- [Corbett] Air does what it wants.

- It was as if the house had flooded and never been remediated, and we're like, "The house hasn't even ever had a leak."

- Something's really wrong.

- All those sorts of chemicals and fumes can work their way into our house.

- [Jason] The duct work was so colonized that it looked like leopard skin.

- The builder has all the power and can really do whatever they want.

- There's a much better way to do this.

- [Announcer] "Home Diagnosis" is made possible by support from: Broan-NuTone, better air, better life; by the GOT MOLD?

Test Kit, real science, real simple; by AirCycler, Retrotec, Rockwool, and RenewAire; by generous support from these underwriters; and by viewers like you.

(gentle music) - How important is air leakage really?

- If you've watched previous seasons of "Home Diagnosis," you know that the science of homes usually starts with air leakage.

- But since it's invisible, it can be hard to remember to take it seriously.

- So quick review of the physics.

There are three forces at work in your home right now.

Pressures from outside.

- [Grace] Wind.

- [Corbett] Pressures from inside.

- [Grace] Fans.

- [Corbett] And between inside and outside.

- Stack effect.

So let's make the invisible visible.

(gentle music) - [Announcer] It's the shields we build (gentle music continues) and the risks we take.

(gentle music continues) It's the disasters that will test us (gentle music continues) and what will grow from them.

It's real life and the physics, chemistry, and microbiology of the science of homes.

(gentle music continues) - Hi, my name is Anil Mittal and I am currently in a three-year-long legal battle with the largest builder in the United States of America.

- [Director] That's fabulous.

I'm gonna hold right there.

- Yes.

(director laughs) Essentially, the superintendent that was building our house was simultaneously building 21 other houses at the same time.

So obviously he didn't have the ability to really keep an eye on what was going on in our house.

And with the construction boom that was happening in Houston, every subcontractor wants to get in, get out really quick, make their money, and do the quickest job possible.

Additionally, in the area of Texas that we live in, there are no inspections.

There's no real permitting.

There's no real inspections by a county organization or a city.

That leaves, really, us as consumers in a bad place because a builder has all the power and the builder can really do whatever they want.

- So a really fast build of five months.

You move into the home, and within eight months, you are bedridden.

- Mm-hm, and I had never been bedridden before.

- As soon as we moved into the house, we had problems with the house.

We tried to have the builder fix those problems with the house.

They did not successfully fix those problems.

Or actually, on second thought, we thought they had successfully fixed the problems.

We became more comfortable in the house, humidity became a little bit more controlled, but then we thought that was the best that we could expect from a house like this.

Between the time that we closed on the house and the time that we moved out of the house, I believe the HVAC subcontractor came back to do some sort of an adjustment or repair about 45 to 60 times.

We had planned a trip to Las Vegas, and because of her health issues, we couldn't go.

So I had decided to put in some recessed lights in our media room, and while I was in the attic crawling around, I put my hand down in the insulation and it was soaking wet and I looked up and I didn't see a leak in the roof at all.

So I started digging around in the insulation to try to figure out if it was a pipe leaking or what was causing the issue and what I found is that it was an air conditioning duct going through a chase down to the first floor, and it was squeezed through a hole that was too small.

It wasn't sealed and I guess there was condensation that was accumulating outside the duct causing that to stay wet.

And all the wood in that area was black.

- So we found it totally by accident.

- Yeah, because we had been through so many trials and tribulations with the builder, we decided let's hire a professional mold inspector.

- Yeah.

- We hired the inspector.

She had come in, run a number of tests, and found very high mold concentrations throughout the house.

Not just in that area, but in many areas of the house.

- I mean, so bad that it was, she said it was as if the house had flooded and never been remediated, and we're like, "The house hasn't even ever had a leak."

- Water leak ever, yeah.

- Nothing.

And this was after Harvey, right?

So, like, we're like, "Yeah, it didn't even have a leak during Harvey."

And so we were just left wondering like, "How is this even possible, right?

Like, how do you have such mold growth when there's never been a leak?"

- For the most part, the dynamic was pretty clear.

You've got a lot of humidity outside.

It makes its way in through the attic ventilation.

And then because of the nature of the HVAC system, the house is actually under negative pressure.

So the air is actually being sucked out of the house.

So of course, air being sucked out of a house, air has to come back in, and so you can follow it and you can see warm waste air being drawn down into the interstitial cavities where it's being exposed to a variety of different temperatures and dynamics because you've got duct work in there where you're gonna get condensation and drips.

That's why you see the ceiling, the drips inside the ceiling.

The ceiling cavity itself seems to be being used as an air conveyance system in certain areas, which is a big no-no, but also not all that uncommon.

And you can see the real manifestation of this, the most egregious example of how bad the mold in that house is, is really in the attic around the HVAC system itself.

HVAC systems, in my professional opinion, should never be located in an unconditioned space.

You're heating and cooling your air, but putting the equipment in the hottest and coldest places.

You're making it work twice as hard.

And you're also introducing the variability that there's likely gonna be a lot of air going into the system through leaky duct work.

The HVAC system in the attic was completely covered in visible mold.

The duct work was so colonized that it looked like leopard skin.

Really amazing, and everything was very dense.

It was a rat's nest of interwoven flex ducts that can never be cleaned by the way.

These are temporary at best, but they're being used as permanent.

It's an unfortunate reality that that is the defacto standard in most construction these days.

Putting air conditioning systems in unconditioned space and then also running these substandard flex ducts as a primary duct system.

- One of the big challenges that we run into with air leakage testing is what to do about the interstitial spaces.

So an interstitial space is the space behind a wall that might be connected to other interstitial spaces.

So this is where you see things like your electrical wiring, your plumbing, your ducts.

- Every home is different.

Every home is going to exchange air from the inside of it with the outside at a different rate.

Older homes tend to be really leaky with lots of cracks.

So that exchange is really fast.

- Air kind of sneaks into the house through a process that we call infiltration.

And so you have this wall cavity that might be filled with an insulation material, and depending on the construction of the home and where very small cracks and gaps in the envelope might exist, over time, what builds up in that wall cavity could find its way into an airflow path entering your home.

- Clearly it's a great idea to train people who are going into homes doing building science on actual homes, but you also have to be able to do it in classrooms and maybe online nowadays.

So we have training props.

This is called a house of pressure.

It's a tiny little plexiglass house you can see into.

You can see you've got a TV with a aerial going through and making a hole in the attic floor and coming out through the roof.

And we've also got this big duct system that you can see we've got a supply and a return on.

And if I wanted to, I could show you what happens when your supply side of your duct system leaks to outside, vice versa on the return side.

And obviously this is a little simplistic, not very sophisticated.

There's a much better way to do this, which looks like this.

This is a big house of pressure and we've got Jake Nuckolls here at the Building Performance Center in Washington that's gonna show us how all this works.

- So we use these props specifically as people are gaining an understanding of how air moves through a building.

And one of the things that we love to play with is just the idea of pressure.

We have the ability to turn on a duct system.

The blue is the return down here.

The red ducts that you can see here with the little fancy ribbon out the top, that's the supply side ducting.

We also have normal elements of a house.

We've got openings in the house like doors.

We can open different areas that replicate windows.

We can have connections between floors here.

So these little sliders here open up gaps between the attic and the main body of the house.

What we like to do is set up our manometer outside and feed that tube inside so that we can begin by getting a pressure for the house.

So what we like to start with is obviously our baseline measurement, which isn't gonna be a huge difference because we're testing inside of a house inside of a warehouse.

But in this case, we do have a small amount of pressure buildup that's inside of our little space here.

And I'm gonna start messing with the ventilation systems that are inside this house.

Around the side here, we've got a bunch of switches where we can operate the kitchen fan, bath fan, and dryer.

And what I can do is choose which one of these I want to start to have operational, to have non-operational, and I can set these up for our learners to come in and find which is the worst pressure that's possible in the house.

That's typically where we start.

So I'm gonna turn on a kitchen fan and a bath fan and you'll see we've color coded these lights so that we can see when they're actually running.

And we take a look at what kind of pressure difference we've made inside of this test house.

This is a small house, this is a tiny house, but what we're trying to replicate is the adjustment to the changes that happen with the pressures inside of our normal houses, and allowing our learners to start to recognize how different ventilation systems will affect the rest of the house.

So let's add our dryer to the situation.

And we can now see what effect the dryer has had on this house as it stands right now.

So we've turned on all of our fans.

Now we're gonna see what effect the duct system has.

So I'm gonna turn on this little rheostat over here.

We can verify that our supply registers are actually blowing the air out into the space.

We have nice ribbon coming out the top on each one of these sides here.

And very lastly, we can close bedroom doors.

And now we've got all of our fans turned on, we've got the duct work turned on, and now we have closed the doors and limited the access to this space and we can see a massive pressure change.

We went from 1.5 negative to -5.6, 5.7.

One of the reasons why we test pressure in houses is to see how the air can move from the outside to the inside of our houses.

And in often cases, it comes through places that we don't want that air to come through.

And in this case, we are measuring a fireplace.

So in that living room space, we have a fireplace and we've depressurized this area.

Now, watch what happens to this smoke, this little smoke pencil right here, when I put this smoke up near the chimney.

You can see the direction that that smoke is going is straight down the chimney and into the house.

Now, it's fairly obvious why we would care that that smoke is going back inside the house.

If we have a fire going during the winter time and our house is set up like this, the smoke from that fireplace and all the additional particulate matter and toxins are coming into our breathable living space, something we want to avoid at all costs.

So additionally with fireplaces, we also want to check our adjacent spaces.

This, you can see by our vehicle right here, is our garage, our makeshift garage, and any pathway from this garage into the house, we have the potential to draw toxic fumes, gas.

I mean, people store all sorts of things in their garage.

And all those sorts of chemicals and fumes can work their way into our house.

And you can see here, my smoke is drifting right alongside that duct system into the living space of the house.

So when we talk about pressure in a home, we're not just talking about random numbers on a screen.

We're not talking about certain regulations that we have that we want to achieve when we go out to a house.

We don't necessarily need to hit a specific number on our manometer.

What we want to see our pressure testing as is really a way to measure the health to a certain extent of the houses that we're in.

Pressure in a house might relate to blood pressure.

Your blood pressure gets too high, you have problems.

Your blood pressure gets too low, you've got problems.

You're at two ends of the extreme.

And we want to measure what that pressure is that's happening in this box to relate to the houses that we live in in order to measure their health as well.

- Yeah, a lab is not a home.

If we just work in a lab and we do this in the equivalent of a test tube, then we would miss all of the rich and interesting chemistry that is what makes a home a home.

We would miss the microbes that live on the dust in the corners of the house.

We would miss that for years, there's been permeation of gases from people being inside the house into the paint and into the drywall.

We would miss the reality of real light coming through the windows and sparking chemical reactions.

What we really needed was a house that was really well understood, one where every temperature on the wall was measured, where the pressure in the house was really well understood, the air flows inside the house between each room and each floor, between the basement, the first floor, the second floor, the attic.

We need to actually work in a real-world environment where there is paint on drywall that's built with insulation and it's got siding behind it.

We need a real home.

We need a place where the air permeates between the indoor and the outdoor environment, even if it's really slow.

We need to understand that, right?

But we need those processes to occur.

And so that's what brought us here to NIST, is that this is a house here where it's incredibly well understood, it's very well modeled, and so we don't need to worry about how air moves around the building.

We just get to ask the questions that we wanna ask.

We've been frying up a lot of bacon to create lots of particles in a home so that we can watch how those particles move through the house.

And we really can see them move from the kitchen upstairs to the various bedrooms.

We can watch that particle pollution move with time.

But we also can do experiments like ask what happens if you have an air pollution event and you bring ozone into your house after you've cooked?

And it turns out to be pretty exciting chemistry.

So all of the oils and other very lovely smelling remnants of your bacon or your fish sticks or your chicken nuggets, once you have some gases in the air and you have some oils on the surfaces, if you add in ozone, air pollution, then you can make these tiny little new particles and you can spur all sorts of interesting chemistry that we're beginning to track down and trace and figure it out.

So the cooking experiments aren't just about, what do you breathe when you cook?

They're really about what happens when air pollution enters your home having done everyday activities.

- Yes, when I first walked in the house, I asked Anil if he had kept the air conditioning on because I noticed that it was cool.

And he said yes.

That was reaffirming because the reality is, is that most people who leave a house because of these conditions will often turn off the utilities.

They'll turn off the heat or the air conditioning.

We call that vacation home syndrome.

This happens a lot where, you know, everyone's gone to a place where they open up the door for their vacation and they smell that smell.

And that's because someone decided they were gonna save a couple hundred bucks on the utility bill and then they cost themselves many, many thousands of dollars in mold remediation bills instead.

And so seeing that Anil was responsibly conditioning the air was reassuring.

But even so, and perhaps also, perhaps because of all of that cooling, we're seeing condensation form.

But that's the way the building is supposed to be managed, and it's manifesting as uncontrolled mold growth.

So if you're doing what you're supposed to be doing in a climate like this and it manifests as significant pervasive mold growth, something's really wrong.

- One thing we've learned watching these houses go up around us is that they go up very quickly, they all go up in the exact same manner, and they go up without regard to the correct order in which you build a house.

They're trying to keep a schedule, they're trying to close on time, and you can see when these houses are going up the type of problems they're going to have in five years and 10 years and 15 years.

These are not houses like our parents had where they last for 50, 60, 70 years.

You're lucky if you get 20 years out of one of these houses without a major rebuild.

They're using materials that are not tolerant to mistakes.

And there are a lot of mistakes made by a lot of subcontractors trying to do a lot of work in a little bit of time.

If you're in a situation where you have to buy a production built house, if you can, visit the house every day, educate yourself about basic building practices, educate yourself on basic building science, watch them like a hawk, and then move out of that house in five years, because building a house is a complicated process and if you don't have somebody there watching that process and stopping and halting work when it needs to be halted to fix an issue instead of just trying to meet a closing schedule, you will have problems.

(gentle music) - [Corbett] Humid air getting pulled inside is bad enough, but this recent client of ours was breathing air coming down the chimney, which is a perfect case for why we never recommend indoor fireplaces in modern homes, even ventless.

Those are bad for us too.

In this case, we tested how much suction the house was creating through the bath fans, kitchen exhaust, duct leakage, and the dryer.

And of course, we had to relieve that suction with intentional make-up air from outside.

But they also ended up removing the chimney completely so they'd never have to worry about getting sick from soot again.

Take this story with you when you plan your future living room.

Fireplaces go outside in the 21st century.

(gentle music continues) - My main focus in my research group is multi-family buildings.

I think it's an incredibly interesting building type because they're often high rise buildings, so they see a lot of air leakage issues that we might experience in high-rise commercial buildings, but at the same time, these are people's homes and everybody uses their home in a different way.

They might open their windows, they might be cooking, they might be smoking.

So in our research, what we're really interested in is air leakage between suites and how air moves between the zones within the building.

That influences things like contaminants from the parking garage getting into occupied spaces.

Uncontrolled air leakage influences things like how effective the central ventilation system can perform.

And then looking at that from the occupant side of things, uncontrolled air leakage means odor transmission, it means sound transmission, it means pest transmission.

So there are a lot of negative consequences to occupants if we don't have that air leakage under control.

When we look at air leakage at the suite level, it becomes a lot more complicated than a single-family home because the suite is surrounded by suites above and below, side to side, and then you have the corridor.

So five sides of your suite are actually adjacent to other interior spaces.

So the way we go about conducting air leakage testing in a suite is an approach that's called sequential pressure neutralization.

Let's break it down.

So if you start off imagining your single suite.

You're pressurizing and depressurizing that suite just as you would a single-family home.

But then one by one, you pressurize the adjacent suites.

Now, each time you pressurize an adjacent suite, the effect of air leakage across that boundary separating the suites drops away.

And so as you add suite by suite, you can isolate the leakage of each of the six sides of the suite.

So using this testing approach, we need six or seven fans, lots of pressure gauges.

It takes about eight hours to do one test, assuming that all goes well.

But it provides us a really rich data set where we can understand exactly where the leakage pads tend to be.

So in most multi-family buildings, the luckiest of the six sides of the suite is the corridor-suite partition.

The ventilation systems in most multi-family buildings, be they post-war or new buildings, tend to be what we call a pressurized corridor system.

These systems are designed to positively pressurize the corridor relative to the suite.

So kind of imagine blowing up a balloon, trying to force the air from the corridor into the suites.

In these buildings, you'll tend to see undercuts in the door and that's there by design to allow that transfer of outdoor air to move from the corridor into the suite.

However, when the weather starts to get colder outside, we tend to see stack effect acting on these buildings.

And as you might imagine, the taller the building, the greater the stack effect.

You have the ventilation unit on the roof trying to force the air down while stack effect, at a much greater pressure, is pushing the air up.

So the net effect is that you end up having negative pressurization of corridors at the bottom of the building, so air now being sucked from the suites into the common corridor space, and then being driven up through vertical chases like elevator shafts, garbage shoots, stairwells, into the suites at the top of the building.

So when it comes to controlling interzonal airflow or suite-to-suite transmission of air, it's actually more effective to tighten up the elevator door and the stairwell door, cutting off those vertical shafts that really drive stack effect, than tightening up the enclosure.

One of the other big challenges we see in multi-family buildings is acoustic discomfort.

So related to what your neighbors are doing, they might be watching TV, they might be bouncing a basketball, they might be moving furniture, because we know that a lot of sound transmission is actually airborne sound transmission.

And so rather than using this really complex, very time-consuming method called sequential pressure neutralization, can we simply set up a loudspeaker in one side with a mic on the other side and get an idea of what the air leakage of those partitions are?

So it can certainly be used as a screening tool.

It's very difficult to actually quantify air leakage using that acoustic method, but it certainly provides a potential easier, more cost-effective, quicker test method to figure out which are the partitions that you might wanna pay attention to when you're considering an air tightness type retrofit.

- So after meeting Anil and Nilima and taking a walk through the home, none of it is very surprising in terms of the health issues she's dealing with.

But in terms of the extreme nature of this, I would say it falls into the top 1%.

And the reason for that is not so much that there's so much mold, but rather that there's so much that's not visible.

Once we started pulling down speakers and going into the interstitial wall cavities, the density of the mold and the scope of the infestation was remarkable.

You see visible mold from the air flows coming out of electrical outlets in interior rooms.

It looks a lot like the tip of the iceberg, right?

That little tiny bit, that few percent that sits above the surface, this is a perfect example of exactly that.

- When you know what to look for, you start to see the labyrinth of air leakage everywhere.

- Air does what it wants.

And as you saw with Anil and Nilima, it can become very dangerous very fast.

- If you wanna be in control of your home, start with controlling your air.

- Next episode, we'll explore another thing that comes through those gaps and cracks: critters.

- To learn more about how to apply this science to your own home, visit homediagnosis.tv.

We'll see you later.

(mellow music) (mellow music continues) (mellow music continues) - [Announcer] "Home Diagnosis" is made possible by support from: Broan-NuTone, better air, better life; by the GOT MOLD?

Test Kit, real science, real simple; by AirCycler, Retrotec, Rockwool, and RenewAire; by generous support from these underwriters; and by viewers like you.