The Green Dream Group Blog

A new era has begun!!  I just passed my BPI written exam (field test and official certification coming soon, I hope). 

The class was excellent.*  Really excellent.  Not only was an enormous amount of knowledge expressed - and mostly absorbed! -  over the course of 6 days, but the clarity of thought you need to accurately apply that knowledge to the bizarre situations that happen all too often in buildings was somehow passed from Corbett to the rest of us taking the class.  Granted, I’ve never tried learning building science from someone else.  But I suspect that Corbett’s clear presentation style and mastery of the the topics he teaches would be hard to match, let alone beat. 

And he doesn’t let knowledge stand in the way of understanding.  Our field “training audits” were an excellent counterpoint to the classroom presentations, and even though I’ve been doing exactly this kind of audit for over a year with him, it felt entirely different to be in the driver’s seat during  that process.  Balancing the time it takes to do a focused inspection with combustion safety testing and a solid blower door test… it takes great presence of mind, not to mention a head for the details that make or break a safe testing situation.  Like, for example, remembering to turn combustion appliances to pilot before running the blower door.  Simple thing.  Enormous safety ramifications if forgotten.  (And now that I’ve mentioned it here, if I don’t remember to pilot appliances on the written exam, I’ll kick myself!) 

I have to say, I thought I would feel more mastery of building science after passing this exam than I do right now.  But it’s probably for the best.  I wouldn’t want to get sloppy, thinking that with this one certification the learning process is over!  After all, there are building science certifications, conferences, books, research, and experiments being advanced all the time, all over the world.  So I don’t expect that these blog entries will change  much, since I’m still  finding my way in  the expansive world of the building performance  professional.  I’ll still share the little things I discover with you, and try to keep the language as clear & comprehensible as possible.

So I’m looking forward to the new era, but I guess it won’t be all that different from the old one.  Here’s to life, and the constant process of learning that makes it awesome!

*I should also mention that I don’t actually work for Green Dream Group any more, other than writing the occasional blog entry, so I’m not being pressured to say that the class rocked!!  In fact, while working for Green Dream, I wasn’t able to take the field exam with Corbett, thanks to the conflict of interest he had with me as an employee that he wanted to see certified.  In case you’re curious, I now work at CNT Energy, as part of their “Energy Savers” team, where the focus is mostly on reducing utility bills for multifamily buildings.  So drop me a line if you own one: llittle at cntenergy dot org.  Looking forward!

Some of the home killers we’ve discussed target your wallet, some target your building.  This final home killer makes it seriously personal.  It targets you - and your family.

Home Killer IV is:  Indoor Air Quality (IAQ).

Surprised?  Don’t be.  Statistics from the EPA indicate that most Americans spend over 90% of their time indoors, breathing air flavored by whatever the building is full of.  And most of those flavors aren’t exactly good for you.  The LEED (Leadership in Energy and Environmental Design) rating system gives points to homes and commercial buildings that use materials known to off-gas smaller amounts of volatile organic compounds, or VOCs.  But, even though some may be carcinogenic, VOCs aren’t anywhere near the worst of it.   The U.S. EPA website has a more complete list of sources of poor indoor air quality, including radon, tobacco smoke, mold & moisture, and carbon monoxide:  http://www.epa.gov/iaq/index.html 

Carbon monoxide is the one IAQ threat that’s most central to the national standards energy auditors use, and  it’s also responsible for several hundred American deaths each year.   You probably know that carbon monoxide is produced from incomplete combustion of fuels, including natural gas.  It follows that the places to watch out for high levels of CO are near the oven, furnace, boiler, and water heater, or in your garage (especially attached garages).  Because it’s produced along with heat, CO tends to rise at first, but over time it will mix with the air in a room fairly uniformly.  Standards vary on what a safe level of exposure to carbon monoxide is.  BPI (the Building Performance Institute) allows exhaust concentrations of CO to reach 35 ppm before recommending repair to the appliance being tested.

Normally, any carbon monoxide produced by combustion-powered appliances is vented directly to outside, so it’s absolutely no problem inside a house.  Problems only arise when something is wrong, which we see far too often for comfort.  Simple things, like closing off the leaky vent above an old oven, can elevate indoor CO levels in a home far above what’s considered safe, even if it seems to be a good idea and makes your kitchen warmer.  Running a ventless gas heater or fireplace indoors is never a good idea; remember that ‘ventless’ means you’re breathing the byproducts of that combustion!  And there are many more complicated ways for combustion to go wrong, though I won’t get too far into them here.

One of the places dangerous mistakes are made is in the area around your combustion appliances, creatively named the “Combustion Appliance Zone”, or CAZ.  Newer appliances may be power-vented, or have a draft inducer which effectively forces them to properly vent gases to outside.  But many more appliances depend on an adequate air supply to work the way they were designed to.  If you have both a furnace and a water heater together in a small, enclosed CAZ with only a few vents, take a second to imagine what could happen when both machines are running.  The furnace is a powerful beast, pulling air to itself with a fan, making sure  it combusts efficiently.  But the water heater isn’t as strong.  It tries to pull air in, it tries to put its fumes out the right pipe, but if there’s not enough air in the CAZ to go around, the furnace may end up sucking combustion gases back down the water heater’s exhaust flue to feed itself.  That doesn’t bode well for anyone.  It’s still possible, even under those conditions, that there won’t be dangerous levels of carbon monoxide in your  house - the water heater might only be producing a few ppm.  But that doesn’t mean it will always be safe, and where your family’s concerned, safe is the only acceptable solution.

Thus ends the exciting Home Killers series!  Post a comment, ask a question, leave a story, argue a point - make sure you understand how  these home killers will try to get to you, so they never get that chance.

 Home Killer III:  Airflow (alias: Pressure)

Like heatflow & airflow...

Home Killer II (Heatflow) and Home Killer III (Airflow) are best pals: they work intimately on all kinds of fronts.  Heatflow is one of the factors that determines the direction of air movement, along with wind outside, or the air movement induced by forced-air heating systems.  Airflow isn’t slowed by fiberglass insulation like heatflow is;  it can only be stopped by an “air barrier” like dense-pack cellulose or closed cell sprayfoam.  Confusing airflow and heat barriers leads to confused houses, which kills your wallet faster than anything else, both in utility bills and in the costs of construction.

Conditioned Space or Not?

Ideally, the pressure and heat boundaries should be in the same place in your house.  Your house gets confused when that isn’t the case, the same way you’d get confused if you realized you had three arms, but couldn’t feel one of them.  Examples of places where heat & pressure boundaries get confused: garages, crawl spaces, partially conditioned areas, and the areas around vaulted ceilings.  I saw one house recently where workers had used more than twice as many materials as they needed to insulate the short side attics below the vaulted ceilings.  Not only was that space insulated at the roof and the exterior wall, which by itself would have achieved the same results; there was also insulation against the interior wall, the floor, and the access hatch.  Ask yourself this:  If there was insulation and air-sealing at the roof, what was all that extra stuff on the interior walls and access hatch insulating against? 

Where Air Escapes

Let’s take another look at how airflow and heatflow work together.  The last entry explained what stack effect is: here’s another piece of how it works.  Average houses in the Midwest can have anywhere from 2 to 5 square feet of what amounts to holes in their envelope, spread out in the form of cracks, gaps, and joints across their entire surface.  Gaps located in the upper area of the house, where buoyant warm air wants to go, let already-heated air slip right out into the world.  The gaps in the lower reaches of the house allow cold air from outside to seep in to replace the air that’s escaping up above. 

Somewhere in your house, there’s a level where the air inside isn’t trying to get out, and the air outside isn’t trying to get in - where pressures are equal inside and outside - creatively named the neutral pressure plane.  That’s actually one of the reasons it’s so important to use a blower door when testing for air leakage in homes.  Because pressure relationships dictate that air seeps in where the pressure is lowest (code for the basement or lowest floor) an infrared scan without a blower door would show lots of leakage from outside in a basement, and no leakage at all on the upper floors.  Believing that infrared scan would be a huge mistake; it would result in advice that’s the opposite of what we usually give.  Sealing and insulating the holes in your upper floors, where air’s always trying to escape, is the best way to slow down stack effect, thereby slowing down the rate at which you pour money into your utility bills.

Stay tuned next week for the final installment of Home Killers.  Next time, it’s personal!

Part II: Heatflow.

Where moisture can literally destroy your building, heatflow is what destroys your pocketbook. 

Let’s start with stack effect.  Stack effect is just a name for patterns of heatflow in buildings, which happen because heat rises.  Basically, it means that hot air will always try to move upward in your home, and cool air will always sink.  In a climate like ours, where most of our energy costs go for heating, that means that the top of the house is where most of our dollars are leaking out.

Radiative Heat Loss

 Here’s another interesting side of heatflow.  You remember in high school science classes, where you learned about conduction, convection, and radiation?  Well, here they come again!  Heat can escape your building envelope by any of those means.  Conductive heat loss could occur through exposed, uninsulated ductwork in your attic, or through any substance contacting both warm and cold air.  Convective heat loss is what the stack effect describes, with nice warm air leaking through holes in the top of the structure.  Radiative heat loss is less of a money sink for homes, but describes the fact that the house will radiate warmth as long as it is warmer than the surrounding air.

Measuring heatflow can be revealing, too.  The units in which heatflow is measured are Btus (British thermal units).  At a 1° temperature difference, one Btu passes through material with a U-value (heat resistance) of 1.0 in exactly 1 hour.  What’s interesting about this is that it shows you exactly where the most important areas of heat loss could be in your home.  High temperature differences coupled with low resistance to heatflow - does that sound like ductwork in your attic to you?  If you want to play around with this, the equation is:

Btus = U-value x Area x Temperature Difference x Time elapsed

Insulation, especially at the top of a house, does a huge amount to slow heatflow

If you want the summary, here it is:  Make sure the warmest, most conductive areas of your home are well-insulated!  Those areas are your ducts, pipes (for water heaters or boilers), and the ceiling plane of the uppermost floor in your home.  Pay especial attention to insulating when those ducts or pipes are on the outside of existing insulation, or run through exterior walls.

Stay tuned to learn about 2 more home killers…

This is NOT home killer #1.

No, this isn’t about murder (it’s a family-friendly blog, come on!).   This home killer is more insidious than that, and much more common… 

Home Killer I: Moisture

Moisture will destroy a building faster and more effectively than any other force - except a natural disaster.  Unfortunately, it’s necessary for our comfort that the air in our homes have some moisture in it - usually between 30 and 50% humidity.  Now, if every building was perfectly constructed, with adequate insulation and well-sealed cavities, that amount of moisture would be no problem at all for most buildings.  It’s when moisture is paired with your average home, with confused spaces, and insulation that’s too old or too thin, that moisture can develop into a real problem.

Psychrometric Chart

There’s a ridiculously complicated chart that’s supposed to illuminate the amount of moisture air can hold at different temperatures, called a psychrometric chart.   (Feel free to see if you can figure out how to read it!)  Broken down into its simplest terms, the chart shows that cooler air holds less moisture.  Where 95°F air holds 8 units of moisture, 72°F air holds just 4 units, and air that’s 50°F holds only 2 units.  Air that’s 32°F holds a measly 1 unit of moisture.  So where do houses come into this equation? 

Warm, moist air...

Imagine you have a nice warm house, with toasty, moist, 72°F air inside.  You’ve just taken a shower, so that air is saturated with moisture (4 units).  Your bathroom happens to be at a corner of your house, and it’s always a little chilly in there.  Maybe it’s an old home, without enough insulation in the walls, and not very well sealed.  So what happens when your nice, warm, moist shower air contacts the cold walls of the room?  You can probably guess: condensation happens.  And if it’s a really cold day, say 32°F, three-quarters of the moisture in that inside air will be dumped somewhere between your bathroom wall and the outside of the house. 

Luckily, building materials are able to absorb a fair amount of water.  But over time, this kind of moist air escaping can literally destroy a house from the inside, not to mention the air leakage inflating energy costs every day you live there. 

Don’t fall prey to the home killers.  There are three more to come….