Guest Post: A Building Science Primer

Call it what you will: Weatherization, Winterization, or Home Performance Upgrading, we’re talking about fixing a sick house to lower its utility bills and create a more comfortable and healthy living environment. And it all boils down to learning basic Building Science, either just enough to fix your own home, or everything you need to know to become an Energy Auditor or Weatherization Contractor.  That’s what I do, in either a 5-hour DIY class or 30+ hours of professional contractor training.  A guest post by Don Dieckman of Better Building Institute. 

Basic Building Science

Basic Building Science mainly covers the movement of air and heat in and out of a building, and the methods used to keep it from happening.  This means that you have to visualize the structure as a sealed envelope, to keep your conditioned air (hot or cold, depending on the season) from escaping and the outside air from entering. Once the air barrier is sealed, the only step left is to install the proper heat barrier. Most common insulation won’t help if there’s an air leak, so air sealing has to be finished first.

Air Sealing

First, the house is tested using a tool called a blower door. This vinyl panel fits tightly in an outside door frame, and a device called a manometer compares air pressure differences between the inside and outside. A fan in the blower door pulls air out of the house, depressurizing it and measuring how many cubic feet are being moved, while also allowing a search for leaks. Once those leaks are sealed, another blower door test confirms that the air barrier is complete, and then it’s time to add (or replace) insulation.


Over the past 200+ years of homebuilding and remodeling in this country, there have been a lot of materials used for insulation. Some of it works well, some only under certain conditions, some not at all, and some can actually kill you! Of the latter, you need to be aware of a substance called vermiculite, which was actually mined in several parts of the country. It usually looks like shiny gravel, about the size of jewelry beads, and you’ll find it in the attic of 60+-year-old houses, lying between the top-floor ceiling joists. About half of the vermiculite mined is ASBESTOS, so DO NOT TOUCH IT!  There are two things you can do about it: the best is to find a PROFESSIONAL to come and remove it, and if they’re not wearing at least a filter mask and gloves they are NOT a professional. The other option is to simply cover it up with new insulation, making sure it can’t ever be exposed again, and then pray that something like a roof leak doesn’t wash it down into the living area. I heartily recommend the first solution.

One of the most common types of safe insulation is also one of worst-performing, depending on how it’s used. Fiberglass is a decent insulator, but only in a completely closed cavity – it is not an air barrier, so you have to provide one around it (A paper lining helps, but not much, and has to face conditioned space). It’s used mostly in exterior walls, where it does a fair job, since that cavity has 6 sides. But it’s also commonly found on attic floors, open to the unconditioned space above, or stuffed against the rim- or band-joists of even the newest houses with a basement.  In this last location it’s not really doing anything.  Check your own basement, and if you can see a small rectangle of fiberglass between the ends of the floor joists, then it’s no wonder the basement (and even the floor above) is cold in the winter.  Now take a closer look with a flashlight.  Are there spider webs, blowing gently in a light breeze? Spiders love damp, drafty areas, and not even the combination of wood joist and fiberglass can totally block air or moisture.  Fiberglass makes a good filter (Why do you think they make furnace filters out of it?), but it’s a terrible air barrier and a mediocre insulator.

These two examples account for only about .1% of the topics covered in my series of weatherization classes. In my next post I’ll talk about new home construction that can result in ZERO energy bills and a house strong enough to withstand the worst that Mother Nature can throw at it!