Knockout Definition in Construction in the USA

Introduction to Knockouts in Construction

In the construction industry in the USA, the term knockout refers to a pre-designed, removable section in concrete walls, floors, ceilings, or metal electrical boxes that allows for future modifications. These knockouts are strategically placed to facilitate easy access for electrical wiring, plumbing, HVAC ducts, and other installations without requiring extensive demolition or additional cutting.

Knockouts are widely used in commercial, industrial, and residential projects to improve flexibility, reduce labor costs, and minimize structural damage. This article explores knockout types, applications, materials, installation methods, and regulatory standards in the USA.

Types of Knockouts in Construction

1. Electrical Knockouts

Electrical knockouts are pre-punched perforations in metal or plastic electrical boxes, conduit fittings, and junction boxes. These knockouts allow electricians to run cables or conduits through walls, ceilings, or floors without additional drilling.

• Commonly found in steel, plastic, and aluminum junction boxes.
• Designed to accommodate various conduit sizes, typically ½-inch to 2 inches in diameter.
• Easily removed using pliers, knockout punches, or a screwdriver.

2. Concrete Knockouts

Concrete knockouts are preformed sections in concrete walls, slabs, and ceilings that can be removed when necessary. These are typically reinforced with lighter materials or voids to facilitate easy removal.

• Used for future openings in structural walls, plumbing, and ventilation ducts.
• Found in precast concrete panels, foundation walls, and tilt-up panels.
• Require precise formwork design and reinforcement considerations.

3. Plumbing Knockouts

Plumbing knockouts are designed to accommodate pipes, drains, and sewer connections in residential and commercial buildings.

• Often found in concrete slabs, prefabricated bathroom modules, and utility areas.
• Simplify drainage and water supply installations.
• Typically marked during the pre-construction phase for accurate placement.

4. Drywall Knockouts

Drywall knockouts are pre-scored sections in drywall panels, allowing for easy removal when installing electrical outlets, switches, or ventilation grilles.

• Found in modular walls, office partitions, and prefabricated construction materials.
• Can be removed using a utility knife or saw.
• Reduces unnecessary wall damage during installation.

Materials Used in Knockouts

1. Metal Knockouts

• Used in steel and aluminum electrical boxes.
• Provide durability and fire resistance.
• Easily removed with a knockout punch or pliers.

2. Plastic Knockouts

• Found in PVC electrical boxes, conduit fittings, and prefabricated wall panels.
• Lightweight and corrosion-resistant.
• Require a cutting tool or pliers for removal.

3. Concrete Knockouts

• Typically made with lighter concrete, foam inserts, or embedded plastic caps.
• Found in precast walls and foundation slabs.
• May require hammering or chipping for removal.

4. Drywall Knockouts

• Pre-scored sections in gypsum boards.
• Easily removable with hand tools.
• Common in modular and prefabricated construction.

How Knockouts Are Created in Construction

1. Electrical Knockout Creation

• Knockouts are pre-punched during manufacturing using CNC punching machines.
• Some knockouts are fully perforated, requiring a simple push to remove.
• Larger knockouts may require knockout punches or electrical tools.

2. Concrete Knockout Formation

• Created using foam, plastic inserts, or removable wooden blocks during concrete pouring.
• Positioned based on structural and architectural plans.
• Removed using chipping hammers, drills, or saws.

3. Plumbing Knockout Installation

• Pre-cut sections in PVC, cast iron, or concrete drainage systems.
• Marked in blueprints to align with bathroom and kitchen layouts.
• Can be removed by cutting or knocking out plastic sections.

4. Drywall Knockout Preparation

• Drywall panels are pre-scored to accommodate switches, outlets, or vents.
• Markings guide contractors and electricians for precise placement.
• Easily removable with a utility knife or drywall saw.

Applications of Knockouts in Construction

1. Electrical Wiring and Conduit Installations

• Knockouts facilitate easy cable routing.
• Common in commercial buildings, industrial facilities, and homes.
• Allow for future electrical upgrades without cutting new holes.

2. HVAC Duct and Ventilation Systems

• Pre-cut knockouts simplify duct routing in ceilings and walls.
• Used in commercial buildings, hospitals, and residential properties.

3. Plumbing and Drainage Systems

• Essential for bathroom, kitchen, and utility room installations.
• Enable quick water and sewer line connections.

4. Fire Safety and Emergency Access

• Some knockouts serve as fire-rated escape openings.
• Found in commercial and high-rise buildings.

Tools Required for Removing Knockouts

1. Knockout Punch Set

• Used for precise removal in electrical boxes.
• Available in manual and hydraulic versions.

2. Chisels and Hammers

• Required for breaking concrete knockouts.
• Helps in controlled removal without damaging adjacent structures.

3. Pliers and Screwdrivers

• Used for removing metal knockouts in junction boxes.
• Essential for small electrical box modifications.

4. Utility Knife and Drywall Saw

• Required for drywall knockouts.
• Ensures clean cuts for switches, outlets, and fixtures.

Building Codes and Regulations for Knockouts in the USA

1. National Electrical Code (NEC)

• Regulates electrical box knockouts for safe wiring installations.
• Ensures proper conduit connections and grounding.

2. International Building Code (IBC)

• Governs structural knockouts in walls, ceilings, and floors.
• Requires compliance with fire safety and structural integrity standards.

3. Occupational Safety and Health Administration (OSHA)

• Ensures worker safety during knockout removal.
• Provides guidelines for protective equipment and handling procedures.

4. Americans with Disabilities Act (ADA)

• Regulates knockouts in accessible electrical outlets and control panels.
• Ensures compliance with universal accessibility requirements.

Advantages of Knockouts in Construction

• Reduces labor costs by minimizing manual drilling and cutting.
• Increases flexibility for future modifications.
• Improves efficiency in electrical, plumbing, and HVAC installations.
• Minimizes structural damage by eliminating unnecessary cuts.

Conclusion

Knockouts play a critical role in modern construction by allowing easy access for electrical wiring, plumbing, and HVAC installations. These pre-scored or pre-cut openings significantly improve efficiency, reduce labor costs, and ensure compliance with building codes. By integrating knockouts in concrete walls, electrical boxes, and prefabricated structures, contractors can enhance flexibility and future-proof buildings while maintaining structural integrity.