Category Archives: Unique Structure
A significant change to the Ontario Building Code (OBC) was just revealed that positively affects the fall arrest anchor and tie-back equipment industry. It was recently announced that wood frame buildings can be built up to six storeys tall in Ontario (which is an increase from four storeys) effective January 1, 2015.
Since roof anchor systems are required for maintenance and window washing equipment on buildings that are eight metres tall (usually over three storeys); our industry will see a dramatic shift from concrete and steel mid-rise to wood frame mid-rise.
The OBC change reflects codes in most European and some North American areas. Specifically, the change was made in British Columbia in 2009 and our Vancouver office is regularly seeing projects come through the door with wood frame (probably because of the affordability to the building Owner and the growing demand for mid-rise by the consumer).
While there are certainly challenges with putting our equipment on wood frame buildings there is always a solution.
The equipment should be close to the edge of the building (parapet) and utilize a pinned down outrigger beam to rig. The close proximity to the parapet eliminates a lot of inboard distance and decreases the force on the structure. This method also pulls the anchor away (perpendicular) upward from the structure which decreases the stress on the structure opposed to pulling horizontally (parallel) with the structure. Check out the pinned down outrigger beam detail below.
Like all roof anchors, the load requirements are still 1,000 lbs. (working) and 5,000 lbs. (ultimate). So to achieve this the structure around it must be “blocked up” similar in fashion to reinforcing certain steel structure (like open web steel joist). There are a couple of examples of a wood structure roof anchors below (however modifications can be Engineered to accommodate the structure).
Also, like all projects, communication with us (the roof anchor manufacturer) and the Structural Engineer is crucial as all parties need to know specifically where the equipment is going and understand the load requirements.
You can read the news release at http://news.ontario.ca/mah/en/2014/09/ontario-increases-allowable-height-of-wood-frame-buildings-to-six-storeys.html
We are often asked to provide our equipment on buildings with a standing seam roof. In the past this request would make even our most knowledgeable designers cringe but alas we have engineered a solution.
What is a Standing Seam Roof?
A standing seam roof consists of a series of sheet metal panels that are connected “above” the panels (creating a “standing seam”) in a manner that does not penetrate them.
These are some examples of connections:
Pro-Bel is an official distributor of S-5!® clamps (as seen in the picture below) which connect the panels by tightening the seams together. You can learn more about this product from their website (http://www.s-5.com/home/index.cfm) and by following them on Twitter @S5_TheRightWay.
The big obstacle with our equipment being on a standing seam roof is that the panels will not support the applied load/force that our equipment is engineered to accept.
CAN/CSA-Z271, Section 6.3.2 – “Strength Requirement” asks that all “anchoring systems shall be designed to resist a force” of five thousand (5,000) pounds. This load/force is indirectly applied to the structure of the roof as well which is where the problem arises.
The Ridge Cap Flashing
Usually with a sloped roof there is a gap at the peak of it between the panels. This is usually covered by a ridge cap flashing which actually does penetrate the flashing and panel (in a strategic way). As seen in the picture below, Z bar connection penetrates the flashing and connects it to the panel. As long as the penetration is “above” and “away” from the envelope (the area inside the flashing) there is no concern for water damage. If the Z bar is installed incorrectly (as shown on the right side of the picture below) then water could potentially enter the envelope and travel toward the unprotected roof material and structure.
The flashing will run along the peak of a sloped roof with a large amount of connections (nails or screws) running along each side of it like so:
Our Engineers agreed that the connections make the flashing the strongest component of a standing seam roof and thus the ideal location to install a piece of our equipment to.
What we did was design a large galvanized rectangular plate with ninety degree angle pieces welded to it (the plate). Our standard stainless steel U-bar is centred on the plate and the angles would be screwed into the flashing (standing seam where the Z bar would be) instead of penetrating the envelope or panel.
We hope to build upon this application as this solution will revolutionize fall protection systems on a standing seam roof.
Every type of roof structure presents its own unique challenges in new construction for companies who supply and install permanent equipment on them. With structural steel its reinforcing, with concrete it can be missing a pour. Hollow core precast can be looked at as one of the most challenging roof construction types for the installation of window washing, suspended maintenance and fall protection systems.
The main issue with precast lies with the fact that there usually is 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 not aesthetically pleasing, 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 bottom of the bolts to be cast in with rebar and grouting. This prevents from 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 up to the general contractor to break open the cores and grout the anchor in. 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 in to the hollow core structure at the appropriate locations. The roof anchor manufacturer goes to the site afterwards 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.