Here's an example: Single-pane R-value of glass that is one-fourth inch thick is around . 90, while R-value of a double-paned window of similar thickness would be nearly double at roughly 1.7. Thus, the window's R-value is referring to that one specific component.
Glass is a substance that can be a good insulator. The thicker that it is, the less likely it will be that heat or cold will transition through this material. It is technically called a thermal insulator, which is why double pane and triple pane windows are highly recommended for areas with extreme temperatures.
It's not the thickness of the glass that gives it the insulating value. Double paned glass has an inert gas, usually argon, between the panes. This minimizes the convective heat transfer between the outside and inside. Thicker glass would simply create more thermal mass to transfer heat/cold.
Windows with high R values include double-glazed windows, triple-glazed windows, and argon-filled windows. Double-glazed windows have two layers of glass with a space in between, while triple-glazed windows have three layers of glass.
There are a number of products available which are designed to improve the thermal insulation of homes, however, without doubt the most well-known energy-efficient glazing product is Pilkington K Glass™.
Install Storm Windows or Window Inserts: These can dramatically improve insulation and are less expensive than full window replacements. Upgrade Window Coverings: Use thermal curtains or cellular shades to provide extra insulation and control heat transfer through the windows.
The lower the U-Value, the better the window is at insulating your home from heat loss. Low-E glass has a marginally better U-Value rating than clear annealed double glazing, meaning it can more effectively retain heat inside the home during winter months while still allowing natural light in.
7mm glass – This is a standard recommended thickness for fire-rated glass. As such, it is commonly used in internal doors and windows. 8mm glass – Typically used for larger tables and shower units. 8.8mm glass (laminated) – Commonly used for large internal doors and windows.
Double-Pane and Triple-Pane Windows
Today's triple-pane or double-pane windows are the most highly recommended for maximum energy efficiency in virtually all climate zones. The insular space between the window panes saves energy and helps reduce electricity costs.
Vacuum insulated panels have the highest R-value, approximately R-45 (in U.S. units) per inch; aerogel has the next highest R-value (about R-10 to R-30 per inch), followed by polyurethane (PUR) and phenolic foam insulations with R-7 per inch.
The best, high-performance, double-pane windows may have a U-factor of 0.30 or lower, indicating that they are very energy-efficient. Some triple-pane windows may have a U-factor as low as 0.15.
Acrylic and plexiglass have high thermal values and insulate buildings better than glass, helping to improve the efficiency of your structure.
The insulated glass unit thickness depends on the type of product and combination, varying from 0.708” to 1.417” (18 - 36 mm). The thicknesses of the glass panes used range from 3/32” to ¼” (2.3 – 6.0 mm) and are offered as annealed, heat treated, tempered or laminated.
Aerogel is more expensive, but definitely the best type of insulation. Fiberglass is cheap, but requires careful handling. Mineral wool is effective, but not fire resistant. Cellulose is fire resistant, eco-friendly, and effective, but hard to apply.
1) Toughened Glass
Also known as tempered glass, this type is stronger and more durable than ordinary glass. A tempered glass window is heat-treated and designed to shatter into small, harmless pieces when broken, reducing the risk of injury.
Did you know: the thickness of glass only relates to the strength or resilience of a window and has virtually no impact on performance in energy efficiency. Thicker glass is typically used to protect against high wind loadings; it's most commonly used in the upper levels of high-rise apartments or office buildings.
Common Thickness Measurements
Residential homes typically use glass ranging from 10mm to 12mm for interior partitions. Offices often choose 10mm clear toughened glass for its visual separation and soundproofing blend. The thickness could be higher for areas exposed to higher impact or load, such as external windows.
In short, yes. Thicker glass can withstand higher tension levels and so-called “smash-and-grab” scenarios, but could still separate if improperly tempered, or during incorrectly placed and drilled holes and notches.
The Relationship between Glass Thickness and Heat Transfer
Glass thickness plays a crucial role in the overall heat transfer process. The basic principle behind this is that thicker glass tends to provide better insulation against heat transfer as compared to thinner glass.
Something else to consider is that low-e windows are known to damage turf and siding. In the right conditions, the solar heat that they reflect can focus into a hot spot creating a magnifying glass effect that melts anything in its path.
Achieving Greater R-Values in Exterior Walls
As with attics or anywhere else in your home, adding more layers of insulation to your exterior walls is key to having a higher R-value and better thermal performance. Foam board insulation is easy to install between wall studs and over existing blanket insulation.
The R-value of a standard single-pane window may range from R-1 to R-2, while a double-pane window can reach R-2 to R-4. Energy-efficient windows with low-emissivity coatings and insulated frames can achieve higher R-values, up to R-6 or more.