Connecting Monopitch Roof to Steel Warehouse Building?

[Redacted]

Hi there,

I’m working on a project with a typical steel frame/cladding warehouse where the architect is trying to put a covering over a new door that will be installed. The covering was initially going to be a gable-pitched covering with timber rafters that were somehow going to be connected to the building's profiled sheet cladding. I’m not sure if that is typical but I felt more comfortable putting in a new structural element for the roof to attach to instead of the cladding, hence the proposed new HSS section that is welded to the existing columns.

To get this system to work, I proposed that they change the roof type to flat/mono pitch as shown in red, where the timber rafters could attach to the steel member HSS using welded joist hanger clips (HU26 Simpson strong ties or something similar depending on rafter size).

The existing building is a typical warehouse-type building with a profiled steel outer cladding.

This has brought about a few questions :

1. The outer cladding will need to have a hole cut to allow the timber rafters to attach through and connect to the joist hangers. How can the cladding around the rafters be sealed to prevent water ingress etc?

2. The two columns that the HSS section will be welded to are oriented in opposite planes (one with the web face facing and the other one flange face facing. If I weld (flare bevel groove welds) the HSS beam to the flanges as shown in the sketch below, what local failure modes should I be checking (the force is not very large, the covering is only extending 4’ out, although I do live in a hurricane prone country where the uplift pressure will be ~2.2kPa).

3. Is it typical that these types of small roof coverings just attach to the exterior steel cladding of warehouse buildings or am I overthinking this?

Sketch below :

Any help or advice would be greatly appreciated.

 

[Greenalleycat]

Only have time for a quick response, I definitely support your proposal to attach this to the main structure
I would not be hanging something like this off the cladding, especially if you're in a hurricane zone

 

[jayrod12]

Another quick answer, they will cut the cladding all the way across for the full depth of the new roof structure, or at least that's what I'd expect. Then a piece of flashing would be jammed up before the new structure went in. Are you on the hook for the building envelope details too, or structural only?

 

[Redacted]

@Greenalleycat Thanks, I'll continue on this path.

@jayrod12 Thanks, that makes sense regarding cutting the cladding along the full length. I'm not too familiar with flashing types but I'm assuming that you're talking about using embedded flashing that goes behind the exterior cladding? I'm also assuming that the flashing would need to extend out and go around each of the rafters as well. See below (is that what you are talking about or are you talking about a different detail?)

I'm really only supposed to be doing the structural but I can see that I will probably get pulled into the building envelope stuff as well, as no one else would be detailing this. I can put a note in the drawing to say flashing required but when construction starts there will be site questions regarding the detail.

My question still stands regarding the welding detail as well (welding to the flange edges). Load is only ~4kN of uplift on each end of the HSS but should I be putting stiffener plates in the existing columns at the locations of the HSS weld for out-of-plane movements?

 

[jayrod12]

Correct, however the new flashing piece would have the intent of lapping OVER the new roofing. So any water coming down the existing building cladding gets directed onto the roofing material.

What I've done in situations like yours is show the flashing, but specifically indicate that all of those items are shown for intent only. Design and detailing of building envelope items are not within your scope.

 

[Redacted]

@Jayrod12 Thanks that makes sense; I'll follow that approach regarding the note on the drawing for the flashing.