High-pressure laminate (HPL) is a proven and popular building product that has been used for both exterior and interior applications for decades. HPL panels have been tested for durability in the laboratory and on many buildings around the world, and they have been shown to perform exceptionally well. Equally appealing, the wide variety of product offerings gives architects great design flexibility and freedom to create exciting, award-worthy facades. When HPL panels are combined with a rainscreen attachment system, the resulting facade can contribute to high-performing, and sustainable buildings. In the field, installation is very straightforward using conventional tools and fastening materials. These traits have been evidenced in all types of buildings, including education, multifamily, mixed-use, transportation terminals, health care, and retail. All of these aspects of using HPL for rainscreen facades are investigated and discussed in more detail in this course.

Photo: JohnClemmer.net

High-pressure laminate (HPL) panels can be used as part of a ventilated rainscreen system on a wide range of building types to provide great design freedom and excellent performance.

HPL Facades Overview

Design decisions related to commercial building facades are usually based on a variety of factors. A common starting point is to blend the desired building form with the intentional locations of both opaque and glazed areas. From there, a series of other design decisions are made, particularly with the opaque areas related to color, texture, pattern, geometrical delineation, etc. The necessary technical decisions also need to be made to assure that the facade achieves all of the desired characteristics for code compliance and owner requirements, including water and air resistance, thermal performance, durability, low maintenance, and sustainability. Considering all of these multivariate demands, a rainscreen solution using HPL cladding has become a system of choice, described as follows.

Rainscreens

Rainscreen facades are defined as a system where the outermost cladding is separated from the underlying water-resistant barrier (WRB) by incorporating a specifically designed airspace in between. In this manner, the outermost cladding acts as the visible weathering surface. The WRB is then able to act as the protective water barrier (and air barrier too, in many cases), keeping the building free from water and/or air infiltration. A properly designed rainscreen system thus creates a ventilated space behind the cladding to allow for free drainage or removal of unwanted water from weather. In most cases, the airspace creates a naturally occurring convective airflow between the cladding and the WRB that is enhanced in taller buildings from stack pressure. This natural airflow allows for drying of the assembly, including the dissipation of any moisture that may develop from condensation. Thus, the ventilated airspace allows for drying of the total wall assembly and protects the underlying wall construction from potential water and/or humidity damage.

Image courtesy of Trespa North America Ltd.

A ventilated rainscreen facade incorporates an outer cladding material held out from the wall assembly with an aluminum support system. It also allows for continuous insulation and a water-resistant barrier (WRB) to be properly installed.

Ventilated rainscreens also have the benefit of using the cladding to protect walls from solar heat gain. The ventilated space allows airflow to disperse any temperature buildup on the cladding and in doing so helps to keep wall temperatures lower. Since the largest energy use in commercial buildings is typically for air-conditioning, a ventilated exterior wall can help provide a welcome reduction in the need for cooling. Accordingly, it can thus help directly reduce the use, cost, and environmental impact of air-conditioning in buildings.

Ventilated rainscreens can allow compliance with energy codes and best practices for sustainability that call for continuous insulation to be placed on the exterior of the structural components of a wall. By placing the insulation outside of the structure, it provides a means to overcome thermal bridging, which is a significant condition when insulation is only placed between wall studs or other structural members. The reduction of thermal bridging reduces energy fluctuations in buildings, making occupants more comfortable, and saves on energy costs. In ventilated rainscreen walls, the continuous insulation becomes part of the base for the WRB to be applied and provides a smooth, continuous surface for that installation.

HPL Cladding

Once the decision is made to use a rainscreen facade system on new construction or a renovation project, attention focuses on the type of visible cladding to be used. While there are many materials to select from, HPL panels have been used on many buildings with great success. Together, the coordinated HPL panels and support systems meet all of the basic criteria for a well-functioning rainscreen facade system.

The basic makeup of HPL as a material has been developed and refined over decades of production and use. It is manufactured by layering specifically engineered materials and fusing them together using heat and pressure. Common to all of them is a core of multiple layers of kraft paper that is impregnated with phenolic resins and fire-retardant chemicals and manufactured to various standard sizes. On top of this core, a decorative layer of impregnated kraft paper with pigmented polyurethane acrylic resin or a melamine layer is applied, either of which provides the finished look of the panel. A decorative layer can be applied to the back side of a panel or a comparable non-decorative layer can be provided. Either way, both sides of the material are balanced by the selection of surface layers over the core. Then, both sides receive a transparent polyurethane acrylic resin covering to protect the surface and provide other characteristics of longevity.

Image courtesy of Trespa North America Ltd.

HPL is made up of a core of multiple layers of resin-impregnated kraft paper, plus outer surface layers that are decorative or colored.

Once the panel layers are determined and assembled, they are laminated together using heat and pressure. The pressure is high, on the order of 10,000 psi (hence the term “high-pressure laminate”), with a moderate temperature of approximately 302 degrees Fahrenheit/150 degrees Celsius. Once pressed, the result is a dense, durable, homogenous product that can be manufactured in various sizes and shipped out for delivery.

The overall success of HPL as a building product is found in both the ease in which design options can be created and the superior performance that it provides. We will focus on these characteristics next.