Frequently Asked Questions

There are many times that the hollow metal industry is asked to provide product for a labeled opening that cannot be labeled. There are many different restrictions that are placed on the industry. The first are requirements that are listed in National Fire Protection Association (NFPA) 80 – “Standard for Fire Doors and Fire Windows.” These include door sizes, hardware considerations, maximum area of glazing in a fire door and so on. The next is the issue of money. It costs about $15,000 to run a fire test. So, manufacturers do not like to run these tests for products that are infrequently used, such as specialty jamb profiles. That is why many manufacturers join together either with the Steel Door Institute (SDI) or The Hollow Metal Manufacturer’s Association (HMMA) to run joint fire tests. The labeling agencies such as UL will fire test anything that you bring to them, but that does not mean that it will meet building codes or NFPA 80 standards.

Each fire test is run for a specific company or for a specific group of companies. For instance members of the Steel Door Institute (SDI) and NAAMM (National Association of Architectural Metal Manufactures, Hollow Metal Division) run joint fire tests as a cost savings to their members. Also, different companies have different manufacturing capabilities, that might limit which hollow metal items that they can produce. Companies are usually continually adding to their labeling capabilities, so even if it is not shown in their catalog or other reference material as an item that they can fire label, you should contact them for information regarding their current capabilities.

The answer to this question can be found by quoting the heading from NFPA 80 of Table 2-8(a): Builders Hardware. “Doors up to 60 inches in height shall be provided with two hinges and an additional hinge for each additional 30 inches of door height or fraction thereof. The distance between hinges shall not be permitted to exceed 30 inches.” Therefore, a 90 inch door (7′-6″) can have 3 hinges. However, as soon as an extra inch in height is added to 91 inches (7′-6″) 4 hinges must be provided. (The exception to this is the use of one continuous hinge to hang the door).

The key to this question is can it go on ANY labeled door. The answer then is no. For instance, an opening with VR X VR exit devices must use doors that were tested for this hardware configuration. So, even though the exit devices are fire tested, they cannot go on doors that are designed for 8″ Panic x VR.

A temperature rise door is used when it is required to retard the transmission of heat from one area to another. It is a measurement of the rise in temperature above ambient temperature of the non-exposed side of the door during the first 30 minutes of a standard fire test. The lower the degrees, the better the rating. The currently accepted norm is 250° rise over 30 minutes. However, 450° and 650° temperature rise doors are also available. It is not required to have a temperature rise rating for a standard labeled fire door. Temperature rise doors are typically 1½ hour fire rated.

They are generally used in stairwells of high rise buildings. The door is used to limit the temperature rise through the door into the stairwell for a period of time. Thus, making it possible for people to exit the burning building by safety passing by the floor of the origin of the fire.

STC stands for Sound Transmission Class. It is a measure of how much sound will be prevented from being transferred from one area to another. The higher the rating the less sound that can be heard on the other side. This is a logarithmic progression, as opposed to a linear variable. Therefore, on the average, a jump of 3 STC numbers, (for example from 37 to 40) doubles the actual performance. A table showing various STC Value ranges, and their description is presented below:

STC Value: Rating Description:
50-60 Excellent Loud sounds heard faintly or not at all
40-50 Very Good Loud speech heard faintly, but not understood
35-40 Good Loud speech heard but hardly intelligible
30-35 Fair Loud speech understood fairly well
25-30 Poor Normal speech understood easily and distinctly
20-25 Very Poor Loud speech audible

Generally, the performance of sound control doors is based in large part on the mass of the door. Sound doors are heavier than conventional hollow metal doors. Since their weight can vary from 10 to 20 pounds per square foot (210 to 420 pounds for a 3′-0″ x 7′-0″ door), it is important to specify proper heavy duty hardware capable of handling the door weight over the life of the installation. Also, the door frame is made of thicker materials than what is used to hang a conventional hollow metal door weighing only 7 to 8 pounds per square foot.

A borrowed lite window frame contains a fixed piece of glass that is installed in the field. The term is thought to have originated from the concept of “borrowing lite” from one room (such as a corridor) to add light to another room (such as an office).

Galvanized sheets are carbon steel sheets coated with zinc on two sides by the continuous hot dip process. This process results in a layer of zinc tightly adhering to the base steel through an iron-zinc bonding layer. Galvannealed sheets are also carbon steel sheets coated with zinc on both sides by the hot dip method. However, immediately as the strip exits the coating booth, the zinc coating is subjected to an in-line heat treatment that converts the entire coating to a zinc-iron alloy. Conversion to the alloy results in a non-spangled matte finish which makes the sheet suitable for painting without special preparation.

The number is a measure of the total weight in ounces per square foot of coating that adheres to both surfaces of the steel. There is 0.60 ounces per square foot on A60 or G60, and there is 0.90 ounces per square foot on A90 or G90.

There are 4 major groups of stainless steel. The Austenitic Group contains the 300 Series Alloys which are most commonly used in the door and hardware industry.
The stainless steels in this group are known as the chrome-nickel series. The two most common alloys used by the door and frame manufacturers are type 304 and type 316. Type 304 is your basic alloy. Type 316 contains a higher nickel content with added molyebdenum to help avoid corrosion. This higher corrosion resistance of the type 316 stainless also increases its cost.

There are numerous surface finishes for stainless steel. The most common for door and frames are either No. 3 or 4 (very similar), or No. 8. Finishes are determined by the abrasive mesh size and number of passes during the process. However, the result can vary slightly from one manufacturer. No. 3 and No 4 Finishes are polished finishes obtained with abrasives approximately 100 mesh (No. 3) or 120 to 150 mesh (No. 4) and may or may not be additionally polished during fabrication. They are general purpose finishes. The common industry term for this finish is “satin”. No. 8 finish, is commonly termed a “mirror” or “polished” finish. It is the most reflective finish that is commonly produced. The surface is essentially free of grit lines. This finish is typically used in store fronts. There are also thousands of other decorative specialty finishes now available for architectural design purposes.

Frame profiles and the curvatures of bend have to do with the equipment used to form the frame pieces. Large stocking manufacturers use roll forming equipment to form their standard jamb width material (such as 5⅞”). Custom manufacturers use press brakes to form all of their material. Although the jamb widths are the same with either method, the curvature of the bends of the profile vary from roll forming to press braking, and from press brake to press brake. Therefore, the material will not make a perfect match when put together. Good installers, however, are able to make material from different manufacturers match on the job, if the pieces are field welded.

Another problem, inherent in knocked down frames, is the system used to fasten the corners of the frames together during installation. One manufacturer may use corner clips on the jambs, that lock into holes in the heads, whereas another manufacturer may reverse this and use holes in the jambs that lock into corner clips in the heads.

The size limitations on doors has to do mainly with the length of the press brakes used to form the material. Some manufacturers have 10 foot press brakes while others have 12 foot brakes and longer. The same limitations do not apply to the frames, as it is fairly easy to splice two pieces of frame material together to form longer sections. This is typically done in one of two manners. The first would be a welded splice that would not be visible after manufacturing is completed. The second would be to prepare the frames for field splicing. This is typically done when the larger piece would not be able to be handled to get into the building for installation. Although steel door sections can be welded together to form taller doors, the resulting door is not always of the quality needed for the opening requirements.

Because, we were limited by what the world wide web capacity is for information. But seriously, if you are a distributor, we would be glad to try to answer your questions directly by either e-mail: or fax: 1-800-851-2131. If we get some good questions, we may add them to this site.