Level of Development (LOD) BIM Specifications for Metal Buildings

When designing and constructing metal buildings, an increasing number of professionals are using a computerized building information model (BIM) as their primary tool. This allows for detailed, three-dimensional computer models to be created, not only to develop the design, but to identify material lists, coordinate details, avoid conflicts between building systems and streamline the design and construction process.

Problem: BIM Coordination

Of course, design is a process that requires some back-and-forth between multiple parties to arrive at the best final solution. So, when a metal-building supplier or manufacturer is asked to provide their information to be incorporated into a BIM process, the question that naturally comes up involves the level of detail. This is common across all trades, and fortunately, there is an organization that is addressing this issue. Known as the BIMforum (www.BIMForum.org), is is the not-for-profit United States chapter of buildingSMART International, and its mission focuses on improving BIM technology, collaboration, education, innovation and open information exchange. As they describe themselves, “Co-sponsored by the Associated General Contractors of America (AGC) and the American Institute of Architects (AIA), BIMForum seeks to lead by example and synchronize with counterparts in all sectors of the industry to jointly develop best practice for virtual design and construction.”

Solution: Level of Development (LOD) Specification

A flagship publication of BIMForum is the 2016 version of Level of Development (LOD) Specification. Having evolved over several years, this publication is “a reference that enables practitioners in the AEC Industry to specify and articulate with a high level of clarity the content and reliability of Building Information Models (BIMs) at various stages in the design and construction process.” Coordinated with other industry standards, it “defines and  illustrates characteristics of model elements of different building systems at different Levels of Development.”

Essentially, it defines and standardizes how much detail is expected in a building information model at different stages of design development. Therefore, if a metal-building manufacturer or any other trade is asked to supply its BIM information, then it needs to ask “What Level of Development?” so that is it providing the right amount of information to coordinate with the larger computer model for the building.

How LOD Works:

The LOD Specification is based first on the familiar Uniformat specification sections used by most spec writers. Metal Buildings commonly fall under Special Construction in Section F1020.40 in the Uniformat approach, or 21-06 10 20 40 in the Omniclass approach, and are found that way in the LOD Spec. From there, five levels of detailing are described by the numbers 100, 200, 300, 350 and 400, as described further below.

  • LOD 100 – This is the most basic of model, described as “Generic mass of special structure with system typically noted with a design narrative for conceptual pricing.” It is likely that this level of BIM is already developed by an architect or engineer and given to a manufacturer or supplier as a starting point.
  • LOD 200 – This level calls for basic primary structural member sizing, generic representation of secondary framing, and general cladding and exterior trim to be provided, including openings.
  • LOD 300 – More-specific sizing of all needed primary frame structural members, web tapers, frame connections and similar details are called for at this level. Similarly, secondary framing needs to be shown, including purlins and bridging, girts, subframes and base conditions. Exterior panel and trim with actual profiles, actual openings and all significant trim and accessories are shown here.
  • LOD 350 – This level starts to show coordination with other elements or building systems. Therefore, for the primary structure, things like base plate locations, bracing/gussets, clips and any reinforcement all need to be included. Secondary framing elements need to include similar details, such as nested members, connections to primary structure, any miscellaneous or secondary steel members, bridging, etc. Cladding and exterior trim would include all actual profiles, closures, downspouts and all minor trims shows at least generically.
  • LOD 400 – This is the full-fabrication level equivalent to shop-drawing level of detail. As such it includes all final details, including welds, bolts, holes, cinching and all other details of fabrication and assembly for primary and secondary framing, plus all cladding and trim.
BIM
Level of Development (LOD) Specification Example – image courtesy of BIMForum.org

By using these standardized Levels of Development, all design and construction professionals can proceed in an orderly sequence to provide the appropriate information, receive coordination feedback and then move on accordingly to the next level.

The full 2016 LOD Specification can be downloaded for free at http://bimforum.org/log/. The specific information for Metal Building Systems can be found on pages 177–186. For information on how to work with a manufacturer to provide the appropriate BIM information, contact your local MBCI representative.

How Energy Codes Influence Metal Roof Panel Selection

On a very basic level, specifiers can look at a climate zone map and get an idea of the metal roof panel best suited to a specific geographic region. The issue, however, is actually much more complex. One must know that overlooking any detail could result, not only in less-than-ideal performance, but also in costly project fail, often related to the project not meeting required energy codes or other standards. With this in mind, an important initial question to consider is how to select metal roof panels that conform to new and fast-changing energy codes and their designated climate zones.

To begin making wise considerations, the architect must know what codes are in play. For instance, is it IECC or ASHRAE 90.1? Which year of the code/standard? Are there additional local code requirements? Even if a state adopts a particular energy code, it doesn’t necessarily mean that all jurisdictions will adopt the code at the same time. Along with this, some local jurisdictions may have their own or additional requirements. To be successful, it is imperative to know what the regional project goals and requirements are. This will require research prior to specifying the metal roof panel and its assembly.

Using IECC and ASHRAE 90.1 for Energy Code Compliance

Three of the basic metal building roof panel types are single-skin standing seam, screw-down and insulated metal panels (IMPs). When using the tables in IECC and ASHRAE 90.1 for metal building roofs it must be remembered that these tables are based on single-skin standing seam roof panels and purlins that are 5′ on center. The tables provide the required R-values and/or U-factors based on climate zones, along with other assembly requirements noted with each tables. In the Appendix of some versions of ASHRAE 90.1, there are allowances for modified roof assemblies, including screw-down metal roofs.

Energy Code
DOE-Developed Climate Zone Map

Often, in certain climate zones, the required R-values and U-factors may be so stringent that the logical first consideration is to use insulated metal panels. IMPs are a great choice for offering high insulation properties in a top-of-the-line product and the R-values and U-factors are readily available for use in compliance calculations.

Keep in mind when deviating from the prescribed assemblies in IECC and ASHRAE 90.1, calculations will be required to show compliance, along with modeling and/or the use of approved compliance software, such as COMcheck.

Making Informed Decisions

Selecting the right metal roof panel is an important step to achieving energy code compliance. Even though energy codes can be complex and are constantly evolving, by making informed metal roof panel selections you will add to the overall success of your project.

 

Top Five Tips:

  • Know your code. Find out what energy code is required for your project.
  • Know your zone. Requirements vary by climate zone. Identify your project’s climate zone.
  • Understand your options. Deviating from specified assemblies will require approved proof of compliance.
  • Choose wisely. Research the properties and assembly requirements of any metal roof panel. Use this information in conjunction with energy code requirements to make wise choices.
  • Call with questions. Call the manufacturer with questions before you get too far down the road.

Reroofing with Steep-slope Metal Panel Roof System Over an Existing Low-slope Roof: Part 2

Let’s continue the discussion about converting low-slope roofs to steep-slope metal roofs. Part 1 discussed attachment of framing, the new attic space, ventilation and condensation issues, and drainage.

Before After Retrofit

Reroofing Code Requirements 

Converting a rooftop is a specialized type of reroofing.  The codes specifically allow this via an exception that says “complete and separate roof systems, such as standing-seam metal roof panel systems, that are designed to transmit the roof loads directly to the building’s structural system and that do not rely on existing roofs and roof coverings for support, shall not require the removal of existing roof coverings.”

To meet this code requirement—and to not have to remove the existing roof system—the loads must bypass the existing roofing system. This is critical to create a load path from the new structure to the existing structure for dead loads, snow loads, rain loads, and uplift (e.g., wind) loads.

Structural Loads & Wind Resistance

IBC’s Chapter 16, Structural Design, includes all the required information and design methods to determine the dead, snow, wind, and rain loads acting on the building.  The new framing members and their connections, as well as the new metal panels and their attachments to the new framing, must be able to resist the loads acting on the building.  The resistance must exceed the loads.  Most often, wind resistance loads control the design.  Manufacturers and structural engineers should be consulted for material specifics and fastener requirements.

Fire Resistance

Fire resistance for a converted roof needs to meet the requirements of the model codes.  Check with manufacturers for fire classification of the system installed, and ensure it meets the minimum class (A, B, or C) required in the project location.  See the blog “Fire resistance of metal panel roof systems” for more information.

Insulation

For all types of reroofing, the most recent insulation requirements need to be met.  In most cases, additional insulation will be necessary.  Insulation can be placed at the attic floor (i.e., on top of the existing low-slope roof) or directly under the new metal panels.  Where the new roof meets the wall is very important for continuity of the overall building envelop insulation; lack of continuity is energy inefficient and may be a point of condensation.  The location of the new insulation needs to be coordinated with the ventilation plan and condensation potential should be considered. See Part I for more information.

While reroofing with metal can be an aesthetic improvement and solve leak issues, structural loads and wind resistance, fire resistance, and insulation requirements are necessary considerations when converting from a low-slope roof to a steep-slope metal panel roof system.  Don’t overlook the basic code requirements, or the need to deal with heat, air, and moisture issues of the new attic space.

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