I recently spoke at the Westford Symposium on Building Science. You may know it better as Building Science Summer Camp, since that's what everyone calls it. I'll fill you in on what you missed if you weren't there.
Today I’m going to explain an important concept in one of the most popular ways of doing duct design. I’ve been writing a series on duct design over at my blog and began with a look at the basic physics of air moving through ducts. The short version is that friction and turbulence in ducts results in pressure drops. Then in part 2 I covered available static pressure. The blower gives us a pressure rise.
Whenever my wife starts a conversation with, “OK, Mr. Building Scientist,” I know I am in some kind of trouble. That proved to be the case one day when we were out hanging laundry on the south side of our house.
Let's face it. The state of home building isn't good. Yes, we have building science and energy codes and green building programs out the wazoo. We have cool new products and home energy raters and even Joe Lstiburek. Despite all this, we still have wild ductopuses, holey air barriers, and insipid insulation installations.
And I've finally lost my patience. I think the only way to improve the state of home building in America is to ban these things.
The I-joists in the lead photo here run across the top of the wall between the dining room and the attached garage in this home under construction in the Atlanta area. In the old days, before anyone worried about air moving through those joist cavities, the builder didn’t bother to do anything beyond securing the joists.
You can see here, though, that the builder of this home knows a thing or two about air sealing because they've put blocking between the joists. But what do they do next?
Full Disclosure: First, there are a lot of different ways to get continuous air and water control layers on the exterior of a building enclosure. You can use housewrap, taped-and-sealed rigid foam insulation, liquid-applied membrane, or either the Huber Zip or Georgia-Pacific ForceField system. Each approach has strengths and weaknesses.
So the United States has announced it's withdrawing from the Paris Accord, the international agreement with nonbinding measures to mitigate the effects of climate change. Now everyone's up in arms, speaking in exasperated tones about the travesty of this decision.
"But... but... the science," they say. Yeah, let's talk about science.
I've been guilty of perpetuating a myth. Not long ago I wrote an article in which I said installing insulation, "cavities [should be] filled completely with as little compression as possible." But is compression really such a bad thing? Here on GBAGreenBuildingAdvisor.com, commenter Dana Dorsett wrote, "Compression of batts is fine (resulting in a higher R/inch due to the higher density) as long as the cavity is completely filled.”
We've had some beautiful cool weather here in Atlanta this spring. It's about 50°F outdoors as I write this, one week into the month of May. The high yesterday was only about 70°F.
We're getting a few more heating degree days (HDDThe difference between the 24-hour average (daily) temperature and the base temperature for one year for each day that the average is below the base temperature. For heating degree days, the base is usually 65 degrees Fahrenheit. For example, if the average temperature for December 1, 2001 was 30 degrees Fahrenheit, then the number of heating degrees for that day was 35.) in the middle of May. (Heating degree days are really just another way at looking at temperature, which I explained in more detail in a look at the fundamentals of degree days.) We occasionally pick up some HDD even in July and August. But it's the winter HDD that matter for heating — and that give us a clue about the climate.
Negative-side waterproofing (NSW) is a tough topic that I have frankly been dancing around for quite some time. Manufacturer claims and homeowner anecdotes of successful interior waterproof solutions for basement walls and slabs did not completely add up. But I did not think that I understood the topic or the physics well enough to challenge the claims or explain my skepticism.
Most new homes in North America are built with sticks. The early home builders used bigger pieces of wood — timbers — and when the smaller dimensional lumber that we use so much today hit the market, they scoffed at those new-fangled little woody things, calling them sticks. Now our home construction industry is full of people who do stick building and the home you live is most likely stick-built. And sadly, many of the techniques used to build many of those homes are the same used before we started insulating them.
Seven years ago, Georgia led the nation. Yep. We were the first state to adopt an energy code that made blower door testing mandatory. All new homes built in the state had to show through performance testing that they had an air leakage rate of less than 7 air changes per hour at 50 Pascals of pressure difference (ach50).