If you work on high-rise construction in NYC, you’ve probably seen these terms used together. But they are not the same thing, and they do not serve the same purpose.
Depending on the building height, phase of work, and perimeter protection strategy, a Site Safety Plan may show one of these systems, multiple systems, or an approved alternative. These requirements are primarily addressed under NYC Building Code Section BC 3308 - Unenclosed Perimeter Protection.
Vertical Safety Netting
Under BC 3308.5, vertical safety netting is required along unenclosed perimeters, subject to the exceptions provided by the code.
Unlike horizontal netting, vertical safety netting is installed at the building perimeter itself.
Where required, BC 3308.5.2 requires the netting to extend sufficiently to cover openings in the unenclosed perimeter to a height of at least 60 inches above the floor, or above the roof when installed at roof level.
The code also establishes requirements for the netting openings, support cables, installation, maintenance, and removal.
Horizontal Safety Netting
Horizontal safety netting serves a different purpose and is addressed under BC 3308.6.
During new building construction or the vertical or horizontal enlargement of an existing building, BC 3308.6.1.1 requires horizontal safety netting once the topmost walkable floor reaches six stories or 75 feet, whichever is less, above the ground or an adjoining roof.
The horizontal net must generally be located no more than two stories or 30 feet, whichever is less, below the applicable working level identified by the code.
For concrete construction, this relates to the stripping floor. For steel construction, it relates to the uppermost story where the concrete floor slab has been placed.
Horizontal netting therefore functions as a protection level below active construction operations rather than simply enclosing the edge of an individual floor.
Cocoon Systems
A cocoon system is not simply another term for vertical or horizontal netting.
Chapter 33 recognizes cocoon systems as an alternative perimeter protection system under certain conditions.
For vertical perimeter protection, BC 3308.5 includes an exception where an equivalent alternative system acceptable to the Commissioner, including a cocoon system, climbing formwork, or enclosure panels has been installed.
Cocoon systems can also affect the requirement for horizontal safety netting.
Under BC 3308.6.1.4.2, horizontal safety netting is not required at a location where an equivalent alternative system acceptable to the Commissioner, including a cocoon system or climbing formwork, covers the full height of the unenclosed perimeter at and above the levels where horizontal nets would otherwise be required.
That distinction is important.
A properly configured cocoon system may therefore serve as an alternative to conventional netting requirements in certain conditions, rather than simply being another layer of netting added to the building.
So What Is the Difference?
A simple way to think about the three systems is:
- Vertical safety netting protects the unenclosed perimeter of a floor.
- Horizontal safety netting provides a protection level below active construction operations once the applicable height threshold is reached.
- A cocoon system is a more comprehensive perimeter enclosure system that may serve as an approved alternative to conventional netting requirements when the conditions of Chapter 33 are satisfied.
Why an SSP May Show More Than One System
Construction conditions change as a building rises.
One portion of the structure may have an unenclosed perimeter requiring vertical protection while another portion has reached the elevation where horizontal netting requirements apply.
There may also be setbacks, podium conditions, adjoining roofs, hoist locations, crane loading areas, façade installation, or changing construction phases that affect how perimeter protection is shown.
For that reason, these systems should be evaluated by elevation, location, and construction phase rather than treated as interchangeable labels.
Bottom Line
Cocoons, horizontal nets, and vertical nets all relate to perimeter protection, but they are not the same system and they are not automatically interchangeable.
Understanding where each system applies and how it changes as construction progresses is an important part of developing and reviewing a high-rise Site Safety Plan.
Code References
NYC Building Code Chapter 33 — Safeguards During Construction or Demolition
- BC 3308 — Unenclosed Perimeter Protection
- BC 3308.5 — Vertical Safety Netting Systems
- BC 3308.5.2 — Height
- BC 3308.6 — Horizontal Safety Netting Systems
- BC 3308.6.1.1 — During Construction
- BC 3308.6.1.4 — Alternative Systems
- BC 3308.6.1.4.2 — Other Alternative Systems
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