Humidity by Trey Farmer

Our local Passive House Chapter likes to throw big geeky parties. Every two years we put on the Humid Climate Conference in Austin. Why not call it the Southern Building Science Conference, or the Hot Climate Conference? Because heat is relatively easy to deal with, humidity on the otherhand, is a bit trickier.


As buildings get better insulated and more air tight (more energy efficient) they become more comfortable, better for the planet and healthier for their occupants - if they are done right. That is a pretty big caveat for comfort and health especially in a humid climate. When those things happen, the heating and cooling loads get smaller and fresh air (ventilation) becomes more important.

We are living in a 2 year old triplex, the middle unit of three, while we work on Theresa Passive. That means our neighbors help to heat and cool our unit, and the amount of energy loss through our walls and windows is pretty small compared to an older home (or even a free standing new home). About 3 months after moving in late-spring hit. Austin gets hot and humid: lots of rain and 95 degree days in May. Our home was regularly reaching 70-75% relative humidity (way too high). This meant that not only were we uncomfortable, we were also at risk of mold growth, dust mites, mildew and elevated VOCs. At one point our salt lamp night light began to melt. It hadn’t been plugged in yet and was dripping salt solution down the bookshelf.

So why was this new home so humid, why do we care, and how can we do better?

First some really basic physics (sorry). Air has water in it. The amount of water a volume of air can hold is dependent on its temperature. Warmer air can hold a lot more water than the same volume of cold air. Relative humidity is the percentage of total possible moisture in the air at a given temperature. What this means is that when it rains in Austin and is 97 degrees the next day, the outdoor air has a lot of moisture in it. When that air comes inside and we then cool it down to 70 degrees, the absolute amount of water stays the same (measured in grains or 1/7000 of a pound) but the relative amount goes way up, because 70 degree air cannot hold as much as 97 degree air. If you want to really get into this and learn how to do grains calculations come to the next Building Science Philosophical Society Meeting.

A more energy efficient home (like one whose neighbors do a lot of the cooling for them), has to use the air conditioner a lot less. The system will turn on less often and run for shorter durations. The home may also use a smaller system. This means that the HVAC system is removing a lot less latent heat (aka humidity, kinda) than one that is running longer and more often in a less efficient and/or larger home. So in our case we had just as much moisture coming into the home from outdoors, but insufficient capacity to remove it. Our house was plenty cool, but wayyy too humid.

Higher humidity makes it harder for our bodies to cool themselves through evaporative cooling so we ended up turning down our thermostat lower than normal to not feel too hot, but then we felt too cold and clammy. It was not fun, but our discomfort was the least of our worries. Take a look at the chart below:

The Goldilocks spot for relative humidity is between 40% and 60%. Go too low and it feels too dry, the mucos membrane has trouble, nosebleeds and cracked skin start to be problems, the list goes on. Anyone who has lived in a really cold climate knows all about these issues. Wintertime is dry (cold air can’t hold much moisture)!

High humidity is even worse. Humid climates might not have the same respiratory infection rates, but they have mold, mites and VOCs. This photo is from the register in our bedroom where warm air in the house hit the cold surfaces from the AC system. The warm air gets colder and drops below dew point and all that extra moisture has to go somewhere. That somewhere in this case is the drywall and metal register, and that steady source of water on an edible surface (the paper face of drywall) and the right temperature is a happy habitat for mold.

Not cool.

Not cool.

So, what to do?

Build an air tight envelope and make sure your HVAC system has the capacity to handle the latent loads whenever they might be an issue. In Theresa and pretty much all of our new construction we like to bring on a high quality mechanical designer to study the project and layout an appropriate system that will deliver comfortable, healthy air to the spaces we live in. In Austin that means putting in a dedicated dehumidifier like the UltraAire 70h (the 70 refers to how many pints of it can remove in 24 hours) . It supplements the VRF heat pump system and removes moisture incredibly efficiently. This is especially important during the long shoulder seasons in Austin when the AC really doesn’t run very much but our humidity is very high.

Theresa Update 1 - Unconstruction by Trey Farmer


Theresa aka Theresa Passive aka The Johnson House is well under construction now. Our pals over at CleanTag have gotten started working their magic - demo is now complete and we are on to framing and foundation. Trade Ready Deconstructors did a great job clearing the slate. They removed the old garage (see the hole in the jungle below?), and all of the main house except for the front porch, the floor and wall framing, and the concrete piers that were put in 15 years back (they were cedar posts for the first 88 years!).

Here lived a tiny garage that was great habitat for local natives (but not our cars).

Here lived a tiny garage that was great habitat for local natives (but not our cars).

The 104 year old house had a lot of little framing irregularities that are getting resolved and brought up to today’s standards - as the new piers get laid out, dug, rebarred, and poured.

What issues?

  • The floor framing was nearly an inch out of level over the span of the building.

  • An area that used to be an outdoor porch has floor joists that are 2x6s with 2x2s on top of them to match the 2x8s everywhere else.

  • The original windows and doors were framed without jack and king studs or headers.

  • The framing around the chimneys was a little wonky.

Headers? Who needs headers?! Blake’s new office is in the background and has a great sunset view.

Headers? Who needs headers?! Blake’s new office is in the background and has a great sunset view.

Funky framing - exploring the forensics of an old house with many stories to tell.

Funky framing - exploring the forensics of an old house with many stories to tell.

What is a Passive House? by Trey Farmer

We are renovating The Theresa House to be a passive house certified project. So, what does that mean and why are we doing it?

Let’s start with the why and then dig into the how and the what.

We will be raising our family in this house and want it to be as healthy, comfortable, and durable as possible. We also want to live lightly and do our part to reduce our carbon footprint while being as be prepared for increasingly extreme weather and all that comes with it. Rather than build a new home out in the country, we bought an old home close to the highway and close to downtown and are breathing new life and fresh air into it. Like one of my architectural icons Malcolm Wells did 40 years ago, we are taking the worst and making it the best.

So, this all sounds good, but what does it actually mean in practice? The analogy I like to use is that a Passive House is like a Yeti Cooler with a nose on it: super insulated, air tight*, bear proof and with dedicated ventilation that filters and preconditions the fresh air coming in (like your nose!).

A Passive House

A Passive House

Passive House buildings can be houses, offices, fire stations, apartment complexes or schools. They can be tiny houses or skyscrapers. Yep, Passive Houses are not actually houses, they also aren’t passive! It’s not the best name but it is part of a lineage so it stuck around.

Their construction can be anything, there are no required techniques or materials. It is not a checklist or points based system like LEED or our local Austin version AEGB but instead is a series of low energy and air tightness targets tha must be met.

To further complicate things there are two sibling certifications with different organizations behind them. Without getting too deep into the family feud, the US based group Passive House Institute US (PHIUS) split off when it introduced climate specific standards to the varied climates of North America, while German based Passive House Institute (PHI) kept the standard static regardless of climate. We are certifying Theresa as a pilot project under PHIUS 2018+, the latest iteration of the US climate based standard. For something with such noble goals and a tiny market share, splitting hairs (and resources) seems crazy to me but such is life.

To build our house to the standard we First had to design our building and vet it through PHIUS and the energy modeling software they use - WUFI Passive. That process told us - based on the size and shape of our house, overhangs, window size and location, efficiency of our HVAC and appliances, and the climate of Austin - how much insulation we needed and where, how good our windows needed to be and how air tight our building had to be. The whole thing is a process - if we added more windows we might have to beef up the insulation or make things more air tight, if we deeper overhangs to shade those windows we might be able to be less airtight. We had all of these little levers to pull on that helped or hurt us in getting to the energy use targets required by the certification.

Insulation is pretty obvious - you add more of it and you lose thermal energy at a slower rate (and thus save money and have a more comfortable space). A couple caveats here though. First, continuous insulation is more effective than insulation with thermal bridging - putting insulation between steel studs can reduce its effectiveness by up to more than half making potentially it less valuable than the cost of installing it. Second, adding more insulation thickness gives diminishing returns - inches 1-3 may give you twice as much value as the 3-6, which will give you twice as much value as 6-9. In NH, where I grew up, the amount of hours below 20 degrees is roughly the same as the hours above 100 degrees in Austin. BUT if we want to keep our homes around 70 degrees, that is a 30 degree difference in Austin and a 50 degree difference in NH. In colder climates those extra 6-9 inches may be worth a lot more than in hot climates.

Windows also vary by climate. We always want them to be well insulated (a low U value) but in hot climates we want to shade them and keep the amount of solar heat gain to a minimum. To understand solar heat gain, think of your arm getting hot from the sun through a window as you drive down the road. In cold climates, we want to let some of that solar heat gain in to warm up the house in the winter, but shade it in the summer. Gratefully, winter sun comes in at a lower angle so this is easy to accommodate. In hot climates like Austin we are primarily focused on keeping direct sun off the glass and our solar heat gain coefficient down so that when sunlight does come through, it does not add to our air conditioning loads by heating up the inside of the home.

Air tightness is the weird one and the one that is hardest to understand - and the one we get most pushback on from builders. This is mainly because it is a “new” metric in the building industry and hard to price. So to start off with: houses do NOT need to breath - people do. We hear this a lot and am not really sure where it comes from. Houses have never needed to breath. A properly built house should strive to be as air-tight as possible. This reduces energy loss (all that air you spent hard earned money to heat/cool just leaking away through your old crappy windows), makes you more comfortable (drafts are gross!), and most importantly improves indoor air quality. You, average american, spend nearly 90% of your life indoors, 70% in your home. Where does your fresh air come from as you sleep? Take a minute to think about it. Hint: It’s not from your air conditioner. You get a tiny bit from opening and closing the front door and you might get some on those spring days when you open your windows. Otherwise, all the air you breathe comes via the thousands of little (or big) cracks in your walls, through your floorboards, down from your attic, through leaks in your duct work, in from your attached garage… These are really gross places that are full of dead pests and pesticides, insulation fibers, mold, dust and motor oil and all that Miracle Grow stored next to your WD-40 and snow tires. That is where the “fresh” air you and your kids breath comes from. If this isn’t freaking you out, read it again. Here is a link for some good air filters. Here is a link to Passive House designers throughout the US who can help you get good clean fresh air in to your house.

The good news is that many new houses are being built with dedicated ventilation, which means that they have a fan than brings fresh air directly from the outside (bypassing the squirrel family in your wall), filters it and supplies it to your living spaces. Passive Houses use an ERV or HRV for dedicated ventilation. These are magical boxes that supply filtered fresh air but they also temper it by pulling the heat energy out of exhausted stale air and putting it into the fresh air, reducing the energy penalty from bringing in all that fresh (but unconditioned) air. By making buildings super air-tight, and then using an ERV, Passive Houses ensure a constant supply of truly fresh, filtered air while being also incredibly energy efficient.

ERV Diagram

This is a very basic explanation of a Passive House building, but it scratches the surface of a lot of topics that much smarter people than myself have written on extensively. If you want to nerd out further, follow the links, listen to a podcast, buy a book, attend a conference. If you are in Austin come to a Passive House meet up or a Building Science Happy Hour to meet some good folks who are also trying to wrap our heads around how to make better, healthier buildings.

1% Productivity by Trey Farmer

Bjarne Olesen was on The Edifice Complex Podcast last week. If you don’t know this one, check it out. I have had the pleasure of hanging out with Robert Bean on a few of his trips to Austin - including when he spoke at the inaugural Humid Climate Conference - and he and his partner in crime Adam Muggleton have a great thing going. They deep dive into building science, and then jump over to development, sustainability, future systems and whatever else they fancy. It is a lot of fun.

Anyways, Bjarne Olesen is the current ASHREA President has more accolades to his name than I can list here. He is a rock star in the HVAC world and great to listen to.

Bjarne Olesen, The President

Bjarne Olesen, The President

One thing he said early on that stood out is that a 1% productivity loss in an office is equivalent to its the entire energy budget. This is one of those quietly monumental statements. He was referring to efforts to broaden the comfort ranges for conditioned space in building codes as a way to energy. If you look at things holistically though, the productivity losses from even a slight change in comfort levels will far outweigh the savings on the energy bill - potentially one of those Cobra Effect situations.

This has really broad implications. Adding natural light or views to trees and nature have been shown to increase productivity in employees and sales in retail environments. Increasing indoor air quality makes your sleep better and improves your cognitive function the next day. These are all things designers want to put in our buildings because they make for more beautiful spaces and healthier humans. Unfortunately we are often asked to justify the ROI of any perceived additional cost (what’s the ROI of a beautiful view or shadows play across your wall, or having kids without asthma?).

Better buildings with more robust walls, better windows, less air infiltration and well designed and built HVAC systems mean that more of the occupants will be more comfortable more of the time. That 1% productivity bump is the all the ROI you need.

The Edifice Complex - Bjarne Olesen

This Old House (Pt. 1) by Trey Farmer

Theresa Ave, known as the Johnson House to those in the neighborhood who have been around a bit, was built in 1914. It was part of the Washington Heights Development and is within a NRHD or National Register Historic District. The City’s website has more info on NRHDs here, and you can see the extent our our specific district below.



It also means that there is some fun history to hunt for. This clipping is from 1942, special thanks to Cara at the Historic Preservation Office for finding it and sharing.

The Austin American (1914-1973); Oct 11, 1942

We also like decorating with roses and ferns…

Another way that we can peer into the past is through the Sanborn Maps that can be accessed here with an Austin Library Card. The maps were originally used to estimate fire insurance and provide a great way to see a city back before Google Maps was around. Below is the plat for our block and the composite key map that is used to locate the “zoomed in” sheet. I also included the key below, there are some great little secrets it has to tell.

Austin’s 1935 Sanborn Map - Sheet 33

Austin’s 1935 Sanborn Map - Sheet 33

Austin’s 1935 Sanborn Map - Composite Key Map

Austin’s 1935 Sanborn Map - Composite Key Map

Sanborn Company Map Key

Sanborn Company Map Key

Theresa Ave by Trey Farmer

Theresa Ave.png

We have lived in a beautiful old (for Austin) house in an amazing (and terrible) location for the past 7 years. Much of this blog will be dedicated to a major renovation/addition that is about to begin, and the why’s, how’s and what’s of all that goes into such an endeavor. We will get into many aspects of this project in the hopes that it might help others avoid some of the mistakes we have made, and learn some of the things that it took us a while to learn, and to give some insight into our process and priorities. Some of this will be specific to Austin, some specific to historic remodels, some to humid climates, some to high nosed architects, some to city living, and some to homeowners.