I am considering specifying seamless-edge doors and trying to decide which design I should specify: vertical seam edge filled, dressed smooth, intermittently welded seams, edge filled and dressed smooth, or continuously welded seam, dressed smooth? How do the three options differ?

Seamless edge doors are specified primarily for aesthetic considerations. Edge-filled and dressed smooth doors are treated with a filler material and subsequently sanded smooth and painted. Intermittently welded seam doors, are welded at intervals along the seam, treated with a filler material and subsequently sanded smooth and painted. Continuously welded seam doors provide an uninterrupted weld the entire height of the door edge with no added filler material and subsequently sanded smooth and painted.

I have a steel door specification with interior door core construction type A, D or F and exterior door core construction type B, C, E or F. Can you tell me what these door cores are?

The references cited are from an outdated SDI 100 specification. The new specification, SDI 100 ANSI A250.8, does not contain letter designations for core material. The updated document provides a performance-based standard, such that an architect can be assured the doors will perform to the performance levels outlined in SDI 100 A250.8, regardless of core material. If an architect specifies a particular core material they will be limiting the number of manufacturers that supply that product, and perhaps the variety and styles of doors available to them. That is why it is better to base your choice on performance characteristics.

Why has the thermal resistance of hollow metal doors changed recently?

The R and U values have been updated as a result of a change to the ASTM testing methods of SDI 113 (Standard Practice for Determining the Steady State Thermal Transmittance of Steel Door and Frame Assemblies). In the previous test method only a portion of the door was tested, which does not reflect operable conditions of the door, frame and hardware. The new version of the standard tests the entire assembly, which represents real-world conditions. Architects should only use the numbers from the new thermal performance standard method.

Can you give me a quick explanation about R and U values?

R and U values relate to insulation performance characteristics. The higher the R value, and the lower the U value, the higher the insulating properties of the product. Polystyrene and polyurethane cores have higher insulating properties than honeycomb and steel-stiffened core doors. 1 ¾” thick commercial steel doors will have R values that range from approximately 1.5 to 3.

What are the different door cores available from most manufacturers, and how do I select the best type for my application?

Steel doors are differentiated by their core, with each type having a different set of properties and performance characteristics. The five most common cores are honeycomb, polystyrene, polyurethane, steel stiffened, and temperature rise. A honeycomb core door is used for interior and exterior openings where high thermal insulation is not required. Polystyrene core doors are the most commonly specified insulated core and are suitable for applications requiring an R or U factor (a measure of insulating performance). Polyurethane core doors provide superior insulating properties 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, non-aesthetic applications. Temperature rise core doors are used when a fire resistance rating is required to retard the transfer of heat from one area to another (a stairwell, for instance).

How do I select the right type of steel for steel doors and frames?

The three most common steel types are cold rolled steel, galvanneal steel, and galvanized steel. Cold rolled steel, suitable for most interior applications, is uncoated steel with a factory applied coat of primer. Galvannealed (A40) steel is carbon steel coated with an iron-zinc alloy. It provides excellent corrosion protection when combined with a coating of quality prime paint and is adequate for most interior and exterior applications. SDI recommends use of the A Series, both A40 and A60, for primer adhesion. A60 is superior to A40 for inhibiting rust. SDI does not recommend the G series because of inferior primer adhesion properties. Galvanized steel is carbon steel treated with a full zinc alloy. It provides superior rust protection but has poor adhesion properties for prime or finish paint.

Are steel doors always ordered with the latch prepared on the center of the edge?

All hollow metal doors are manufactured as two pans with an edge seam. Some are made with an offset concealed edge seam, which is 1/4″ from the push side of the door. This is suitable for the commonly specified mortise locks and mortise exit devices that have 1-1/4″ faceplates, and are automatically centered when abutted to the 1/4″ edge seam. (1/4″ 1-1/4″ 1/4″ = 1-3/4″).

Where is the recommended location of the electric hinge?

A hollow metal door manufacturer can locate the prep for an electric hinge at most any location a customer would desire. As the load bearing capacity of the reinforcement is reduced to accommodate the additional holes for the wiring, the middle location on a 3 hinge door would be recommended. The third hinge down on a 4 hinge door would be the recommended location. These locations also closely match the level of the strike.