Category Archives: Passive House

Nauhaus Primer: Talking Head About Carbon Neutrality and the Nauhaus Prototype

We recently recorded this video intended as a draft to help us work on our public spiel. It needs a lot of work, but I thought I’d post it anyway because it’s a fairly thorough introduction to what we’re doing generally and the prototype in particular.  Just pretend you’re in high school and lunch is next period…Go generic sports team with some sort of mammal as its mascot!

Carbon Neutrality and The Nauhaus Prototype from Clarke Snell on Vimeo.

Building Fundamentals: Energy Efficiency Geekout – Anatomy of Windows and Doors Part I

This article by Clarke Snell was originally published in the New Life Journal.

If you ask 10 kids to draw a picture of a house, I can almost guarantee that they’ll all include a door and at least one big window. Ask those same kids 25 years later to describe their dream houses and I predict they will all be crammed full of windows. What I’m saying here is that in my experience, we all love windows. What’s wrong with that? Well, if our goal is to create an energy efficient building, typical glass-filled openings are actually a real pain in the astragal because compared to modern wall systems they perform horribly. In this month’s column, I’ll explain the basics of why this is true. Then next month, I’ll tell you what you can do about it.

Sidebar: R-value vs. U-value

Resistance to heat flow in building materials is usually quantified as R-value. The higher the R, the better the insulation. Just to confuse us, the insulation value of windows is expressed as U-value which is the inverse of R. To find out the R-value of a window, divide 1 by its U-value. For example, U= .4; 1÷.4 = R2.5

Heat Loss

Other than keeping rain and snow out of your bed, perhaps the most pivotal function of your house is its ability to create a different temperature inside than the temperature outside. This is accomplished by wrapping the interior space with insulation, a generic term for a material designed to resist the flow of heat. To oversimplify for our purposes, the better this insulation cocoon functions, the less heating or cooling the building will need. Since heating and cooling both cost money and usually involve global warming creating carbon emissions (our buildings are responsible for about 50% of our collective carbon footprint), improving insulation has been a focus of the green building movement. In recent years, we’ve made incredible strides and now have access to insulation systems that can produce walls systems with R-values (see sidebar) in the 20’s, 30’s, and even 40’s. Typical new windows, however, have R-values of only 2 or 3, 10 or more times worse than the wall itself. This is almost equivalent to a thermal hole in the wall. Therefore, the main performance flop for windows is their inadequate resistance to the flow of heat.

Mean Radiant Temperature

Mean radiant temperature is basically the average temperature of the surfaces of everything in the vicinity of your body. In a house, that means the surface of windows, walls, furniture, dusty knickknacks, and everything else. All of these surfaces radiate heat outward toward your skin, and your skin in turn radiates toward them. Since windows are so bad at slowing heat movement, their surface temperature will tend to be very different than that of other surfaces in your house. If the surface temperature of an object near you is considerably less or more than that of your body, you feel it as cold or warmth. This is why on a cold winter day, the thermostat can read 70F and you’ll still feel cold standing by a window. Low surface temperature, then, is another way windows drag down the overall thermal performance of our wall system.

Air Leakage

Doors and operable windows are basically huge holes that can be opened and closed. By definition, though, that closure is never perfect. The hole always leaks. Gaps and cracks in our wall will allow air to bypass insulation resulting in the movement of heat in or out of our building. Therefore, another strike against windows and doors is their contribution to this air leakage.

Solar Heat Gain

Responsible energy efficient designs incorporate a basically infinite, free source of energy: the sun. In our climate this means letting the sun in during the winter.  We need glass-filled openings to accomplish this. Different glass types and configurations let in more or less of the sunlight that hits them. This is quantified as a number called the solar heat gain coefficient (SHGC) which is basically the percentage of potential solar heat that glass lets into the building. For example, a SHCG of .5 means that 50% of the potential solar heat is making it through the glass. There are situations where we want solar heat gain and others where we don’t, so the wrong glass type in the wrong place can be a major detriment to building performance.


The point I’m making here is that windows and doors are typically VERY weak spots in the performance of a modern building. Next month, I’ll give you the skinny on how to choose the right windows and doors for new construction and remodeling or how to spiff up the performance of your existing underachieving glass units.

Building Fundamentals: Energy Efficiency Geekout – Anatomy of Windows and Doors Part 2

This article by Clarke Snell was first published in the New Life Journal.

Last month I ragged on windows and doors, pointing out that they are generally a very weak spot  in the performance of a modern, environmentally conscious building. To summarize: they don’t insulate very well, are a source of air leakage, can cause perceived discomfort, and can either let in too much solar heat when it’s not wanted or block too much solar heat when it is wanted. The obvious question is, “What can we do about it?”

Luckily, a lot of really smart people have been working on window technology in recent years and they are making big strides. If you are looking to build a new house, there are good choices to be made to improve the energy efficiency of your doors and windows. Similarly, if you want to increase the performance of your existing house, replacing windows and doors is a good place to start.

Sidebar: R-value vs. U-value

Resistance to heat flow in building materials is usually quantified as R-value. The higher the R, the better the insulation. Just to confuse us, the insulation value of windows is expressed as U-value which is the inverse of R. To find out the R-value of a window, divide 1 by its U-value. For example, U= .4; 1÷.4 = R-2.5

If you want to understand the mechanics, there’s a lot to learn. For example, most windows have two glass panes separated by a space filled with air or another gas, but triple pane windows with much lower U-values (see sidebar) are becoming more common. Then there’s the issue of low-e coatings, basically coatings that increase efficiency by reflecting heat energy. Windows can have different numbers and types of coatings configured to reflect heat in or out. Frame type is also important with choices ranging from metal to vinyl to wood to fiberglass. Glazing spacers, thermally broken frames, gas fills, closure mechanisms…the list goes on.

You really don’t need to worry about most of that stuff because all of this technology is synopsized in three quantifiable performance characteristics: U-value, solar heat gain coefficient, and air leakage rate. The National Fenestration Rating Council has created a standardized rating system that requires computer modeling and lab testing for verification of these variables. The results of these tests are prominently displayed on a label you’ll find on any new window or door. If it’s not labeled, don’t buy it. If you are talking with any professional, be sure to reference these numbers and make clear that you want values for the whole window or door unit, not just the glass. Armed with this basic knowledge, I can now offer you some simple rules of thumb summarized in the following chart:

Wind or Door Facing

U-value (BTU/hr-sf-F)


Air Leakage (CFM/sf)







East, West, North1














* My advice is for you not to go below these performance ratings

1East, west, and north facing openings. In terms of winter solar heat gain, these windows will be a net loss. No matter how much sunlight you can let in, the energy gained won’t be enough to offset the energy lost when the sun isn’t shining through the glass. Therefore, choose windows and doors with the lowest SHGC, U-value, and air leakage rates that you can afford.

2South facing openings. For glass that faces south AND gets full sun at least between 10:00am and 2:00pm all winter, choose windows and doors with the lowest U-value and air leakage but highest SHGC. NOTE: There is a new building code in effect setting a maximum SHGC for windows which is well below the desirable SHGC for south-facing windows that get full winter sun. There are ways around this glitch that are too involved to describe in this column. Just be sure to get this worked out with your builder and code officials before ordering windows.

As you start to shop for windows and doors, you may think that some of my chart numbers are wrong. According to NFRC specs, they aren’t. Right now, there are a huge range of performance levels and corresponding prices for windows and doors. Windows made in Europe, such as by the German manufacturer Optiwin, are the best, but they can cost more than $100/square foot. (Compare this to perhaps $15-20/sf for a decent off the shelf window in the US.) Canadian and US manufacturers are catching up in the performance category, so you just have to look around.

On the other hand, if you can’t afford the premium windows, there are other low-budget strategies. Covering glass openings with thick curtains anytime you aren’t in a room will increase window efficiency. If you live in an old drafty house, you can buy shrink wrap plastic to cover your single pane windows in the winter probably for less than $20. You’ll most likely immediately experience an increase in comfort due to higher radiant surface temperature (see last month’s column) and reduced air infiltration.

Regardless of the specifics of your situation, my point is simple. If you want to reduce your heating and cooling bills, improve interior comfort, and reach carbon reduction nirvana, don’t neglect your doors and windows.

A sample NFRC window label

Footloose and Carbon Free: The Passive House Standard

This article by Clarke Snell was originally published in the New Life Journal.

Okay, by now everyone has gotten the “human induced global climate change” memo, right? If not, here’s the executive summary: We burn a lot of fuel for heating, cooling, manufacturing, generating electricity, and driving stuff around. That burning releases carbon dioxide (CO2). As CO2 levels increase, the atmosphere basically traps more solar heat, causing temperatures to rise. The dynamics of all this are pretty complicated and the details are debated, but there is a frighteningly solid majority of climate scientists who agree that we need to drastically reduce emissions of CO2 (and other “greenhouse gases”) if we are to avoid catastrophic climate change.

In the US, our buildings are responsible for about 50% of our carbon footprint. Therefore, if we take this somber warning seriously, we need to do a major overhaul of how we build…and fast. Luckily, since carbon emissions come from energy use, the solution is simply to use less energy, something that saves money, reduces pollution, and makes us more self-reliant. That’s right, it’s patriotic, baby!

The concept is really pretty simple. First, we greatly improve the efficiency of the building itself. We do that by reducing heating and cooling demand by increasing insulation levels and carefully sealing up air leaks. We then install a nifty device called an energy recovery ventilator which allows us to bring in fresh air with only minimum energy loss. Next, we focus on the sun, letting it in the winter for heat and blocking it in the summer for cooling. We also add  interior thermal mass to help store this energy. Finally we choose the most efficient systems, including mechanicals, appliances, lights, and anything else that uses energy.

If we do all of this right, we can reduce heating and cooling loads by 90% over the norm and cut electrical consumption by at least 70%. At this point, we’ve significantly reduced the carbon emissions associated with our building. However, to reach carbon reduction benchmarks based on climate science predictions (translation: to save the world as we know it, yeah!!) we need to go even further. We have to make all of the energy our building needs without releasing carbon, which basically means without burning fossil fuels (coal and petroleum). No big deal. Solar, wind, and hydro electric power are all available options. What’s more, our energy demand is so low now, these systems can be much smaller and therefore more affordable.

To go all the way, we need to make enough surplus renewable, non-carbon emitting energy to offset the carbon emissions produced to build the building, even to make the solar panels and other renewable systems we have installed. If we do all of this, we have reached carbon neutrality. In other words, our building is not involved in carbon emissions and is therefore doing its part to avert “human induced climate change” (see memo…you did get the memo didn’t you?) What’s more, the building will cost almost nothing to run and will have wonderful indoor air quality.

What’s the catch? Well, though the concept is simple, the application isn’t. First of all, when we get to this level of energy efficiency, some of our typical building components are woefully inadequate. For example, conventional windows and doors are just sieves for heat and air loss. Though high performance fenestration is available, it’s very expensive. In addition, the tiny air leakage allowable to make this work is simply outside the experience of US builders. Very careful attention to a variety of construction details is required, often using tapes and gaskets that are hard to find for sale in this country. There are other difficulties, all of which have to do with money. Though these buildings cost considerably less in a lifecycle analysis, the fact is that it simply costs more money upfront to save money, energy, and carbon emissions in the long wrong.

Luckily, if we want to move in the direction of carbon neutral construction, and I feel we have to, there are sensible, proven methodologies already in existence. The one I like the best is a certification program called Passive House. There are many thousands of buildings that have been built to this standard and performance monitored throughout Europe, mostly in Germany, though almost none to date in the US. The Passive House standard is laughably simple to grasp. You are allowed a given amount of heating and cooling energy per square foot of building as well as a defined rate of allowable air leakage. You then have to design a building envelope (basically insulation and air leakage strategy) and mechanical system that will perform at that level regardless of the climate in which you live. In other words, you can’t take a common “out” popular in the US green building movement: build a low efficiency building then attach a huge, expensive solar electric system that provides 25% of a large household energy demand and call it efficient.

The Passive House standard is administered in the US by the Passive House Institute US. These wonderful folks are hard at work training consultants, certifying buildings, helping to import or develop requisite materials, and educating the public. For more information, visit their web site at . If you want to see the process up close, we are hoping to build a Passive House certified building in West Asheville starting later this spring. To find out more, go to our project website at

Eco-Panels Installed

Eco-Panels came out on Tuesday and Wednesday and installed the S.I.P. roof.  The finished roof system for the Nauhaus Prototype will have an insulation value of about R80 when completed, because the spaces between the 8″ rafters will be packed with cellulose.

Some information about Eco-Panels, from their website:

For a truly superior building envelope Eco-Panels manufactures the only R60 panel on the market today coming in at just 8.5″ in thickness.  This panel, designed specifically for use in arctic regions, is perfect for the passive house or net zero energy designs where most modeling software calls for an R40 wall and R60 roof (of course this will vary based on region).  This roof panel will perform at better than R60 at 20deg F (-7deg C) using LTTP (long term thermal profile) and temperature vs k-factor performance data provided by the foam component manufacturer.

  • 8 1/2″(21.6 cm) = R60+
  • Maximum panel length is 12′-0″ (360 cm) although this can be increased to 16′-0″ for large opportunities
  • Maximum panel width is 4′-0″ (120 cm)
  • The insulation is high-R-value polyurethane foam injected at a density of 2.5 pounds per cubic foot.

Click here to view the entire Nauhaus Prototype Construction Chronology.

Garnet Igneous delivers supplies.
Garnet Igneous delivers supplies.
The framing is ready to receive the Eco Panels S.I.P.s.
The framing is ready to receive the Eco Panels S.I.P.s.

Chris Cashman
Chris Cashman
Eco Panels Truck
Eco-Panels Truck
Matt, Mike and Tim
Matt, Mike and Tim
The Eco Panels S.I.P.s are attached to a special bracket and lifted with a crane.
The Eco-Panels S.I.P.s are attached to a special bracket and lifted with a crane.
Craig Payne
Matt and Elijah install panels.
Matt and Elijah install panels.
Matt prepares for an Eco Panel.
Matt prepares for an Eco Panel.
Matt and Elijah attach panels to the North side of the roof.
Matt and Elijah attach panels to the North side of the roof.
8.5" R-60 Eco Panel on Rafter
8.5" R60 Eco-Panel S.I.P. on 8" Rafter
Eco Panels being installed on the South side of the roof
Eco-Panels being installed on the South side of the roof
Northeast Corner
Northeast Corner

West Gable
West Gable
All of the Eco Panels are installed.
All of the Eco-Panels are installed. Next we will add the overhangs and metal roofing.

Passive Solar Design

This is the second article in a series originally written for New Life Journal.

By: Clarke Snell

Let’s not beat around the bush. In this day and age, heating and cooling our houses amounts to spending a lot of money to create a lot of pollution. That’s because most of the energy we use for this purpose comes from burning fossil fuels. What’s worse, as a society our response to skyrocketing oil and gas prices has been to keep making the skies dirtier. The weird thing about this whole scenario is that everything we’re burning is just stored solar energy.

Here’s the process: Plants turn sunlight into energy which is turned into living tissue. Animals eat the plants. Plants and animals die. Wait several hundred million years. Drill deep wells and dig big holes to access resultant oil, gas, and coal. Transport all over the planet and burn copiously until supply begins to get scarce. Fight wars and panic until lights go out and heat goes off.

I don’t know, wouldn’t it make better business sense to skip the “middle man” and go directly to the source, i.e. the sun? Duh. The technique is called passive solar design: the conscious manipulation of the sun’s direct energy to affect the temperature inside a building. It is clean burning, runs for free after installation, has no moving parts, comes with a lifetime guarantee, isn’t susceptible to power outages or unexpected supply shortages, requires no special maintenance, and can be accomplished by simply rearranging the materials used in a conventional modern house at little or no extra expense.

Though its most effective real world implementation is a beautiful dance between science and art, the concept behind passive solar design is elegantly simple: if you want heat, let the sun in; if you want cool, don’t let the sun in.

Our loving star has made the process so much easier by methodically changing its path through the sky throughout the year. In our region, the winter sun rises to the southeast, stays low in the sky to the south, and sets to the southwest. The summer sun rises to northeast, stays high in the sky most of the day, and sets to the northwest. This is an amazing stroke of luck because it means the sun is low in the sky when it’s cold outside and high in the sky when it’s hot outside. Low sun is easy to let into a building, while high sun tends to be blocked by the roof and other protrusions of the building itself. Perfect!

With this basic observation under our belts, we’re ready to realize a passive solar masterpiece. First, we need to find the right place to build. In our region, that means a site that will give us unobstructed access to the low southern winter sun. Some trees or other obstructions to the east and especially the west would be great to block the hot rising and setting summer sun. (A ridge or evergreens to the north might block some winter winds, but wind is very site specific so we’d have to spend some time on site to make that call.)

Next, we’ll design our building to let in a lot of winter sun and block a lot of summer sun. Building shape is the most basic parameter. In our area, the best shape is longer on the east-west axis, creating more wall surface on the south and less on the east and west.

The main avenue for sun to enter the building will be through glass. From a heating point of view, only south-facing glass will create a net solar heat gain, so other glass should be minimized. However, north, east, and west glass are an important part of our natural ventilation cooling and daylighting strategies. This is where the delicate interplay of science and art comes in, in other words we’ll find beautiful compromises.

The heating equation, in any case, is straightforward, we simply have to carefully match the square footage of our southern glass windows and doors to the amount of “thermal mass” we place in the building. Thermal mass simply means something that stores heat, so technically everything is a thermal mass. Dense heavy materials usually store heat well. Water, concrete, stone, and earth are good examples. A great place to put mass in a building is in a concrete or earthen floor. Sun flows in through glass covered openings and is stored in the mass of the floor. The mass sucks up heat, thus preventing the house from overheating during the day, then slowly releases the heat after the sun goes down keeping the house warm at night. The trick is creating the right balance. Science to the rescue! We have everything from rule of thumb glass to mass ratios to computer assisted thermal modeling at our disposal.

Next, we’ll need to design our roof overhangs and other protuberances so that they follow our mantra: block sun when it’s hot, let in sun when its cold. The poster child for this is the southern trellis covered with deciduous vines (grapes and hops are two options for you vintners and brewers out there). Thick leaf cover that blocks the sun in spring and summer dies back in fall and winter to let the sun through. Since we know where the cooperative sun will be in the sky at any time of year, roof and window overhangs can be sized to interact with the sun exactly as we like.  We’ll add covered patios on the east and west, again to block low hot sun, and one on the north to create an outdoor room that will be shaded all summer long.

Finally, we’ll work with the surrounding landscape to heighten our design. In tandem with our patios, we’ll add shade trees, especially to the west and north. Plants not only create shade, but evaporative cooling which is the natural technology mimicked by your refrigerator and clanking, polluting window A/C or HVAC unit. We’ll also create a focus to the south, perhaps placing an outdoor kitchen under the trellis with a kitchen garden in front of it. We’ll place doors and windows that encourage cross-ventilation and allow effortless transitions to outdoor rooms. Don’t forget that in our climate a little tweaking back and forth between sun and shade makes the outside comfortable for most of the year. Outdoor rooms are inexpensive access to the mansion of nature. Of course, we’ll also design a unified insulation strategy that includes measures to slow convective, conductive, and radiant heat loss through the building, but that’s another story.

Ta-da! A passive solar masterpiece that will supply a baseline of heat and cool at the right time of year which can then be enhanced to create the specific indoor environment of your choosing. Though you may not get the picture from this frantic overview, none of these design features need to control the look or feel of the building. Passive solar is flexible if you are. It’s a pivotal design concept, not an architectural gestalt.

Disagreement abounds even on some of the basics. For example, some people feel that our climate is too wet to allow for natural ventilation as a cooling strategy because open windows plus humidity can result in mold. In the end (here’s where you refer back to that lovingly pawed copy of my column from last month that’s taped to the fridge), the right approach to passive solar is going to have to match the specifics of who you are with the specifics of the place your house will sit.

I will however be unequivocal about one thing: you are going to heat and cool your house with solar energy one way or another. The only question is if you want it free and clean or expensive and dirty. This may sound like a laughably obvious choice, but a cursory glance at any cityscape or subdivision will show that the sun is presently laughing at us, not with us.


Employee lounge at the Sleep Inn in the beautiful strip mall section of Urbana

Jeff and I are at the Passive House training. Things are going well. Cool geeks, incredibly stringent performance standard. Today, we were looking at an assembly that included an R-40 wall (12 inch TJI studs with cellulose, OSB on both sides, then another insulated 2×4 stud wall), R-75 subslab insulation, and R-10 perimeter insulation. In this configuration, an uninsulated bottom plate created a thermal bridge that wasted 8% of the available heating load for the entire building under the Passive House standard. Yikes!

Optiwin makes the nicest windows I've seen. This is a window at a house we toured today. You are looking at a great sill flashing pan. Incredibly sturdy and designed with a counterflashing corner that goes up under the trim. This will be covered with a brown aluminum flashing piece to match the window. All of this can be yours for $100/sf.

Anyway, it’s not all hard work. For fun Jeff is testing the pH of Coca-Cola in the hotel. (That’s pH… not PH for Passive House. Get with the program!) According to Jeff this was necessitated because they have been planning on stepping up to kegs for Kombucha. The keg guy thought the acid levels in Kombucha would corrode the kegs. They’re made for Coke, so if that shit has a similar pH to Buchi, then the kegs will survive.

Internal Nauhaus Institute memo: By the way, Scobie didn’t make the label. They’re going all high brow looking for she-she crowd or somethin’. Scobie Lives!!

Anyway, here are the Coke study results:

High tech Coke testing contraption
Coke pH leveled out after the demons were excorcised
Coke pH leveled out after the demons were excorcised
Just another mad building scientist
Just another mad building scientist

— Clarke