Your building envelope has one job, to keep the elements out. To accomplish this job, the envelope is composed of a system of components that collectively creates the physical barriers called walls, roofs, and floors. Together, these systems separate your structure from the outside and protect it from the elements.
One element that can wreak havoc on your building is water. That’s why it’s essential to make sure you’re choosing water-resistant materials for your building envelope. Waster-resistance includes everything from your choice of insulation to the selection of exterior finishes.
As you consider your options for insulating your building’s exterior, you may be wondering—is polyiso insulation water-resistant?
What is Polyiso Insulation?
Polyiso insulation is a rigid thermal insulation board that is available in multiple thicknesses and panel sizes. The insulating properties come from its closed-cell polyisocyanurate foam core. The foam is bonded to facers, on one or both sides, for protection and to add additional properties. The facers can be made of various materials to meet specific envelope goals.
Common polyiso facers include:
Aluminum Foil Facer (such as Rmax Thermasheath®)
Glass Reinforced Facer
Coated Glass Facer
OSB or Plywood
Is Polyiso Insulation Water-Resistant?
Depending on your facer selection, polyiso insulation can be water-resistant. The core (polyisocyanurate foam) itself does not absorb water—so if you pick the right facer, the polyiso insulation can be water-resistant. Aluminum-faced polyiso insulation has superior water-resistance properties, and passes ASTM testing with flying colors for water absorption and permeability of water vapor.
Foil-faced polyiso outperforms common polystyrene (EPS) insulations in the water-resistance categories with a water vapor rating of .03 perm and .3% water absorption. These values meet or even exceed those of XPS, a building material that is widely accepted as a water-resistant insulation.
How is Polyisocyanurate Made Water-Resistant?
It’s a common misconception that polyiso-based insulations cannot be used in damp applications. Since the core material (polyisocyanurate) is made of a thermoset plastic, its molecular structure is actually inherently water-resistant.
It’s the facer that determines whether the overall product is water-resistant. It’s true that paper-based (cellulosic fibers) facers are not waterproof, which means you’ll want to choose an aluminum facer for your polyiso in order to make the insulation product water-resistant for your application.
Foil facers help to shed water away from the insulating core so that the polyiso can function at full thermal capacity. Without any facer, polyiso can become more susceptible to damage, and compromise the material. Rmax Thermasheath® takes advantage of reinforced aluminum foil facers to ensure a water-resistant polyiso product.
Where Can You Use Polyiso Insulation?
Polyiso insulation is versatile. It can be used both above grade and below grade. That means it’s a great product for cavity walls, foundations, exterior walls, and roofs.
Above Grade Use of Polyiso
Polyiso provides high thermal insulating values per inch. This makes them ideal to use on your building’s envelope without taking up too much space. Using polyiso as your wall insulation can help you minimize your wall thicknesses and reduce material and installation costs. The thinner profile can also help reduce costs by allowing shorter screw lengths in roofing applications, and easier installation.
Foil-faced polyiso is an excellent solution for vertical wall applications since the facer assists with water shedding off of the wall system rather than soaking into it or through it. This is a requirement for cavity walls and other types of backup facades, such as behind rainscreen wall panels.
Below Grade Use of Polyiso Insulation
Since polyiso is water-resistant, it’s an ideal material to use in below grade applications, such as around foundations. Aluminum-faced polyiso can be applied directly against the soil, and its high compressive strengths also make it a suitable material to protect your building’s foundation.
How to Install Polyiso Insulation
Common methods used to install polyiso insulation panels include gluing, screwing, loose-laying, or backfilling. Gluing is common in roofing applications and requires compatibility between the adhesive and the facer. Screwing is common in wall installations and roofing. Loose-laying is acceptable for backfilling against water-resistant foundations or on roofs where the membrane is weighted down with ballast.
Why Choose Polyiso Insulation for Your Building?
Choosing polyiso insulation for your construction projects has many benefits. In addition to its water-resistant properties, numerous applications, and flexible installation methods, polyiso also:
Reduces the risk of condensation
Is easily installed in a continuous fashion
Increases usable building space (when used on the outside of the wall space)
Eliminates the freeze/thaw cycle from occurring directly against your foundation
Is readily available in North America
Is cost-effective
Provides high insulating R-value per inch
Choose Rmax Polyiso as Your Go-To Water-Resistant Polyiso Insulation
Figuring out which products to use on your project can be a daunting task. Luckily, some products can be used throughout different parts of your building’s envelope in order to simplify the construction process. Rmax provides water-resistant insulation solutions that work for multiple parts of your project.
Contact your Rmax representative today to find out which of our products will make your project run smoother while also staying within budget.