First Inspection : Pre Wrap Inspection

The first stage of any mechanical inspection is the Pre Wrap Inspection. It’s the check that must be done before ducts are insulated or enclosed. Once the ductwork is wrapped, you can’t see what’s underneath; so if you skip this inspection, you’d have to tear off the insulation later. That’s why the duct must be fully connected and approved before insulation begins.

 

A Rough Start

I went in half excited, half nervous but things didn’t go smoothly at first. I fumbled a bit during the initial inspection, and the inspector asked me to get better prepared and reschedule.

 

Then, we submitted two more inspection requests, but both were canceled by the GC. Their reason was that the installation “wasn’t perfect yet.” Technically, though, Pre Wrap isn’t a final inspection it’s more of a mid stage check, before the ducts are covered. A few minor imperfections are fine.

 

Still, the GC insisted that everything must look perfect before inspection. Looking back, I think they just wanted to avoid any red flags, since the overall schedule was tight. After about two weeks of delay, they suddenly rebooked it on their own, and ironically, the inspection passed easily almost anticlimactically.

 

Preparation

The first thing the inspector said when he arrived was:

“Do you have the approved plan set?”

 

I didn’t realize what that meant at first, but the GC handed over a stamped, approved plan set and that’s what the inspector wanted. He flipped through each sheet, verifying that the installed units matched the approved mechanical schedule exactly.

 

We tried showing him our tablet version of the drawings, but he refused, saying he only reviews the official stamped plans.

• Lesson learned: Always have a printed copy of your Approved Plan Set ready on site.

 

The Inspection

The inspector started by saying,

“Let’s go through each unit according to the drawings.”

He asked for the tonnage of each unit, then had his assistant take photos of the labels to verify against the schedule. Then came the big question,

“Where’s your seismic bracing?”

This project didn’t include any seismic bracing details in the design. Our boss had casually said, “It’ll be fine; we’ll deal with it later.” Well… we learned the hard way that “later” usually means “too late.” 😂

 

Even without specific bracing details, if the plan states SDC-D (Seismic Design Category D), you’re still required to follow CMC Section 605 and ASCE 7 for seismic restraint.

 

Fortunately, since this was just the Pre Wrap stage, the inspector agreed to defer seismic bracing to the next inspection (after insulation was complete).

 

What the Code Actually Says

1. Joints and Seams (Based on CMC Section 603.9)

Each duct joint should be tightly fixed with screws so that there’s no movement or air leak and sealed airtight using approved materials such as UL 181A or UL 181B tapes, mastics, or gaskets.

 

We used DP-1010 (UL 181 approved) sealant, and all joints were S & Drive connections, fully sealed after fastening.

At the grille connections, the ducts were wrapped with a blue self adhesive wrap, then taped over once more to prevent any air gaps or dust infiltration around the collar/boot.

 

2. Supports and Hangers (Based on CMC Section 604)

Duct supports must follow SMACNA standards or the manufacturer’s installation requirements. Additional supports are required near changes in direction or at transitions. Rod nuts must be double nutted or locked to prevent loosening.

 

We kept the support spacing within 8 feet, used 26 gauge galvanized steel ducts, and installed trapeze hangers at every elbow section. Any dents or visible damage on the duct surface can be grounds for rejection so visual inspection before wrapping is crucial.

 

3. Bracing (Based on CMC Section 605)

All duct systems must be braced and restrained to prevent excessive movement or lateral/horizontal swing due to vibration or earthquakes. Braces are usually set around 45°, and all anchors must be ICC-ESR approved.

 

We didn’t have the bracing installed yet, so this will be the focus of our next Seismic Bracing Inspection.

 

Helpful Resources

• Inspection Checklist (Unofficial Reference)
  It’s an old version, but still a good baseline for inspection prep.
  buildingincalifornia.com/checklists
  
  
• California Mechanical Code (Free Online Viewer)
  The official public version, searchable and always handy on site.
  epubs.iapmo.org/2022/CMC/index.html
  
  

Wrapping Up

The night before the inspection, I studied CMC Section 603 - Section 605 like I was preparing for a presentation…
and then, of course, the inspector didn’t ask a single code question 😅. After about 10 minutes of walking through the units and drawings, he signed off the plan, took a photo for records, and left. And just like that  Pre Wrap Inspection was done.

 

Next up: Seismic Bracing Inspection. Let’s hope I can nail that one too.