What Is a Category B Door | Things You Should Know

Category B door basically represents a type of fire door. You can find six categories of fire doors in the United States. But among them, the category A and category B doors are mostly used, especially in commercial buildings. By definition, a category B door is a fire door that can typically resist fire and smoke for 90-120 minutes, so that they can’t escape the source room and bring chaos throughout the building. 

Detailed Information of Category B Fire Door

To know a Category B fire door better, you need to know some specific details about it. To make it convenient, we’re presenting major information regarding the category B door. Check the out –

1. Design and Material

Category B fire doors can be both stain-grade and paint-grade. For your information, stain-grade doors are designed to withstand a stain and are comparatively more expensive, whereas paint-grade doors are made of wood that has a coat of paint and are comparatively less expensive. Both doors are made of wood in this case. Basically, category B doors consist of wood and steel materials. 

2. Dimension and Area

The minimum thickness of this door is 1-3/4 inches. The maximum height of the door is 8 feet and the maximum width is 4 feet and 8 feet for single and pair doors respectively. The fire glass maximum area is 3145 square inches. 

3. Fire Resistance

Category B doors are tested and certified to meet the positive pressure requirements of ASTM E-152, NFPA 80, NFPA 252, UL10B, and UL10C standards. From this, it’s clear that the fire door rating of a Category B door ranges from 20-90 minutes, meaning this door can hold the flames or smoke for up to 90 minutes depending on the material and seal to prevent spreading. However, it has been found that this door can withstand for a maximum of 120 minutes or 2 hours.

NOTE –

• The exact fire/time rating of a category B door is based on that specific door. Many building codes now refer only to the time rating of a fire door and not a classification. The simple reason is classification is changeable.
• Category B doors don’t come with in-built sealing systems on the door edges and require specific additional edge sealing systems that are basically surfaces applied between the frame and door. 

Frequently Asked Questions and Answers (FAQs)

What is the major difference between Cat A and B doors?

The major difference between Category A and B doors is that Category A doors don’t need additional edge seal systems to fulfill positive pressure requirements, while Category B doors do require such additional edge seals to attain positive pressure.

What is the exact Class B fire door rating?

The exact Class B fire door rating of a door is directly dependent on that particular door. But if you consider the overall research-based information, the Class B door rating is 2 hours of stability, 1 hour of integrity, and 1 hour of insulation. 

Conclusion 

So far, we’ve shared the significant aspects of a category B door so that you can have an overall concept of this door. This is a common door type for residential buildings but commercial, industrial, hospital, etc buildings. But you can use this door in your living place if you prefer. If you have any more questions or find this post helpful, it’ll be very supportive to share it through your comments.