# Thermal insulation

Figure 1. The photo above shows Aerogel, an extremely good thermal insulator, between a blowtorch and matches. The insulating properties of the Aerogel prevent the matches from burning.[1]

Insulation is the term used for a variety of materials used to reduce heat transfer. It is part of the building envelope, used to limit heat loss through walls, roofs or floors. There's also electrical insulation, which is similar but for electricity.

## Housing Insulation

In most climates the exterior temperature is very different from the desired interior temperature. This is why people heat or cool their homes. These systems require energy to operate so the purpose of insulation is to allow the internal temperature of the building to be as unrelated as possible to the external temperature. If a building is insulated properly, this can result in large energy savings. This is beneficial from an economical, environmental and social point of view.

### R-value

Because of the large number of insulation types on the market, it is important to have a common rating system. North America uses a unit called the R-value (Resistance value) to measure the performance of an insulation. The Metric unit for thermal resistivity is the RSI. The R-value measures the material's resistance to thermal conduction. It is important to note that heat transfer occurs through three different mechanism; conduction, convection and radiation. A limitation of the R-value is that it only accounts for conduction. This can result in a slightly inaccurate representation of the true resistance to thermal transfer of a material. R-values, however, are a simple way to compare materials' insulating qualities

The R-value is found using the following formula:

R-value
• is the temperature difference on each side of the material
• is the heat transfer per area per time

The SI units of an R-value are m2·K/W

Since the R-value is inversely proportional to the heat transfer through the object, the higher the R-value, the better the insulator. That is, the greater the R-value, the greater the resistance to heat transfer. A typical 2"x4" wall assembly, insulated with fibreglass batt insulation, will have and R-value of about 13.73.[2] Fibreglass insulation is one of the most common types of insulation in walls. The R-value is reduced to 2.73 when the insulation is removed. R-values can be added normally. So if two materials are together the total R-value is just the R value of one plus the R-value of the other.

### R-values of Common Materials

Below is a table of R-values.[3]

Material R-value per inch Insulation R-value per inch
Drywall 0.90 Fibreglass Batts 3.0 - 3.8
Hardwood 0.90 Cellulose 2.8 - 3.7
Sand and Gravel 0.09 Rigid Board - Extruded Polystyrene 5.0 - 6.3
Cement Mortar 0.20 Spray-Foam Polyurethane 5.6 - 6.2
Brick 0.20 Vacuum Insulated Panels[4] 39
Stucco 0.20 Silica Aerogel[5] 10.3

## References

1. Wikimedia Commons. (July 30, 2015). Aerogel [Online]. Available: https://upload.wikimedia.org/wikipedia/commons/b/b4/Aerogel_matches.jpg
2. All Wall Systems. (July 30, 2015). R-Values [Online]. Available: http://www.allwallsystem.com/design/RValueTable.html
3. Grassroots. (July 30, 2015). Building Material R-Values [Online]. Available: http://www.grassroots.ca/homeowner_help_articles/building-material-r-values.php
4. Dow Corning. (July 30, 2015). Insulation [Online]. http://www.dowcorning.com/content/publishedlit/62-1556-01.pdf
5. HubPages. (July 30, 2015). AeroGel - The Perfect Home Insulation [Online]. Available: http://liambean.hubpages.com/hub/AeroGel-The-Perfect-Home-Insulation

## Authors and Editors

Bethel Afework, Jordan Hanania, Kailyn Stenhouse, Jason Donev
Last updated: June 25, 2018
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