built up roof and 2" layer of urethane insulation). Benchmark estimates that the total existing R-Value for these two roof systems, including attic space, interior insulation, etc., is R = 25 for A, and R = 18 for B.

The existing 24-year old adhered EPDM roof system was

experiencing leaks at several random locations throughout the complex and had been for some time.

Emergency repairs have been completed on more than a few occasions as a result of storm damage. Several other repairs have been completed over the course of the last 14 years in response to leaks and other roof deficiencies.

In the spring of 2006, Linn County authorized Benchmark to conduct the necessary field work to develop a "preliminary" roof replacement scope of work, estimated cost of construction and timetable to prepare plans and

specifications, solicit bids and complete the project.

Upon completion of the field work, we concurred with Linn County officials that these two roof systems should be replaced.

Our "preliminary" scope of work called for the complete removal of both roof systems to the plywood deck and constructing the new roof system from the deck upward.

As with the vast majority of building jurisdictions, Linn County Building Code permits up to two roof systems on a building when designing a roof replacement - a third roof system would not be allowed. Our estimated construction cost for this "preliminary" scope of work was $455,000.

Following a review of Benchmark’s "preliminary" scope, and related estimated cost of construction, Linn County officials came back to us inquiring about possible options that would reduce our "preliminary" estimated cost. There were three major challenges to address before considering other options, two of which would require further investigation and additional cost:

1. Code Requirements:

We contacted the Linn County Building department and explained our design/budget challenge. Several roof replacement / recover options were discussed. To our pleasant surprise, we learned from the building official that we could satisfy the code requirement by only removing the existing adhered EPDM single-ply membrane and leaving the polyisocyanurate and (or) fiberboard insulation in place. With this information, we recommended to Linn County that the following two issues be further explored:

We needed to determine the existing live and dead load capability of the roof deck and structure. Benchmark and Linn County subcontracted with a local structural engineering firm to evaluate the structure and to determine the amount of weight (new roof system) that could be added to the existing roof, if any. Fortunately, the existing structure (framing and plywood deck) was designed and constructed with a conservative safety factor in mind. The structural evaluation conducted revealed that the existing structure could accept up to an additional 5.5. pounds per square foot of dead load. We estimated that the proposed new roof system (one layer of 1" polyisocyanurate insulation, one layer of 1/2" gypsum board overlay and new single-ply roof membrane), would add approximately 2.00 pounds per square foot), well within the structural capability.

With two roof systems present and a somewhat lengthy leak history at the ABBE Center, we were confident that there were areas of wet roof insulation in both the original and the second (1983) recover. Random core sampling during our field gathering indicated several areas of wet roof insulation. The challenge under these circumstances was to locate and determine an accurate amount of wet insulation in BOTH roof systems.

Conducting an infrared moisture scan would reveal areas of wet insulation in the top roof system, but would most likely not reveal any wet roof insulation in the original roof system. The only option to consider was a nuclear moisture scan. Benchmark and Linn County subcontracted with an Omaha based nuclear moisture scan testing service to conduct the scan in late August, 2006.

On the roof sections with the polyisocyanurate insulation, the scan revealed eight areas of wet insulation, totaling approximately 2,000 square feet, or just over 4% of the total roofing square footage. Core sampling conducted following the scan confirmed that four of these areas had wet roof insulation. On the roof sections with the 1/2" fiberboard insulation, the scan revealed wet roof insulation at several locations, totaling approximately 1,500 square feet, or 30% of the total square footage.

Armed with the information above, Benchmark prepared the roof replacement plans and specifications that called for tearing out all the wet areas only on the polyisocyanurate insulation roof sections and completely removing the fiberboard roof sections down to the original roof prior to installing the new roof system. The bid documents were ready to go to bid by the end of September, 2006. Due to the late date in the year, Linn County and Benchmark agreed to postpone bidding this project until the summer of 2007. Five base bids (adhered EPDM single-ply) were received with the highest base bid only 13% higher than the lowest base bid of $320,772.

Benchmark recommended to Linn County that one of the alternate bids (adhered PVC single-ply) be accepted as the cost was only 2.25% higher than the lowest base bid. As this article goes to print, the roofing contract has been awarded and the project is scheduled to commence in late August.

The roof replacement design and bidding of the project took well over a year to complete. The extra time, due diligence, and costs associated with subcontracting with a structural engineering firm and nuclear moisture scan testing service resulted in several benefits. By changing from an original design that called for a complete tear off to a design with a limited tear off, the existing high R-valued roof insulation is being preserved, the amount of debris that will go to the landfill is significantly reduced (not to mention the landfill fee savings), and the project duration should be shorter. These combined elements have resulted in reducing the original cost of construction estimate by $127,000 or almost 35%! The ABBE Center will soon have a new roof and at a great value for the taxpayers of Linn County Iowa.

FM then ceased publication of the Approval Guide. While noble of purpose, ROOFNAV has caused much irritation among contractors, designers and manufacturers. Based on ROOFNAV assembly searches, the user often finds hundreds of approvals to further review, one link at a time, until the exact collection of desired roof components can be found. The other extreme, finding that no assemblies match your desired roof assembly, is just as maddening.

FMG has promised enhancements of ROOFNAV to make it more user-friendly, but we have not seen much if any improvement in the search and tracking functions since its inception.

From time to time, FMG updates their Loss Prevention Data Sheets. Sometimes these changes hardly cause a ripple through the industry, but recently one change created quite a tsunami. In February of this year, FMG revised their FM LPDS 1-29. The roofing industry was taken by surprise, and reaction from the various roofing associations was quite resounding. One of the largest complaints was the FMG made these changes without any preview or notice to the roofing industry. LPDS 1-29 changed for example, the treatment of roof perimeters and corner zones in roofs requiring an FM 1-90 wind uplift approval. Overnight, roofs that were thought to comply with FM 1-90 wind requirements lost that designation.

FMG also recently updated another data sheet, LPDS 1-52, which addresses field uplift testing of completed roofs. In this update, FM requires field testing of newly installed roofs for wind uplift resistance. This testing is controversial as some question the reliability of the testing results.

FMG wind design requirements technically only apply when the building owner is FM insured, yet due to a lack of a suitable wind design standard, specifiers often rely on the FMG requirements, sometimes without understanding the impact on cost or roof design.

To address this void, representatives of various roofing organizations including SPRI, RCI, NRCA and ARMA met to develop a consensus ANSI standard for wind design. The standard has been written and submitted to a wide group of industry representatives, users, etc., for approval. At this time, the objections and commentary are being reviewed.

In addition to participating in the development of a new wind standard, the NRCA developed a free on-line wind design calculator, based on the ASCE 7 "simplified method". This provides the industry with another tool to quickly access the wind loads on a roof.

Loss of gutter and edge metal, exposing roof insulation.

In the long term, all these changes will result in more wind resistant roof design, clearly a good thing for life safety and loss prevention. In the short term, it will cause a certain dislocation between the practices of the past and present. Tracking these changes, distilling their meanings, and putting them into practice takes time and commitment on the part of the roof designer. Funding the inevitable increase in roofing costs falls obviously on the building owner.