Popular Chain Restaurant in SC Has Ducts That May Be Illegal
One of the things that happens when you learn building science and HVAC design principles is that you can no longer go into any building without looking at the building envelope and mechanical systems. Now that my smart phone doubles as a high-resolution camera, I usually get photos of the interesting things I see, too. For example, that photo of the duct donut fed by 3 air handlers at left is something I saw at Pike's Nursery in Atlanta a few weeks ago. Beautiful!
You know from the title, though, that I'm not here to talk to you about beautiful design today. No, in this article I'm going to look at something that most likely violated the local building code where it was built in South Carolina. The photo below shows a panned joist duct used for supply air in a popular chain restaurant famous for its homestyle cooking, peg board games, and country kitsch. I visited this one in South Carolina yesterday on my way to IECC climate zone 5 (i.e., the North Carolina mountains).
Why is this bad, you ask? Here are a few reasons:
- Most building codes don't allow building cavities to be used for supply ducts (the ones that move the conditioned air into the space).
- Building cavities are very difficult to seal properly.
- If the top side of that panned joist is part of the building envelope, it could cause serious moisture problems and grow mold.
- If the top side is part of the building envelope, there could be a lot of heat loss or gain because insulation isn't always as it should be in attics.
It's called a panned joist because what they've done here is screwed a piece of sheet metal across a ceiling joist cavity, thus 'panning' it. This is allowed for return ducts, but it's not a good idea for them either. Haven't I mentioned that before?
Granted, all I could see was the outside, so it's possible that the inside of that cavity was lined and insulated with approved duct material. Possible, but who knows really. I've seen so many bad duct installations of all varieties that I'm skeptical. It just has the look of a 'screw it up [the sheet metal, that is] and let's get out of here' kind of job. I do give them points for neatness, though.
The really bad thing is that if these really were code-violation panned joist supply ducts, the ceiling was full of them. They had strips of them all across the restaurant, spaced only about 6-8 feet apart and running almost the full length of the restaurant from front-to-back.
If you're installing a duct system, make sure you use approved duct materials: sheet metal (hard pipe), flex duct, or rigid fiberglass ductboard. I've put them in the order that I prefer, and even though ductboard is approved, I'd never spec it for a job.
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