Envelope

Sealing building envelopes in new condos

Tips for property sustainability
Wednesday, July 3, 2019
By Doug Kramer

An efficient building envelope is the Holy Grail for builders looking for energy efficiency and cost savings. This is especially true when constructing large-scale residential buildings, where the savings potential is even greater.

Creating an envelope in a residential tower where balconies, windows and exterior walls come together in multiple layers is challenging and increases the likelihood that thermal bridges will form. This can happen where insulation is interrupted, forming gaps. Typically, this occurs at connections between building components, such as at the junction between two walls or where a wall and floor meet.

Thermal bridges can also form wherever a building structure changes its composition, such as where a concrete balcony extends its floor slab through the building envelope. A thermal bridge not only creates a loss of heat, but it also causes the warm air inside the unit to cool down where it meets a cold surface. This could potentially result in condensation and other unwanted challenges.

The key to an efficient building envelope is continuous insulation (CI), and for decades, fibreglass batts were the material of choice. More recently, rigid polystyrene foam panels have been used to increase energy efficiency, but these must be joined and sealed together, increasing the likelihood of air gaps occurring. Foam panels also require builders to add other components such as a vapour barrier, which adds to construction time and costs. When spray foam (SPF) insulation came into the market, builders saw that it solved several problems at once.

Spray foam can be installed much faster than rigid foam boards, and since it expands to seal gaps and cracks, temperature fluctuations and drafts for occupants can be dramatically reduced or eliminated altogether. Not only is it an excellent insulator, but it also acts as an air and moisture barrier, which allows builders to use fewer products while saving time, since there are no joints to treat.

Even before energy codes required an individual air barrier material, CI in the form of SPF was already being implemented in construction. It drove the movement to remove other materials from the wall and rely on insulation to act as an all-in-one air, water and vapour barrier. Initially it was used on single-family homes, but developers and builders of multi-storey buildings are increasingly noticing its efficacy for use in larger projects.

SPF is sprayed onto the exterior sheathing (or masonry back up wall), adhering to the surface, and expanding outward to create the desired thickness. Spray foam will self-support and adhere to common construction materials, including itself.

The Royal Connaught, an iconic luxury hotel in Hamilton, Ont. that opened in 1916 and hosted celebrities, prime ministers and royalty for decades, was slated for conversion into a modern condominium development. As an architectural highlight of Hamilton’s downtown, the developers sought to retain as much as possible of the hotel’s brick exterior while rebuilding the interior and adding a modern tower to the project. Establishing an airtight building envelope was a central goal of the project.

Closed-cell SPF was chosen as the insulating material due to its high 7.1 per square inch R-value and air-sealing capabilities. It was applied to the building’s exterior walls, rooflines, shafts and soffits, the health club area and the parking garage.

The challenge in an older building is that each floor may be different; the key is to ensure consistent coverage with no breaks. In this case, SPF was applied between steel wall cavities against a variety of surfaces – precast concrete or brick, new masonry or glass sheathing and original surfaces of the historic structure.

Specialists ensured that, despite varying depths and surfaces, the integrity of the building envelope was maintained. In addition, the adhesion and structural rigidity of SPF solidifies and strengthens the entire wall system. Building studies conducted in 1992, 1996 and 2007 have shown that applying SPF to wall cavities can increase racking strength (such as resistance to horizontal forces like high winds) versus those without SPF. In addition, SPF is proficient at sound attenuation – a major consideration in multi-family dwellings.

The advancements in continuous insulation materials has helped engineers and manufacturers build a wall that’s better, stronger and greener. It provides several benefits to a building besides the elimination of thermal bridges. It increases the overall durability of the wall assembly and increases energy efficiency, which over time, can reduce the building’s energy bill. If also installed as an air barrier, it can reduce the risk of condensation and moisture infiltration.

Flat roofs can also benefit from the application of SPF as a seamless, stable and energy-efficient addition to the building envelope. SPF keeps heat out in the summer and in during the winter, lowering energy costs, while a silicone top coating resists UV light, protecting the foam and reducing heat absorption. SPF paired with silicone coatings, which in most cases, can be applied over existing roof substrates, can extend the life of an existing roof, increasing durability of roof systems and lowering life-cycle costs. Whether you are planning to retrofit an existing building or embarking on a new build, multi-purpose continuous insulation is key to establishing an effective building envelope, creating a quieter, stronger, energy efficient structure that will endure.

Doug Kramer is president of Icynene-Lapolla.

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