Every type of roof structure presents its own unique challenges in new construction for companies that supply and install permanent equipment. With structural steel, reinforcement is required; with concrete, a pour can be missing. Hollow-core precast is often one of the most challenging roof construction types for installing window-washing, suspended maintenance, and fall-protection systems.
The main issue with precast is that there is often no drop ceiling beneath it. It is quite often finished with stucco or plaster, which means bolting through the structure would require leaving a backplate exposed on the underside of the precast.
Not only is this not aesthetically pleasing, it also presents a potential danger to workers using the roof anchors, as the base securement of the anchors is exposed and could potentially be tampered with.
This leaves two possible options: cracking open the cores and grouting the anchor in, or having the precast manufacturer embed plates.
Grouting a Roof Anchor Into Hollow Core Precast
This option requires two cores to be broken open, with embedded plates cast at the bottom of the bolts using rebar and grout. This method eliminates the need to bolt through the structure, but is very labour-intensive and therefore costly.
Ideally, in new construction, the roof anchor company would supply the anchor only, leaving the general contractor to break open the cores and grout the anchor in place. Grouting into hollow core precast is a fairly common practice.
Having the Precast Manufacturer Embed a Plate
This option is the most cost-effective solution when bolting through the structure is not possible; however, it is highly impractical and rarely used.
An embed plate is provided to the precast manufacturer along with an engineered, stamped layout showing the roof anchor locations on the roof plan. The precast manufacturer then embeds the plate into the hollow core structure at the specified locations.
Once the panels are installed, the roof anchor manufacturer returns to the site and welds the pier and U-bar in place. The main drawback of this approach is that precast manufacturers are generally unwilling to take responsibility for casting embedded plates.
In most cases, bolting through the structure remains the preferred solution. However, when this is not possible, these are alternative options to consider.