Volume 48, Issue 7- July 2013


New BIM Standard Could Give
Glaziers Precise Modeling Details

TA new standard for establishing the minimum requirements of building information models (BIMs) at different stages of design and construction currently is under review. The goal of the 2013 Level of Development (LOD) Specifications, under development by the Associated General Contractors’ (AGC) BIMForum, is to allow all participating parties, from architect to glazing contractors, to articulate clearly how complete model elements for the different building systems are, or need to be, throughout the design and construction process.

The specification uses the LOD definitions developed by the American Institute of Architects for the G202-2013 Building Information Modeling Protocol Form. The specifications will allow model authors to define on what their models can be relied and help other users to understand the value, and limitations, of models they receive, says Dmitri Alferieff, director of the BIMForum and director of virtual construction with AGC.

“Nobody benefits if everybody has a different idea about how much information should go into each element of a building model or for what uses those models are suitable,” Alferieff says. “These specifications will allow everyone using BIM to accurately define what will go into a model and prescribe its intended uses based on the completeness of its content.”

It’s a step in the right direction for glass professionals who want to see more complete BIM drawings.

“As with any information, be it BIM or 2-D drawings, the more detailed [it is], the better the response can be,” says Chuck Knickerbocker, curtainwall manager for Technical Glass Products in Snoqualmie, Wash. “We’d like to [someday] see the structure modeled to a point where anchors and embeds, when required to support the exterior skin, can be effectively modeled and also the surrounding substrate to which the windows and curtainwalls can be sealed. That often falls to the glazier’s scope of work.”

Not all glass professionals are sure that the industry is prepared to meet these detailed specifications.

“One challenge that we see is the specification’s modeling requirements that are beyond the capabilities of some software packages,” says Jon McFarland, BIM coordinator for Wheaton & Sprague Engineering Inc. in Stow, Ohio. “An example would be the requirements for modeling exterior operating windows (section B2020.10) to the 400 LOD (see box on page 34), which requires that ‘glazing sub-components (gaskets)’ and ‘attachment components’ are modeled in addition to the elements modeled in the lesser LODs. Many of the components of a window, especially gaskets and hardware, have features that are smaller than the minimum size that Revit can model. This causes the modeler either to omit the element, bring it in from another software package or model it inaccurately, none of which are optimum outcomes.”

Among other issues the document aims to address is the fact that, “during the design process, building systems and components progress from a vague conceptual idea to a precise description. In the past there has been no simple way to designate where a model element is along this path. The author knows, but others often don’t.” The new guidelines also are expected to help clarify whether a model shows a generic component or a precisely specified component; to let glazing contractors and other subcontractors know when measurement and other information has been finalized, rather than acting as a placeholder; and to let all parties know when missing information will be available in order to better facilitate planning.

Although the goal of easing the planning process is an admirable one, McFarland points out that challenges arise when project management teams require modeling of parts that could be accounted for in schedules. “We’ve seen BIM execution plans with curtainwalls specified at the 500 LOD and passages clarifying the requirements such as: ‘All elements of an assembly are to be modeled’ and ‘Each element must include finish information and a maintenance schedule.’ These requirements not only add time, cost and often unnecessary data to a project, they also can result in large and unwieldy files. In a curtainwall model, this would require that each gasket, boot, fastener, washer and line of sealant be included in the model,” McFarland says. He recalls working on a project where every extrusion component was modeled, resulting in a 90 MB file for each floor of the building. “We understand the goal of using the BIM model as a facility management tool, but requiring the maintenance schedule of objects that should not require maintenance, such as anti-buckling clips and setting blocks, should be reconsidered. Clips, gaskets, fasteners and other small elements can be attached to objects as attributes and accounted for in schedules. Finishes, especially when an object has more than one finish, are best addressed in shop drawings rather than the model. The LOD Specification does not address LOD 500.”

However, because this specification aims to move toward more precisely dictating scope of work, it may further reduce the questions about liability when something goes wrong on a BIM-coordinated project. Knickerbocker’s reading of the draft reference standard suggests that the new document might better protect glazing contractors from the liability of inaccurate architectural renderings by asking architects to address up front such questions as “if you didn’t want that window there, why was it there and how were we as subcontractors to know where it was supposed to go? If you didn’t locate it in the model correctly, and it’s installed where the model shows it, who’s going to pay to move it? The owner? The general contractor and glazing subcontractor aren’t. The architect? You bet there’s some liability,” Knickerbocker says.

He adds, “The battle’s going to be how much the architect or general contractor is contractually obligated to the owner to develop the model(s), to what LOD does the finished model need to be completed and who’s responsible for getting it there. That’s going to insert itself into the architects’ and general contractors’ contracts. More importantly, are the owners up to speed to direct this BIM process, or are they looking to the architect and general contractor to take that responsibility? What is the owner willing to pay for those services?”

McFarland says he’d like to see further elaboration on the responsibilities of the trades in cases where the trades cross requirements. By way of an example he cites Section B2070.10 on exterior louvers, which states that at the 300 LOD and above the “opening for louver is cut from host wall.”

“The contractor responsible for the louver usually is not in the same organization as the one responsible for building or modeling the wall. Who creates the void, dimensions the rough opening and addresses design changes?” McFarland asks. “The same questions exist with windows and embedded curtainwalls. When the architect wants to add a proximity card reader or handicap door opening button to a storefront mullion, is it the responsibility of the curtainwall engineer team to model this, the MEP contractor or the architect? All of these entities need to take part in the process.”

Knickerbocker expects the specification, if used, will mean that “the architects are being held to a greater standard to complete the ‘whole’ of a building.”

While this may prove challenging, it potentially solves many of the problems that exist with BIM projects currently.

“It’s evident that this is a significant step toward identifying the requirements for a BIM project,” McFarland says.

Once completed, the BIMForum will encourage design and construction professionals to use the document as a reference standard in BIM agreements and execution plans. —Megan Headley

Experts Offer Conservative but Constructive Outlook

Though experts predict the construction market may still have a ways to go before it reaches a full rebound, Kermit Baker, chief economist for the American Institute of Architects (AIA), Ken Simonson, chief economist for Associated General Contractors of America (AGC), and Bernard Markstein, chief economist for Reed Construction Data, shared positive perspectives during a webinar hosted by Reed Construction Data.

“We’re still seeing many markets across the country that are still digging out from this dramatic downturn that we saw in housing market conditions,” said Baker. “We’ve seen a lot of progress on the housing front but we’ve still got a long way to go … Housing prices plummeted from their high in early 2006 to what we thought was the trough in 2009 but they’ve really been bouncing around that since then.

”On the nonresidential construction side, Baker said the main issues affecting his outlook “are the market fundamentals—things like rent and vacancy rates. They’re generally healthy and moving in the right direction.”

However, Baker was conservative in his predictions, noting that the overall economy will play a role in the recovery.

“Until the broader economy gets better, [until] we see better job numbers … the construction outlook is likely to remain relatively muted by historical standards and there are still a lot of challenges for this industry as we move toward the recovery,” he said. Property values also are a factor.

“We’ve seen a downturn in activity in construction activity levels in the nonresidential building sector, almost as dramatic as it was for residential, but we’ve also seen a downturn in property values for commercial properties,” said Baker.“The commercial property downturn began about a year later than residential but the declines were every bit as dramatic as they were for homes. A big difference for this market is that while housing prices hit bottom or near bottom in 2009, and we’re just now starting to see some improvement in 2012, commercial property values hit bottom and immediately began to turn around and they’ve gained a good share—40 percent—of what they lost and are already trending upward at a healthy pace.”

Additionally, the commercial market didn’t have the excess inventory to work off that the residential market did when the downturn struck. “Without so much excess inventory to work off the recovery should come faster than it should in the residential sector,” said Baker.

Simonson noted he “see[s] somewhat of a mixed picture but clearly a positive picture for housing overall.”

“Single-family [housing] could flatten out by the end of the year,” he said. “There are a lot of markets where prices may start getting away from what people can afford to pay particularly with the tighter restrictions on who’s eligible for a mortgage.”

Simonson noted, however, that there are some less positive factors playing a role in the recovery as well, including a continued slowdown in government spending.

The [2009] stimulus legislation was adding a lot to federal spending and those [projects] wound up in 2011 by and large, and the same summer the president and the leadership in congress agreed to very tight caps on discretionary spending,” he said.

While he said sequestration has “been a slope and not a cliff,” Simonson said it has also meant a cut in federal construction spending.

“With this slope federal discretionary spending is expected to continue to decline for many more years,” he said, and many local governments are having to follow suit.

Still, Simonson remains somewhat positive, though, for 2013. “By the end of the year I think we’ll see growth in the nonresidential and private spending and in residential spending,” he said.
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