Home Project FYI. Your Home Project Information and Idea Place

Help and Ideas For Your Home Remodeling Project

Home Project FYI. Your Home Project Information and Idea Place - Help and Ideas For Your Home Remodeling Project

Tag Archives: thermal resistance

Understanding Insulation R-Value

R-Value of insulation can be a a little hard for some to understand.  This article can help you learn more about the insulation in 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.
The right R-Value of this wall insulation is important 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 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, 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 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, 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.

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 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.

R-value

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-value will be in a better position to utilize this rating most effectively when it come to their home’s insulation and overall energy efficiency.

Here are some very useful and informative videos for insulation installation and use.

TumblrShare

Polyurethane Foam Insulation

Polyurethane Foam Insulation

Polyurethane spray foam is a versatile insulation material that is sprayed into building cavities where it quickly expands and molds itself to its surroundings. It is available in “closed-cell” and “open-cell” varieties, each of which offers advantages and disadvantages, depending on the requirements of its application. The following guide briefly explains the differences between these polyurethane insulation options.Spraying the polyurethane foam

Closed-Cell Polyurethane Foam

Closed-cell polyurethane foam (CCPF) is composed of tiny cells with solid, unbroken cell walls that resemble inflated balloons piled tightly together. The cells are inflated with a special gas selected to make the insulation value of the foam as high as possible. Like the inflated tires that hold up an automobile, the gas-filled bubbles, when dried, create a material that is strong enough to walk on without major distortion. Wall-racking strength can by enhanced when CCPF is applied, and its strength makes it preferable for roofing applications. The high thermal resistance of the gas gives CCPF an R-value of approximately R-7 to R-8 per inch, according to the U.S. Department of Energy (DOE), which is significantly better than its open-cell alternative. It also acts as a vapor barrier, making it the product of choice if the polyurethane insulation is likely to be exposed to high levels of moisture. Its density is generally 2 lb/ft3 (32 kilograms per cubic meter [kg/m3]).

Over time, the R-value of CCPF can drop as some of the low-conductivity gas escapes and is replaced with ordinary air, a process known as thermal drift. Research performed by the DOE revealed that most thermal drift occurs within the first two years after the insulation material is applied, but then the foam remains relatively unchanged unless it is damaged.

Open-Cell Polyurethane Foam

Open-cell polyurethane foam (OCPF) is a soft, flexible, spongy insulation with broken cell walls that permit air to fill them. They typically have a density of 0.5 lb/ft3 (8 kilograms per cubic meter [kg/m3]), which is significantly less than closed-cell insulation, as well as having a reduced R-value per inch, although OCPF still has excellent thermal-insulating and air-barrier properties. The polyurethane foam is weaker and less rigid than closed-cell foams, too. It will require trimming and disposal of excess material as it expands to over 100 times its initial liquid size.

Builders often choose open-cell polyurethane foam for the following advantages it affords, including:

  • its low cost. Where economical yield is important, open-cell polyurethane foam is generally chosen over its more costly alternative;
  • providing a sound barrier. OCPF forms a more effective sound barrier in normal-frequency ranges than closed-cell foam. For this reason, OCPF is well-suited for installation beneath floors and around theater rooms;
  • its flexibility. Open-cell polyurethane foam is more flexible than closed-cell polyurethane foam, which allows it to adjust to weather-induced expansion and contraction of framing members. CCPF, by contrast, may develop hairline fractures because it cannot flex sufficiently; and
  • its permeability to moisture. While often cited as a reason to avoid the use of OCPF, in certain situations, it can be helpful for moisture to pass through insulation. Open-cell polyurethane foam used in roofs, for instance, will allow a roof leak to make its way to the space below where it is more likely to be discovered. Closed-cell polyurethane foam used in the same application would trap the moisture, hiding the leak and potentially leading to wood decay. In most situations, however, OCPF should not be used in any place where it might become wet, as moisture will diminish its insulative value. InterNACHI inspectors may call out open-cell insulation discovered in moist areas, such as in external applications or below grade.

FINAL FYI, polyurethane foam is available in two varieties that are suited for different applications.

TumblrShare
SEO Powered by Platinum SEO from Techblissonline