2024 Portal Frames

[Energystar]

The braced wall code in the 2024 IRC has a significant change that might easily be overlooked. Notes have been added on each of the drawings for portal frames in R602.10.6—the PFH, PFG and CS-PF. The new note reads, “Note: Header shall not extend over more than one opening.”

This change can have profound implications especially for the CS-PF. The “Continuously Sheathed Portal Frame” (CS-PF) is relatively easy to construct and is (was) useful in walls with lots of openings and can even be used on subfloor. Take the now illegal example below where a portal frame is used to support three separate window openings. Keep in mind that one of the openings could also be a doorway. By code, one could use a portal frame to support a 20’ wide garage door, but not this case with a much smaller opening. If the three windows were replaced with a triple, mulled unit, I would assume it would be acceptable, which seems somewhat ridiculous.

Portal frames are not just used for garage doors (except for the PFG). I have done work on 2-storied townhouses that are 20’ wide and 44’ deep. The front and back walls are nearly all fenestrations since the sides are party walls. We commonly use a CS-PF to span the entire 20’ on the main level to get enough bracing. Doing away with this option will mean getting rid of a lot of opening or going to a moment frame.

Can anyone shine some light on the engineering thinking behind this and am I correct in my definition of "opening"?

 

[classicT]

In the picture provided, I would say that is still a single portal frame opening. I think the intent was to prevent two portal frames immediately adjacent to each other using a common header. Example would be at the garage, where for example, multiple garage door openings are on the same wall plane and configured to use a common header over 2+ portal frames - that would be prohibited.

 

[classicT]

Something similar to this image from Simpson; albeit, Simpson shows it correctly by using a single-portal frame immediately adjacent to a double-portal frame. If this image below were modified to have a single header and the center panel was shared by the two portal frames, that would be a violation.

 

[Energystar]

I would agree. This is more in line with the diagrams from the 2018 Wood Wall Bracing Provisions.

 

[Energystar]

These images do not appear in the IRC and so they added the note which is very misleading.

 

[Inspector Gift]

You asked, ...am I correct in my definition of "opening"?

Did you state a definition?

I believe the illustration that you provided functions structurally as a single opening, and therefore complies with the Note.

 

[Energystar]

So, if I have two 8' garage doors with 2' in between that is not a portal frame, can I span the header all the way across, since this could be considered one opening structurally?

 

[classicT]

So, if I have two 8' garage doors with 2' in between that is not a portal frame, can I span the header all the way across, since this could be considered one opening structurally?

Theoretically, yes. Your opening is meeting the maximum opening width of 18-ft. One could say that the 2-ft panel should not be framed tight to the beam and must allow for the beam to deflect to make the 2-ft panel a truly non-structural element, but that would be an extreme interpretation IMHO.

 

[Energystar]

Perhaps the note should be amended to read, "A portal frame header shall not continuously span more than two portal panels."

 

[TheCommish]

Could someone explain why portal frame header is not across 2 garage door opening and it appears that the vertical frame is on one end only, please?

 

[classicT]

Could someone explain why portal frame header is not across 2 garage door opening and it appears that the vertical frame is on one end only, please?

A portal frame is limited to spanning over a single opening. In the picture I posted from Simpson (below again), the image illustrates both a single- and a double-portal frame being side-by-side. Single-portal frames are far less common but are allowed where there is a brace wall panel on the end opposite the panel. See the note near the bottom center of Fig. R602.10.6.3 (second image), which uses a broken sketch to illustrate both a single- and double-portal frame.

 

[TheCommish]

Let me try this, if we have a 24 foot wide garage with 2) 8 foot doors, portal frame at each end with center support. Why is the the header spliced near the center as indicated by the orang line below, rather the having the header span outside to outside? Please the engineering behind the answer no the design requirement

 

[jar546]

Just to clarify, this new note about the header limited to one opening. It does not apply to the ABW method. That new note is not present for Alternate Braced Wall Panel.

The blue text clarifies a few other things.

 

[jar546]

Let me try this, if we have a 24 foot wide garage with 2) 8 foot doors, portal frame at each end with center support. Why is the the header spliced near the center as indicated by the orang line below, rather the having the header span outside to outside? Please the engineering behind the answer no the design requirement

It depends on what portal method you choose.

 

[wwhitney]

Let me try this, if we have a 24 foot wide garage with 2) 8 foot doors, portal frame at each end with center support. Why is the the header spliced near the center as indicated by the orang line below, rather the having the header span outside to outside? Please the engineering behind the answer no the design requirement

This is a guess, maybe one of the engineers here can provide a more definitive answer:

As far as I can see, there's no difference in how the lateral loads on the header(s) would be distributed between the 3 supporting panels. But there is a difference in how the vertical loads would be distributed. With two simple spans, half the vertical load from each span would be distributed to each of its two supports. While with a single continuous span over 3 supports, the center support gets more than 1/2 of the total vertical load.

Thus I'm guessing it's an issue of the combined horizontal and vertical loads on the central panel. Often in members there is a tradeoff, where increased loading in one direction will decrease the allowable simultaneous loading in another direction. In which case to maximize the horizontal capacity of the 3 panels, it's desirable to spread the vertical loading out more evenly.

Cheers, Wayne

 

[bill1952]

Has anyone looked up the code change record to see substantiation and any discussion on modifications?

 

[Paul Sweet]

The portal frames in IRC R602.10.1.2.3&4 are a pre-engineered prescriptive method of framing based on a maximum span and load. A structural engineer could design a multiple span frame utilizing portals, but he would have to size the header, straps, nailing patterns, hold-downs, etc. instead of using the details in the code.