Low-emittance - or Low-E - windows are an increasingly common way to control temperature within the building envelope. Traditionally, windows were accepted as being “energy losers” - they lacked the insulation found in the rest of the building frame, so they were prime locations for heat to escape in winter or for cool air to escape in summer (either being conducted through the glass or slipping through cracks in the window frame).

Along with weatherstripping, caulking is one of two essential techniques for sealing air leaks in your home. It is ideal for sealing gaps that don’t open and shut - for instance, where your fireplace or an air vent is built into the wall. It works best where cracks or gaps are less than ¼ inch wide. Caulking consists of applying a thick substance called caulk directly over gaps. The substance soon dries, forming an airtight barrier between the inside and outside. As an added bonus, caulking will also help prevent moisture from seeping into your home, which will help keep mold out, and it can be an effective barrier against insects.

Weatherstripping is an ideal solution to air leaks at the edges of windows and doors. Affixing a material to the space between door and window closures, or on their sides, can stop the leaks. There are many different types of weather-stripping materials; foam, felt, metal and vinyl are the common ones.

One important alternative to fiberglass (link) insulation is cellulose. Cellulose is installed with machines that blow it into attics or spray it into wall cavities. Cellulose is made from shredded newspaper and is a good insulator because wood, from which the paper is derived, has a heat-resistant cellular structure. Typical R-values range from 3.5 to 3.7.Cellulose loose-fill offers the same benefits over fiberglass blankets as fiberglass loose-fill does: it is more effective at insulating an entire space because it can fill oddly shaped spaces and let less air through. In spaces like attics where the insulation rests on the floor, dry cellulose can be blown in, while in vertical spaces like wall cavities the shredded newspaper can be purchased that is dampened and sprayed into place to ensure even, effective application. This technique is used more often in new constructions.

Weatherization experts, those friendly folks that insulate and air seal homes, have developed several tools to aid them in diagnosing air leakages in a home. A blower door test is just such a diagnostic tool; this specific test artificially creates a vacuum between your home and the outside, which causes a pressure difference between the two areas. To begin the test, the weatherization technician will first close all exterior doors and windows in the home and will then set up a large fan in the front door of the house. This fan faces outside and is sealed on all sides to the edge of the door with small hoses running both outside and inside to measure the air pressure. When the fan has created a pressure difference of 50-pascals in cubic feet per minute (CFM) the airflow through the fan is then measured. This number can be translated into a ‘level of leakage,’ which tells a weatherization expert how much air sealing needs to be done. The harder it is to pull air through the fan the harder it is to pull extra air through exterior cracks or holes, which means the house is at a lower level of leakage.

R-value is a measure of a material’s thermal resistance – the degree to which a material allows or does not allow heat to be conducted through it. In our context it applies to the insulation used to keep houses warm in the winter and cool in the summer. It’s measured both by the thickness of a given insulation material and by the structure of that material, so 2 different types of insulation with the same thickness can have different R-values. Comparing the R-values of various types of insulation is one of the most important ways to determine what type of insulation to use, and how much.
If a home had no insulation at all, the thermal resistance would be measured by the amount of air within the wall cavity, the air would have an R-value of 1 per inch (extremely inefficient). Fiberglass, a common type of insulation, ranges from an R-value of 2 to 5 per inch, depending on the type. Although R-values are measured by thermal resistance per inch (like an R-value of 3 per inch), the reference to thickness is usually not used (so instead we just talk about an R-value of 3).
As we’ve said before R-values and insulation make up only one of the two parts of the “envelope.” The other equally important component of the envelope is Air Sealing.

Insulation is material that essentially serves as a barrier between your home and the heat or cold outside. Good insulation will conserve the heat within your home in winter, and will help keep heat from entering your home in the summer. A material’s ability to do this is measured by its R-value. There are many types of insulation, and many places in your home to put it.