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Building Science

Understanding Indoor Air Quality (2) — Building Science Podcast

Your eyes, nose, and the back of your hand are surprisingly accurate IAQ diagnostic tools

This podcast series is excerpted from a two-day class called “Building Science Fundamentals” taught by Dr. Joe Lstiburek and Dr. John Straube, of Building Science Corporation.

Last week, Dr. Joe outlined a simple way of looking at air quality in a building: people, pollutant, path, pressure. This week, he describes his IAQ diagnostics procedure: Trust your gut, follow your nose, punish the youngsters and CEOs. __________________________________________________

A common IAQ nightmare: brick buildings with dropped ceilings

We have a dropped ceiling air handler, right? You put two or three air handlers in a dropped ceiling; the supply system is fully ducted, the return isn’t. You’re just simply pulling air out of the dropped ceiling. So that entire dropped ceiling goes to a negative pressure. So air is injected down, air is pulled up into the negative pressure field above the dropped ceiling, and we have air circulation. But this negative pressure field intersects the exterior at the roof/parapet connection. You rarely have the interior gypsum board connected to the top. And even if you do, it’s not sealed. Someone just shoves in a little bit of mineral wool. So whatever is in that exterior wall or parapet is being sucked right out of that exterior wall, into the return system, and ejected out the supply system, into the breathing zone of the occupied space. You’ve actually coupled your building enclosure to the occupant. The parapets are often the fresh-air intake for most buildings. And if it’s hot and humid outside, what kind of air are you bringing in? Hot humid air. And if it hits a cold surface — say a chilled water line — what’s going to happen? It’s going to condense and it’s going to drip.

Beware of humid air

The mechanical engineer doesn’t account for humidity load. This is a hidden load, a latent load, a humidity load that he’s unaware of. You know, he’ll know it’s there. It’s not in the calculations — it’s in the real world, but nobody thinks about it. This is a big deal. Now, if you’re lucky (and you rarely are) you’ll get enough condensation that it actually drips through, so you can actually see a stain. But you normally get just enough condensation to cause the humidity to rise in the dropped ceiling, but not enough for it to stain through the material. And when the humidity goes up, the thing that you notice is it begins to stink. And there are several distinct odors. How many people remember what puke smells like? Well, puke has a distinctive odor, and it’s actually called butyric acid, which comes from the fermentation of starch. Well, butyric acid is emitted from ceiling tiles that are made from cellulose and a starch binder. When the humidity goes above 80 or 85 percent, the butyric acid is emitted, and you have the odor of vomit. So one of the most common things you do when you lose control of the relative humidity because of the coupling of the negative pressure plenum to the outside wall is you get a whiff of vomit.

Your nose is a great diagnostic tool

Now, when I go into a building and I go — [inhales] — I don’t let the client know that I’m using my nose — my built-in gas chromatograph — to figure out that that’s what’s going on. But if I smell butyric acid, I know I’ve lost control of the relative humidity, and I know it’s the darn ceiling tile. It’s like, you know, the smoking gun that, if you’ve ever smelled it, you now know the connection and you know what’s going on. So that’s the first distinctive odor. They usually stay much wetter longer, because there’s moisture there that nobody anticipated being there. And you will often get a red bacteria growing on the coil, and it gives off the odor of John’s socks. We don’t call it John’s sock syndrome; we call it dirty sock syndrome. There’s a distinctive odor — it’s like a locker room. So you go in and you go [sniff] and if you smell vomit, or you smell a dirty sock, you’re immediately focusing on what? Dropped ceiling return plenum negative pressures coupled to the exterior wall. So you smell mold, or musty odor, you smell vomit, or you smell a dirty sock, and those are distinctive. I mean they’re not there all of the time, but eight out of ten times — you’ve pretty much got it sourced out that you’ve basically coupled your return plenum to the exterior wall. Remember, I’m talking as an engineer; I’m not talking to you as a scientist or a physicist. I’m just telling you my experience has taught me when I walk into a building and I’m thinking what? People, pollutant, path, pressure, hot wet, UV, ozone — this relationship is true. This is so common I don’t go to the projects anymore. Or I don’t want to go. I’m bored, I’m tired. I send the youngsters in the office. But they don’t want to go either cause they’re bored too. And so, you know, the client gets all annoyed because John or I get the work, but we don’t go out there. They get all pissed off they say, “We hired the great Oz and they sent us Toto.” So sometimes I have to go and so I take a youngster with me to abuse them.

Your eyes and gut can tell you a lot about a building

We get the call and we go, and I don’t want to get out of the car in the parking lot. I don’t _have_ to get out of the car in the parking lot. I was with Kohta at the time and he said, “Joe, you gotta get out of the car, get out of the car, come on get out of the car.” “I’m not getting out of the car! I don’t have to get out of the god damn car! It’s stupid! Look!” And, you know, Kohta’s going, “what, what, what?” “You don’t have to get out of the car!” I have brick, so I have — what? A reservoir cladding. I don’t need to put a hole in the wall to know I’ve got — what? Mortar droppings. You know that it’s steel studs cause they’re all friggin’ steel studs. You know that they’re Dens-Glass Gold cause they’re all friggin’ Dens-Glass Gold. You know that they all have Tyvek and if they don’t they have tar paper. You know they’ve got friggin’ fiberglass in the wall cavity and it’s a fifty-fifty chance that I’ve got a plastic vapor barrier or vinyl wallpaper on the inside. Now, what kind of a mechanical system do I have? Nine times out of ten I’m going to have what? Dropped ceiling return plenum. So before I get out of the darn car, out of the parking lot, I have a nine out of ten certainty that whatever’s in that wall is not going to be good, and is in the breathing zone of the occupied space. But they’re paying me, and so I have to get my fat ass out of the car, and go in. So I’m not happy about it. So the first thing you do is you pop the ceiling tile, but you do it in the corner office to piss off the CEO who made you go there. And what do you see? There’s no connection between the gypsum board and the underside of the roof. You can actually see the exposed fiberglass, right? We knew that! And it’s dusty. Why is it dusty? You’re pulling the air through it. So we’re just actually sucking on it. You know? Because I knew it was a problem, because after it rains, three or four days later we always get this musty odor. You know? So, “Well, OK, we’ll send somebody out.” “We want you!!” “Well, OK.”

First, seal the gaps

So off I go, I’m out of the car, and I’m laughing at this. So how do we fix it? Well, we run the gypsum board up to the underside and we now try to make a positive connection by spraying PVA — polyvinyl acetate — and some pookie. But we want pookie that doesn’t burn. It ain’t easy to find pookie that doesn’t burn. So you’re gonna use something, you know, like FireDam from 3M, cause it’s a pookie that doesn’t burn.

Then, equalize the pressure

Are we done yet? No. Then what do we do? We add something called a return duct to the air handler. This is something engineers don’t know about. It’s not very big, it’s very very short. It just has to attach to the unit, and go right down through the ceiling tile. Are you with me on this? So I’m no longer sucking from where? I’m not sucking from the dropped ceiling, I’m sucking from the space. So then I take every fifteenth tile and I throw it away, and I put in a grille. And what’s the function of the grille? Well, to equalize the pressure. I don’t want to suck on the wall any more, so I’m bleeding the negative pressure field. I’m bleeding it two ways: One, I’m putting a return duct on it, and two, I’m perforating the ceiling. Well, why won’t the return duct itself work? Well, because you know the air duct, the air handler, and all of the pieces are going to leak no matter how good you are. And you don’t know where that leakage is going to be — on the return or the supply side. You just know what? It’s going to leak, and so by perforating it, it means you’re going to equalize the pressure regardless of what’s going on. Because what you’ve done is you’ve put that thing in the middle of the room. If you put it in the middle of the room, from a pressure-field perspective it’s doing only what we wanted it to do in the first place, which is to circulate the air without causing a pressure difference. So that’s it! So, you disconnect, you fill the hole, you bleed the pressure field, and you’re done.

What if you only seal the gap?

If I had just run the gypsum board to make that connection and I didn’t do anything else, would there have been a problem? And the answer is: it depends on how good of a connection I made between the ceiling and the gypsum board. It’s very, very difficult to make a good connection. And so we would still have stuff being pulled out of the wall. We just wouldn’t have very much being pulled out of the wall. Well, now it becomes a dilution question. What’s the rate of removal ventilation, versus the rate that we’re sucking it in? And that’s impossible to determine unless you do what now? Measure. But measuring isn’t easy. What are you measuring for? See, do you measure the tiny particles? Or the medium-sized particles, or the big-sized particles? And are they viable, or non-viable? Well then, you have to plant them, and grow them, and nurture them like a farmer, you know? And depending on what relative temperature you incubate them at, is going to determine what you get. Anyway there’s about forty-two different combinations that you’d have to do for each sample. At that point it’s more difficult to figure out what’s going on with sampling than to just say, screw it! I should just take the ceiling tile out, and put in the return and bleed the pressure — because the cost of the diagnosis is going to be more expensive than the repair, you know? The big decision should be: is my wall getting wet and soggy, and should I intervene and fix that? And more often than not, we don’t get a shot at that. Why? Well, I’ll talk to you about the politics. Who called me into the space? It was usually the tenant, not the landlord. So I’m fixing what I can within the tenant’s control.

After you solve the moisture problem, is mold a problem?

Behind the vinyl wallpaper in moist buildings is where we often find the dreaded black mold. So? So freaking what? It’s not — where? Inside! Can I leave it there? Yeah! Well, what are the consequences of leaving it there? Well, depends on how much moisture is coming in. At some point the gypsum board might get — what? Soft. And so you’re going to have to intervene in the places where you have an actual breakdown of the product. That’s not usually everywhere. It’s usually on the south and west exposures. You only rip it out if you have access to — what? OPM — other people’s money. And so if you have access to money, the conservative, safe bet is to do what? Rip it out, because the world is filled with stupid people that think it’s dangerous. If it’s not coming out of the wall, I don’t care. If I have access to money, I’m going to take it out because someone’s going to think it’s going to affect the real-estate value. You know what? That in itself is a justification to take it out. If you have access to what? Money. But if you don’t have access to money, leave it there. We get all kinds of people who have moldy crawl spaces . And they’re poor. They don’t have twenty thousand dollars to decontaminate a friggin’ crawl space. Which we scare them about — “you’re all gonna die!” Well, you friggin’ close the crawl space vents, put in a hundred-dollar exhaust fan, or radon fan, and suck on it and the air moves in the other direction. What have we done? We’ve left the mold in place. Big friggin’ deal. But that’s not a popular view, because there’s an awful lot of money available to do — what? Mold remediation, and scare people. Now, what do I do? Well, at the end of the day, you have to solve what? The mold problem. You solve it by solving the water problem that caused the mold problem. What you should probably do is take the vinyl wallpaper off. Now what happens is, when you take it off you have to be careful, because what’s going to be behind it? Mold. And one of the ways you should deal with mold is deal with it like you deal with drywall dust, right? Because if you rip it off, that’s when you trash the rest of the building! Right? So you ought not to have it spread around. So if you’re going to take it off, you may as well hire someone to take it off correctly. But you only do that if you have access to people who can actually pay for it. Otherwise you’re going to do what? Leave it alone. So, a pretty fundamental example of people, pollutant, path, pressure.


  1. marty | | #1

    Puke smell from mdf
    We have a shop in Perth, we had mdf installed 3 months ago It is on a bracket system, away from the wall, and now the whole shop every morning smells of vomit.The mdf came from asia.Any ideas what we are facing???

  2. Anonymous | | #2

    Dirty Sock - Red Particles
    We had a coated heating coil installed last year which resolved our dirty sock odor. However last year and now this year, red tissue like particles are coming out of the hot air ducts when the fan comes on. Last year the particles were analyzed as algae. I've called the contractor for service. Any thoughts on what's going on? Is this a health issue? Is this a red bacteria?

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