Pushing boundaries in residential construction
Covestro’s PUReWall™ takes wall panelisation for residential buildings to the next level. PUReWall™ panels are constructed in a panelisation facility with the insulation and weather-resistant barrier installed there too. As a result, a completed wall arrives at the construction site ready to be erected. This structural, high-efficiency wall assembly is made of insulation materials that function both as an air barrier and vapour retarder, providing long-term durability for years of comfortable living.
As a leading global manufacturer of polyurethane raw materials, Covestro has been developing and refining polyurethane formulations for the construction industry for decades. PUReWall™ takes this expertise and experience to the next level, while simultaneously tackling two of the pressing issues facing residential builders in many countries: the shortage of skilled labour and increasingly strict continuous insulation code requirements. Covestro’s development of a new, highly structural spray polyurethane foam (SPF) formulation allows for residential wall panel production using polyisocyanurate rigid foam board and SPF instead of traditional sheathing for the structure. The result is PUReWall™, a lighter, more energy-efficient and moistureresistant wall panel manufactured in a controlled environment and installed at the construction site with a minimum of effort and skill required. Studies by the US Structural Building Component Association (SBCA) show that panelised constructions can reduce the amount of time needed to erect walls at a building site by up to 75 per cent.
What is PUReWall™?
The innovative panelised wall design of PUReWall™ replaces traditional exterior sheathing with a combination of polyisocyanurate continuous insulation on the exterior and spray polyurethane foam (SPF) in the wall cavity, both of which are installed at a panelisation facility. PUReWall™ is not only a continuously insulated, highly energy-efficient wall; its new SPF formulation works in combination with the polyisocyanurate and wooden stud frame to create a structural wall panel. The SPF is applied in an environmentally controlled setting in the panelisation facility, which allows for repeatable, tight-tolerance construction. The continuous insulation, with taped joints, also functions as a weather-resistant barrier, whicheliminates the need for the plastic house wrap traditionally used as a moisture barrier. Moreover, as the thickness of the continuous insulation can be varied, PUReWall™ is suitable for use in any climate zone in the United States.
On the surface, PUReWall™ is simply a framed wall with continuous insulation sheathing and closed-cell SPF in the wall cavity. But the key is in the details and Covestro’s PUReWall™ technology actually addresses several key issues in the construction marketplace:
• Energy codes: The polyisocyanurate used as the continuous insulation exterior sheathing features a coated glass facer. This not only allows PUReWall™ to meet energy codes that require continuous insulation; the coated glass facer also acts as a weather-resistant barrier, which eliminates the need for a house wrap.
• Shear and racking strength: To ensure the structural integrity of this residential wall, Covestro brought the power of polyurethane science to bear with the innovative development of a new high-strength SPF insulation to bond and reinforce the PUReWall™ structure. Like all PUR systems, this SPF formulation has great adhesive properties, which brings several benefits. Besides the well-known highperformance insulation properties of polyurethane, this innovative SPF adheres extremely well to the wooden stud frame and the coated glass facer of the polyisocyanurate. In other words, the SPF acts as the glue that holds the wall assembly together, providing structural strength. Decisive proof of the strength of these panelised walls came when Hurricane Irma hit Jacksonville, Florida, and 100 mph winds did no damage to the walls of a home built with PUReWall™.
• Air and moisture resistance: In a traditionally constructed residential building a plastic house wrap is often used to provide an air and moisture barrier. This involves a separate on-site construction step, which adds time and labour to theconstruction schedule. Even a properly installed wall can suffer from moisture condensation within the wall assembly when the insulation is air-permeable, which may result in mould formation and structural rot. PUReWall™, in contrast, is constructed with air-impermeable insulation, an attribute shared by both the closed-cell SPF and the polyiso board. And as there is minimal risk of water condensation in the wall assembly, the risk of mould is minimised.
• Cost-effective and consistent production: Traditional building techniques require the use of skilled labour at the construction site, e.g. for stick framing. But such skilled labour is in increasingly short supply. To address this problem, the market is increasingly moving towards panelisation, where wall sections are efficiently built in a factory and simply erected on site. PUReWall™ is leveraging this trend by installing both the polyisocyanurate sheathing board and SPF in the panelisation facility. The outcome is a fully insulated, structural wall that is transported to the construction site ready for installation. This brings a number of benefits. First, set production processes mean each PUReWall™ panel meets the prescribed qualit requirements for the performance of the wall. And since the process is repeatable, there is only minimal margin for deviation between panels. Second, the economies of scale typical of any production process allow for standardised wallpanels and savings in production costs. Third, SBCA studies show that manufacturing wall panels in a factory produces up to 30 times less waste than constructing walls at the construction site and can also save up to a quarter of the wood otherwise used in the frame. Moreover, the SBCA figures show that two and a half componentbuilt homes can be constructed in the time it takes to stick-frame one house. Last but not least, builders and construction site operators do not suffer from the delays typically associated with on-site SPF application. As soon as the walls are installed, other trades can begin working on and around them.
Cost-effective and demonstrated code compliance in fire tests
Covestro, consultants and several US builders have analysed the cost proposition for PUReWall™ and come to the conclusion that there is a measurable perhouse cost-savings advantage over traditional wall assembly methods. This is primarily due to the efficient construction ofPUReWall™ units in a factory and lower carrying costs because the components are made up of fewer parts than a traditional wall assembly. Generally speaking, the typical cost of PUReWall™ per linear metre has been calculated to be comparable to or lower than a traditional panelised wall assembly.
With the fire safety of buildings increasingly in the public eye, the question of how safe PUReWall™ panels are in the event of fire is particularly important. The reassuring answer is that all PUReWall™ components are tested by the ASTM E84 flame spread test, and meet the requirements of building code.
Enhanced downstream technology
For Covestro, PUReWall™ represents a new direction. Whereas traditionally Covestro’s focus has been on innovativechemistries and manufacturinghigh-quality raw materials that allow its customers to produce some of the best-performing construction products in the industry, PUReWall™ is the result of an opportunity Covestro saw for improving downstream technology. Over the past five years, Covestro’s own experts developed, tested, tweaked and ultimately proved this PUReWall™ technology. Its recent commercialisation initially took place in the United States where most residential construction still relies on historical building techniques: stick-framing on site, traditional sheathing for structural strength, fibreglass insulation, and an exterior house wrap to create an air and moisture barrier. All in all, Covestro sees the PUReWall™ development as an effort to bring residential construction into the 21st century with a cost-effective solution powered by innovations in polyurethane chemistry.
Summarising, Covestro’s new PUReWall™ is an innovative approach to residential construction that embraces the panelised construction methodology, meets structural and flammability code requirements, satisfies or exceeds current energy codes, and reduces concerns about air and moisture management of the wall assembly. Through utilising a new CC SPF formulation in a wall system designed using sound building science principles, PUReWall™ highlights the best attributes of polyurethane chemistry to take the technology to a wider market and provide a polyurethane answer to the construction industry’s needs.
With 2016 sales of EUR 11.9 billion, Covestro is among the world’s largest polymer companies. Business activities are focused on the manufacture of hightech polymer materials and the development of innovative solutions for products used in many areas of daily life. The main segments served are the automotive, construction, wood processing and furniture, and electrical and electronics industries. Other sectors include sports and leisure, cosmetics, health and the chemical industry itself.