Home Inspection FYI

Providing Help, Knowledge and Other Useful Information To Home Owners Everywhere

Home Inspection FYI - Providing Help, Knowledge and Other Useful Information To Home Owners Everywhere

R-Value Ratings for Insulation

R-Value Ratings

As energy efficiency has become an increasing concern among builders and homeowners, the attributes and performance of building materials and components are being scrutinized more closely.  In order to maximize levels of energy efficiency by examining the details of how each individual component of a house performs on its own and as part of a dynamic system, very specific properties are measured and taken into account.  This can be especially helpful when trying to select the best building materials for a given application.insulation r value R Value Ratings For Insulation

R-value is the measurement used when quantifying a specific material’s level of thermal resistance, which is the inverse of U-value, which measures thermal conductance.  R-value is often the standard consideration when discussing the effectiveness of insulation.  It’s good to be familiar with the specifics of R-value ratings, especially when wanting to understand insulation, energy efficiency, heat transfer and energy audits.

How Does R-Value Relate to Insulation?

Heating and cooling costs account for 50% to 70% of energy used in an average U.S. home. Inadequate insulation can account for a lot of wasted energy, so it is important to be sure that insulation installed is doing its job properly and increase energy efficiency.

The function of insulation is to provide resistance to the flow of heat, and R-value is the measure of exactly this attribute for a given material.  A higher R-value equates to higher resistance to heat flow and greater effectiveness in insulating.  An insulation material’s R-value, in conjunction with how and where it is installed, will determine its overall thermal resistance and energy efficiency effectiveness.  Adding the R-values of each layer of material contained in one building component, such as a wall or ceiling with multiple layers of insulation, will help determine the thermal resistance of the whole component.  The way the insulation is installed, as well as other factors, will also affect its thermal resistance, heat transfer and energy efficiency.

Important Factors to Consider When Measuring R-Value Thermal Resistance

When considering R-value as a means to determine the thermal resistance of a building component, there are other factors that must also be taken into account.  While R-values are an excellent guide for comparing the attributes of different insulation products, they apply only when the insulation is properly installed.  For example, if two layers of insulation are smashed into the thickness intended for one layer, the R value does not double.  Likewise, if a single layer of insulation is compressed during installation, it will not be as effective.  Stuffing batt insulation sized for 5 inches into a 4-inch wall cavity will actually lower its R-value.  Ensuring that insulation is correctly installed will help allow the product’s full benefits to be realized.

Also important to consider is the fact that even when installed correctly, insulation affects heat transfer through the insulation itself but not through other materials, such as glass windows and studs.  If there are structural gaps in any building penetrations, even insulation with a high R-value that’s installed properly cannot mitigate heat loss from air leaks.  Studs and windows provide a parallel heat transfer conduction path, and insulation between studs in a wall does not restrict heat flow through the studs.  This heat flow is called thermal bridging, and the overall R-value of the wall will be different from the R-value of the insulation itself.

Calculating and Converting R-Value

The equation used to calculate R-value may be of interest to some inspectors because if the R-value is known, the equation can also be used to help calculate heat loss.  The equation for determining R-value is as follows:

R-value = temperature difference x area x time ÷ heat loss

The temperature difference is expressed in degrees Fahrenheit, the area in square feet, the time in hours, and heat loss in BTUs.  Since European R-value uses different units of measure (Celsius, Kelvin, meters, etc.), it may be helpful to know how to convert a European R-value into a U.S. R-value.  This is done by multiplying the European value by 0.176 and dividing 1 by the result.

The FTC and DOE on R Value

In the 1970s, the Federal Trade Commission (FTC) created a rule requiring insulation manufacturers to disclose R-values at the point of sale and in some ads.  This is intended to protect purchasers from false claims made by manufacturers and to create a standard of comparison for products.

insulation r value1 R Value Ratings For Insulation

The U.S. Department of Energy (DOE) has issued recommendations for insulation R-values in new and existing homes.  The recommendations are based on a comparison of the cost for installing insulation versus potential future energy savings.  Their recommendations for attics, cathedral ceilings, walls and floors are generally greater due to more heat flow than what is actually required by most current building codes.

R-value ratings are a useful tool, especially when comparing the effectiveness of insulation products for energy efficiency, heat transfer and controlling heat loss. Understanding a bit about how other factors such as heat flow affect a building component’s thermal resistance is important if insulation is to be used to its full benefit.

 R Value Ratings For Insulation

Energy Efficiency With Aerogel Works to Control Heat Transfer

Energy Efficiency as an Insulation Material

 

Aerogel and silica aerogel are used as an insulation material which is good for reducing heat transfer and thermal conductivity. Controlling heat transfer and heat loss is becoming more and more of value in energy efficiency.


 aerogeltorch Energy Efficiency with Aerogel Works to Control Heat Transfer

Aerogel is a class of porous, solid materials that exhibits an impressive array of extreme properties. Invented in 1931 and used for decades in scientific applications, aerogel is becoming increasingly feasible as a building insulation, largely due to a decrease in the price of the material.

 

Aerogel is still prohibitively costly for most homeowners, and the few who can afford it probably don’t know what it is. At expensive properties with environmentally friendly features, however, inspectors should be prepared to encounter the material. Also, the prevalence of aerogel is likely to increase in the coming years as it becomes more affordable and widely known.

Physical Properties and Identification of Aerogel

Aerogel holds 15 world records for material properties, a few of which are listed below. Aerogel is:

  • lightweight. It is, in fact, the lowest-density solid on the planet. Some types are composed of more than 99% air, yet they still function as solids;
  • extremely high in surface area. It can have a surface area up to 3,000 square meters per gram, meaning that a cubic inch of aerogel, if flattened out, could cover an entire football field; and
  • strong. It can support up to 4,000 times its own weight. In the picture at right, a 2-gram piece of the material is supporting a brick Energy Efficiency with Aerogel Works to Control Heat Transfer  5-pound brick.

The following qualities will also assist with identification. Aerogel:

  • appears blue due to Rayleigh scattering, the same phenomenon that colors the sky;
  • feels like Styrofoam® to the touch. Although a slight touch will not leave a mark, pressing more firmly will leave a lasting depression or even produce a catastrophic breakdown in the structure, causing it to shatter like glass; and
  • is rigid. Despite its name, it is hard and dry, little resembling the gel from which it was derived.

Energy Efficiency of Silica Aerogel Performance as an Insulator

Composed almost entirely of gas, which is a poor heat conductor, aerogel can almost nullify the three methods of heat transfer (conduction, convection and radiation). Boasting an R-value of 10 to 30, NASA has used the material to protect astronauts and equipment, such as the Mars Rover, from the extreme cold of space. As compared to conventional insulation material, the R-values of vermiculite, rockwool, fiberglass and cellulose are approximately 2.13, 3.1, 3 and 3.1, respectively. Silica aerogel is especially valuable insulation material because silica is also a poor conductor of heat and creates less heat transfer.  A metallic aerogel, on the other hand, would be less useful as an insulator allowing greater heat transfer.

Production of Aerogel and Silica Aerogel

Aerogel is derived from gels, which are substances in which solid particles span a liquid medium. The first aerogel was produced from silica gels, although later work involved alumina, chromia, carbon and tin oxide. Through a process called super-critical drying, the liquid cabotranules Energy Efficiency with Aerogel Works to Control Heat Transfer  component of the gel is removed, leaving behind the hollow, solid framework. The resulting aerogel is a porous, ultra-lightweight lattice composed of more than 90% air. Ordinarily, drying of a gel results in its shrinkage and collapse (think of Jell-O left out for a few days), but super-critical drying is performed under intense heat and pressure that preserve the structure of the gel.

Energy Efficiency

Manufacturers offer the material in a variety of forms, such as the granules pictured at right, made by Cabot, which are sometimes used as insulation in skylights. Aspen Aerogel® offers 57-inch wide rolls of the material in 0.2- and 0.4-inch thicknesses, while Thermoblok® comes in 1.5-inch wide strips that are used to cover framing studs and help prevent thermal bridging at a cost of about $1.99 per foot. Silica aerogel is also becoming more widely used.

 

Safety as an Insulation Material

Aerogel safety is dependent on the safety of the gel from which it was made; it will be carcinogenic, for instance, if the gel from which it was derived had this quality. Fortunately, silica-based aerogel is not known to be dangerous, although it may irritate skin, mucous membranes, eyes, the respiratory tract, and the digestive system. Aerogel is hydroscopic and extremely dry to the touch, which can, in turn, cause it to dry out unprotected skin. Gloves and goggles are recommended for inspectors and contractors who must handle the material.

Aerogel does not seem to be an environmental threat. Aspen Aerogel’s® website states: “Aerogel blankets do not meet any of the characteristics of a U.S. EPA hazardous waste,” and further notes that scrap aerogel may be disposed of in landfills that are approved to accept industrial waste.

Controlling thermal conductivity, supercritical drying and energy efficiency are all benefits of Aerogel.

In summary, aerogel is a safe, remarkably effective thermal insulator whose use should become more widespread as it becomes more affordable with greater energy efficiency.

Thanks To Nick Gromicko and Rob London

Insulation and Energy Efficiency

Insulation R-Value and how it effects your home’s energy efficiency.

That is a very common question. People often wonder how much insulation is enough and what R-Value is best. Well there are many answers to those and other question about insulation and what can be done to increase the energy efficiency of your home.

As energy efficiency and energy conservation has become an increasing concern among builders and homeowners, the attributes and performance of building materials and components are being scrutinized more closely.  In order to maximize levels of efficiency by examining the details of how each individual component of a house performs on its own and as part of a dynamic system, very specific properties are measured and taken into account.  This can be especially helpful when trying to select the best building materials for a given application.  R-value is the measurement used when quantifying a specific material’s level of thermal resistance, which is the inverse of U-value, which measures thermal conductance.  R-value is often the standard consideration when discussing the effectiveness of insulation.  Homeowners who may want to add attic insulation or re-insulate their home may want to be familiar with the specifics of R-value ratings.

How Does R-Value Relate to Insulation?

Heating and cooling costs account for 50% to 70% of energy used in an average U.S. home. Inadequate insulation can account for a lot of heat loss and wasted energy, so it is important to be sure that the insulation installed is doing its job properly.

Fiberglass insulation1 300x225 Insulation and Energy EfficiencyThe function of insulation is to provide resistance to the flow of heat and heat transfer.  R-value is the measure of exactly this attribute for a given material.  A higher R-value equates to higher resistance to heat flow and greater effectiveness in insulating and increased energy efficiency.  An insulation material’s R-value, in conjunction with how and where it is installed, will determine its overall thermal resistance and effectiveness.  Adding the R-values of each layer of material contained in one building component, such as a wall or ceiling with multiple layers of insulation, will help determine the thermal resistance of the whole component.  The way the insulation is installed, as well as other factors like heat transfer, will also affect its thermal resistance and energy efficiency. Attic insulation is one of the most common incorrectly installed insulated areas.

Important Factors to Consider When Measuring Thermal Resistance

When considering R-value as a means to determine the thermal resistance of a building component, there are other factors that must also be taken into account.  While R-values are an excellent guide for comparing the attributes of different insulation products, they apply only when the insulation is properly installed.  For example, as with attic insulation, if two layers of insulation are smashed into the thickness intended for one layer, the R-value does not double.  Likewise, if a single layer of insulation is compressed during installation, it will not be as effective.  Stuffing batt insulation sized for 5 inches into a 4-inch wall cavity will actually lower its R-value.  Good energy conservation is met by ensuring that attic insulation and all insulation is correctly installed. This will help allow the product’s full benefits to be realized while increasing energy efficiency and improving energy conservation.

Heat Transfer with Insulation

Also important to consider is the fact that even when installed correctly, insulation affects heat transfer through the insulation itself but not through other materials, such as glass windows and studs.  If there are structural gaps in any building penetrations, even insulation with a high R-value that’s installed properly cannot mitigate heat loss from air leaks.  Studs and windows provide a parallel heat conduction path, and insulation between studs in a wall does not restrict heat flow through the studs.  This heat flow is called thermal bridging, and the overall R-value of the wall will be different from the R-value of the insulation itself.

Calculating and Converting Insulation R-Value

The equation used to calculate R-value may be of interest to some inspectors because if the R-value is known, the equation can also be used to help calculate heat transfer and heat loss.  The equation for determining R-value is as follows:

R-value = temperature difference x area x time ÷ heat loss

The temperature difference is expressed in degrees Fahrenheit, the area in square feet, the time in hours, and heat loss in BTUs.  Since European R-value uses different units of measure (Celsius, Kelvin, meters, etc.), it may be helpful to know how to convert a European R-value into a U.S. R-value.  This is done by multiplying the European value by 0.176 and dividing 1 by the result.

The FTC and DOE on Insulation R-Value

In the 1970s, the Federal Trade Commission (FTC) created a rule requiring insulation manufacturers to disclose R-values at the point of sale and in some ads.  This is intended to protect purchasers from false claims made by manufacturers and to create a standard of comparison for products.

insulation r value Insulation and Energy Efficiency

The U.S. Department of Energy (DOE) has issued recommendations for insulation R-values in new and existing homes.  The recommendations are based on a comparison of the cost for installing insulation and increased energy efficiency versus potential future energy savings and increased energy conservation.  Their recommendations for attic insulation, cathedral ceilings, walls and floors are generally greater than what is actually required by most current building codes.

For good energy conservation, R-value ratings are a useful tool, especially when comparing the effectiveness of insulation products. Understanding a bit about how other factors affect a building component’s thermal resistance is important if insulation is to be used to its full benefit.

Homeowners who know more about insulation R-values will be in a better position to utilize this rating most effectively when it come to their home’s insulation and overall energy efficiency.

More About Insulation Here