energy efficiency Archives - Dawn Killough, Freelance Construction Writer

*R-value affects heat loss in a building*

The insulation value, or R-value, of a building is a sum of the components that make up the outer shell. This often includes siding, insulation, framing, and drywall. There are certain parts of a building, however, that detract from its ability to insulate. These parts affect R-value negatively, and though they can’t be totally eliminated, they can be mitigated.

Doors and Windows

As much as we love, and need, doors and windows, they are not good for a building’s insulation value. Doors open and close, allowing air to move freely inside and out. Additionally, it can be tough to completely seal the gap around a door, causing even more air leakage even when the door is closed.

Windows are also not very insulating. Recent changes in glass technology and the use of multiple panes of glass have improved their insulating properties a bit, but they still can’t compare with other materials.

Just to further confuse the issue, windows have to have their own label to measure their insulating value – the U-factor. U-factor is the inverse of R-value, so the lower the number, the better insulation the window provides.

One of the characteristics that affects the insulating ability of a window is SHGC (solar heat gain coefficient), a measurement of the amount of heat caused by sunlight that is allowed through the glass. The lower the SHGC, the less solar heat the window transmits. It is important to note that both of these measurements, U-factor and solar heat gain coefficient, only apply to the glass in the window, not the frame.

How can you increase the insulation value of a window? Options include: insulating window shades, window tinting or film to prevent solar heat gain, and the use of multiple panes of glass with insulating gases (such as argon) inserted between the panes.

*Doors create opportunities for air to flow in and out, reducing energy efficiency*

Air Gaps

Air gaps are the bane of insulation! As much as insulation and other building materials try to keep the outside out and the inside in, gaps between materials, or holes within materials, defeat their purpose.

The fix is easy – no air gaps! Completely sealing the space where materials meet with caulking and making sure that no holes are allowed will help decrease air gaps substantially. They can’t be eliminated completely, but the less there are, the better.

Bridging

Bridging, or more formally thermal bridging, can best be described by the phrase “taking the path of least resistance.” Air temperature will travel through the areas of a roof or wall with the least R-value, providing a “bridge” for the hot or cool air to reach the inside of the building. This may seem a bit confusing. An example from Green Building Advisor will help:

“Suppose your walls have 6″ fiberglass batts… Every 16 inches on center in that wall is a 2×6 or 2×4 stud. The fiberglass has an R-value of around 3.5 per inch, and the stud is around R-1.2 per inch. The wood studs allow heat to flow through the wall assembly at a rate that is 3 times faster than the heat flow through the surrounding insulation. While the advertised R-value for a 6-inch fiberglass batt is R-19, the building assembly’s effective R-value is about R-3 lower.”

What a bummer! How do we fix this? A few options are available: use advanced framing techniques to limit the number of studs, install insulation between the studs and the inside or outside surface to break the bridge, or use alternative building materials that do not require the use of studs, such as straw bale or SIPS (structural insulated panels).

Putting It Together

R-value isn’t the only characteristic to consider when choosing building materials, but it can play an important role in improving the energy efficiency of a building. Wall and roof assemblies should be evaluated at their weakest point, and steps taken to combat the infiltration of air or temperature whenever possible. Purchasing efficient windows and doors will also help improve efficiency.

Photos courtesy of Depositphotos.

*R-Value affects the amount of heat lost through walls, doors, and windows*

What Is R-Value?

R-value is a measurement of how much a building material protects one side from the heat or cold on the other side. A higher R-value means that a material insulates better than one with a lower value.

In order to get an idea of what these values are, here are a few examples of common building materials and their R-values:

1/2″ drywall – 0.45
1/2″ plywood – 0.62
4″ wide brick – 0.80
1″ of concrete – 0.52
Single pane of glass – 0.91
2″ insulated metal door – 2.00

R-Value of Building Insulation

Building insulation has different R-values depending on the type of material being used and the thickness of the material. Insulation made from different materials is used in different areas of a building, and is designed to be used in many types of construction.

*Roll of fiberglass insulation material*

Here are a few common types of building insulation:

Fiberglass – This is the most common material used in residential construction, and it is made up of blown glass threads that are either matted together into batts or distributed loosely. The fiberglass batts are either stuffed into the spaces between the studs in the exterior walls of a building, or they may be laid down on the bottom of an attic space. Other forms of fiberglass insulation, such as loose fill or boards, are used in other locations, such as a basement or crawl space. Fiberglass insulation comes in a wide range of R-values, most commonly from R-11 to R-38.

Foam – Spray foam insulation is made by mixing two chemicals (isocyanate and polyol resin, if you are interested) that react to create foam that expands to fill the space it is placed in. It can be shot into spaces through small access holes, making installation in retrofit projects easier than standard batts. There are two types of spray foam – open and closed cell – with closed cell being the most dense and therefore having a higher R-value. Foam averages R-5 to R-6 per inch, compared to R-2 to R-4 per inch of fiberglass.

Recycled denim – Blue jeans and other denim products are shredded and the cotton fibers are woven together to form batts, similar to standard fiberglass insulation. The denim used to produce this insulation is post-consumer, so it removes products from the waste stream and repurposes them. Denim batts provide slightly better R-values than similar thicknesses of fiberglass.

What Does It Mean?

So, why is all this important? R-value is an additive property, meaning that by layering several materials on top of one another, the insulating value of the assembly will be the sum of the individual products. For example, a wall made up of a sheet of drywall, R-11 insulation, and a sheet of plywood would have a total R-value of 12.07 (0.45 + 11.00 + 0.62). Think of it as adding multiple blankets of varying thicknesses and materials to keep warm.

There are a few more things to consider when determining how insulating a structure is, but for the most part, the higher R-value the building shell has, the easier it is to heat and cool and less energy is needed to keep it that way. Of course, there are things like doors and windows that don’t insulate as well or let in outside air, lowering the insulating ability of the building.

When designing a new structure or remodel project, it is important to try to increase the R-value of as much of the exterior walls, roof, and floor as possible. A well-insulated building is more energy efficient and less expensive to heat and cool.