Sustainability as a team sport
A Seattle case study at the Station at Othello Park.By Greg Gilda, P.E., S.E., LEED AP, and Brent Robinson, P. E., S.E.
From a structural engineering perspective, the building was pretty conventional: five stories of wood framing over three stories of concrete. Due to the nature of this type of structure, LEED accreditation is often difficult to attain. Certified lumber, one of the contributors for LEED accreditation, is not cost-effective for framing on this size of project and there is only so much you can do with concrete to improve the sustainability (for example, increasing fly-ash content, using local materials, or using tested non-potable water). As a result, the project team had to find other ways to embody the notion of sustainability.
By the end of the design and construction process, not only did the team attain the LEED accreditation goals, but also saved the project construction time and money. Designing and delivering a sustainable project is not just about adhering to a point system but looking deeper for resources that can be used efficiently and in innovative ways.
At the first design meeting with the architect, contractor, and developer, it was clear that all team members were committed to being involved and working together from start to finish.
While the team discussed LEED goals, economic requirements were a priority. Working together, the team identified key areas that affected the project’s value either by reducing construction cost, reducing construction risk, reducing lifecycle cost, or increasing project value. Several opportunities for positive impact on these parameters as it relates to sustainability quickly emerged.
It is not uncommon for a project to be built strictly based on the original design or bid, likely because revisions often result in longer lead and approval times or increased construction costs. As a result, nobody wants to stir the pot with cost-saving suggestions. However, it didn’t take long to realize that the entire design/construction team on this project had a focus toward building the project with an eye for cost-savings. With the responsiveness of each individual, the roadblocks usually associated with design/construction revisions quickly dissipated and, as a result, the team effort paid off.
Reducing costs by cutting the cut
A project of this size and type typically consists of one to two concrete levels of below-grade parking, one concrete level of at-grade retail (possibly combined with parking, depending on the building footprint), and five stories of wood framed residential space. Due to the large footprint and the reduced parking requirements for the Station — located near the light rail station — it was not necessary to utilize the entire footprint for parking for the residential and retail areas.
The minimized parking area requirement provided an opportunity to reduce the footprint of the below-grade level, which provided significant savings in the costs for excavation and temporary soil shoring. The perimeter walls were pulled in at the lower level to create more distance between the wall and the property line, allowing the excavation to be slope-cut (see Figure 1 on page 18), thereby minimizing the shoring. In turn, this decreased the area of elevated slab and reduced costs. It also generated savings by reducing conflict issues with adjacent utilities and easement requirements from neighboring properties.
Pulling in the perimeter foundation walls created another challenge, related to supporting the large perimeter column loads. Without the foundation walls to help distribute loads, the perimeter column footings still needed to be founded between 10 and 15 feet below-grade in some areas in order to avoid surcharging the perimeter walls and footings.
The design and construction team considered bearing the perimeter column footings just below grade. Due to past construction on the site, the varied soil stratifications created a potential for differential settlement that was greater than what the team was comfortable with. Through a series of brainstorming sessions with the contractor and the geotechnical engineer, the team determined that a series of end-bearing caissons would be more cost effective than similarly acceptable options, such as a deep-founded continuous foundation. By utilizing caissons and piles at the building’s perimeter, bearing stayed in the same geologic stratum, without the cost of additional excavation.
Reducing finish repairs through innovation
One of the structural details often neglected on wood-framed projects is the detailing of “non-structural” walls. If the lowest level of the studs is not supported by foundation or slab (i.e., a crawlspace), this condition may not be an issue as the wall will simply link the floors together and provide load sharing throughout the building levels. However, if the lower level is supported by a slab, it doesn’t take too many calculations to realize that a wall built in the middle of a room will take approximately half of the load from the joists framing perpendicular to it, thus mandating an increased number of studs in the wall to support this load. While many design teams provide details to address the condition, many do not. When this situation arises, the issue is further exacerbated by the number of framers and contractors who fail to recognize the potential challenges associated with detailing a non-structural wall.
DCI Engineers’ approach to addressing this condition is that non-structural partition wood walls should remain “non-structural” and that the detailing required to ensure this should be provided. Failure to do so often leads to a number of issues, including ongoing cracks in wall and ceiling finishes and undesirable sound transmission. Not only does this create unsatisfactory serviceability conditions, but it also opens up the floodgates for potential lawsuits.
The traditional detail for these conditions uses proprietary hardware to provide a gap below the joists to allow the floor framing to deflect without loading the partition stud walls below. The detail works well when installed properly. If the hardware is nailed too tight or askew, the clips have a tendency to squeak. In addition, the detailing requires that the framing studs for non-structural walls need to be cut shorter than the bearing wall studs to create the necessary gap. The design team wanted to find a way to avoid similar problems with the Station project, which was the catalyst for the development of a new innovative piece of hardware that was used for the first time during construction of this structure.
On the Station, DCI Engineers and Exxel Pacific Contractors worked together to improve the non-structural wall detail, with particular attention to mitigating the “squeak risk” of the connection.
The new hardware — the “Deflector” — developed by Exxel Pacific’s Matt Stodola and distributed through Fastcap (http://www.fastcap.com/estore/pc/Deflector-4p12840.htm), is a sleeved screw that allows the joists to move vertically to create the gap. The deflector not only solved the sound issues for the Station, but also reduced construction waste by minimizing the need for different stud lengths by using a 1x top plate (see Figure 2). When used with a ceiling backing system, such as Stodola’s newly developed “F-Corner,” the deflector significantly minimizes cracks in the ceiling finishes as well. The result was a very effective and efficient installation, which translated into a reduction in cost and time spent on callbacks for things such as ceiling cracks and floor squeaks.
Paneling isn’t just for your basement
By far the largest non-renewable resource used in any construction project is time. Not only is there the time that goes into the initial construction of the project, but there is also a significant amount of time that is “at risk” due to quality and coordination issues that occur during construction. To mitigate this risk and minimize the on-site construction time, the team chose to use panelized walls, which use pre-fabricated wall panels that are prepared offsite in controlled conditions and delivered to the project site on an as-needed basis. While the process of producing and reviewing the shop drawings for panelized framing can be tedious, it does provide a great deal of risk mitigation as it requires the project team to coordinate all of the openings, framing members, shear wall nailing, and hold-down posts prior to installation.
Since the wall panels are constructed in a shop environment, most of the work is completed before the podium slab is ready for wall layout. This means that the panels can be delivered and be ready for installation as soon as the podium slab is cured enough to walk on. By using the panelized wall system, framing for the Station was completed two months ahead of schedule.
Not only do panelized wall systems save time, but they are environmentally friendly. The typical wood waste factor for a stick-built building is approximately 7 to 9 percent. With panelized walls, this is reduced to approximately 2 percent. This also results in a cleaner work environment with less waste lumber lying around. In addition, panelized walls are delivered to the site in approximately one week, whereas stick-built buildings require a constant flow of delivery trucks throughout the wood construction process. As an additional benefit, the overall vehicle travel time is reduced, hence lower emissions.
Getting the air out
One of the big contingency items carried for the wood framing for this type of project is the budget to address “risks” presented by the installation of the various trade work that needs to penetrate the wall and floor systems. For those who haven’t seen a lot of wood framing up close, just picture a typical mild-reinforced concrete slab and triple the number of reinforcing bars. Now imagine trying to get electrical conduit and mechanical ductwork through the structure after the concrete is cast — that is what the process is like for wood framing.
Even if the framing is constructed perfectly the first time, the framers are usually not done until the plumbers and electricians leave the site. These trades are often fighting with the framing in order to place their conduits and pipes in the proper locations. It’s very difficult to run a 3-inch diameter horizontal pipe through a 2×6 wall without a lot of careful coordination. By far the most challenging trade work is the installation of the vent ductwork. Even with building information modeling (BIM) programs that aid in the coordination of these trades, it is difficult to ensure that the ventilation systems will not interfere with the structural framing system. On the Station project, the design and construction team coordinated early to provide routing details for the major ductwork and plumbing in the building. This early effort resulted in very few significant framing repairs or redesigns during installation.
The Station at Othello Park was a unique project for us in numerous ways. Besides the motivating synergy of teamwork, the team also found new and resourceful ways to embody the core principles of sustainable design. Due to the nature of the structure, the team had to expand the normal definition of sustainability, and think beyond the typical list of requirements that go into such a project. By using a panelized wall system to save time and reduce waste, minimizing shoring, and reducing the need for post-construction repairs with the development of the innovative “deflector” screw, the team was able to further enhance the already sustainable nature of this transit-oriented development.
Greg Gilda, P.E., S.E., LEED AP, is a principal and Brent Robinson, P. E., S.E. is an associate principal at DCI Engineers in Seattle, Wash. Contact them at firstname.lastname@example.org; email@example.com.
The Station at Othello Park has many elements that are inherently desirable in a sustainable development — although this is not usually the type of building developed as such.