Rigid foam is the undisputed winner if you're looking for household insulation with the highest R-value you can find. With an R-value of R-4 to R-6, 5 per inch thick, it's ideal for insulating exterior walls, including basement walls. In the construction context, the R-value is a measure of the resistance of a two-dimensional barrier, such as a layer of insulation, a window, or an entire wall or ceiling, to conductive heat flow. The R value is the temperature difference per unit of heat flow needed to maintain a heat flow unit between the warmer surface and the coldest surface of a barrier under steady-state conditions.
Therefore, the measure is equally relevant for reducing energy bills for heating in winter, for cooling in summer and for general comfort. The R-value is the term used in the construction industry to designate thermal resistance per unit area. It is sometimes called an RSI value if SI units are used. An R value can be given to a material (e.g.
in the case of polyethylene foam) or for a group of materials (e.g., in the case of materials, it is often expressed in terms of R-value per meter). R-values are additive to layers of materials, and the higher the R-value, the better the performance. The R-value per unit of the exposed surface area of a barrier measures the absolute thermal resistance of the barrier. As long as the materials involved are dense solids in direct contact with each other, the R values are additive; for example, the total R value of a barrier composed of several layers of material is the sum of the R values of the individual layers.
Note that the R-value is the term used in the construction industry for what in other contexts is called thermal resistance for a unit of area. It is sometimes called an RSI value if SI (metric) units are used. An apparent R value quantifies the physical quantity called thermal insulation. The R value is the reciprocal of the thermal transmittance (U factor) of a material or assembly.
However, the construction industry prefers to use R values because they are additive and because higher values mean better insulation, which is not true for U factors. For R values there is no difference between U, S. and imperial units, so the same I-P unit is used in both. Some sources use the RSI when referring to R values in SI units.
In countries where the SI system is generally used, R values are also usually expressed in SI units. This includes the United Kingdom, Australia and New Zealand. There are many factors that come into play when using R-values to calculate the heat loss of a particular wall. The manufacturer's R values apply only to properly installed insulation.
When you crush two layers of wadding to the intended thickness of one layer, the R value will be increased, but not doubled. In other words, compressing a fiberglass block reduces the R value of the block, but increases the R value per inch. The practical implication of this is that the R-value of the insulation installed between the elements of the structure could be doubled and a reduction of substantially less than 50% could be achieved by percent in heat loss. When installed between wall studs, even perfect wall insulation only eliminates conduction through insulation, but does not affect conduction heat loss through materials such as glass windows and studs.
Insulation installed between the uprights can reduce, but usually does not eliminate, heat losses due to air leaking through the building envelope. The installation of a continuous layer of rigid foam insulation on the outer side of the wall covering will interrupt the formation of thermal bridges across the posts and, at the same time, reduce the rate of air leakage. Like resistance in electrical circuits, increasing the physical length (for insulation, thickness) of a resistive element, such as graphite, for example, increases resistance linearly; doubling the thickness of a layer means doubling the R value and half the heat transfer; quadrupling, quarters, etc. In practice, this linear relationship is not always valid for compressible materials, such as glass wool and cotton wadding, whose thermal properties change when compressed. Thus, for example, if a fiberglass insulation layer in an attic provides R-20 thermal resistance, adding a second layer will not necessarily double the thermal resistance, since the first layer will be compressed by the weight of the second.
To find the average heat loss per unit area, simply divide the temperature difference by the R value of the layer. Thermal conductivity is conventionally defined as the speed of thermal conduction through a material per unit area per unit thickness per unit of temperature differential (ΔT). The inverse of conductivity is resistivity (or R per unit thickness). Thermal conductance is the rate of heat flow through a unit of area with the installed thickness and any given ΔT.
Experimentally, thermal conduction is measured by placing the material in contact between two conductive plates and measuring the energy flow necessary to maintain a certain temperature gradient. For the most part, insulation R-value tests are performed at a constant temperature, usually around 70°F (21°C) with no surrounding air movement. Since these are ideal conditions, the R value indicated for insulation is almost certain to be higher than it would be in actual use, since most situations in which insulation occurs under different conditions. In document C168 published by the American Society for Testing and Materials, a definition of the R-value based on apparent thermal conductivity has been proposed.
This describes heat transfer using the three mechanisms: conduction, radiation, and convection. The use of a single laboratory model to simultaneously evaluate the properties of a material to withstand heating by conduction, radiation and convection has weaknesses. The surface temperature varies depending on the heat transfer mode. If we assume an idealized heat transfer between the air on each side and the surface of the insulation, the temperature of the insulator surface would be equal to the temperature of the air on each side.
In response to thermal radiation, surface temperature depends on the thermal emissivity of the material. Low-emissivity surfaces, such as shiny metal sheets, will reduce heat transfer by radiation. Convection will alter the rate of heat transfer between the air and the insulator surface, depending on the flow characteristics of the air (or other fluid) in contact him. With multiple modes of heat transfer, the final surface temperature (and, therefore, the observed energy flow and the calculated R-value) will depend on the relative contributions of radiation, conduction, and convection, even though the total energy contribution remains the same.
This is an important consideration in building construction because thermal energy comes in different shapes and proportions. The contribution of radiative and conductive heat sources also varies throughout the year, and both contribute significantly to thermal comfort. The question of how to quantify the performance of other systems, such as radiant barriers, has caused controversy and confusion in the construction industry due to the use of R values or “equivalent R values” for products that have completely different heat transfer inhibition systems. In the EE.
UU. , All the products mentioned at the end are examples of this. It is important to pay due attention to air sealing measures and to take into account vapor transfer mechanisms for optimal operation of bulk insulators. Air infiltration can allow convective heat transfer or the formation of condensation, which can degrade insulation performance.
One of the main values of aerosol foam insulation is its ability to create an airtight (and, in some cases, airtight) seal directly against the substrate to reduce the undesirable effects of leaks of air. Other construction technologies are also used to reduce or eliminate infiltration, such as air sealing techniques. Thermography is applied in the construction sector to evaluate the quality of the thermal insulation of a room or building. Thermal bridges and inhomogeneous pieces of insulation can be identified using a thermographic camera.
However, it does not produce any quantitative data. This method can only be used to approximate the U value or the inverse R value. The U value can also be calculated by taking the reciprocal of the R value. That is, the derived R value and the U value can be accurate to the extent that the heat flow through the heat flow sensor is equal to the heat flow through the construction element.
Recording all available data makes it possible to study whether the R value and the U value depend on factors such as indoor temperature, outdoor temperature or the position of the heat flow sensor. To the extent that all heat transfer processes (conduction, convection, and radiation) contribute to the measurements, the derived R value represents an apparent R value. Vacuum insulated panels have the highest R value, approximately R-45 (in U.S. units) per inch; aerogel has the next highest R value (around R-10 to R-30 per inch), followed by polyurethane (PUR) and phenolic foam insulation with R-7 per inch. They are closely followed by polyisocyanurate (PIR) in R-5.8, expanded polystyrene impregnated with graphite in R-5 and expanded polystyrene (EPS) in R-4 per inch. Loose cellulose, fiberglass (both blown and in blocks) and rock wool (both blown and in blocks) have an R value of approximately R-2.5 to R-4 per inch.
Note that all of the examples above use the U.S. This is a list of insulating materials used around the world. Typical R-values are given for various materials and structures as approximations based on the average of the available figures and are ordered by the lowest value. The R value at 1 m provides R values normalized to a thickness of 1 meter (3 ft 3 inches) and orders them by the average value of the range.
In practice, the above surface values are used for floors, ceilings and walls of a building, but are not accurate for closed air cavities, such as between glass panels. The effective thermal resistance of a closed air cavity is strongly influenced by radiative heat transfer and the distance between the two surfaces. Refer to insulating glazing to compare the R values of windows with some effective R values, including an air cavity. Ask the manufacturer for R-value tests for your specific assembly.
The primary purpose of the standard is to ensure that the home insulation market provides the consumer with this essential pre-purchase information. The information provides consumers with the opportunity to compare the relative efficiency of insulation, select the product with the highest efficiency and energy savings potential, make a cost-effective purchase, and consider the main variables that limit insulation effectiveness and the realization of stated energy savings. The standard requires that specific information on the R-value of household insulation products be disclosed in certain advertisements and at the point of sale. The purpose of the R-value disclosure requirement for advertising is to prevent certain statements related to insulating value from misleading consumers.
At the time of the transaction, some consumers will be able to obtain the necessary information about the R value on the label of the insulating package. However, since evidence shows that packages are usually not available for inspection before purchasing, in many cases consumers would not have the labeled information. As a result, the Rule requires that consumers have a fact sheet to inspect before making their purchase. Porous insulations achieve this by trapping air to eliminate significant convective heat loss, leaving only conduction and reduced radiation transfer. In most countries, the properties of specific materials (such as insulation) are indicated by thermal conductivity, sometimes referred to as a k-value or a lambda value (lowercase λ).
However, the R-value is widely used in practice to describe the thermal resistance of insulating products, layers and most other parts of the building enclosure (walls, floors, ceilings). Talk to a Mooney & Moses insulation contractor to help you decide between cellulose, fiberglass, spray foam and rigid foam panels. However, this only holds roughly because the effective thermal conductivity of some insulating materials depends on the thickness. Reducing heat flow in your home keeps your energy costs low, so good insulation is essential, regardless of the age or size of the house.
Understanding the R-value range of different insulating materials can help you choose the right product for your insulation project. Referencing an insulation R-value table can help you insulate the attic, walls, floors, and mezzanines appropriately for your particular climate. A house with adequate insulation should reduce heat flow and help keep the air warm inside during the winter and outside during the summer. Brick has a very poor insulating capacity, with only R-0.2 per inch; however, it has a relatively good thermal mass.
Like a parallel set of resistors, a well-insulated wall with a poorly insulated window will allow a greater amount of heat to pass proportionately through the window (low R), and additional insulation in the wall will only minimally improve the value R general.
