Structural sprayfoam: Transforming building design for complex enclosures
By Rockford Boyer, B. Arch. Sc., MBSc, BSS, AND KEVIN Nagle, PMP, CTR
Based on the progression of modern building design and construction, it appears buildings will become more complex. To achieve success in enclosure performance, architects need to change the materials they use.
Many believe that sprayfoam insulation, also known as closed-cell sprayed polyurethane foam (ccSPF), is a new product in the construction industry. However, Otto Bayer invented it in the late 1930s, and it was one of the first recorded building insulations using sprayfoam in the mid-1950s. The main benefit of ccSPF, other than its high RSI value, is it inherently has product characteristics that can assist in controlling all four control layers (moisture, air, vapour, thermal) needed for a high-performing, resilient building enclosure.
Although ccSPF has been around for more than 80 years, the main building applications for sprayfoam were in exterior walls (above- and below-grade) or exterior ceilings/roof systems. Compared to board stock fibrous and foams with a membrane, sprayfoam was not traditionally used in below-grade applications under the concrete slab. Its application below a concrete slab separating a conditioned space from an unconditioned space would greatly enhance the potential for higher-performing sub-grade enclosures due to its inherent product qualities. While ccSPF can control all four control layers, an added benefit would be the monolithic application and its ability to receive structural loading without long-term product movement.
Advantages of structural foam for below-grade applications
Canadian sprayfoam manufacturers saw a need to create a structural foam below a slab to minimize failure in connecting to the building enclosure above and to minimize the potential of product creep over time.
Traditionally, extruded polystyrene (XPS) insulation, and sometimes mineral wool insulation, was used below grade. However, additional measures were needed to control the moisture, air and vapour drives. These additional measures could be achieved by supplementary membranes, or in the instance of XPS, the joints could be taped to ensure the continuity of the system.
With mineral wool use being very limited in this space, this article will focus on comparing XPS and ccSPF insulation in structural applications. These structural foam applications can be installed on horizontal (i.e. below slab, plaza deck, and civil applications) and vertical (i.e. blind side or positive side) foundation scenarios. Before discussing the material application, it is important to understand the difference between the two types of foamed plastics, XPS and ccSPF. XPS is a thermoplastic that is manufactured in a factory. In contrast, the ccSPF is a thermoset plastic typically foamed onsite. The main performance differences between the two types of insulation materials are discussed below.
In the eyes of the design community, foam plastics are perceived to have the “same” product qualities; however, this is not the case in practice. Two major performance quality differences in thermoset versus thermoplastic foams are structural performance at elevated temperatures and strength over time. Medium/high-density thermoset insulations, such as sprayfoam have a higher tolerance to elevated temperatures than thermoplastic insulations due to their chemical linking bonds. The thermoset insulation will inherently maintain its form, whereas the thermoplastic insulations (XPS/expanded polystyrene [EPS]) have the tendency to deform and warp at higher temperatures. This can be easily observed during lab fire testing scenarios—thermoset plastics will burn/char and maintain their shape, while the thermoplastics will melt, drip, and deform. This is why sprayfoam and XPS/EPS have different requirements for fire testing.
The Queen Central Residential Building
90 Queen St, Toronto
The Queen Central project is a notable addition to urban architecture. It features a 34-storey residential building with 369 units supported by a three-level underground garage. This development boasts a gross floor area (GFA) of approximately 29,270 m2 (315,060 sf).
A significant challenge in this project was preserving an adjoining 120-year-old brick and concrete party wall, which holds heritage status. The preservation required a positive side waterproofing application to protect the integrity of this historic structure.
Initially, the project specifications recommended conventional membrane solutions. However, these were deemed unsuitable due to the high risk of seams and punctures, which could lead to future failures. RDH, the consulting engineering firm, had recently completed extensive testing on a spray-applied, two-component polyurea waterproofing system and proposed this solution to the construction management firm due to its monolithic seal, high impact and abrasion resistance, and self-sealing properties when penetrated by fasteners.
These qualities made it ideal for attaching insulation boards to the above-grade party wall. The condition of the concrete below grade posed another challenge. Its brittle and decaying state meant no product could reliably adhere to the substrate, regardless of preparation. To address this, 51 mm (2 in.) of high-compression structural sprayfoam was used instead of the originally specified rigid board. This solution provided a more reliable and durable base for the below-grade portion of the party wall. The material compatibility offered additional benefits, eliminating the need for a primer on the below-grade concrete. This decision resulted in significant cost savings in labour, materials, and schedule time compared to the alternative of pouring a new wall.
Stickpins were affixed to the high-compression structural sprayfoam before the two-component polyurea waterproofing system was spray applied. This setup allowed the dimple board to adhere securely over the waterproofing system, providing additional protection and drainage as required by the project specifications.
The Queen Central project is a testament to innovative engineering solutions and meticulous preservation efforts, ensuring modern functionality and the protection of historical architecture.
Addressing the issue of creep in structural foam
On the other side of the spectrum, thermoset insulation consistently outperforms thermoplastic insulations in harsh cold climate scenarios as well. This is again due to their chemical composition and adhesive characteristics.
Structural foam under heavy loads must remain resilient over time and under certain operational conditions. When using foam plastic insulations such as extruded polystyrene (XPS) in structural applications, designers and engineers are particularly concerned about long-term “creep.” Creep refers to time-dependent deformation, especially under elevated temperatures and consistent stress. Over time, an insulation material can become “liquid” and change its shape due to constant loading, where the material can never achieve its original shape. In structural applications, this can lead to loss of thermal performance, but more drastically, complete structural failure.
Thermoset plastic insulations are not susceptible to creep, whereas thermoplastic insulations are prone to creep, especially when there are elevated temperatures. A recent data sheet review of structural thermoplastic foam insulations identified creep and its requirements.1 The requirement stated on the datasheet is that this thermoplastic insulation needed a 3:1 ratio of loading requirements to account for creep. This means that if the design is made to resist a creep of 138 kPa (20 psi), a thermoplastic insulation resistance of 413 kPa (60 psi) must be used. Thermoset insulations have a ratio of 1:1 when accommodating creep. CcSPF structural foams have resistance ratings of 275 kPa (40 psi) and up to 689 kPa (100 psi), which can accommodate most loads requiring thermal insulation.
The future of structural sprayfoam in construction
Structural foam insulation can be used in many applications on the construction site. Initially, many structural foams were designed for below-slab applications; however, other applications are being considered and utilized due to their ease of application and versatility. Applications such as structural pipe coverings, plaza deck insulation, and blindside applications were specified and installed.
In addition to the previously discussed creep issue, there are many benefits to using a thermoset plastic insulation such as ccSPF in these heavy load applications. Sprayfoam products create a monolithic continuous insulation (c.i.) that controls air, moisture, vapour, and thermal, which can be easily connected to the other control layers above. Where XPS or EPS insulation needs to be installed with a substrate with tolerances (i.e. compacted subgrade), ccSPF can be installed and formed onsite to accommodate deviations in the substrate. The monolithic application of the insulation can ensure the four control layers are maintained during the installation of rebar and concrete placement. Board stock insulation can easily be damaged and become incontiguous during concrete placement, especially when the concrete hose is dragged across the vulnerable insulation application. Plaza decks are a great application for ccSPF based on the site installation, where the thickness can be built up to provide specific grading to drains. Liquid-applied polyurea waterproofing can be applied directly to the top surface of the foam, creating a resilient and high-performing “roof type” system. Vertically, the structural foam has been used in blindside applications and positive side applications to resist the loading of specific soils and cast-in-place concretes. In these applications, liquid-applied waterproofing has also been installed to maintain a thermally insulated waterproofing system. These applications are common for thermoset plastic insulation; however, they can be used in any situation where thermal insulation is required. Contacting a local manufacturer for approval of unconventional applications of their product is always recommended. The versatility of these products opens the opportunity for new design ideas and techniques.
Environment is also an important consideration when selecting materials. Sprayfoam manufacturers continue to focus on sustainability and climate change in their product innovations, manufacturing practices, and applications. Structural foam is no different; some Canadian manufacturers have been able to eliminate synthetic blowing agents in their closed-cell foam to reduce their overall environmental impact. In 2021, Canada banned all high global warming potential (GWP) blowing agents, reducing the current GWP for blowing agents to one, significantly minimizing their environmental impact.
For application with structural foam, manufacturers have also been able to limit the need for fire retardants as applications are typically installed between soil and concrete, which will also reduce the impact on climate change. Depending on the density (i.e. psi 40, psi 60, and psi 100), the yield per set of foam is higher than any board stock structural insulation currently available. The ratio of truckloads is 4:1; every four trucks of XPS/EPS insulation is equivalent to one truck of ccSPF structural foam insulation. Reducing the number of materials in an assembly may reduce the overall carbon footprint of the assembly. Since ccSPF controls all four control layers, no additional membranes are needed for a resilient design. The application speed and duration of installation also have an impact on the building’s overall carbon footprint. Closed-cell foam has been proven to decrease project timelines, contributing to reducing the overall carbon footprint of a project.
Many manufacturers have conducted individual EPDs (environmental product declarations) for their products or systems. These EPDs account for how much energy is needed (equivalent carbon creation) for the extraction, manufacturing, transportation, use, and end-of-life of the product in question. Sometimes, industry organizations join as a consortium to complete an industry-wide EPD.
Conclusion
Following proper building science principles is key to achieving a successful design and installation in the field. Successful design starts on paper/computer and can be transferred to the site as intended. There is a big difference between thermoplastic insulation and thermoset insulation; using the right product for the application is key to its success. Eliminating the need to include a safety factor for creep is important, as overdesigning the system will impact cost and, more importantly, the environment. When comparing EPDs of various insulation products, the EPDs show a higher energy/carbon footprint for products with higher densities (i.e. 3.6 kg [8 lb] mineral wool insulation will be higher than 1.8 kg [4 lb] mineral wool insulation). The increase in energy/ carbon is due to more raw material added, heavier products for shipping, and more finished products needed due to a reduced RSI-value.
Temperature also drastically impacts the overall performance of foam plastics; eliminating foam plastics, which are susceptible to dimensional changes due to temperature, will potentially increase the durability of the enclosure throughout its life cycle. Sprayfoam has been around for more than 80 years; however, structural sprayfoam is a newer innovation that has gained traction in the construction industry over the past few years. Temperature also drastically impacts the overall performance of foam plastics; eliminating foam plastics susceptible to dimensional changes due to temperature will potentially increase the durability of the enclosure throughout its life cycle. Sprayfoam has been around for more than 80 years; however, structural spray foam is a newer innovation that has gained traction in the construction industry over the past few years. Structural sprayfoam manufacturing is similar to standard closed-cell sprayfoam with only small modifications to the recipe. These modifications include eliminating blowing agents, reducing the number of flame retardants—since the risk of fire between soil and concrete is very low—and adjusting the foam densities to accommodate various load requirements. The application of structural foam remains the same as standard sprayfoam using a plural component spray system.
The intent of structural foam was initially for horizontal applications; however, due to its versatility and ease of application, it is making its way into many other important applications. Always contact a manufacturer when a new design idea or application arises and to ensure the product is suitable.
Structural sprayfoam offers numerous advantages for below-grade applications regarding durability, resilience, and strength. This material’s versatility allows architects to integrate it effectively into their designs, creating buildings that are energy-efficient, long-lasting, and resistant to damage while contributing to a reduced carbon footprint. As the demand for sustainable and high-performance construction continues to grow, structural sprayfoam will undoubtedly play a pivotal role in shaping the future of architecture.
Notes
1 For more data on structural thermoplastic foam insulations identified creep and its requirements, visit fictiv.com/articles/thermoplastic-vs-thermoset -plastic-mechanical-properties-overview.
Authors
Rockford Boyer is an experienced building science leader at Elastochem with more than 20 years of expertise in sustainable building design. He holds an undergraduate degree in civil engineering and architecture and a master’s in building science. He is also a member of Passive House Canada and the Ontario Building Envelope Council (OBEC). Boyer is also a part-time professor at Sheridan College, teaching in the architectural technology program and sharing his knowledge and expertise with future generations of architects and designers.
Kevin Nagel, PMP, CTR, is Elastochem’s waterproofing technical sales representative. With more than a decade in construction, he specializes in building envelope enclosures. He holds certifications from the International Institute of Building Enclosure Consultants (IIBEC) and Construction Specifications Canada (CSC), and his academic background is in business administration and recreation facility management.
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