By: Joseph Contreras
When property owners, contractors and engineers prepare for an exterior restoration project, it is important that they effectively communicate and assess the various on-site accessibility options. Too often, restoration contractors are left autonomous, figuring out how to gain access to immobilized work areas. However, with the help of a building manager or owner, contractors can methodically conjure up different access alternatives and determine the safest, most cost-effective means to access those hard to reach areas. In this excerpt, we will cover commonly used access systems and discuss the advantages and disadvantages for each.
We can divide access systems into two categories: scaffolding and mechanical lifts. Scaffolding is defined as being: a temporary or movable platform for workers to stand or sit on when working at a height above the floor or ground. For larger-scale exterior projects, the most common forms of scaffolding are, pipe scaffolding, system scaffolding and suspended scaffolding. Though there are several variations, the two most common mechanical lifts are scissor lifts and boom lifts.
Pipe scaffolding, commonly referred to as supported scaffolding, is widely used for NYC restoration projects. This system is typically installed on buildings with plumb vertical façades and although the design of pipe scaffolding can be manipulated to account for setbacks or other variations in façade structure, it is usually raised vertically. There are many benefits to using pipe scaffolding as a means of access. It creates the ability to work on multiple areas within the same elevation simultaneously, allows the workers to stage the construction materials close to the work area, gives the opportunity for the use of hoists allowing for easier movement of materials and debris, and allows for many workers to occupy the same area. Pipe scaffolding is often best suited for large scale jobs, where the cost of scaffold installation is outweighed by the anticipated productivity of the construction crew. Supported scaffolding is relatively expensive to install as it requires trained installers, planking, netting, and often a sidewalk bridge. Alterations to pipe scaffolds can be quite costly too, warranting the need for additional components, labor and time. Building owners usually rent materials from the installer, and this cost can add up over a lengthy project which can create tension between residents, contractors and management. Subsequently, residents subjected to this disturbance could potentially become frustrated.
Another alternative type is called system scaffolding. System scaffolding, made up of different sized vertical posts, horizontal and diagonal tubes, shares many of the same attributes as pipe scaffolding. It is relatively expensive to install, encapsulates the façade, allows many workers the ability to work on the same area at the same time, and allows for a large work platform that can be used to stage materials or equipment. Where pipe scaffolding is typically used on a plumb vertical façade, system scaffolding can be easily designed for changes in façade structure, allowing the erector the ability to install components around variations in exterior elevations. The installation of a system scaffold is more labor intensive than installing a traditional pipe frame, but less intensive than its predecessor, pipe and knuckle scaffolding. A system scaffold was adapted from the earlier tube and clamp (pipe and knuckle) scaffold and allows the installer the ability to make easier more systematic connections instead of manually attaching clamps to the tubes. Like pipe scaffolding, building owners can benefit from the use of a system scaffold when the cost of installation and rental is outweighed by the maximization of worker output. System scaffolding can be an excellent alternative when a building with irregular shape needs to create access to multiple areas at the same time.
Suspended scaffolding, also referred as swing staging, is another commonly used type of scaffold in the NYC area. The scaffold is supported by steel hooks attached to the parapet and tied back to a structural member of the building or outrigger beams that cantilever the plane of the façade, are weighed down with counterweights and tied back to an acceptable structure. There are many advantages to using a two-point suspended scaffold. The installation and assembly of the scaffold is relatively easy. The scaffold rarely needs to tie-in to the building which limits or eliminates the number of destructive anchors needed to stabilize the scaffold, the workers can work in an ergonomic position, and the system does not encapsulate the building. A disadvantage of suspended scaffolding includes limiting the number of workers and weight on a scaffold. Suspended scaffolds are limited by a two-man occupation and usually a working load of 1,000 lbs. These parameters can create difficulties when a project requires increased manpower in a given area or when there is significant movement of material. Another disadvantage is the requirement of obtaining a CD-5 for outrigger beams. In NYC, a CD-5 is issued by the DOB and requires a contractor to obtain an engineer to design, test, plan and draw the proposed installation of the scaffold and its components. This can be a substantial cost when performing a small project. The use of swing stages can be seen throughout the NYC Metro area and while there are disadvantages to this type of scaffold system the pros often outweigh the cons.
Another access option is the use of an aerial work platform: scissor lifts and man lifts. These platforms operate using handheld controls and can be driven on a variety of surfaces. Scissor lifts come in an array of sizes and options that allow the contractor to choose the appropriate lift for the job. Some scissor lifts utilize outrigger stabilization for use on uneven ground. While others can accommodate a working load of 2,000 lbs. and reach heights of 60’. If a construction project requires a small footprint and can be accessed by a lift, a scissor lift may be the right choice of access. Man lifts are commonly referred to as boom lifts or cherry pickers. Boom lifts also come in a large selection of sizes with varying options. They typically range from 30’ to 150’ and can be an excellent choice when the required work in an area is relatively small or the use or cost of a scaffold is not feasible. Man lifts usually are not meant for heavy work, instead they can be used for light duty or investigational work. Similar to scissor lifts, boom lifts can minimize the footprint of a construction project, allowing the workers to move the lift to and from the work area with ease. It is important to note that adequate space is usually needed for storage of this type of equipment.
Presenting these different options and communicating with the building owners and managers will considerably improve the overall life cycle of the project. After reviewing the properties, advantages and disadvantages of each system we can determine the correct means of access for a project.