(tone beeps) - [Narrator] Coming up on Home Diagnosis... - The spookiest part: water.

Is it going to cost more to do it right?

Yes.

Is it going to take more time to do it right?

Yes.

- [Grace] You know, we love science, but this whole first part became really frustrating.

- Taking my hat off again, because this time it's for bad news.

- [Grace] Then it started raining, and it just rained and rained and rained.

- [Corbett] Several dozen different kinds of mold and mildew.

- [Rob] A species that one culture really enjoys is another culture's pest.

- [Grace] Woo, we're pouring.

- [Narrator] "Home Diagnosis" is made possible by support from the Alfred P. Sloan Foundation, by Fantech- 'Breathe Easy', by Broan-NuTone- 'Come home to fresh air', by Aprilaire- 'Everyone deserves healthy air', by AirCycler, Retrotec and Santa Fe Dehumidifiers, by generous support from these underwriters, and by viewers like you.

- You've seen water damage in other home shows, and there's always a terrifying reveal of tearing open a wall to find splotchy green and purple fuzz.

And then the house gets renovated, and everything's beautiful and fine.

- But today, we're going to explore the more subtle science behind how water, in all its forms, flows through every home, every day, in healthy and unhealthy ways.

- [Grace] They say home is where the heart is.

- [Corbett] And we certainly put our heart into building our first house.

So how hard could it be to build another one?

- I'm Grace.

- And I'm Corbett.

- [Grace] In our TinyLab, we helped homeowners gain control of their homes through scientific testing.

Now, as we build our forever home, we're testing ourselves.

- [Corbett] Even though we know a few things about the invisible dynamics of homes, we're teaming up with scientists and building experts to design and build a perfectly tuned home for our family.

- [Grace] The physics, chemistry and microbiology of a home might seem mysterious, but it doesn't need to be.

- [Corbett] While this is a personal story full of twists and turns... - [Grace] It's also the story of the science of homes.

- [Corbett] Join us to unlock the mysterious science of your home too.

So if you remember, day one found some stuff in the dirt.

Had to go immediately over-budget and behind schedule.

And so we took out the trash, brought in new dirt, compacted it down, but that's not the end of the story.

- No, because then it started raining, and it just rained and rained and rained.

And so poor Corbett is out there as the temperatures are starting to drop, literally wet-vac'ing away the water so he can get to the earth.

- Is it going to cost more to do it right?

Yes.

Is it going to take more time to do it right?

Yes.

If I wanted to be really extreme, I would have erected a circus tent over this site.

And I would have put a line of sandbags up the hill there to make sure that the water diverted.

Everyone always either says, "Wow, you started your build at exactly the right time."

Or, "You started your build at the perfectly wrong time."

The rain, especially in the wintertime, doesn't dry out.

And I know, now that we've been on this land a little while, it actually rains all the time here, so you could start whenever.

The issue was that this was one of the rainiest months on record.

- And so when all that water is happening, too, one of the interesting things that happens that our geotechnical engineer informed us is that if you step here, about five feet away the soil shifts, which is just something you don't even think about.

- Corbett did do things the right way.

Placed a lot of fill in here, and we talked through the whole process when he was putting it in.

So he's compacted it in layers, and everything was great.

But it's like having a recipe to bake a cake.

If you got the perfect recipe, but you eliminate some ingredients, you'd have a problem.

So similar thing here- things were done, but it's been a few weeks.

We've had some weather and some activity with equipment and people- - Just walking.

- Walking around that has softened the upper eight to twelve inches of soil directly beneath the footing.

- And the reason this is all so important is because over there, the house will sit on rock.

That's not going to move.

This stuff, if this all moves and that doesn't move, my house is out of true, and it's going to start cracking and weird stuff is going to happen.

And now it's not structurally stable anymore.

- And I hate to be the bearer of bad news, but you will be calling me in six to 12 months and saying, "Why are my doors and windows not opening like they should?"

- [Grace] So we dug the entire strip footing down by 12" with a shovel, and made sure the bottom of the trench was nice and hard before we packed gravel into the trench.

Now we can pour the concrete footings that the entire weight of our house will rest on.

- [Nanette] Is this house going to be heavy to move?

- Yes, this house will never, ever move.

Forever.

- Why?

- Because we don't want it to move.

We have a house that moves already.

Most people's houses don't move, did you know that?

- Why?

- Because other people are not as crazy as we are.

Or they're crazy, but they hide it.

- Second huge construction day on this build: pouring the foundation walls.

But of course, the day after we poured, torrential rain.

Which now starts eroding the ground underneath my concrete foundation foot, which is supposed to be the foundation of everything that gets built on top of this.

So of course, now I'm having a heart attack.

These rocks that are underneath the footing are starting to get washed away.

Because they're really good at being compacted, but they don't weigh much.

Water is no joke.

It will carry away anything you put in its way.

So all of the rain that's falling uphill from us, and the rain that's falling now inside the footprint of our house is trying to get out, and it's taking things that are in its way with it.

The whole thing becomes a real race against the geography and the geology of what you're doing, which again, those are scientific ideas.

But really, when you get down to it, it's just a bunch of dirt and water doing what it wants to do.

Big adventure- would not want to do it again.

Dear "Home Diagnosis," what's up with my crawlspace?

Is it supposed to be like this?

- Some builders had a great idea once for keeping homes dry: build them up off the ground.

You can see houses on piers at any beach, and it works.

- Then people started trying to hide stuff under their homes, so they asked for fences around the underside.

Then we started installing the heating and cooling equipment and ducts down there, and we put up actual walls and called it a 'crawlspace.'

- And this is when we start doing the opposite of what we intended.

Instead of making the home drier, we made it wetter.

Now, any moisture evaporating from the dirt under the house, and there is a lot of it, can't escape to the outdoors, and it humidifies the house above, bringing with it gases and life forms in the ground, too.

- So to try and combat this, we put vents in the walls and called it a 'vented crawlspace.'

Research and testing since the 1980s has proven that this does not work the way it's supposed to.

The idea is that if we flush it with outside air, the crawlspace will be just like the outdoors but with no animals, precipitation, or wind.

- This idea is terrific, until you consider that the sun will never shine in the crawlspace in humid months, which makes it cooler, and makes it wet with condensation.

Just like a cold drink on a hot day, the crawl space surfaces, especially any ductwork, will sweat.

- As we always explore in "Home Diagnosis" homes have been changing for the past century, whether we know it or not.

Bringing the crawl space inside is almost always the right way to go.

It's important to have the right tools for testing dynamics and the right systems built into your home to control those dynamics.

- Hey guys.

See these little spots?

You see these nasty little things?

I thought it was pollen.

It's moving.

Y'all, those are bugs.

- What I study in homes includes things that are microbes, and also bigger things.

And so the microbes are just all those life-forms that are too small for us to see.

And so that world is a big part of what we study in the home, and it turns out that that world is astonishingly diverse.

I think one of the interesting questions we can ask is: 'what's a pathogen' or 'what's a pest?'

What's a good species?

What's a bad species?

A species that one culture really enjoys is another culture's pest.

And so is a spider a pest?

Well, I don't think a spider is a pest in a house.

Most of the time a spider in your house is doing you a service.

Spider bites are extraordinarily rare.

Neighbor bites: far more common.

And so if you're worried about two things, your neighbor: far more dangerous.

And so in that context, in terms of actual harm, your neighbor is a pest and the spider is beneficial.

And so that boundary...

I mean, I don't know who you live next to, but in broad terms...

In a preschool, a kid is probably a thousandfold more likely to be bitten by another kid, relative to a spider.

And there have been great tests done where if you take the most dangerous spider in North America, and if you rub its back it, it will flee.

If you hold it down, it will flee.

If you hold it down twice, the odds that it bites start to go up.

In parts of tropical Asia, there are jumping spiders that specialize in eating the mosquitoes that transmit Dengue virus.

And they eat those mosquitoes only when they're blood-fed, so only after they've already bitten somebody.

And they're attracted to the odor of those mosquitoes.

And so they're definitely a beneficial spider.

They save lives.

If someone sprays pesticide in the house with those spiders, it kills the mosquitoes and the spiders.

But the pesticide eventually wears off.

And what then happens is the mosquitoes readily fly right back in- the spiders struggle to re-colonize.

What we welcome into our homes is really framed by our personal history, the culture to which we belong.

And I think that's important because those perceptions change dramatically over time.

We find ourselves in a kind of a paradoxical situation in that people become more aware that we depend on all these species that live on our bodies and in our bodies.

And at the same time, we're spending more on chemicals that kill those species than ever before.

And so somehow that's got to resolve.

- Hey guys, it's nighttime in the highest-performing tiny house on wheels in the world, which is a house just like other houses, except for a few important things.

First thing that I'd like to show you, which is what this video is about, is this: our lovely cats who are supposed to be fierce predators, and yet we have these ants.

We don't like to kill bugs, but these guys are one of the few things that we absolutely no mercy, it's a war.

Now, normal people would use pesticide.

They have a pest service who comes and sprays.

We live in a tiny house.

- [Grace] Shh.

- There's our baby girl.

And there's our three-year-old.

And this is the whole of the house.

We're not going to spray in here because it's a tiny house.

We have cats, we have kids, there is really no space, so you will be breathing all this stuff.

Do you have anything to add?

- Yay, toothbrushing!

Well, since a couple of people are going to say, "Use diatomaceous earth."

We've done that.

- Did it.

- "Use cedar oil."

- Did it.

- "Use natural insect repellent, put out traps."

- Yep.

There's just some things that you just can't know unless you live it, and we're living it.

This lumber has been only sitting here for a week, week-and-a-half tops.

It's been cold.

It's winter time.

It has rained.

But when it arrived, I covered it with plastic.

And then when it's sunny out, I uncover it to make sure that it gets a chance to dry out.

And while I've been doing that, covering and uncovering, and you can imagine how many construction sites you drive by are not covering their lumber at all, I have developed several dozen different kinds of mold and mildew on all of these pieces of wood.

Some of it is green, some of it is white, some of it is bright orange, it's beautiful.

This stuff is happening before you even put this lumber into the house.

- So the species that causes 'toxic black mold,' 'deadly black mold,' is a really mysterious species that we know very little about in nature.

And one of the things we didn't understand about this species relative to its wild nature and houses is how it gets in the houses in the first place.

Because what one often sees is if you have flooding in an area, suddenly it's everywhere.

And yet, if you sample the air in a house, which we've done lots of times, it's very rare in the air in houses.

And so the mystery in the literature for a long time, and there are plenty of mysteries about this fungus and so it wasn't even the one that was focused on, was where is it coming from?

How is it getting into a house and how does it seem to 'know' when a house has been flooded?

And then Birgitte Andersen, who's here in Denmark, she started to wonder if maybe what was happening was that it was actually lurking in the drywall.

That when you bought new drywall, that it was already there.

And longer story short, what she found was that in fact, this is the case, at least in Europe, and almost certainly in the US.

That a subset of drywall comes preloaded with several fungus species, which if your house never gets wet, they just sit there and they wait and they're, you know, they're kind of sad that they don't have the things that they need, but they're hopeful.

And then if your house floods, suddenly they encounter exactly the conditions they need, and they're just there waiting, and they grow like crazy.

- I am taking video for insurance purposes.

So our water bag has broken and gone completely under the floor of our airtight tiny house.

As you can see, there's lots of water down here.

The leak happened down there.

So where is our mattress right now?

- It's in the sun.

- Ah, on top of our - Solar panels.

- Solar panels.

And life is not always rosy.

- Yes.

(both laughing) Suffering is part of life.

Actually, a good thing: we're in Phoenix, Arizona.

It's the driest place this could possible happen.

- And in case you can't hear us very well, it's because we've got two massive fans trying to dry all the water out from underneath the cork flooring, which is now going UP.

Which, we hope it goes DOWN.

(Corbett laughs) - Welcome to my parents' crawl space.

When we first got here, the floor was dirt and the testing of the house revealed that this crawl space was not performing in the way that was ideal for what we wanted.

And once we fixed the floor of the crawl space here with this beautiful white membrane, we made this room drastically drier.

And we made it the coolest room in this entire house because the ductwork is down here, and the ductwork is a little leaky.

And so, of course, we've got a lot of air conditioning spilling.

We were able to jack the furnace up and slide this membrane underneath it, to be able to get it continuous there.

But we were not able to find an easy way to get this water heater out of the way to get this in, so the water heater is still sitting on a dirt floor.

That means a couple of things: one is that the moisture, and radon potentially also, is able to come up into this space, and we know enough to predict and hopefully prevent those things, or have a plan, at least.

And the second thing is that all of the rest of the dirt underneath the membrane can potentially send its stuff out here because that seam, where the plastic meets the dirt, cannot be taped like the rest of it can.

So now we can potentially pick up all of the rest of what's coming out of the dirt, and concentrate it coming out right here.

So this is our solution for right now.

As you can see, this looks a little experimental.

It doesn't look like a permanent install, and it's because it is an experiment.

What we are doing with this fan right here is pulling air through this pipe, and pushing it outside.

This is called an inline fan.

It's often used for radon mitigation systems.

This is not a radon mitigation system, for several reasons that we won't get into right now.

You'll see a real radon system in our build.

But this is a way to get the radon that is coming up into this crawlspace, where people are not walking around and living, to leave the house.

So essentially, what we're doing is making the crawlspace, suck on the house, and then exhausting air to outside rather than vice versa and having the house suck on the crawlspace.

Because of stack effect and the way that cool air moves down and warm air moves up, we've got some interesting dynamics happening just because of weather.

But this is going to equalize that and make sure that we always have a depressurized space down here.

Not an energy efficiency fix, but it is a performance fix because this is now helping us to control these invisible dynamics of physics and chemistry.

There is no manual or best practice on how to do this.

This is just playing around creatively with the four elements of home performance.

So once we're monitoring the radon levels upstairs, that's where the proof is.

- To start thinking about drying a home, we first need to consider whether we want to dry the air or dry stuff, because those are two different things.

- Of course, if you watch "Home Diagnosis," you know every home is a system.

So the air and stuff in your home are interacting with each other all the time, but it's always best to know what the goal is.

- If you're aiming to dry the air, first seal against humidity coming in, then make sure you're pushing out any humidity that's created inside, usually with showers or cooking.

- Keeping your stuff dry is really hard when there's water leaking anywhere.

So obviously that's a big one.

But what you might not have realized until now is that the moisture in the air, it gets pulled into the soft stuff in your home.

And when you dry the air a bit that moisture comes back out of the stuff and into the air.

- Soft stuff in your house is like a battery for moisture.

All of your furniture, your curtains, walls, rugs, beds, they're all soaking up moisture when your home gets humid, and they're saving it for later.

- If you want to control moisture swings, then the air-sealed, insulated skin of your home needs a dehumidifier running inside.

We prefer not to depend on the air conditioner by itself to dehumidify the air for reasons we'll get into later in season two of "Home Diagnosis."

So at the base of the entire foundation is the footing.

It's an extra-wide portion- you can see it right here.

Now you're going to need something to drain the water around the house, generally outside and also inside.

And you're going to need something that is a hollow container that has slots cut in it to allow water to get in here so that then it can be directed away from the house.

This is going to also enable us to hookup a radon mitigation system, which you're going to see down the line if you keep watching "Home Diagnosis."

This is going to immediately start working as soon as it's installed, but also we're going to need to wrap it in some filter fabric to make sure that water is the only thing that's getting into these slots- that we're not also packing this with clay sediment and other dirt particles.

So this is an important component, but of course, remember that it's a system, and you need to treat it that way.

So now the foundation wall concrete has cured, it's nice and strong.

We need to make sure to protect it from water.

There's a bunch of different ways to do this.

We are using a dimpled drainage mat, which you can see there are these bumps on it.

They go right up against that foundation wall.

This is plastic, so it's going to keep water from getting through it.

Any water that does get all the way through all of the layers on the outside of this foundation wall, that will be here eventually (and stay tuned for that), it'll just fall straight down and won't get stuck and go through this concrete.

This is only part of a system.

Outside of this there is going to be insulation.

Outside of that there is going to be some kind of a cladding.

And above all of this, there's going to be roof eave that's directing water away from the ground, which is sloping, again, away from the house.

We're going to put gravel here so that there won't be much chance at all for water to get back up here and to my foundation wall.

But if it does, it's going to be able to fall straight down and get into our drainage pipe.

Now to get us completely away from worrying about rain inside of our footprint, we finally poured the slab floor of the conditioned crawlspace.

Welcome to our crawlspace.

As you might guess, there is more here than meets the eye.

Everything we're thinking about throughout the house is controlling the flows of heat, air, water, and pollutants.

And the stuff that's underneath the slab, and outside the foundation walls obviously, is doing that.

The sandwich that we have down here is first of all, a bed of gravel.

Followed by insulation.

We'll talk about that more in later episodes.

Followed by the vapor barrier, which is also termite-proof.

And that's one of the things that we're worried about here in Georgia, is bugs are a part of the conversation.

They are technically a pollutant.

So if you're doing air sealing, you're also doing pest control in one sense.

And all of that gets topped then by this two-inch slab.

Now the slab is obviously only two inches thick- It's going to crack, basically as soon as it dries.

So those cracks are going to be then places where moisture, bugs, et cetera, can get up through.

What you can see at the edges of the crawl space is the vapor barrier, which is stopping the movement of moisture, in its vapor form, up from the ground.

Soil is one of the major places where you can get a lot of water moving into your house.

So if you have an open crawlspace with a dirt floor, there is going to be some moisture associated with that.

We don't have to worry about that, because we've got this continuous plastic layer right underneath this.

We poured right on top of it.

You can see that it's sticking out at the edges here, and we want to make sure to tape that edge, because now that is the only seam that remains in this conditioned crawl space.

Ultimately, we're going to have this space be exactly the same temperature and humidity levels as everywhere else in the house, so it'll be perfectly comfortable down here.

It will be totally inside the house, which is what that skin is really for.

But right now, while we're under construction, before we have the roof on, we still are vulnerable to rain getting on the floor, and getting all the way down here, which is why I also have a dehumidifier, which is a pretty hefty one.

It's what's going to be installed in this crawl space, ultimately, to dehumidify this entire house.

And I have it running right now because the lumber that you see here above me was delivered, and potentially, maybe, got a little wet, or it wasn't as dry as we thought when it first got here.

Then I'm going to enclose it in this space and not let the sun shine on it to dry it further.

Then I'm going to rain on this whole thing, and I'm going to have a lake forming in here.

And unless I'm down here emptying that out on a regular basis, we're going to have some moisture issues developing before the house is even finished with construction.

Which is why steps like this are ways of handling the physics and chemistry of the house while it's being built, before you move in.

- In the last ten years, I went on a major journey to better understand my gut health, and learned about the amazing world of the microbiome in my own body.

Now, as a mother of two, I protect their health by making sure that they have a balanced gut, full of good bacteria.

For my girls, it mostly comes in the way of breast milk, kefir and yogurt.

But I also like other options for good bacteria, like fermented foods and drinks.

Our work alongside indoor chemistry researchers has shown us that even this house has its own microbiome, and it's much more complex than I had ever imagined.

And what we do, like cooking and cleaning inside our house, can affect its microbiome.

Just like drinking kefir can affect our gut health.

There are billions of creatures breathing, eating, and working in our homes along with us.

Be a good steward of your home's microbiome.

Water flows through and around our homes in a variety ways.

Predicting and preparing for these can be a challenge, and accidents happen.

It's just part of life.

- But if a home's materials can dry to the air in all directions, and if you can plan ahead to install sensors and machines to encourage drying and exhausting that moisture, you've got performance under control.

- Arm yourself with more education about all of this at HomeDiagnosis.TV- See you next time.

- [Grace] This snake is our neighbor.

Do we touch snakes?

- No.

- [Grace] Don't touch snakes.

- No, it could bite me.

(upbeat music) - [Narrator] "Home Diagnosis" is made possible by support from the Alfred P. Sloan Foundation, by Fantech- 'Breathe Easy', by Broan-NuTone- 'Come home to fresh air', by Aprilaire- 'Everyone deserves healthy air', by AirCycler, Retrotec and Santa Fe Dehumidifiers, by generous support from these underwriters, and by viewers like you.