Keeping it Simple, Keeping it Right


Designing the Building Envelope

Think of a building envelope as protecting the product within. Therefore, it must insulate efficiently and control vapor flow while providing a durable interior and exterior finish. Two common building envelope systems are discussed below.

Insulated Metal (IMP) Panels. As defined by the Metal Construction Association (MCA), Insulated metal panels (IMPs) are “lightweight, composite exterior wall and roof panels with metal skins and an insulating foam core.” IMPs offer several advantages in their use in food processing facilities.

Installation. IMP wall panels can be quickly installed in all weather conditions and perform effectively in all seismic zones. Metal panels have a “tongue and groove” joint edge configuration. A nearly impervious vapor barrier is produced by placing continuous sealant in the joints on the “warm” side of the panels during installation. Vapor barrier transitions will also need to be installed along the top, bottom, and vertically in room corners, sealing the wall panels to floor vapor barriers and the skin of the ceiling panels.

Energy efficiency. IMP walls provide superior thermal insulation capabilities and can maintain interior climate control in any weather conditions.

Key considerations in selecting an insulated panel for energy efficiency should include:

The thickness of insulation.

The type of insulation.

Prefabricated panels have a laminated or foam-insulated core, both offering excellent “R” values. For example, two-inch-thick polyurethane core panels will have an R-value of 17.5, three-inch-thick panels a value of R-26.2, and four-inch-thick insulated panels a value of R-35. Insulation thickness choices should be a function of both internal processing and/or storage temperatures and external conditions year-round.

Sanitation. IMP walls provide a sanitary finish that can easily be washed down. Some finishes will withstand harsh chemical cleaning. The facing of IMP can be stainless steel, factory paint galvanized steel, or painted aluminum. Stainless and galvanized steel are the two types of panels most often utilized in process areas. Of those two, stainless steel provides the best long-term value in terms of durability and sanitation, but it is also the most expensive of the various types available to both fabricate and install.

Sustainable. IMP walls include a minimum of 30 percent recycled steel content, making them 100 percent recyclable and reusable, contributing to LEED credits and Net-Zero Energy targets.

Aesthetics. Aside from their thermal performance capabilities, IMP walls have the versatility to achieve countless aesthetics for walls and roofs. The two wall steel faces profiles range from a flat, smooth profile to a deeply corrugated rib, increasing aesthetic opportunities, as well as the option for horizontal or vertical application. Also, the two facing sides can be of different materials. For example, the interior face can be stainless steel, and the exterior can be painted galvanized steel.

The galvanized steel face has a factory-applied paint finish that comes in multilayered coil coat systems formulated to withstand various aggressive environments. Specifically, these specially formulated paint finishes act not only as an excellent barrier against corrosive or extreme weather conditions but will enhance resistance to surface chalk and fade.

Precast Concrete. An alternative to IMP is insulated pre-cast or cast-in-place (on-site) concrete panels, whose primary attribute is long-term durability. In this application, panel joint sealing is critical, especially in refrigerated areas. A plastic sheet vapor barrier may be used at the insulation core between the interior and exterior widths of pre-cast joints.  In Ready to Eat (RTE) areas, it is advisable to coat the potential food contact side with an impervious coating to aid in cleaning and minimize microbial growth possibilities.

Roofing. Roofing is a critical area in food and beverage plant construction. There are several options for roofing systems for these facilities, the basic types being:

Single-ply membrane systems (fully adhered, mechanically attached, and ballasted)

Built-up membrane systems

Modified bitumen membrane systems.

Fully adhered single-ply systems are desirable because leaks are more readily detected and repaired, and there is no thermal transfer associated with metal fasteners.

Single-Ply Synthetic Membranes. First widely utilized in the 1970s, single-ply synthetic membranes are easy to install and of relatively low cost. Today, PVCs (polyvinyl chloride), TPOs (thermoplastic olefin), CSPEs (Hypalon), and PIBs (polyisobutylene) are also available as membrane material. Hypalon is extremely chemical resistant once they have reached a cured state.

Built-Up Membrane Systems & Modified Bitumen Roofing Membranes. While occasionally used in food facilities, these types of roofs, which are “hot applied” using asphalt, often have organic issues related to their installation and are labor-intensive and thus not very cost-effective.

Some of the main issues to consider in a roofing system for a food-processing facility are:

Durability. Process plant roofs usually have large amounts of equipment that require servicing on a regular basis. The roofing must be able to withstand both constant traffic and the potentially degrading properties of equipment lubricants, chemicals, and exhausts from production areas.

Weather Tightness. The roofing membrane system must be weather-tight and have a long-term lifespan for facility protection.

Vapor Barrier. Manufacturing buildings and food processing plants need to have a good vapor barrier on both the outside and inside of the building. The roofing system used must be able to provide for such diverse conditions as high heat and moisture levels in processing areas, as well as thermal properties for refrigerated areas.

Heat Retardance. Roof insulation R-value is a critical aspect in the retardance of heat flow in and out of the facility.

Maintenance and Repair. As equipment and processes will change over time, the selected roofing system must be able to change with it efficiently.

Sanitation and Aesthetics. Roof membrane systems should be light-colored and free of surface stone or other ballast to allow moisture, vegetation, and other organisms to establish a foothold.

This is an ongoing series designed to cover the basics of food plant design. Join us next month when we cover FDA guidelines. Learn more about Austin’s food and beverage experience here.


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