The main purpose of building codes in Canada (e.g. Ontario Building Code) and in the USA (e.g. International Code Council) is to protect public health, safety and general welfare as they relate to the construction and occupancy of buildings and structures.

Insulation is a major topic covered by all building codes, which specify the minimum R-value that various parts of the house (e.g. exterior walls, ceilings, floors and foundations) must meet during winter conditions. For example, walls might require a R-19 insulation and ceilings, a R-38 insulation.

Ideally building codes should mandate how R-values are to be determined, yet in reality they just don’t. Although there are a multitude of products on the market, there are two basic types of insulation: open cell and closed cell. Fiberglass is an OPEN CELL insulation because the air pockets are not fully enclosed and air can enter and escape freely. In comparison, expanded polystyrene (EPS) used in Thermapan SIPs is a CLOSED CELL insulation where air cannot enter and escape at all.

A material’s R-value is a measure of its resistance to heat transfer. What very few people realize is that building codes do not mandate how R-values are to be determined. So insulation manufacturers design the R-Value of their product in a laboratory using a device known as a “guarded hot plate”, according to common standards such as ASTM C518 or ASTM C177.

This is known as a steady state test because the test samples are completely sealed from air infiltration. In these tests, fiberglass and EPS insulation easily achieve building code minimum R-values. But let’s turn now to the real world, where unlike in the lab, air infiltration is unavoidable.

Air infiltration is the amount of air leaking in and out of a building through cracks in walls, ceilings, windows and doors. It results from differential indoor and outdoor pressures, such as when wind – even a gentle breeze – is blowing up against your house. You experience air infiltration whenever you feel a cold draft along the floor on a winter day. The cold draft is a result of unequal air pressures penetrating the air barrier and cracks in your exterior walls. Even though air barriers are installed underneath the exterior cladding of today’s homes, unfortunately they still allow some air to infiltrate.

You may have heard the sayings, “airtight buildings are unhealthy” or “your home needs to breathe.” These proponents of “Good Old Fashioned” building construction do not realize that homes with higher rates of air leakage are less energy efficient and are still prone to moisture and mold damage.

The way that fiberglass insulation is designed in the laboratory does not reflect the way it is installed in today’s homes. Real-time studies provide evidence that the R-values of fiberglass insulation decrease significantly during winter conditions. Two research studies stand out in particular: Brock University’s Determination of Thermal and Moisture Behavior of the Structural Insulated Panel and the Oak Ridge National Laboratory’s Attic Testing at the Roof Research Center. Let’s take a look at the conclusions found in the following two studies.

This agency of the U.S. Department of Energy conducted an in-depth study of insulation behavior and thermodynamics in a common residential attic construction.

Conclusions:
- EPS insulation R-value remained constant throughout winter temperatures.
- Fiberglass insulation R-value decreased by 50% in winter conditions. Therefore, R-38 fiberglass insulation decreases to as low as R-19 during winter conditions.

In a typical roof attic, the fiberglass is in a non-sealed environment or non-steady state environment – unlike when it was tested in a laboratory. In winter conditions, cold air enters through attic roof vents. The OPEN CELL fiberglass allows the cold air to infiltrate the insulation, displacing warmer air pockets.

By measuring the actual energy loss in two identical homes – one built with SIPs and one built with stud-and-batt walls – Dr. Tony Shaw came to a number of revealing conclusions:

Conclusions:

1. The 2x6 wall house had 68% more air leakage than the SIP house.
2. The R-19 fiberglass insulation performed at an equivalent R-4 level when the outdoor temperature was -10.5ºC (13.1ºF).
3. The SIP wall house with R-17 EPS insulation maintained its true R-value throughout the duration of the 1 year study.
4. The R-17 EPS SIP wall house used 33% less energy than the R-19 fiberglass wall house.

The reason why the fiberglass R-19 decreased to an R-4 is because air infiltration is occurring in the wall cavities through the OPEN CELLS. The fiberglass is in a non-sealed environment or non-steady state environment – unlike when it was tested and rated in the laboratory.

The reason why the SIP EPS insulation averaged an R-17 R-value throughout the duration of the study is because the EPS insulation was installed in a steady state environment, just as when it was tested. The CLOSED CELLS of the EPS insulation do not allow air infiltration to occur.