Three Fundamental Rules for Houses

I’ve noticed over the years how some people will tolerate things like an engine dash board light or a dripping faucet because of their fear of learning how it works.

Sound familiar? I am not a technically minded guy, so I don’t succumb to this same fear. I have worked on cars growing up. I even rebuilt a 1967 fastback Mustang and sold it in Hot Rod Magazine. Boy, I wish I still had it. So I know how an engine works. I learned through hands-on experience (kinesthetic) what it really meant to ‘throw a rod.’ No, it’s not a dance step.

Picture of Mustang before I sold it!


Most of us live in some kind of building, but how many actually know how buildings work? You might think that anyone who works on houses knows how houses work, but you’d be wrong. Builders and trade contractors know their part of building and repairing homes, but most lack knowledge of the fundamentals of building science.

The good thing is, it’s not rocket science. Yeah, you can study engineering or physics and go as far as the outer limits with this stuff, but I’m going to focus the telescope to three fundamental rules for understanding.

A house is a system.

Not unlike the body is a system, a family is a system, a business is a system and so forth. This is the first thing that a lot of people who work on houses don’t understand. A house is a system built with many interacting components: framing, electrical, plumbing, HVAC…, each with its associated trade system. Mostly, these trade contractors look at a house with blinders on; they see what affects their work and not much else.

house system

In terms of how a house performs, we can break it down into weather shell, building envelope, and mechanical systems.

  1. The weather shell keeps the elements out but isn’t usually the boundary between conditioned and unconditioned spaces.
  2. That would be the building envelope (or the thermal envelope), which comprises:
    1. continuous air barrier and
    2. insulation that’s right up against the air barrier. There are many ways that the building envelope gets compromised, and even spray foam insulation isn’t a panacea.
    3. Mechanical systems have a huge impact on how a home performs. We know they increase the temperature difference between inside and outside, but did you know that they also can create a big difference in moisture content and air pressure between inside and outside? As you’ll see in the last rule below, those things can have a huge effect on comfort, durability, health, and efficiency. For best performance, you want heating and cooling systems that are properly sized and have distribution systems that are designed and installed for optimal efficiency.

Build for your climate.

Ever pick up a home improvement magazine or watch a TV show about renovating your home? (I hate the TV shows because they over dramatize everything.) And when they installed that vapor barrier, did they tell you what climate zones that works for and where you should never use one? I didn’t think so. As it turns out, you can’t build the same house to the same specifications in all climates, period. You actually have to pay attention to whether your climate is wet or dry, and whether it’s hot, mixed, or cold.

That vapor barrier, for example, may be a good idea in Chicago or Tampa, but forget it in Memphis. It’s OK in a one-way climate, since the purpose is to limit the diffusion of water vapor from humid air into a wall cavity. In Chicago, the humid air is mostly inside the house, so the vapor barrier goes on the inside. In Miami, it’s mostly outside, so it goes outside. In Memphis, if you choose a side for the vapor barrier, you’re going to be wrong for half the year.

Control the flow of moisture, heat, and air.

Ever hear of the laws of thermodynamics? Heat, air, and moisture all naturally flow from an area of more to an area of less. Moisture moves from wet to dry. Heat moves from hot to cold. Air moves from high pressure to low pressure. That’s from the second law of thermodynamics, and any attempt to go in the opposite direction must be done with the utmost care.HVAC

You can see that all three of these rules are related to one another. To control moisture, for example, you have to consider what kind of climate the house is in, which determines how you treat the building envelope and what kind of mechanical systems you install. It’s all interconnected much like much of life is, you know.

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