As the number of metal door manufacturers grew, so did the need for standards for the use of metal doors in buildings. The Chicago-based National Association of Architectural Metal Manufacturers (NAAMM) established in 1938, with roots reaching back to 1907, emerged as a preeminent organization representing members engaged in metal manufacturing. In 1969, they created a separate division known as the Hollow Metal Manufacturers Association (HMMA) which is today its largest division. HMMA is a voluntary, non-profit business association comprised of more than 60 member companies throughout North America that manufacture hollow metal doors and frames. In addition, the Steel Door Institute (SDI) was established in 1954 as a voluntary, unincorporated, non-profit business association whose mission is to promote the use of steel doors and frames in the construction industry. Representatives of SDI member companies create and publish manufacturing, quality, and performance standards and distribute them to licensed architects and construction specifiers at no charge.

With this history and level of development, hollow metal doors are fairly predictable in their types, styles, and elements of their systems. The door panel itself is actually less “hollow” today and typically incorporates an internal framework, reinforcements for hardware, and a core material beneath steel skins on each side. The core material used can vary based on desired door performance criteria and can include honeycomb cardboard spacers, urethane or polystyrene insulating cores, gypsum for fire doors, and even wood. The steel door skins are attached to the internal core and framework, and are most commonly joined together around the perimeter of the door panel creating a visible lock seam. In cases where the aesthetics of that seam are undesirable, it is filled, ground, or welded to cover it.

Similarly, metal door frames have evolved to be fairly simplified and predictable. They are usually manufactured by the same companies that manufacture the doors and are intended as a matched set. There are a variety of profiles possible to accommodate a wide range of wall thicknesses and design conditions in both rigid, welded frames and “knock-down” frames that assemble on site. These have become fairly standard and relatively easy to incorporate into many building projects.

Based on the aforementioned, hollow metal doors can be evaluated for use in buildings with the following common pros and cons:

 

Acknowledging these pros and cons of metal doors helps to determine when it is appropriate to use them and when it may not be.

Fiberglass Doors and Frames

Unlike metal, fiberglass is a newer, although well-proven material for doors. The first fiberglass doors were manufactured nearly 40 years ago in 1975—almost 100 years after the first hollow metal door. Initially they were developed for the petrochemical industry where the focus was chemical resistance to replace hollow metal doors in highly corrosive environments. The metal doors were not holding up in these locations and an alternative was needed.

Although its history may be shorter, there are indeed organizations and standards that have been developed for them as well. The American Architectural Manufacturers Association (AAMA) has been in existence since 1936 with a goal to develop standard test methods and performance specifications for the fenestration industry in order to protect customers by providing them a basis for an “apples to apples” product comparison. As a material-neutral organization, AAMA brings together window, door, skylight, curtain wall and storefront manufacturers, suppliers, and test labs to represent individual and shared concerns. Their membership is comprised of large and small companies that are both residentially and commercially focused. They have created a Fiberglass Material Council as well as a Door Council, both of which provide relevant information and standards for fiberglass doors. They point out that since fiberglass doors are often mechanically assembled in the factory through chemically welded or bonded assemblies, they provide a high degree of quality, consistency, and reliability

Functionally speaking, fiberglass doors are conceptually very predictable and similar to hollow metal door systems. They are manufactured with fiberglass door skins that are produced first using a full gel coat finish in a pre-selected color and then laminated to a solid core material. Similar to a metal door, that core material can be selected based on performance needs from lightweight balsa, durable polypropylene, insulating urethane, or fire-resistant gypsum. The perimeter of fiberglass doors are then filled with a fiberglass matrix, giving the door a clean, monolithic finish.

The exterior faces of a fiberglass door are manufactured first in the process and provide the long-lasting gelcoat finish when installed. Photo courtesy of Chase Doors