Every type of roof structure presents its own unique challenges in new construction for companies that supply and install permanent equipment on them. With structural steel, it’s reinforcing; with concrete, it can be missing a pour. Hollow core precast can be considered one of the most challenging types of roof construction for the installation of window washing, suspended maintenance, and fall protection systems.
The main issue with precast is that there is usually no drop ceiling underneath. It is quite often stucco and even plaster, which means bolting through the structure would require leaving a backplate exposed to view at the underside of the precast. Not only is this aesthetically unpleasing, but it also presents a potential danger to the workers who use the roof anchors, as the base securement of the anchors is exposed and could potentially be tampered with. This provides us with two 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 and embed plates at the bottom of the bolts to be cast in with rebar and grouting. This prevents having to bolt through the structure, but is very labour-intensive and thus costly. Ideally, in new construction, the roof anchor company would supply only this anchor and leave it to the general contractor to break open the cores and grout the anchor in place. Grouting in hollow core is quite common.
Having The Precast Manufacturer Embed A Plate
This option, although the most cost-effective when you cannot bolt through, is unfortunately very impractical and rarely used. An embed plate is sent to the precast manufacturer along with an engineered stamped layout showing the location of the roof anchors on the roof plan. The precast manufacturer then embeds this plate into the hollow core structure at the appropriate locations. The roof anchor manufacturer then visits the site and welds the pier and U-bar in place. The problem with this approach is that the precast manufacturer will usually not want to take responsibility for casting the embeds in.
At the end of the day, bolting through is the best way to go, but when you cannot, here are a few options for you to consider.