Musings of an Energy Nerd

Houses are changing. Anyone buying a new home in 2018 expects the home to be quite different from one built in 1918, of course.

What “new features” is the typical buyer of a new home seeking out? It depends. Some buyers are looking for a foyer with a 20-foot ceiling and a master bathroom with a big Jacuzzi. Others, including the typical GBAGreenBuildingAdvisor.com reader, are looking for low energy bills and superior indoor air quality.

A surprising number of people don’t understand the causes of condensation. If you ask a stranger on the sidewalk, “Does condensation happen when cold air encounters a warm surface, or when warm air encounters a cold surface?,” many people will shrug their shoulders.

Here’s an example of this type of confusion: When drivers see condensation on their windshield during the summer, they are often unsure of the best remedy. Should they turn on the heater or the air conditioner?

Let’s look at four different scenarios.

One of my first construction jobs in Vermont, back in the late 1970s, was at an architect-designed home with a massive brick chimney with four flues: one flue for the oil-fired boiler, and three flues for the home’s three wood stoves. The chimney worked fine — mostly because the house had so many air leaks that the wood stoves were never starved for combustion air.

Massive chimneys like the one I remember from that job are expensive to build, but they are often a source of pride for the owner. They provide interior thermal massHeavy, high-heat-capacity material that can absorb and store a significant amount of heat; used in passive solar heating to keep the house warm at night. ; they are durable; and they are handsome to behold.

If you’re concerned about indoor air quality, you may have noticed ads for a type of appliance called a portable air purifier. Purchasers hope that these boxes will suck in dirty air and discharge clean air, but few homeowners know how these appliances operate.

In this article, I’ll try to answer a few basic questions about portable air purifiers:

• How many kinds of portable air purifiers are on the market?
• Do they work?
• Who needs one?

It’s fairly common for cold-climate builders to install a very thick layer of cellulose on an attic floor (that is, above the drywall ceiling of the floor below). Many green builders aim for a ceiling rated at R-60, R-70, or even R-100. When it comes installing cellulose, the usual advice is to “pile it on.”

Cellulose rated at R-60 is about 16 or 17 inches deep. Cellulose rated at R-100 is about 27 or 28 inches deep. That’s a lot of cellulose — so much, in fact, that some builders ask, “Is my drywall ceiling going to sag?”

Three years ago I wrote an article about a problematic recommendation in the 2012 building codes — namely, the “R-20+5” recommendation for walls in Climate Zones 6 through 8. This recommendation — actually, a prescriptive minimum R-valueMeasure of resistance to heat flow; the higher the R-value, the lower the heat loss. The inverse of U-factor. requirement for walls — gives code approval to walls with R-20 fiberglass batts and R-5 exterior rigid foam. (Image #2, below, shows the relevant code table.)

We live in strange times. It's clear that our politicians have been remarkably inept at addressing the climate change crisis. Scientists tell us that we have already injected so much carbon dioxide in the atmosphere that, especially in light of the ineptitude of political leadership, it is almost certainly too late for the human race to avoid environmental catastrophe.

In short, the chain of events we have set in motion is in all likelihood irreversible.

The Love Song of J. the Builder
With apologies to T. S. Eliot

How much insulation should you install in a ceiling or a roof? When the question comes up on GBAGreenBuildingAdvisor.com, I usually advise builders to install at least as much insulation as is required in the prescriptive table found in the International Residential Code (IRCInternational Residential Code. The one- and two-family dwelling model building code copyrighted by the International Code Council. The IRC is meant to be a stand-alone code compatible with the three national building codes—the Building Officials and Code Administrators (BOCA) National code, the Southern Building Code Congress International (SBCCI) code and the International Conference of Building Officials (ICBO) code.) or the International Energy Conservation Code (IECC International Energy Conservation Code.).

This prescriptive table is known as Table N1102.1.1 in the IRC (see Image #2 at the bottom of the page). In the IECC, the identical table is known as Table R402.1.2 (Image #3).

Most residential builders understand that window rough openings need sill pan flashing — either a site-built sill pan made with peel-and-stick tape, or a commercial sill pan made from metal or plastic. Window manufacturers’ installation instructions began requiring sill pans about 20 years ago, and by now these details are standard at most residential construction sites.

For some reason, though, many builders are neglecting to install sill pans under exterior doors. It's time for a gentle reminder: If you skip the sill pan under an exterior door, you are risking a very expensive callback.