Cold weather is coming back to Atlanta this week, so let’s talk about heat. An increasingly popular way to heat buildings these days is with heat pumps, even in cold climates. But how do they work?
Typical pins on moisture meters are ½ inch long, meaning you can only determine moisture content by weight near the surface of building assemblies and materials (including wood, gypsum wallboard, and concrete). But I often find myself needing to assess moisture content of first condensing surfaces in walls and ceilings or well below the surface of basement slabs.
This article looks at ways to extend the reach of a moisture meter. (For introductory information on moisture meters, see Tools of the Trade: Moisture Meters.)
Because I've written so much about moisture in buildings, I get a lot of questions on the topic. Some are about walls. Some are about the attic. Some are about windows. Some are about the crawl space (which generates the most questions on this topic).
The key to answering a lot of those questions boils down to an understanding of how water vapor interacts with materials. Once you know that, it's easy to see the two rules for preventing damage from humidity.
Building science is an odd subject. Few colleges and universities teach it. The majority of those who work on buildings call themselves engineers, architects, and contractors, not building scientists. And many of those who do invoke the term can explain at least one implication of the second law of thermodynamics (we'll get to that below) but may not know what the other laws of thermodynamics are, why their numbering is so peculiar, or even how many there are. Do you?
We live in this invisible stuff called air. (But of course you knew that.) We pump it into and out of our lungs. We exhaust it from our bathrooms and kitchens. We cycle it through our heating and air conditioning systems. If we're lucky, we live in a home that even brings outdoor air inside as part of a whole-house ventilation system. But we're missing something.
When we bought our home (built in 1907), I called in a favor from an electrician friend of mine to upgrade the 60-amp to a 100-amp service. Having worked together in New Hampshire where many of our projects were on sites full of ledge, he smirked when he told me: “Here, you go try and drive this 12-foot copper grounding rod.”
Most people don't know that simply closing a door in their home can make them sick, increase their energy bills, or reduce their comfort. We live in this invisible stuff called air. We pull many pounds of it into our lungs each day. A typical air conditioner, heat pumpHeating and cooling system in which specialized refrigerant fluid in a sealed system is alternately evaporated and condensed, changing its state from liquid to vapor by altering its pressure; this phase change allows heat to be transferred into or out of the house. See air-source heat pump and ground-source heat pump., or furnace easily moves 20 tons of air a day. (Yes, I'm talking about 40,000 pounds! We'll save that calculation for another day, though.) And the simple act of closing a door changes the dynamics of a house in ways that can have profound impacts on the people inside the home.
Your bedroom really doesn't aspire to be a balloon. Yet, because of the way your heating and air conditioning system was installed, it may be acting like one. At least to an extent. It doesn't expand the way a balloon does, but it does get blown up.
Think about it. If your bedroom has a supply register from your HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. system but no return grille or other pathway for the air to make its way back to the unit, what happens to that air blowing into the room when you close the door?
Here in the southeastern U.S., we have a lot of crawl spaces. Most are vented. Even most new ones are vented. It's not because it's the best way to keep them dry. That's certainly not true. We have enough research on crawl spaces to know better. No, they're vented because foundation vents got into the code decades ago and, once there, they’ve been difficult to dislodge.
So if you have a vented crawl space, especially in a humid climate, it most likely has moisture problems. And where does that moisture come from? Let's take a look.
What if a builder refused to build from plans drawn by an architect? What if a tile installer refused to implement designs handed to them and instead did their own thing? What if an HVAC(Heating, ventilation, and air conditioning). Collectively, the mechanical systems that heat, ventilate, and cool a building. contractor told a potential client they wouldn't install a system designed by a third party to ACCA protocols?
One of those questions is more real than the others. Of course builders build from architects' plans and tile installers don't throw out designs they're asked to implement. But third-party HVAC design is a different animal.
I first “learned” about VersaDry when a colleague of mine here at BuildingGreen — our materials and product expert, Brent Ehrlich — sent me the photo reproduced at right. I was in the same boat you are right now: “OK, thanks for the photo, Brent, but what the hell is this VersaDry bent-metal thingamajig?”
He replied, “Oh, yeah, here is another photo that will help.” This time he sent me the photo reproduced as Image #2, below.
When you approach the subject of building science, especially regarding heat, air, and moisture flows through a building enclosure, it's easy to get confused. There's a lot to learn: blower door testing, insulation grading, R-value, vapor permeance, radiant barriers, combustion safety, solar heat gain coefficients, and on and on. That's why we break things down into simpler pieces.
I recently taught a class called What the Duct!? at the Builders' Boot Camp in Virginia. Paul Francisco was one of the other instructors (teaching about indoor air quality), and on the last evening at dinner, our conversation turned to building science. (Imagine that!)
I've got the curse, you know. I can't walk into a building and not check out what's going on with ductwork, windows, and anything else that lets me apply what I know about building science.
Recently, I went to lunch at a trendy restaurant near Emory University and of course looked up at the ceiling. You can see what caught my attention in photo at right. The restaurant is only three or four years old, so I've been watching this problem get worse for a while now.
I have a few ideas about what's happening here. Do you?
Back in the early days of airport noise mitigation programs, there was a pretty strong link between air leakage and sound. A document titled “Tips for Insulating Your Home Against Aircraft Noise” noted, “Sound travels from the exterior to the interior of the home in two ways: through solid structural elements and through the air…. Wherever air can infiltrate a home, sound can as well.”
Al Gore is in the news again. His new climate change movie, An Inconvenient Sequel: Truth to Power, is in theaters now. And that means the folks who don't believe in climate change — or at least folks who don't believe that humans have any impact on it — are out in force trying to discredit the message.
As was the case 10 years ago when Gore’s original movie came out, they're going after his carbon footprintAmount of carbon dioxide and other greenhouse gases that a person, community, industry, or other entity contributes to the atmosphere through energy use, transportation, and other means. and making the case that he's a hypocrite. Let's take a look at the issues.