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Construction is underway on the Hilton Garden Inn, a 12-story high-rise on the University of Iowa campus. The team working on this 5110-m2 (55,000-sf) steel-framed hotel—including Cities Edge Architects and contractor Rushton Sheet Metal—has found a strong solution to the project’s variety of insulation-related challenges.
The Iowa City project required energy-efficient insulation to act as a barrier to three elements: thermal, air, and moisture. Using insulation for the latter two functions allowed for savings on materials and labor, but posed a challenge—the team had to ensure the building’s insulation and taping was seamless if it was to properly function.
A continuous insulation (ci) solution was selected to overcome this—one that both fits the requirements of the project and is readily available near the jobsite. The high RSI/R-value, durability, and water resistance of this material—composed of Class A fire-rated, closed-cell polyisocyanurate (polyiso) rigid foam core—allow it to provide the energy efficiency and high performance being sought by the team.
The insulation has foil facer on both sides, with an embossed white acrylic-coated aluminum variety on the front and a reflective variety on the back. It is available in a variety of thicknesses and RSI/R-values, and its ability to serve multiple purposes, eliminating extra steps, helps users save both in labor costs and in up-front expenses.
For the majority of the Hilton Garden Inn, 63-mm (2 ½-in.) thick insulation with an RSI of 2.82 (R 16) was used. The remainder of the hotel was insulated using a 76-mm (3-in.) thick variety with an RSI of 3.47 (R 19.7). Polyiso was installed on the exterior of the studs and gypsum board.
Apart from cost and labor savings, what made this an effective solution? Continuous insulation is required by codes and standards such as the International Energy Conservation Code (IECC) and American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) 90.1-2010, Energy Standard for Buildings Except Low-rise Buildings. The building concept saves energy, forming an uninterrupted thermal barrier over the entire wall (while most insulation only forms a barrier in wall cavities between studs). To be considered ‘ci,’ an insulation solution must continue across all structural members with no thermal bridges but fasteners and service openings.
This could only be achieved with correct installation, sealing, and securing of the insulation. To ensure this could be done, the insulation manufacturer provided mockup wall training in which the architect and contractor participated. The training involved the complete building of a small section of wall, wherein attendees added insulation, caulks, sealants, attachment systems, and cladding to garner clearer understanding of how the system works and how to eliminate seam leaks.
The Hilton Garden Inn is set to open in the summer of 2017.
I’m sure somebody thought of this, but given the near perfect vapor barrier on the outside of the wall, is there any threat of condensation on the inside face of the insulation? Hard to tell without seeing a wall section and doing the math.
Greg,
As long as the wall system does not have another vapor barrier located somewhere on the interior side of the wall, then any moisture that may find its way into the interior stud cavity (between interior gyp board and exterior gyp sheathing) should be able to dry to the interior through vapor diffusion. The wall system is more than likely interior gyp board, metal studs w/ no cavity batt, exterior gyp sheathing and taped and flashed polyiso acting as the thermal layer and the air and moisture barrier. As you mentioned, the polyiso is also a vapor barrier whether intended or not
If the building’s energy maintains the gyp sheathing’s interior face at near 60 degrees during the winter, this means it is likely that the entire gyp sheathing material will stay above the dew point during the coldest days in Cedar Rapids, IA. If the architect specified the correct amount of insulation (thickness/ total R-value) for the coldest design temperature in Cedar Rapids, then there would be no risk of condensation anywhere behind the insulation.
In fact, the most attractive condensing surface will more than likely be the foil face of the polyiso just behind the cladding. You see, the right amount of exterior insulation for the climate zone all but eliminates the risk of condensation from assembly materials that are either at or below the dew point. As opposed to a vapor concern, bulk water and air infiltration over time is more of a concern with any system that relies on taped joints as the primary defense. The good news is the exterior insulation will keep all the materials sufficiently warm so they will dry faster in the chance a wetting event does occur through failure or design flaw.
So I don’t see any concern with condensation risk on the inward foil facer of the polyiso as long as the insulation thickness is correctly chosen. With the correct amount of insulation, the inward foil facer should be close to 50 degrees during the winter months. John Straube’s book “High Performance Enclosures” has a section and table on how to some very basic calcs to understand the condensation risk of any wall and it also accounts for interior humidity levels. There would be much more condensation risk if this wall also used interior insulation(a hybrid approach) and the ratio between interior and exterior insulation were not well thought through.
Can someone post the wall section with call outs that we can review the system.