Tales From The Jobsite

What’s Your Job? Are you a Glazier or Building Envelope Contractor?

By Craig Carson

In this current building cycle, we’re seeing an increase in design-assist projects. This is partly because architects want to bring specialty contractors on board to help finish the design, and also because developers want to control costs to meet the budget.

Involvement can vary depending on the architect’s approach. I’ve been on projects where the architect really didn’t want input from the specialty contractor, and others that were just the opposite, where we almost drew the project for them. Which brings me to my question: are you a glazing contractor or a building envelope contractor?

“What’s the difference?” you ask. Here’s a closer look.

THE BASICS

We’re all glazing contractors. We start the bidding process by reviewing a set of construction documents and formulating our bids from there. But what do you do if you’re given a concept and asked to provide suggestions? When this happens you’re now bridging over to the world of a building envelope contractor, where there’s more responsibility placed on your shoulders—and more liability. Frequently, you’ll be asked if you can provide design liability insurance. If you don’t have this, you should get it. You’re now part of the design team and can be held responsible, just like the architect, if something goes wrong in the final design.

Engineering is another aspect to understand. You’ll need to know the current building codes and how they affect the design, thermal, windloads, seismic and structural needs of the project, as well as the systems you’re providing. That includes reviewing the design of the structure. You don’t have to supervise the engineer of record, but make sure you know the design’s limits for seismic, deadloads and liveloads.

Your review of these items will man-date whether or not you can use a standard, off-the-shelf system, a modified standard system, or a new custom system.

CONCERNING ISSUES

Live load deflection is one of my soapbox items. Be sure to check this, as I noted in my last column (see the April 2018 issue). Manufacturers have limits for this in their designs. Don’t recommend a system that cannot meet the liveload movement of the building. In some cases you’ll have to go back to the design team (remember, you’re now part of it), and explain that in order to keep your budget on track, the live load deflection has to be reduced to the system’s limitations. If not, you have to modify the product to accommodate the movement, increase the caulk joints to give more room for movement (an unlikely choice the architect will want), or go with a custom system.

Overall system thermal properties is another of my soapbox items. When asking if a supplier can meet a certain overall U-value, make sure that the glass performance they based the model on meets or performs worse than that of the glass you intend to use. If you use a better per-forming glass in the model, the performance is artificially flawed. Then, when it’s time to provide the thermal modeling of your final layout of the verticals and horizontals, you may find that it doesn’t perform as planned. Remember, the glazing almost always outperforms the framing. More glass vs. metal provides better results.

DELVE INTO DETAILS

As a member of the design team, you also have responsibility for the perimeter conditions of the shim space between the framing system and the surrounding conditions. We’re seeing many ways to address this issue and it deserves your attention. Building envelope designs have changed. We’ve learned more about thermal and moisture drive through walls, making caulk joints more of a consideration. Do you still install your windows into an opening after the exterior fenestration has been installed?

This has all changed (or will change), as the primary seal to the framing has to be installed where the vapor barrier is applied to the building. And since you won’t get a chance to fix this seal once the fenestration is installed, it needs to be designed to last.

As a building envelope contractor, you must delve into more detail and know more about the other building products that will be used on the project. Don’t be afraid to add professional help to your team. There are many professional engineers specializing in glazing systems who can help.

To view the laid-in version of this article in our digital edition, CLICK HERE.

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