Most insulated concrete forms exceeds the ASHRAE 90.1 minimum R-value requirements for continuous insulation for all climate zones in Texas. Therefore, by merely choosing the an ICF Wall System, Texas homeowners and builders are assured of an insulated wall system with R-values that are code compliant with all climate zones throughout Texas.

What is the R-Value of Insulation?

The R-value (resistance value) of insulation represents its resistance to heat flow through a given thickness of a material. Expression of the R-value is often in imperial units as°F ft2 sec/BTU. However, the metric equivalent of R-values is the relative strength index (RSI) value expressed as °C m2 sec/J.

The International Energy Conservation Code (IECC) and the ASHRAE 90.1 mandate the R-values of insulation required to achieve best practices in insulating commercial and residential structures. It is based on eight geological climate zones in the United States. The state of Texas includes three of these zones, ranging from hot and mild to humid and dry climates. All zones in Texas have different insulating requirements to achieve energy-efficient, durable, healthy, and comfortable buildings and homes.  

The R-value Rule

In response to rising fuel costs in the 1970s and the Organization of Petroleum Exporting Countries (OPEC) oil embargo of 1973, the R-value of insulation, or the R-value Rule, was developed by the Federal Trade Commission and the insulation industry as an objective method for evaluating the performance of residential insulation materials. The objective of the Rule was to make it easier to compare different brands of similar insulation products. 

The R-value Rule requires installers, home insulation manufacturers, new home sellers, and retailers to provide the R-value of the insulation. The R-value is determined by ASTM methods for thermal testing and quantifying of an insulation product’s ability to restrict heat flow-values.

When it comes to R value vs U value make sure you understand the differences because they are very similar to each other.

Calculating the R-Value of Insulation

Calculating the R-value of insulation requires knowledge of its K-factor, R-factor (a mathematical term), and the amount of installed insulation.

The K-factor is the thermal conductivity or ability to conduct heat of an insulation product.The ASTM Standard C168 describes thermal conductivity as the amount of heat (in BTUs per hour) that passes through one square foot (unit area) of 1- inch thick insulation to cause the temperature to rise or fall one degree Fahrenheit from one side of the insulation to the other. 

The K-factor is not dependent on the thickness of the material. The lower the K-factor, the better the insulation. Most insulation materials have a K-factor of less than one. Determination of K-values is commonly done by either the ASTM C 177 or ASTM C 518.

  • ASTM C 518, Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Heat Flow Meter Apparatus.
  • ASTM C 177, Standard Test Method for Steady-State Heat Flux Measurements and Thermal Transmission Properties by Means of the Guarded-Hot-Plate Apparatus.

The R-factor represents a product’s thermal resistance and measures its ability to block heat rather than radiate heat. Thermal resistance is defined as the product’s resistance to heat flow and is the reciprocal of the product’s thermal conductivity. The higher the R-factor, the better the insulation. 

If the K-factor is known, the R-factor is calculated as R-factor =1/K-factor.

If the K-factor is unknown, the R-value is determined by placing a one-inch thick, square foot of insulation material between two plates in a laboratory apparatus and measuring heat-flow through the insulation. The test specimen usually consists of a square foot of material, precisely one inch thick, and surfaces with a temperature differential of 1ºF. 

R-factor = (°F ·  sq ft of area · hours) / Btus of heat flow

The R-Value of Insulation

The R-value of an insulation product is simply the R-factor of an insulation product multiplied by the amount of applied insulation.

R-Value = R-factor  X Thickness of Insulation

The Required R-Values of Insulation for Texas Homeowners

In Texas, the required R-values are according to the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE 90.1) and IECC. The R-values take into account wall system type, the climate zone, and in some cases the occupancy classification. Also, commercial and residential projects (more than three stories) and residential buildings (less than three stories) have different R-value of insulation requirements.  

All commercial and residential projects more than three stories, must meet the standards minimum R-values required for the building envelope, based on the building’s climate zone, occupancy classification, and opaque wall system (mass walls, metal buildings, metal framed, and wood framed), as specified in the 2018 IECC Table C402.1.3

All residential buildings (three stories and less) must meet the 2015 IECC requirements for the quantity of insulation (as indicated by the R-value), based on the climate zone and type of opaque wall system (mass walls and wood frame walls). Table R402.1.2, of the 2018 IECC, provides the most current R-value requirements.

Understanding the IECC Climate Zones

In 2003, the U.S. Department of Energy (DOE) at the Laboratory at Pacific Northwest National Laboratory with input from Building America team members developed of the International Energy Conservation Code (IECC) climate zone map. The purpose of the map is to achieve climate-specific best practices in insulating homes and buildings by directing the quantity of insulation (as indicated by the R-value) based on the structure’s climate zone. The 2004 IECC Supplement first presented the climate zone map. It first appeared in the 2004 edition of the ASHRAE 90.1. 

Today’s Homeowner Tips

The climate zone map divides the United States into eight temperature zones. Parameters defining the climate regions include heating degree days, average temperatures, and precipitation.

Further divisions in the map divide the regions by moisture levels labeled A, B, and C. So, there are 24 potential climate designations within the IECC map. For reporting reasons, the zones are divided into five more climate categories: hot-humid, hot-dry/mixed dry, mixed- humid, marine, cold/very cold, and subarctic.

In Texas, there are 93 counties in climate zone two, 133 counties in climate zone three, and 28 counties in climate zone four. Each of these climate zones has specific IECC requirements. 

Understanding Occupancy Classification

Occupancy Classification groups commercial buildings and residential structures, greater than three stories, according to their primary purpose. Table C402.1.3 of the 2018 IECC classifies buildings according to those in Group R and All Others. 

What is Residential Group R? 

Residential Group R are buildings that include sleeping rooms, but are not institutional or regulated by the International Residential Code (IRC). Group R are buildings or portions of buildings that contain any of the following occupancies as established in the IBC. 

  1. Group R-1 includes temporary use buildings like hotels, motels, and boarding houses.
  2. Group R-2 includes permanent use buildings, like apartments, dormitories, condos or assisted living facilities with more than 16 resistants.  
  3. Group R-3 buildings have no more than two units. Group R-3 also include adult and child care facilities that accommodate five or fewer people, less than 24 hours a day. If the facilities are in a single-family home, they must comply with the IRC. 
  4. Group R-4 buildings include residential care and assisted living facilities with between 5 and 16 occupants. 

Texas R-Value Requirements for Above-Grade Walls for Commercial and Residential Structures Greater than Three Stories

The standard mandates that wood-framed walls have an R-value of 20 or an R-value of 13 plus an extra R-value of 3.8 continuous insulation (CI). 

Texas R-Value Requirements for Residential Above Grade Walls

For wood-frame walls the first value is for cavity insulation. The second value is for continuous insulation

For mass walls, the second value applies when more than half of the insulation is on the interior of the mass wall.

The R-Value of Insulated Concrete Block

Texas builders, architects, and homeowners can achieve the right wall system insulation R-value requirements for all climate zones of Texas, as dictated by the ASHRAE 90.1 standard, by choosing an ICF Wall Assembly, a mass wall product. 

Furthermore, an ICF Wall Assembly outperforms framed buildings with comparable stated R-values, because ICF walls provide continuous layers of insulation with no thermal bridges, which ensures accurate whole-wall R-values that take into account the whole opaque wall system.

The R-value of ICF Blocks per inch is 1.84. The whole-wall R-value for ICF Blocks is R-14, without interior or exterior finishes. A structure with ICF block continuous insulation with brick veneer achieves a whole-wall R-18 system. An R-value that far exceeds the ASHRAE 90.1 climate zones two, three, and four minimum R-value requirements for continuous insulation (above grade, mass walls) of R-4 and R-8. 

ICF Wall systems meet the ASHRAE 90.1 minimum R-value of insulation requirements for all climate zones in Texas. Importantly, the ICF Wall System creates a high whole-wall R-value that stops thermal bridging, improves energy efficiency and can save Texas homeowners, in all three climate zones, money for years to come.

Editorial Contributors
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Matt Greenfield

Matt Greenfield is an experienced writer specializing in home improvement topics. He has a passion for educating and empowering homeowners to make informed decisions about their properties. Matt's writing focuses on a range of topics, including windows, flooring, HVAC, and construction materials. With a background in construction and home renovation, Matt is well-versed in the latest trends and techniques in the industry. His articles offer practical advice and expert insights that help readers tackle their home improvement projects with confidence. Whether you're a DIY enthusiast or a seasoned professional, Matt's writing is sure to provide valuable guidance and inspiration.

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