Rigid Roof Insulation R Value: A Guide to EPS and Polyisocyanurate

Rigid roof insulation is a crucial component of a well-insulated building envelope. It provides a solid barrier against heat transfer and can significantly reduce energy costs.

EPS insulation has an R-value of R-4 to R-6 per inch, making it a popular choice for many builders. This value can vary depending on the specific type and brand of insulation used.

EPS insulation is also known for its lightweight and easy-to-handle properties, making it a favorite among builders. It's often used in combination with other insulation materials to achieve optimal results.

Polyisocyanurate (PIR) insulation, on the other hand, has an R-value of R-7 to R-8 per inch, making it a more efficient option for buildings in colder climates. This increased R-value can lead to significant energy savings over time.

Rigid roof insulation is a crucial component of any building's energy efficiency. It's essential to choose the right type of insulation to ensure optimal performance.

There are several types of rigid roof insulation available, including Expanded Polystyrene (EPS), Extruded Polystyrene (XPS), and Polyisocyanurate (Polyiso). EPS is the most versatile option, with a high R-value per dollar and a wide range of applications. It's also approved for ground contact and can be treated to resist insects.

XPS, on the other hand, is a popular choice for below-grade applications due to its better moisture resistance and higher R-value. However, it can be more expensive than EPS. Polyiso is considered an eco-friendly option, containing roughly 9% recycled materials and having a higher R-value of 6.5 per inch. However, it's also the most expensive option and tends to absorb water, making it unsuitable for below-grade applications.

Here's a brief comparison of the three types of rigid roof insulation:

Ultimately, the choice of rigid roof insulation will depend on your specific needs and budget. It's essential to consider factors like R-value, cost, and moisture resistance when making your decision.

Expanded polystyrene, also known as EPS or beadboard, is generally the best budget option for people who need rigid foam insulation. It's a versatile option used in various applications, including roof, wall, floor, below grade, and structural geofoam applications.

It's used most widely in insulated concrete forms and structural insulated panels. Expanded polystyrene has the highest average R-value per dollar, about 4.6 R per inch, and costs the least while meeting or exceeding all required building and energy codes.

It's approved for ground contact, below grade applications, and can be treated to resist insects. Expanded polystyrene does not retain water over the long term, so it's a good option for areas with high moisture exposure.

It's essential to use expanded polystyrene over house wrap or with a product that incorporates a factory laminated option. Faced products are considered vapor retardant, and specialty products are considered vapor barriers.

Expanded polystyrene can be expected to have a range of around 3.6 to 4.2 R-value per inch, making it a good way to add R-value in an attic, on top of a roof, or in wall cavities.

Rigid roof insulation comes in various types, each with its own unique characteristics. Expanded Polystyrene (EPS) is a budget-friendly option with a slightly lower R-value, but it's cost-effective and suitable for various applications.

Extruded Polystyrene (XPS) is the best choice for applications below grade due to its better moisture resistance and higher R-value. It's also denser and more durable than other types.

Polyisocyanurate (ISO or polyiso) is considered an eco-friendly option as it contains roughly 9% recycled materials. However, it may not be suitable for below-grade applications due to moisture absorption.

Polyurethane (EPU) rigid foam insulation is intended for insulated concrete forms and remains in place as concrete cures. It offers an average R-value of 5.9 per inch and is exceptionally durable.

Mineral Wool is a non-toxic, non-petroleum-based foam product that maintains its R-value over time. It also offers soundproofing, is fireproof, and unaffected by moisture, but it's generally more expensive than fiberglass.

Here's a comparison of the most common types of rigid foam insulation:

Each type of rigid foam insulation has its strengths and weaknesses, so it's essential to choose the right one for your specific needs.

Polyisocyanurate, also known as polyiso, is considered the eco-friendly option when it comes to rigid foam insulation, containing roughly 9% recycled materials and having a higher R-value of 6.5 per inch on average.

Polyisocyanurate is often used in commercial building applications and residential building projects, with a typical R-value of 7.0 to 8.0 per inch of thickness.

The reflective foil facing on polyisocyanurate makes it an excellent insulation board when radiant heat is involved, and it's also very easy to seal with good quality foil-faced tapes.

However, polyisocyanurate is the most expensive of the foam board insulation products, but it has the highest R-value.

Here's a comparison of polyisocyanurate and polyurethane:

Note that polyurethane and polyisocyanurate are both closed-cell foams, containing low-conductivity gases in the cells, which can lead to a couple of disadvantages, including off-gassing of HCFC or CFC gases, and reduced R-value over time as the gas escapes.

Polyisocyanurate is not recyclable and has to be sprayed against a substrate to form a rigid panel, making all ISO panels faced. Different facings affect the performance of the panel in both durability and perm rating.

Moisture Resistance is a crucial factor to consider when choosing a rigid roof insulation type.

EPS foam provides excellent moisture resistance due to its closed-cell structure, which protects against mold and water damage.

In damp locations, EPS foam performs well where other types of insulation may not.

Its closed-cell structure prevents moisture from entering the foam, making it an ideal choice for areas prone to high humidity.

Understanding R-Value is crucial when it comes to choosing the right insulation for your project. The R-value measures an insulation material's resistance to heat flow, with a higher R-value indicating better insulating properties.

A higher R-value means the material will keep warmth in during the winter and out during the summer. This is especially important for energy efficiency, and it's a key metric for anyone looking to ensure their homes or buildings are well-insulated.

The R-value of an insulation material is typically listed per inch of thickness, making it easier to compare different materials. For example, a material with a low R-value per inch would need to be much thicker to achieve the same level of insulation as a material with a high R-value per inch.

Here's a rough guide to R-values and their corresponding insulation performance:

EPS insulation, for instance, typically ranges between R-3.9 to R-4.4 per inch, making it a superior choice for energy efficiency.

Temperature can significantly affect the thermal performance of an insulation product.

The R-value Rule doesn't account for temperature, which is an application-specific factor that affects in-service performance.

In other words, the R-value of an insulation product can vary depending on the temperature of the surrounding environment.

This is because some insulation materials expand or contract with temperature changes, altering their thermal performance.

R-value is a measure of an insulation material's resistance to heat flow. A higher R-value indicates a material with better insulating properties.

EPS insulation provides excellent thermal resistance, with an R-value ranging from R-3.9 to R-4.4 per inch, depending on its density. This makes it a superior choice for optimizing energy efficiency.

The R-value Rule was developed to simplify the many technical issues that affect thermal performance, but it doesn't account for all factors, such as moisture content and temperature. This means that actual in-service performance may vary.

EPS maintains its R-value and insulating properties even in extreme temperatures, ensuring consistent performance. This is a significant advantage over other insulation materials.

Rigid foam insulation is a continuous insulation layer that helps reduce energy loss through the framing members, leading to lower energy costs and a more comfortable space. It's also resistant to water and pests, making it ideal for use in crawlspaces and basements.

The R-value of rigid foam insulation is determined by factors such as foam insulation board type, thickness, and density. A higher R-value indicates better insulating properties.

Here's a rough guide to R-value:

Keep in mind that this is just a rough guide, and actual insulation performance may vary depending on the specific material and application.