How We Work With
What Are Parapets?
Parapets are wall elements that extend above the roof plane. They are typically on the exterior walls but can be found in the middle of a roof. They are ordinarily only found on flat roof structures.
POTENTIAL COMPLICATIONS & CHALLENGES:
Parapets are one of the biggest challenges in non-load bearing cold-formed steel framing. This is because parapets receive wind loads from two surfaces — positive wall pressure on one side and negative (suction) roof or wall pressure on the other, which results in much higher forces. There is roughly twice the amount of load on a parapet stud as opposed to typical wall framing. Parapets are usually constructed by cantilevering the wall stud from below the roof or bypassing the roof spandrel beam.
Bypass framing is the best way to construct a parapet. This provides a backspan and much better anchorage. When you have in-line framing (stud framing in-line with structural steel), you are required to cantilever a stud off the edge of the roof. When this happens, the parapet framing either has to be anchored with a moment-resistant connection or use a kicker at an angle back to the roof deck. The moment-resistant connector is usually difficult to make work with attachment to a very thin metal roof deck and sometimes doesn’t have full bearing. The kickers can create issues with the roofing and insulation details. Early coordination is key.
There are a lot of challenges with parapets that typically aren’t examined by the structural engineer during the design phase.
Extremely tall parapets are usually well designed by the structural engineer, as they are obvious considerations in the early design. We see the most issues with small to mid-sized parapets.
Examples of good parapet details are included below. These show in-line framing with good attachment for the base track and the kicker to the metal roof. The bypass framing has a good backspan and is anchored to the spandrel beam.
Examples of Good/Bad Parapets
These are some examples of bad details. The in-line stud framing is not really detail on how it is to be anchored nor is there much in substance to anchor to. The bypass framing detail shows a parapet built over a curtain wall (glass) system with very little anchorage opportunities into the side of a wood CLT roof.
Some really ugly details show in-line framing with a very tall parapet and no anchorage into a metal roof deck. The bypass framing detail is shown out in space over a curtain wall system. Now these details are a little comical in their absurdity. However, it is an example of the lack of attention to detail that parapets typically receive from design teams.
Solutions for potentially problematic parapets
Check with your LGMF structural engineer
- Iron Engineering often gets asked to look at details for estimators to help them quantify or predict any problem areas such as these during the bidding phase of a project.
Request anchorage details from the project structural engineer
- Just by asking the question of the structural engineer, you will cause them to pay more attention to these details, and they may resolve them ahead of time.
Request kickers
- For in-line framing, this is one of the easiest fixes to make a structure work. The challenge is working with the roofing and envelope consultant to provide a detail where all parties are happy with the design.
Request structural steel posts (angles, channels, or HSS) in the plane of the spandrel beam.
- Iron Engineering often gets asked to look at details for estimators to help them quantify or predict any problem areas such as these during the bidding phase of a project.
Kickers/posts don’t need to be at every stud
- As mentioned with stanchions, kickers can be spaced at larger than 16” or 24” if it aids in the design of the roof.