New York City is a hotbed for ICF construction with several dozen mid-rise projects completed in the past few years.
The focus of this article is why Curtis + Ginsberg Architects (C+GA), along with developers, have chosen to use ICF, what the pitfalls of ICF are, and how these can be overcome.
C+GA has designed nine ICF multi-family residential buildings in New York City, eight of which have been completed. Seven are ICF and plank construction; two have been metal joist construction. All have been affordable and/or mixed income housing with subsidies from the city, state, and/or federal government. The two most recent projects are also designed to meet Passive House standards.
The most important advantage of ICF in construction is that the system creates a very energy-efficient envelope—a typical ICF wall has a minimum R-value of 23 or more, double the standard construction—and as importantly, has a built-in air vapor barrier. The standard ICF form has approximately two and a half inches of insulation on each side, with the ability to add additional inserts at two-inch increments. An energy consultant providing blower door tests on ICF buildings has found them to be the tightest buildings they have ever tested. For Passive House construction, where creating an airtight building is essential to meeting standards, ICFs take care of the major air sealing, and the issue becomes the detail between the wall and the window and the ICF joints around
ICF construction’s design flexibility allows for a wide range of design styles. As a reinforced structural concrete wall, ICFs provide greater flexibility in the variation of openings than typical block bearing wall construction. These pages contain a few images of C+GA ICF buildings, which complement other projects highlighted throughout this magazine.
Architectural renderings of Third Ave. closely match actual construction photos of the project taken.
Another exciting aspect of ICF construction is that it does not have the same height limit restrictions as block and plank construction. A number of 20-story-plus ICF buildings have been completed in Canada. An advantage we have not yet been able to fully explore, is the ability to use plank construction in buildings over twelve or thirteen stories, which should result in cost savings.
ICF in construction reduces the number of trades that are on the site, and contractors indicate this as being a big advantage. When an ICF wall is complete, it includes insulation, air barrier, studs and is water tight. Once a temporary roof is put on the building and the exterior openings are sealed, the building is effectively weather tight and construction can proceed at a faster pace. ICFs are also a clean construction method, the cleanup work is less than with masonry construction.
C+GA’s first project with ICF required obtaining special permission from the Department of Buildings in New York City. In going through this process, we documented the qualities, particularly related to fire safety, of four ICF manufacturers. In giving approval, the Department required that the foam of the ICFs be removed in elevator shafts and stair halls to prevent the possibility of a fire burning the foam and creating smoke in the egress passages. At the time, nearly ten years ago, this meant that after the walls were constructed, the foam in these spaces needed to be scraped off. This proved to be a time-consuming process that then required finishing of the rough surfaces in the stair hall. Since then, we have been able to use one sided ICFs with traditional formwork on the other side, which can be easily stripped and removed, simplifying the process.
After the Grenfell Towers tragedy in London, fire safety of the ICF foam has become a concern that is receiving additional attention. Although I cannot address all the technical issues with this, besides noting that American requirements related to combustibility are more rigorous that British standards, we have practical examples of how ICFs react in a fire. One of our early ICF buildings was next door to two building that were destroyed in a gas explosion (for additional details, see the cover feature of the Sept 2015 issue of this magazine). The wall facing the buildings that exploded and burned was ICF with a stucco finish. As can be seen in the picture, the ICFs were charred by the adjacent fire but most of the foam did not burn. Water from fighting the adjacent fire caused the most damage in the building. Everyone was safely evacuated from the building and after repairs were able to move back in.
Regarding cost: a contractor we’ve worked with on seven ICF buildings analyzed the cost of ICFs vs. block construction, along with the additional labor and materials for insulation, air vapor barrier and cleanup, and found that ICFs were significantly less costly.
Finally, in New York we have many sites that have significant noise requirements due to their proximity to an elevated subway or highway, which often have rail and traffic noise. ICF construction creates a very high performing acoustical wall, significantly helping to deal with noise issues. ICF have a minimum OITC rating of 43, depending on the exterior and interior finishes.
If ICFs sound the like the best thing since sliced bread, why hasn’t their use in midrise residential construction grown exponentially? There are seemingly two reasons for this: lack of experienced contractors who know how to do the work and the time it takes to erect.
There are very few contractors in the New York market who have done ICF construction. However, this should not be a big issue since there are many concrete contractors who should have the necessary knowledge to build with ICFs. Over the last six years, construction has been on a tear in New York, to the point that many contractors have more work than they can handle. We have been seeing delays across many trades. It seems that the contractors who would naturally do ICF construction have not been interested because they have plenty of work so why learn something new? This means that there are few qualified installers, making the bidding for the ICF construction uncompetitive. We hope that over time this issue is resolved, since a smart contractor would expand their services to stay ahead in the
Until we reach that point, there are ways to mitigate this. On an ICF building we designed, one of the contractors paid to have the manufacturer’s representative on site for the first two floors of construction, providing onsite training to the workers in the proper way to assemble and pour ICF walls.
The second issue is that erection of an ICF wall onsite is a time-consuming process. A typical block and plank building has one floor being constructed per week, but with ICF construction, the experienced contractor is only able to erect a floor every other week. Because building a block wall can be done by many masons simultaneously, they go up quickly, while ICF walls require trained crews working sequentially. Building walls that are true and reinforced properly takes longer to assemble. At least two days are required after the pour before the plank can be dropped. If proper procedures are not followed, the wall can buckle or bulge, requiring remediation.
There is a solution to the issue of time for erection. Steve Bluestone, a developer and ICF proponent with whom we have completed multiple projects and Mike Cleary, an ICF builder/developer, have created a new business called ICF Panels, LLC. The company is prefabricating ICF walls off-site in a factory building, with reinforcing pre-installed. There are several advantages to this system. The work is done off-site in a controlled environment. The time to build a floor can be reduced to the same one week timeframe typical for block and plank. The first building in New York to be built utilizing this system is to be erected this fall. If it works as planned, it will push the use of ICF forward.
As this article represents, I am bullish about ICF construction being used for mid-rise residential construction not only in New York, but across the country. It is one of the simplest answers to lowering the carbon footprint of a building by creating a more energy-efficient envelope. This is not only a good method of construction for residential buildings, for the same reasons it is attractive for commercial and institutional buildings. The issues slowing the adoption of ICFs are surmountable and the advantages are real and significant.