Insulation R-value

R-value is the ability of thermal resistance of a specific type of insulation based on the thickness of this insulation to transfer heat through the insulation. In fact the higher the R-value the better the insulation properties when it comes to roof insulation. In fact what this means is by increasing or decreasing the thickness of the insulation one can change the effectiveness.

Importantly remember that compressing insulation will reduce the value of the compressed thickness of the insulation. With regards, U value the lower the better. A lower U-value equals a higher R-value. All Roof Insulation and Ceiling Insulation products will always be quoted in R-value.

In fact, the value of Roof Insulation is the standard measure of Roof Insulation and Ceiling Insulation ability to reduce heat flow.  In all cases, the thicker the insulation the higher the Insulation R-value will be. Having said that not all insulation products are equal. 

In fact, some Roof Insulation products will achieve a higher value on a thinner Roof insulation. The Higher the R value the better the Thermal Insulation Properties will be.

R-value of Roof Insulation

In fact, some insulation products will achieve a higher R-value on the same thickness than other Roof insulation products. Sometimes this can be affected by the Roof Insulation density. As some manufacturers will have a lower density and a higher thickness.

Other manufacturers will have a higher density and a lower thickness. What is better you may ask? Well, nothing really because the R-value will be the same.

However, in my opinion, I would rather opt for the achieved R value of the thickest insulation. Roof Insulation products like Aerolite Insulation and Isotherm Insulation achieve the recommended R-value.

So how would we calculate the thermal properties of roof insulation of the specific roof insulation material using K-value? In fact, this is quite simple. Check the thickness of the roof insulation in relation to one meter and multiply this by the K value of the roof insulation. So if the roof insulation is 145mm thick you will multiply .145 ÷ K value= R-value.

  • This in simple terms R-value is measured in meters squared Kelvin per Watt ( m2K/W)
  • For example, let's say we have Aerolite insulation that is 135mm thick and the insulation has a K-value 0.04.
  • 135 divided by K value 0.04 = R-value 3.37. This would be SANS compliant for the Western Cape region.
  • Remember R-value only takes conduction into account and not convection or radiation.
  • There are times when you would only take U-value into account. On the building of walls and window options etc.


In fact, the U-value of a home is a combination of the opposite of the total thermal resistance of this element. This is the measure of heat loss through the thickness of insulation. However, this includes all three heat loss factors. Namely Conduction, Convection, and Radiation.

Remember the ambient temperature outside the home plays an important roll in the calculation of U-value. Importantly remember the lower the U-value the more effective the Insulation will be.

In fact, this same formula can be used when calculating brickwork for side walls. Once you have factored the value of the walls with the cavity space you can then work out what thickness insulation to fit between the walls. Insulating the walls with polystyrene or Isoboard will give a huge Rvalue. This, in turn, will make the home far more energy efficient.

Calculating U-value

Calculating U-value is a very complicated exercise and is better done on a U-value calculator.

  • Giving an example of the value of standard brick walls with cavity gap approximate U value 1.6 W/m2K approximately.
  • Another example of drywall partitioning with cavity space value 1.5 W/m2K with the correct thickness U value 0.18 W/m2K. This is almost six times more efficient than the drywalling.
  • A solid wall will give a U value 2 W/m2K approximately.
  • However, remember when considering Rvalue or thermal resistance the higher numbers are better.

As energy has become an important factor in the building of all new homes the U-value has become an important factor when building homes. The lower the U-value of windows doors and walls the better the energy saving. When it comes to the roof space R-value is King and the higher the Rvalue the more efficient the Roof Insulation properties.

Some examples of U value in Buildings

  • Solid brick wall 2 W/m2K
  • Cavity space wall without insulation 1.5 W/m2K
  • Insulated Cavity space wall 0.18 W/m2Single pane glass windows 4.5 to 5.5 W/mK
  • Double glazed glass windows 1.2 to 3.2 dependent on type and thickness of the glass.
  • Triple Glazed glass windows 0.9 W/m2K
  • Solid wooden Doors 3 W/m2K
  • As we can see some options have rather large U value in effect this is not effective in energy conservation.

The 145mm Isotherm will achieve an R value 3.70 when installed. This takes into account the R-value of roof and ceiling at R-value 0.40. For more specification on Isotherm read this.

The 135mm Aerolite will achieve R value 3.70 when installed. This is also including Roof and Ceiling at R0.40. For more technical specifications on Aerolite read this.

Insulation R Value


It's summer and this is the best time of year to review and upgrade any heating and insulation on your property. Don’t wait till winter, upgrade your insulation and heating while you still have plenty of time so you are not left in the cold. In this post, we discuss what is R-value

During your search for new and improved heating and insulation, there is a very good chance you will come across the term R-Value. People with no understanding will advise you to look for it and those so-called experts in stores or at suppliers will sell you on it. But what is  R-Value and what does it mean to you when insulating your building?

What is R-Value

All products have what is called Thermal Resistance and the R-Value defines the speed any material or product will lose heat. It iswhat is r-value Roof Insulation benefits save energy common sense for insulating material to retain heat well and the R-value is a measure of how good a product or material is at doing so. The R-Value is proportional to the thickness of the products or material. Likewise, the value is inversely proportional to the thermal conductivity (K-Value) of the product. Read the specifications of the Isotherm as well as the specifications of the Aerolite. In fact, read the specifications of any insulation that you would need to purchase. This will give you a good idea of selecting the correct insulation.

In simple terms, the best insulation material has a high R-Value because it is generally thicker and denser and has a high level of thermal conductivity. Thermal conductivity is the measure of heat transfer which in insulation refers to the amount of heat lost and how fast.

There are many different types of insulation product on the market, each claiming to be better than the other. The truth lies in the R-Value and the K-Value. All insulation products are sent for testing to ascertain the K-value after manufacture. Having the R and the K values helps you determine the most suitable insulation product for your building. Installing the correct Thermal insulation is critical.

Different types of insulation

Essentially there are four main types of insulation and each has its own benefits and advantages over the other.

Rolls and Batts

The first type of insulation is Rolls and Batts. These flexible products come in fibrous sheets and are often referred to as insulation blankets. Rolls and batts are made for a number of materials that include fiberglass, polyester, and ceramic fiber.

Loose fill

Often made from cellulose loose-fill insulation is a pellet form products that is blown into spaces and cavities. It is a very popular form of insulation and highly effective when applied professionally.

Rigid Foam

Rigid foam is more costly than many insulation materials but the cost is outweighed by the generally high R-Values. The product is essentially a rigid, solid block of foam or polystyrene that can be cut to size. The high R-Value material is then set in the walls or in the ceiling. Rigid Foam often has two R values new R value and an aged R-value.

Foam in Place

If you have small, tricky places to get to the foam in place is a superb solution. Generally blown into smaller cavities it expands and hardens to provide outstanding insulation.

Shopping using the R-Value

Understanding What is R-Value and the K-Value and knowing that some manufacturers cheat is important. When being advised in the values always ask if the values and the testing were accurate and correctly undertaken. Any quality product will have the R-Value and K-Value test reports available and this is important for those buying in bulk who need peace of mind.

The R-Value is merely a guide; it is not telling you how good an insulator a product is for your particular job. Each building has different insulation needs and these must always be factored in. If you are just replacing out-dated rolls of insulation and that insulation has been adequate the R-Value is not of great importance. If you are working on a complete insulation upgrade or a new build the R-value helps determine the insulation as part of the construction. All buildings are different, different materials, roof angles, windows and roof spaces and all these make a difference to the insulation material used.

Remember that some insulation products will be more suitable for certain uses and one mustn’t be afraid to mix and match to achieve an overall better result.

Finally here are 5 simple tips when buying insulation

  1. Always seek advice
  2. The thicker the product the higher the R-value will be
  3. If there is no R-Value reconsider your choice of product
  4. Looks for quality assurance such as SABS
  5. Ask about the lifespan of the product – you don’t want to have to replace it every year

What is R-value of Insulation That You Want

Make sure you know what is R-value of the insulation that you would like to purchase, Remember not all insulation products with the same thickness will have the same R-value. Some insulation products are designed to have the correct R-value at a slightly thick level than others. For example, 145mm Isotherm insulation achieves the correct R-value for the Western Cape. While 135mm Aerolite achieves the R value for the Western Cape, Having knowledge of what is R-value is very important when insulating your home. as the incorrect R value would be a waste of money. So install correctly and save energy.

Does R-value work On Thickness Of Insulation

All Roof insulation products are a measure to check the heat flow up or down. Based on the findings of these tests R-value will be established. No bear in mind some insulation products will achieve the recommended R-value on thinner Roof Insulation. Other Roof Insulation products might achieve this R-value with a Thicker insulation. In fact, this does not mean the one insulation form is better or worse than the other. The fact is the R-value is the main guiding factor.

Are all Insulation Products Equal Based on The Same R-value?

When choosing the Roof Insulation for your home. Firstly you will need to check on the correct R-value for your region. Secondly, a decision must be made on what Roof Insulation to Install. Look for a product like Isotherm Insulation with a 30-year guarantee or Aerolite with a 25 to 30-year lifespan. This will then give you years of energy saving benefits. If you choose products like blown in

Look for a product like Isotherm Insulation with a 30-year guarantee or Aerolite with a 25 to 30-year lifespan. This will then give you years of energy saving benefits. If you choose products like blown in

If you choose products like blown in the paper the lifespan is very short in spite of guarantee. When we vacuum these paper type insulation products out of the roofs of unhappy homeowners we discover that as all the chemicals have dissipated the paper burns quite freely. So think long-term and get years of energy saving.

Finally, make sure the Roof Insulation that you choose is a roll form Insulation. As roll form insulation products do not get affected by the wind. Roll form insulation will lay in place regardless of wind speed. However fine dust like paper that is blown into roofs will absorb water and be affected by the wind. We often find heaps of paper dust on one side of the home and very little on the other side of the home. This, in turn, leaves you exposed as to the insulation properties of your roof space.

Is R-value Affected by Compressing Roof Insulation?

In fact, any Roof Insulation that is compressed will only achieve the R-value of what the insulation is compressed to. So be sure to never lay boxes or other products directly on your insulation in the Roof as this will reduce the Roof Insulation R-value. In order to retain the Roof Insulation R-value do not compress the Insulation in any what at all. As the R-value is based on density and thickness of a given insulation.