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model. In the month of May, you have anywhere from 200 to 400 Lod in the model. this is where the power of the dsM is so compelling. By leveraging the dsM, you can control the acceleration of model content and manage the job more efficiently. now you know when information is required at Lod 400 and when information can remain at Lod 200. You can also streamline coordination during design by prioritizing the building components and MeP systems efficiently (we’ll discuss this topic more in chapter 5, “BIM and construction”).
Lastly, with organizational knowledge, your team can accurately budget for the project.
300 400
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300 Site Package
Structural Package
Conceptual Schematic Design Design Development Construction Documents
Core and Shell Package Interior Package 300
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Figure 4.16 LOD schedule
the first step to solving the incremental dilemma is understanding the “what”
and assigning the dependencies to determine the “when.” this allows you to strategically plan the design as opposed to chasing it with BIM. once all the elements are identified and prioritized, you can use a software program like Pull Plan (www.pullplan.com) to schedule from the construction milestones. this will help you determine the durations required for each iteration to meet the demands of the fast-track schedule.
The design manager needs to be crystal clear about the level of detail needed for each design submittal. For example, the detail needed for early permits may be less than that required for bid packages for equipment and subcontractors, or for the final construction documents.
charles Pankow Foundation, Design Management Guide for the Design-Build Environment, Version 1.0
Constructability Review
Constructability review, means and methods, and project construction feasibility all refer to the evaluation of whether the design can actually be built by a construction team and how it will be done. aligning to the promise of BIM, the purpose of models in the constructability review phase is to simulate and analyze the actual construction issues while they’re cheap. It would be a disservice to assume that every job will use
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one of the Integrated Project delivery methods, prioritize design information with a dsM, schedule with pull-planning, and model all trade content to Lod 400 in a live
“real-time” consolidated or federated model. this is achievable, but it’s not our current state, as seen in the 2014 SmartMarket Report (Figure 4.17).
McGraw Hill conStruction’S, Smartmarket report, 2014, “tHe BuSineSS valueof BiM forconStructionin Major GloBal MarketS: How contractorS aroundtHe world are drivinGinnovation witH BuildinG inforMation ModelinG”
Figure 4.17 BIM use according to the SmartMarket Report
constructability review during design is all about the ability to see “beyond the clash,” meaning not everything is solved with a click of a button. as we discussed in chapter 2, design models typically show design intent and do not carry the level of development during the dd or cd phase that would be required for construction installation or fabrication. until BIM authoring software creates Lod 400 out of the box, there will always be an evolution of detail contained within the model elements during design. another reason for this is due to efficiency and speed. architects and engineers like to keep their models on a diet during the design process. More information equals a heavier and slower model to manipulate in the authoring
software. this will be less of an issue as computers get faster and we increasingly move toward cloud computing, but it’s important to note. these two factors further reinforce the fact that in order to achieve the ideal MacLeamy curve of cost savings, you will need to have an in-depth knowledge of construction installation and use a hybrid approach of 2d and 3d analysis in order to see “beyond the clash.”
Leverage the Plans
It’s amazing how the model has hypnotized experienced architects, engineers, contractors, and subcontractors. the transition to clash detection for constructability
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review since 2007 has been radical, with tools like navisworks and tekla BIMsight emerging. at first, people said, “You can’t rely on the model. It won’t be built like that.”
now they say, “How can I coordinate if it’s not in the model? It has to be in the model!”
People have become so dependent on the model content that they have started neglecting the drawings. they will spend hours reviewing 3d models instead of spending 15 minutes reviewing plans. I’ll give you an example from construction 101: door framing and ductwork. Figure 4.18 shows typical framing around a door. there are two king studs that go from floor to floor and a header across the top. these studs are referred to as “critical studs” because they have to be in that exact location to support the doorframe. they take priority over MeP systems, but MeP engineers are notorious for routing duct or system racks directly over these “critical studs” during design.
Figure 4.18 Door frame detail
ST404 TYP
TYP TYP 1B
ST403
TOP OF SLAB/DECK BOTTOM OF DECK
CEILING LINE
ST403 6
6A ST4036A
ST404 BUILT-UP OR PRO-X HEADER PER 1/ST404 (TYP)
BUILT-UP OR HDS JAMB STUD PER 6/S4-8.03 (TYP)
1A
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the majority of architects do not model framing, so how do you identify a clash between something like ductwork with an element that doesn’t exist? Well, you can’t, but because of the hypnotizing effect of BIM, some may spend hours searching the 3d view of the model trying to find these conditions. What seems like a logical solution is to bring the framing subcontractor in early to model studs during the design. often what ends up happening is the framing subcontractor tries to catch the butterfly, because the design program is still evolving, which results in muda. even if clash detection were leveraged in this scenario, it would still take a considerable amount of time to look at each condition one by one. now look at Figure 4.19 and Figure 4.20.
Figure 4.19 Mechanical plans before markup
ScrippS HealtH
Looking at the plans makes it much easier to identify potential issues with critical studs, which saves you a significant amount of time in design review and detailing. the plan views are produced from the model; therefore, they represent what is to be built. If it’s a problem in the plans, it’s going to be a problem in construction.
once you’ve identified the issues, you can talk through the solution with the mechanical engineer and the framing subcontractor to resolve them efficiently. this method may not require modeling every stud; it may simply require a construction mind-set and early collaboration. It’s essentially going back to a light table review, and as professed in the Toyota Way, often the best option is a simple solution. the same process can be used for plumbing racks, electrical racks, and electrical fixtures.
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clash detection is an incredible tool, but common sense and readily available information can save significant time and allow team members to reach their
coordination goal faster. In this sense, a balance between plan and 3d views are often the most viable option.
Leverage the Details
In chapter 2 you read about the new project engineer who was surprised by the structural kickers in the field. the kicker was annotated in the drawings but wasn’t in the model, which forced the ceilings to be lowered. that’s a tough lesson to learn and you never want to disappoint a client, but that issue pales in comparison to the disappointment a client will have if you overlook water infiltration or fire-life safety. those two items can be very hard to identify using clash detection software, but they are critical to the design and performance of a building. In this section, we will focus on water infiltration.
the national roofing contractors association (nrca), founded in 1886, “is one of the construction industry’s most respected trade associations and the voice of roofing professionals and leading authority in the roofing industry for information, education, technology and advocacy.” (http://www.nrca.net/About/) The NRCA Roofing Manual: Membrane Roof Systems—2011 lists common details that are industry standards for constructing a roof and are typically referenced in design documents and roofing manufacturers’ submittals. Figure 4.21 shows the minimum horizontal distance of separation between elements for waterproofing.
Figure 4.20 Mechanical plans after markup
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Figure 4.22 shows the minimum vertical distance that must be achieved for waterproofing.
Figure 4.21 Guide for clearances between pipes, walls, and curbs
reprintedByperMiSSionoftHe national roofinG contractorS aSSociation
12″
2′–0″
CLEARANCE MINIMUM
MINIMUM
12″ CLEARANCE
MINIMUM 12″
CLEARANCE MINIMUM 12″
CLEAR MINIMUMANCE
reprintedByperMiSSionoftHe national roofinG contractorS aSSociation
8″ MINIMUM FLASHING HEIGHT
2 × 6 MIN. WOOD NAILER ATTACHED TO SUBSTRATE–
OVERALL THICKNESS TO MATCH INSULATION
SEALING MATERIAL
SHEET-METAL RECEIVER WITH REMOVABLE COUNTERFLASHING FASTENERS APPROX.
8″ O.C.–MIN. TWO FASTENERS PER SIDE
APPROX. 4
″
OPTIONAL: EXTENDED FIELD PLIES ABOVE TOP OF CANT
MOP- OR COLD-APPLIED MEMBRANE FLASHING SHEET ADHERED TO BACKER
BACKER WOOD CURB ROOFTOP EQUIPMENT FRAME
GASKETED FASTENERS–
MIN. TWO FASTENERS PER SIDE
CANT
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once you’ve reviewed both Figures 4.21 and 4.22, examine Figure 4.23 out of a model at 50% dd to see if you can apply those best practices. How many areas are at a high risk for water infiltration?
Figure 4.23 Roof image
ScrippS HealtH
Before we discuss how many areas might lead to water infiltration, let’s first look at how many conflicts appear in the model. You’ll have to look pretty hard to see one. What you’ll notice is that none of the elements in Figure 4.23 are clashing. If you ran clash detection on the duct versus the fire standpipe, you wouldn’t have a conflict.
they’re close, but they’re not clashing. now let’s compare that to the number of detail issues (Figure 4.24).
I counted five, but you probably noticed others. Let’s take a look at the ones I identified. (refer to Figure 4.25 for the following list.)
Item 1 the minimum distance from a curb to a wall should be 24″. the duct is only 8″ off the wall and the curb hasn’t been modeled. the curb is at least 2″
larger than the duct, as shown in Figure 4.22. If the curb had a cant (triangular shaped block at the bottom of the curb), the distance off the wall could be as little as 0–2″, because you would measure from the bottom of the cant, as shown in Figure 4.21.
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Figure 4.24 Roof image with detail issues
ScrippS HealtH
Item 2 the minimum distance the pipe should be penetrating next to a curb is 12″.
the fire standpipe is only 10″ away, and again the curb and cant aren’t modeled. If they were modeled, the pipe would be anywhere from 2″ to 4″ away from the curb.
Item 3 this is a tricky one, so you get bonus points if you found it. the doorsill is too low for the 8″ inches of overlap required for waterproofing at a vertical face. However, that’s only one piece of the issue. take a look at Figure 4.25, which shows the closest drain to the door.
If the roof doesn’t have a natural slope, built-up roofing (commonly referred to as a cricket) will be necessary to create a slope to the drain. the drain is approximately 37′ away from the door. at a minimum slope of 1/8″ per foot, there would have to be around 4–5″ inches of built-up roofing at the door before the 8″ of overlap.
Item 4 Four is the “daily double,” because it wasn’t shown in Figure 4.21 or Figure 4.22.
the railing system and ladder are both penetrating the flashing that would be required at the edge of the roof. this is another high-risk area for water infiltration that would need to be reviewed with the design team.
Item 5 the pipes that you are seeing are known as davits. they are used to support the window-washing system. the davits are only 6″ off the parapet wall. they would need to move off the wall another 6″ or more depending on the cant.
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In the sidebar “the devil’s in the details,” we’ll look at the potential impact of item 1 on the design process.
Figure 4.25 Roof drain distance
ScrippS HealtH