HMMA FAQs - Products and Applications
What is the most commonly used steel substrate for steel doors and frames?
The three most common steel substrates are cold rolled steel, galvanneal steel and galvanized steel. Cold rolled steel, suitable for most interior applications, is untreated steel and requires a coat of primer. Galvanneal, a basic steel coated with an iron-zinc alloy, provides excellent rust protection when combined with a coating of quality prime paint and is adequate for most interior and exterior applications. And galvanized steel is basic steel treated with a full zinc alloy and provides superior rust protection. Galvanized steel is most commonly specified for exterior openings.
Where did the term "borrowed light" come from?
This term originated from the concept of borrowing light from one room (such as a corridor) to add light to another room (such as an office). A borrowed light window frame consists of a fixed piece of glass.
Do I need to use intumescent sealants for fire rated steel doors?
Generally speaking, no. These products are typically used for a smoke and fire barrier on wood doors. Given the basic properties of steel (e.g. it expands when exposed to heat), steel door manufacturers have not been forced to use intumescents to obtain fire ratings.
What are the different types of doors available from most manufacturers?
Steel doors are differentiated by their core, with each type of core having a different set of properties and performance characteristics. The five most common cores include kraft honeycomb, polystyrene, polyurethane, steel stiffened and temperature rise. A honeycomb core door is a basic, general purpose door used for interior openings with medium traffic. Styrene core doors are the most commonly specified insulated core and are suitable for exterior applications requiring an R factor (a measure of insulating performance) of 6.5. Urethane core doors boast superior insulating properties (R factor of 11.1) and are suitable for exterior openings in cold climates. Steel stiffened core doors feature steel ribs in the interior of the door and are ideal for high traffic situations where durability and security are important. And the specialty temperature rise core doors are used when heat from one area to another (a stairwell, for instance) must be retarded.
What is STC?
STC stands for "Sound Transmission Class", a measure of the extent to which sound is prevented from being transferred from one area to another. The higher the STC value, the less that sound can be transferred from one area to another. The STC scale is a logarithmic progression, meaning that, for instance, a jump of 3 points in an STC rating equates to a doubling in a door's ability to prevent sound transmission. Sound retardant doors are tested as a unit together comprised of the door, the frame, the hinges and the sound sealing system. The following chart illustrates the sound retardant performance associated with a range of STC values.
| 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 |
How can I find a name of an HMMA member?
The fastest and easiest way to find one of HMMA's 60+ members is to go to the Directory section of this Web site. At the present time there is an alphabetical listing of all HMMA members. In the very near future the page will allow users to search for members by region and by area of speciality. Links to members with their own websites will also be found in the Directory.
Are there any advantages associated with purchasing hollow metal door and frame products from an HMMA member?
Virtually every leader in the manufacture and distribution of hollow metal door products is a member of the HMMA. Our members are united in their desire to improve the quality and performance characteristics of hollow metal products, as well as enhance the collective know-how and professional expertise of their companies. You can thus be assured that an HMMA member is as committed to the success of their firm and their industry as they are to the satisfaction of designers, construction professionals and end-users everywhere.