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Building owners who want to improve energy efficiency often focus on equipment upgrades. Some examples are replacing fluorescent lighting with equivalent LED products, or replacing window air conditioners with ductless mini-splits. However, the building envelope is also important, and it must be be designed to minimize summer heat gain and winter heat loss. Insulation can greatly improve the thermal performance of a building.

There are many types of insulation, using a wide range of materials and installation methods. Some insulation types are embedded in the building envelope, making them more suitable for new constructions, while others have a superficial installation that adapts to existing buildings.

Understanding the R-Value of Insulation

Building enhancements that improve energy performance have metrics with numerical values that describe the benefits gained. Just like LED fixtures have luminous efficacy and water heaters have an energy factor, insulation has the R-value.

In simple terms, the R-value describes resistance to heat flow. This means that R-40 insulation reduces heat movement by half compared with R-20 insulation, assuming the same temperature difference between indoor and outdoor spaces. When multiple insulation barriers are stacked together, you can simply add their R-values to obtain the total; for example, if you stack R-10 and R-20 insulation, you get an R-30 barrier.

The procedure to calculate heat flow across insulation is the following:

1. Multiply the R-value and the surface area of insulation to calculate thermal resistance.
2. Determine the temperature difference.
3. Divide the temperature difference by the product of step 1 (thermal resistance) to calculate heat flow.

Note that the R-value has units of (m2 °C / W) and thermal resistance has units of (°C / W). Temperature difference and heat flow are measured normally in °C and W. As a simplified example, assume that R-20 insulation is used to cover 10 square meters and the temperature difference is 15°C.

1. Thermal resistance = (20 m2 °C / W) x (10 m2) = 200 °C / W
2. Temperature difference = 15 °C
3. Heat flow = 15°C ÷ (200 °C / W) = 0.075 W

When a wall is equipped with insulation, the overall R-value differs from the rated R-value of insulation. Consider that windows are not covered, and many structural features that go across the entire wall are not covered either. Also, insulation should not be compressed during installation, since this reduces its effective R-value.

Heat transfer increases in spots where the building envelope has a low R-value, a behavior called thermal bridging. This must be prevented at all costs, since it works against the benefits of insulation - a good suggestion to detect thermal bridging is getting a professional energy audit from consulting engineers.

Building insulation can be considered an investment in your property. An additional cost is assumed upfront, but the long-term benefit is a reduction of heating and cooling loads, allowing the use of smaller heating and cooling equipment. If you are considering HVAC upgrades, improve your insulation first and you may have the chance to use new HVAC equipment of higher efficiency and reduced capacity.

Types of Insulation

There is a wide range of insulation products, and the best option changes depending on project conditions. Also note that some types of insulation are deeply embedded in the building envelope, and their installation in existing properties is not viable or very expensive. The main insulation types are summarized in the following table:

 Insulation Type Description Blanket insulation: batts and rolls The most common type of insulation, designed to be installed between structural elements such as joists and beams. Normally made from fiberglass, although other materials are available. Concrete block insulation Insulation designed to be installed with concrete blocks. There are various configurations: foam boards, beads and inserts, or even prefabricated masonry units with embedded insulation. Foam board Also known as rigid foam, suitable for almost any area of a home. Some common materials are polystyrene, polyiso and polyurethane. Insulated concrete forms (ICF) Prefabricated insulation assemblies with a high thermal resistance, designed for poured concrete walls. Insulation is embedded in walls during the pouring process. Loose-fill / blown-in insulation Foam or fiber particles that are blown in place, adapting to spaces with complex shapes, where other insulation types are difficult to install. Radiant barriers Unique system that reflects back heat, unlike normal insulation that slows down heat conduction and convection. Commonly used in attics to reduce summer heat gain. Rigid fiberboard Insulation made from fiberglass or mineral wool, normally used to insulate air ducts and resistant to heat. Sprayed foam Insulation that is sprayed, injected or poured. Solidifies after application and adapts to complex shapes. Structural insulated panels (SIP) Prefabricated structural elements that include insulation. They provide uniform insulation and air tightness, enhancing the building envelope.

Conclusion

There are many insulation options for buildings, and the best option changes depending on the application. Also consider that some insulation types are intended for new constructions and very difficult to deploy in existing buildings - ICF and SIP are two examples.

Insulation improves your building envelope, reducing summer heat gain and winter heat loss. This leads to a reduction of heating and cooling loads, lowering the operating cost of HVAC equipment. Professional MEP engineers can help you achieve the highest building performance possible, combining an optimal building envelope with efficient and properly-sized HVAC units.