Are All Solid Core Doors Fire Doors?

SOLID-WOOD DOOR between Dwelling and the Attached Garage

Section 302.4 of the 1998 CBC provides an exception to the one-hour separation requirement between Group R, Divisions 2.1, 2.2, 2.2.1 and 3 and Group U occupancies as follows:
The separation may be limited to the installation of materials approved for one-hour fire-resistive construction on the garage side and a self-closing, tightfitting solid-wood door 13/8 inches in thickness, or a self-closing, tightfitting door having a fire-protection rating of not less than 20 minutes when tested in accordance with Part II of UBC Standard 7-2…

The following frequently asked questions and answers are provided as a reference only

Frequent Asked Questions
Q1: Is a “solid-wood door” the same as a “solid-core wood door”?
A1: No, the two are different. “Solid wood” means wood material from face to face throughout, as opposed to wood veneer or laminated multi-ply wood veneers. A “solid-wood door” is a door that is made of solid wood. A “solid-core wood door”, on the other hand, is a composite door with wood veneers on both faces and a variety of infill in between.
Q2: Does a solid-wood door have to be made of a single-piece lumber to meet the requirement in Section 302.4?
A2: That is no longer the case. The UBC prior to the 1949 edition required a “solid slab wood door”, which means a single-piece solid wood construction. The subtle change from “solid slab wood door” to simply “solid-wood door” allows the door to be made of multi-strip solid wood, and thereby cut down its cost considerably.
Q3: Can a 13/4-inch solid-core wood door substitute for a 13/8-inch solid-wood door?
A3: As the lumber cost continues to rise, solid-wood doors are expensive and not readily available. That is why the 1991 edition of the UBC expanded the exception to allow other types of doors as alternatives to the expensive solid-wood doors. Those alternatives, however, must be rated 20 minutes or more when tested per Part II of UBC Standard 7-2.

The most economical and widely used alternative is the solid-core wood door. Though the thickness of the door is not an issue, a fire-rated solid-core door typically comes 13/4 ” or 21/4 “ thick. The fire rating of a solid-core wood door ranges widely, depending largely on its core materials. Price difference between a 20-minute rated and a non-rated 13/4 -inch particle-core door is about 10%, or 5 to 6 dollars. The code only accepts the rated one as an alternative.

Q4: Is the “S” rating required for the 20-minute label?
A4: Yes. Part II of UBC Standard 7-2 is a test standard for smoke- and draft-control. Doors that pass the test will bear a label showing the fire rating followed by the letter “S”. A fire-door label without the letter S means that the door passed the fire-endurance test per Part I of UBC Standard 7-2, but either was not tested for smoke leakage control per Part II of the standard, or failed to pass the test.
Q5: How can an inspector tell whether a door is a solid-core door or a solid-wood door if it has been painted?
A5: First and the easiest, you can tell the difference by knocking on it. The uneven density of materials in a composite door tends to deaden the sound when you knock on the door. A solid-wood door sounds distinctively louder, clearer, more resonant and with a higher pitch. Secondly, a particle-core door, which is the most readily available solid-core door, is much heavier than a solid-wood door. And thirdly, as a common practice in the industry, the top and bottom edges of a door are either not painted or just painted with a thin finish coat that still allows the texture of the door edge to show through.


All Rated Fire Doors Will have A Metal Plate And Stamp.