June, 2019

Inspection News and Views from the American Society of Home Inspectors

A Science Teacher’s Take on Home Inspection Work


The basis of science is observation and conclusions based on reasoned, discussable phenomena. Good communication is key to the advancement of science. This is true in the home inspection business, too. Let’s explore some more connections.

Science Tries to Explain Systems

Our planet, for example, can usefully be understood as a single organism. Its many interconnections are complicated. Yet, the better we understand the interconnections, the more likely we are to be able to keep it a safe home for all of us. Similarly, the better we understand how systems in a home work, the safer we can keep the home and the better inspectors we will be. 

One example of house science confusion is “filtration lines”—those dark stripes along the walls of carpets (Photo 1). The presumption is that fine particles get sucked toward the walls by negative pressure provided by the forced air system. Some sources say it’s even due to holes in the ductwork.

Questions to Ask:

Occam’s Razor is a standard for testing hypotheses and it proposes that simple solutions are more likely to be correct than complex ones. In this example, surely, the tack strips make it more difficult to clean next to the wall. Carpet cleaners who say these areas can’t be cleaned are not pretreating the area with a brush or using a small enough vacuum head. It seems to make the most sense that these stripes are primarily just dirt that is not easy to vacuum.

Maybe, in some cases, dust comes out of the ducts! A situation like Photo 2 would certainly be cause for comment. It’s important for home inspectors to stay humble and keep trying to get a bigger picture, say, from multiple causes. 

Occam’s Razor also can help home inspectors explain simple solutions to homeowners and protect them from less knowledgeable or unscrupulous contractors. “Please, just get the gutter cleaned before you have the basement waterproofed!” is something I’ve said to my clients many times. 

Cleaning the gutters and adding downspout extenders are a simple surface solution to wet basements. Even adding expensive foundation floor drains means that the water still has to pass over the whole basement wall before it gets removed. But how about this drainage solution (Photo 3) that saved a house from the waterproofing expense?

Science Can See Into The Future

We know when the sun will expand and melt the earth because of how other stars like our sun have behaved. Similarly, because of home inspectors’ experiences in older homes, we can predict what will happen to a poorly supported expansion tank, for example (Photo 4).

Here’s one expansion tank attached to chlorinated polyvinyl chloride (CPVC) pipe that looks like a catapult. In some new homes, these are still being installed straight up on 18 inches of ¾-inch copper pipe. Water is supposed to cycle in and out, but if the internal bladder fails, the tank remains filled with water. I have seen two-year-old tanks full of water that bend the lower joint. One plumber told me of a situation in which a tank torqued off and did $75,000 worth of damage to the basement. Therefore, these tanks need to have shelves placed under them or straps set up to support them so they stay upright.

Expansion tanks are installed because water takes up more space when it’s heated (as does everything else). The pressure causes weeping valves and joints nearby and, in one of my clients’ houses, a CPVC joint to pop out in the bathroom just above the water heater. These effects happen regardless of the absence of backflow preventers. 

Utility has to be balanced with safety in science

There are always trade-offs between function and safety. Think about the moon mission: Astronauts have to stay alive while riding on a bomb. The more complicated the system, the harder it might be to understand the safety concerns. 

Now, think about water heaters and electric panels. Real estate agents will say they “work,” yet these systems contain safety devices that can’t be tested until they’re needed…and that could be too late. Circuit breakers are supposed to trip before the wires melt. Thermostats on water heaters are supposed to turn off before superheated water comes shooting out of the temperature-pressure relief (TPR) valve, which is not desirable, but better than the tank exploding. However, if the TPR valve doesn’t work, then it’s astronaut time. 

In addition, gas furnaces eventually get holes in the heat exchanger. All of these circumstances are unlikely to cause death, but why take the chance with a Federal Pacific or Zinsco panel, a water heater more than 15 years old or a gas furnace over 25? 

In summary, as teachers of house science, we need to do our best to understand how the different parts of a house work together, link our recommendations to observable facts as we discuss them with homebuyers, be humble (we might not have the whole picture) and look out for the future of our clients by making sure their new house is safe.

Useful Science Terms

Condensation: Condensation is a process. It’s the opposite of evaporation. That stuff on your iced tea glass in August is condensate.

Galvanic corrosion: When different metals come into contact with each other, an electrical current forms, which can lead to the degradation of the materials. Scientist Alessandro Volta used this property to invent the battery. One of the oddest occurrences of this in homes is those green spots all long the bottom of copper pipes (Photo 5). These are caused by steel flakes, from old water heaters, settling along the pipes, eventually causing pinhole leaks. 

When water passes through a substance or, like on metal ducts, simply touches it, salts are drawn out.

Three ways that heat moves: Conduction occurs through touching. Convection occurs through air movement. Radiation is invisible infrared electromagnetic radiation. Insulation with a foil face prevents all three kinds of heat movement.

Adiabatic cooling: This principle is part of why air conditioners work. Have you ever cleaned your keyboard with a can of air? A volatile fluid (meaning that it has a low boiling point) is compressed in a can. It has a certain amount of heat in a small space and, when you reduce the pressure by opening the valve, it has the same amount of heat in a larger space, so it gets cold. 

Also, the change of state from a liquid to a gas absorbs heat from the surroundings (in the same way that sweat from your body takes the heat with it as it changes into a gas). 

This all happens when the high-pressure line shoots coolant into the interior coil. Well, the low-pressure line (the big line-set pipe) then takes it out to the compressor/condenser to get pressed into a liquid again so the cycle can repeat itself. No net heat is lost, it’s just transferred outside. The only energy added is by the work the compressor does (and the exterior fan).  

Adiabatic cooling is also how water vapor that leaves the ground turns to water droplets in clouds because the air pressure decreases with altitude. The air literally weighs less as you go up. The weight of air pressing on us at sea level is like being under 10 meters of water. 

More Random Science

Stomach: I’m just throwing this one in because it bugs me. Our stomachs are under our rib cages on the left, lower side. So, you can never really hit someone “in the stomach.” It’s our abdomens that hurt (even when they have not been hit) because the intestines do most of the digestion and have most of the taste buds that can sense a problem and make us throw up or go the other way. 

To get more science refreshers, check out my website (www.nosurpriseshomeinspection.com/). I offer a nice 25-page history of the universe and a Bill Johnson Home Inspector mystery story, involving a Bosnian spy, a Saudi prince, military investigators and very hazardous houses!

The opinions expressed in this article are those of the author only and do not necessarily reflect the opinions or views of ASHI. The information contained in the article is general, and readers should always independently verify for accuracy, completeness and reliability.

Paul Cummins, owner of No Surprises Home Inspection NOVA-DC, LLC, has had a variety of careers and lived in three foreign countries. He taught science for 16 years before becoming a home inspector. His published works include books on science and religion. Contact Paul at info@nosurpriseshomeinspection.com.