Prefabrication, full 3D model sharing among all trades and bathroom pods built in a factory in Ohio are things that don’t happen on every project in Iowa. The Hawkeye State is one of only seven where design-build remains a limited option. Still, thanks to innovative delivery and some lessons learned from a similar project, Iowa is now ground zero for one of the most integrated hotel projects in the U.S., the $101-million, 330-room Hilton Des Moines Convention Center.

Officials in the state capital were tired of losing out on national and regional convention business to the likes of Omaha, Kansas City and St. Louis. With the Wells Fargo Arena completed in 2005, Des Moines had a downtown convention center event space and room for other events at nearby Veterans Memorial Auditorium, which was renovated in 2011. All that the city of 215,000 lacked was a convention center hotel to house the crowds that would fly into town.

The answer, in 2015, was a 330-room, 28-suite convention center hotel project. Planning and ownership involved a public-private partnership that made the Iowa-based Weitz Co. take substantial risk as both the general contractor and the developer. The Iowa Events Center Hotel Corp.—a nonprofit established by Polk County and Des Moines officials in partnership with lender Bankers Trust—entered into a lease-purchase agreement to buy the hotel after construction finishes this week, while Hilton Hotels & Resorts agreed early on to operate the hotel. Design architect DLR Group and architect of record RDG Planning & Design delivered a design that made its site the focal point of downtown Des Moines. If the project’s debt is paid in 30 years as planned, ownership will transfer to Polk County.

That meant Weitz took on extra risk and was responsible for the total capital cost of the project, all operating supply costs and Hilton’s training and marketing costs prior to opening. When IEC Hotel Corp. takes ownership next week, Weitz’s $101-million investment will be paid in full by income from the sale of municipal bonds.

Cleveland as Harbinger

A similar problem concerning conventions and major events plagued Cleveland before it hosted the Republican National Convention in 2016. Cleveland’s new convention center Hilton was delivered just in time for that event thanks to some innovative teamwork after rough weather chopped 57 days off its schedule.

As both developer and contractor, Weitz studied the delivery of the Cleveland Hilton and worked closely with Ellis Katz, director of Project Management Consultants, the owner’s representative on both projects, to design a lean delivery process that the Des Moines project could follow from Day 1.

“Every subcontractor had written into their contract that creating an exterior skin was part of their scope of work. They had to supply plumbing, electrical systems and everything that connected to it,” says Ben Bunge, project manager for Weitz. “We then virtually clashed all of those models with the design model. Once the models agreed, they were shipped out to fabrication.”

Model sharing was done via BIM 360, and cloud-based updates were provided by the architect to Weitz, mechanical contractor Waldinger and electrical contractor Baker Electric several times a day during design. Both Waldinger and Baker had fabrication shops in the Des Moines area, so the production of all piping, electrical conduit, junction boxes, server cabinets, cable trays and other systems was done entirely off site in a controlled environment. Levels of development, according to the BIM Forum specification, were used as design progressed to show the evolution of the design of every system. All geometry for installation was shared to onsite staff via Trimble Total Stations.

“We used bridging design-build to deliver both projects,” Katz says. “You have a design architect, Cooper Carry on Cleveland and DLR on this project, that led the design for the exterior and interior of the building and then there was a transfer of design to the architect of record, who was involved from the very beginning. That allowed us to work in a design-build fashion and allowed us to be incredibly efficient. In the case of Weitz, it was an even more unique deal because they took on the risk that they did and that allowed them to expedite the construction process to meet this tough schedule and tough budget.”

Prefabricated components included bathroom pods for all non-suite rooms, structure/exterior skin assemblies, all HVAC equipment and ducts, 80% of the plumbing including complete drain assemblies, PEX risers, solvent, domestic water risers and aquatherm polypropylene pipe, electrical room kits, all studs and drywall, and all pre-hardware doors.

A centralized layout using Trimble Total Stations allowed all rebar and sleeves to be placed correctly via Weitz’s construction model so there was 100% rebar modeling, sleeve modeling and 100% direct rebar fabrication accuracy. All concrete placements were made based on points from the 3D model.

“A project we worked on previously was the Iowa State University south end zone expansion,” Bunge says. “As the construction manager, we needed to make up eight weeks. We put up our hand and said ‘as construction manager, we will build the rebar model and when we’re done you can hand it off to whoever has the low bid and they can build it.’ We took what we learned there and did a similar thing with this project to prefabricate all of the rebar the same way.”

Bathroom Pod People

While this isn’t the first project to use bathroom pods, it is the first in Iowa and the first by Hilton. The 10-ft by 5-ft non-suite bathrooms for the hotel were built on an assembly line by PIVOTek in suburban Cincinnati. 

Bunge says that while the pods didn’t likely save any costs by being built off site, they did save installation time and construction costs, and gave city inspectors and other officials a much smoother process since all of them were alike.

“To get prefabrication going you need to have some repetitious things, it has to be something unique and challenging you can install quickly,” he says. “When they actually started prefabricating things, they took the model and created it 100%. All the hangers, ductwork and other things that can clutter up a site were included.”

From a lean perspective, prefabrication allowed Weitz to reduce waste on site by 15 tons and enabled small batch deliveries to arrive just in time so the site was less congested. Bunge and his team also instituted a “nothing hits the floor” plan that allowed everything from piping assemblies to large electrical equipment to be delivered as one unit so that debris never hit the floor from building electrical and mechanical systems on site.

Teams built physical model rooms with several different layout options in October 2016, while the steel structure of the hotel was still being built. Hilton’s head architect, head of engineering, housekeeping head and other officials analyzed the models from an efficiency and building operations standpoint. Meanwhile, Weitz, Waldinger, Baker and the other subcontractors looked at the models from a constructibility standpoint. When Levels 1 and 2 were completed in 2016, Weitz began roughing them in so Hilton’s staff could occupy the business areas of the building before construction of the actual hotel rooms even started on the higher levels.

3D Model as Hotel Advertisement

Weitz’s as-built construction model went to Hilton after it was finalized, and the company used the model as a virtual sales tool.

“What we’re trying to do is ultimately give the guest a great experience,” says Katz. “With technology today you can integrate things like electronic lock sets tied to thermostats to not only give the guests that great experience but help the property save some energy as well. This building method actually made those connections easier to accomplish.”