Perforated steel strapping is an indispensable component of commercial and industrial HVAC systems, providing adjustable, durable support for ductwork. This strapping features holes punched along its length, allowing for screw or bolt attachments at any point. In this comprehensive guide, we’ll examine the benefits of perforated steel strapping, proper installation techniques, and key applications for suspending HVAC ductwork.
We’ll cover different types of perforated strapping, load capacities, span distances, and compliance with HVAC codes and standards. Safety, inspection, and maintenance recommendations will also be provided. By the end, you’ll understand the versatility of perforated strapping and how to leverage it for an efficient, long-lasting duct suspension system.
Benefits of Using Perforated Steel Strapping
Perforated steel strapping offers several advantages that make it a go-to solution for HVAC ductwork support:
Durability and Weather Resistance
Perforated strapping is constructed from heavy-gauge galvanized or stainless steel, providing tremendous tensile strength and corrosion resistance. The metals withstand UV rays, rain, snow, and temperature swings, allowing ductwork to be securely suspended outdoors.
Adjustability and Reusability
The continuous perforations allow duct supports to be adjusted or relocated by simply moving strap attachment points. Strapping can also be removed and reused on other projects, making it very versatile.
Steel strapping is economical compared to fabricated steel supports. It also reduces installation time and labor compared to welded hangers or framing.
Lightweight Yet High Strength
Perforated strapping weighs less than solid straps but maintains excellent loading capacity. This facilitates easier installation while still supporting ductwork weighing hundreds of pounds.
Perforated Steel Strapping Types and Specifications
To select the optimal perforated strapping, consider these key specifications:
Galvanized vs. Stainless Steel
Galvanized – Zinc coating resists corrosion indoors and outdoors. Most economical option.
Stainless Steel – For highly corrosive or coastal environments. Holds up better outdoors.
Dimensions and Gauges
Widths – 3/4″, 1″, 1-1/4″, 1-1/2″ common for ductwork.
Thicknesses – Minimum 24 gauge for light ducts, up to 18 gauge for heavier stacks.
Perforation size – Holes typically 1/4″ to 3/8″ for fastener flexibility.
Finishes and Coatings
Pregalvanized – Basic zinc coating applied before perforating.
Post-galvanized – Hot-dipped coating applied after perforations. More corrosion protection.
Epoxy – Added epoxy layer for very corrosive and outdoor settings.
Standard round holes – Most common pattern, allows for strapping flexibility.
Square holes – For specialized high-load applications.
Slotted – Horizontal slots instead of holes in some heavy strapping.
Load Capacities and Usage Considerations
To ensure adequate support strength, match perforated strapping specifications to ductwork requirements:
Lighter 24-26 gauge works for ducts up to 50 lbs.
Medium to heavy strapping handles ducts from 75-500 lbs.
Consult engineering data for exact weight ratings.
Perforated straps can safely span up to 14 feet depending on load.
Reduce distances for heavier stacks or weak mounting surfaces.
Limit spans to 8 feet for exterior rooftop ducts.
Indoor vs. Outdoor Usage
Indoors, pregalvanized strapping suffices in non-corrosive air.
For outdoor usage, specify post-galvanized or stainless strapping.
Ensure straps are loose enough to account for system vibration and jostling.
Anticipate expansion/contraction with temperature swings.
Proper Installation Techniques
Follow these best practices when installing perforated steel strapping for duct supports:
Securing Straps to Building Structure
Use lag screws or welded anchors to attach strap ends to joists, beams or concrete.
Install washers under bolt heads for extra holding power.
Attaching Straps to Ductwork
Use sheet metal screws driven through the perforations into the duct walls.
Pre-drill duct walls first when using larger screws to avoid tearing metal.
Allowing Room for Expansion
Leave a 1/4″ gap between strap ends and mounting surface.
Prevents binding as ductwork expands and contracts.
Using Sealants at Connections
Caulk gaps with silicone sealant to prevent air leakage.
Foil tape over screw heads further reduces air leaks.
Applications in Commercial HVAC Systems
Perforated strapping has broad usefulness across commercial HVAC installations:
Suspending Supply and Return Ducts
Use adjustable straps to neatly align duct banks to joists and beams.
Group multiple lightweight ducts on larger straps.
Anchoring Major Equipment Units
Suspend heavy HVAC units like VAV boxes, fans, and heat pumps.
Allows convenient leveling and repositioning.
Managing Exterior Rooftop Ductwork
Safely suspend exposed outdoor ducts above roof level.
Provide needed elevation and slope for drainage.
Compliance with Codes and Standards
When designing ductwork hanging systems, consult:
Sheet Metal and Air Conditioning Contractors’ National Association
Defines best practices for duct construction, installation and support.
NFPA Fire Rating Requirements
National Fire Protection Association
Perforated straps must meet flame spread and smoke development ratings.
Building Code Spacing and Fastening Rules
Local jurisdictions specify maximum strap spans and fastener types.
Straps must be designed to withstand seismic forces where required.
Inspection, Maintenance, and Safety
Routine inspection and maintenance ensures long perforated strap lifespan:
Checking for Wear, Corrosion, and Damage
Visually inspect strapping from below and above ducts.
Look for deteriorated or buckled straps requiring replacement.
Retightening Loose Connections
Vibration can loosen strap attachment hardware over time.
Snug and re-torque any loose nuts, bolts, and screws.
Following Fall Protection Procedures
Use ladders and lifts to safely access elevated ductwork.
Wear fall arrest gear when inspecting rooftop level ducts.
Comparison to Alternate Duct Supports
Beyond perforated strapping, other common ductwork hanging methods include:
- Very flexible but have lower load capacity than straps.
- More vulnerable to sharp bends and joint failure.
- Limited adjustment ability compared to perforated straps.
- Can transmit vibrations through support system.
- Require welded fabrication so less adjustable than straps.
- Difficult to expand or reconfigure once installed.
Conclusion and Key Takeaways
Perforated steel strapping is the ideal choice for most HVAC duct suspension needs. The combination of strength, corrosion resistance, ease of installation and flexibility of support adjustment offered by perforated strapping is unmatched. Following the recommendations in this guide for proper product selection and installation ensures ductwork will enjoy decades of secure, dependable support.
Frequently Asked Questions
What gauges of perforated strapping are available?
Gauges range from thin 24 gauge for light ductwork up to very heavy 12 gauge for loads exceeding 1,500 pounds. 18 to 22 gauge straps work for most typical commercial ducts.
How long can perforated strapping safely span?
Perforated strapping can safely span up to 14 feet depending on the load weight and gauge. Limit spans to 8 feet or less for outdoor rooftop ducts.
Is perforated strapping reusable?
Yes, perforated strapping can be removed and reused on other projects as needed provided it is still in good condition.
Can perforated strapping corrode over time?
Galvanized strapping can corrode if exposed to water repeatedly. Stainless steel offers the best corrosion resistance for wet environments and outdoor use.
Is stainless or galvanized strapping better for outdoor ducts?
Stainless steel strapping is recommended for exterior rooftop and exposed ductwork since it withstands weathering and UV exposure better than galvanized.
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