Every building loses heat, but how much depends on the quality of the insulation. To make a space energy-efficient, it is key that you understand a product’s thermal performance. The most important measurement when comparing insulation products is their R-values.
From PIR insulation boards and mineral wool to loft and acoustic insulation, every product has an R-value. An R-value indicates how effectively the product prevents heat from escaping. Choosing the right R-value for the project will improve the overall energy efficiency, reduce heating costs, and ensure that the project meets the UK Building Regulations requirements.
This guide explains what insulation R-values are, how they are calculated, why they matter, how to compare them to U-values, and how to choose the correct insulation products for your project. It is suitable for homeowners, builders, property developers and architects.
Quick Answer: What is an R-Value?
An R-value measures a material’s heat flow resistance. The higher the R-value is, the better the insulation products will be at reducing heat transfer. R-values are calculated by the material’s thickness and thermal conductivity (otherwise known as the Lambda value).
What Does an R-Value Mean?
The R-value, otherwise known as the resistance value, measures a material’s resistance to heat.
Naturally, heat will move from warm to cold areas. For example. During winter, warm air wants to escape a property, whereas in the summer, the heat tries to enter. Using insulation products, this helps slow down the process.
The higher a product’s R-value is, the more effective it is at reducing heat transfer.
This can help:
- Improve thermal efficiency
- Lower heating costs
- Reduce energy consumption
- Improve comfort
Why Are R-Values Important?
The cost of heating bills in the U.K. is continuously increasing, which means having an energy-efficient property is important.
A building that isn’t properly insulated will lose heat quickly. This means that central heating systems will have to work harder, which in turn increases bills. Choosing products with a high R-value improves thermal performance.
Benefits of using products with a high R-value include:
Lower Bills
Better insulation products mean that less heat will escape, while also reducing the amount of energy needed to heat a property.
Energy Efficiency
High-performing products contribute toward a property’s EPC rating. Using products with a high R-value can reduce a property’s overall energy consumption.
Compliance with UK Building Regulations
Making sure you choose insulation with the best thermal performance will make it easier to meet the requirements of building regulations.
How Does Heat Escape From A Building?
Heat is transferred in 3 ways:
Conduction
Heat moves through solid materials.
This includes:
- Brick walls
- Concrete floors
- Roof structures
- Timber
- Steel frames
Using insulation slows this process down.
Convection
Warm air rises.
Without loft or roofing insulation, heat is likely to escape more quickly.
This is a key reason why loft insulation is one of the most cost-effective improvements.
Radiation
Heat travels through infrared radiation.
Insulation products that have reflective qualities, like PIR boards with foil facings, can help reduce heat transfer by reflecting the heat back into the building.
How To Calculate An Insulation R-Value?
An insulation product’s R-Value is calculated using the formula below.
By totalling the R-value of each product and layer of insulation, this will give you the combined total value of the structure.
R-value of outer bricks + R-value of insulation + R-value of plasterboard = Total structure R-value
You can use the image below to display the calculation.
What Is Thermal Conductivity?
Thermal conductivity measures how easily heat passes through a material.
In comparison to R-values, it is important to have a lower Lambda value.
Low thermal conductivity means the property has a good insulation performance.
What Is The Difference Between The Values?
It is easy to confuse R and U values, but they do measure different aspects of thermal performance.
| R-Value | U-Value |
| Resistance is measured through heat flow | Heat loss measured through building elements |
| Higher levels are better | Lower levels are better |
| Applies to individual products | Applies to multiple layers/products |
| Shown as m2K/W | Shown as W/m2K |
This is why it is key to add insulation, as it improves the overall U-value of a building.
What Factors Affect an Insulation Product’s R-Value?
Many factors can influence the thermal resistance of a product. We’ve listed a few below.
Thickness
Increasing the thickness of an insulation product will increase its R-value.
For example, a 150mm insulation board has a higher R-value than a 100mm insulation board, even if they are made from the same material.
Material Type
Different materials will offer different levels of thermal performance.
PIR Insulation Boards
Rigid PIR insulation boards offer great thermal efficiency, as when installed, they will remain thin.
Common uses include:
- Floors
- Flat roofs
- Pitched roofs
- Solid walls
- Timber frames
Mineral Wool
Mineral wool offers a variety of benefits, these can include:
- Excellent acoustic insulation
- Fire resistance
- Vapour penetration
Although these products can be thicker than PIR insulation boards, they continue to remain a popular choice for cavity walls, lofts and partitions.
EPS and XPS
Expanded and extruded polystyrene both offer great moisture resistance and compressive strength. These factors make them a suitable material for flooring installations. Although they are a good alternative, these products don’t have as good a thermal rating as PIR insulation boards.
Does Moisture Affect R-Value?
Yes, moisture levels will affect the R-value of a product.
Wet insulation performs worse than dry insulation. This is because moisture increases thermal conductivity and allows heat to travel easily through the product’s material.
To ensure your products perform their best, insulation should be installed with the necessary vapour layers and, where necessary, ventilation.
Why Does the Quality of Installation Matter?
If not installed correctly, high-performing insulation products cannot deliver their R-value.
Common mistakes when installing can include:
- Gaps between insulation boards
- Incorrectly sealed joints
- Missing cavity sections
- Thermal bridges around the overall structure
Following the best practices and methods will ensure that the products you use will perform their best.
What Is Thermal Bridging?
Thermal bridging happens when heat bypasses the insulation products via materials with higher thermal conductivity.
Thermal bridges are most common in the following materials:
- Steel beams
- Timber studs
- Wall ties
- Ends of joists
- Window frames
This is something to be aware of when completing your project, as it can have major long-term effects.
Choosing the Right Insulation for Your Project
All applications have different requirements R-value requirements.
Loft Insulation
- Mineral wool roll
- Fibre glass roll
These products work best if you are trying to reduce heat loss through roofing, and they are also budget-friendly if this is a priority.
Pitched roof Insulation
There are 3 main spaces where PIR insulation boards are installed: between, under and over rafters. These give you a better chance at achieving the results your project requires.
Floor Insulation
The best places to install rigid PIR insulation boards are underneath screeds and concrete floors. This is due to their strength and high levels of moisture resistance.
Wall Insulation
Installing wall insulation can depend on the way a building has been constructed.
Common Mistakes When Choosing Insulation Products
- Choosing your insulation products based just on the thickness
- Not taking note of the thermal conductivity
- Focusing only on price
- Not making sure they suit your fire performance requirements
- Leaving gaps when installing
- Ignoring building regulations
Frequently Asked Questions
What is a good R-value for insulation products?
The best R-value for your project depends on where in the building you are insulating, as different spaces require different R-values. A higher value will provide better quality insulation.
Is a higher R-value better?
Generally, a higher R-value is best. However, there are a few factors to consider, for example. The size of the space, its moisture and fire resistance should be considered.
Can R-values be added together?
Simply, yes. Multiple layers of insulation can be added together to combine their respective R-values.
Will insulation lose its R-value?
Good quality insulation will retain its thermal performance if it has been correctly installed and the area has been checked for moisture.
Having a good understanding of R-values is important when selecting the right products for your project. As we have covered in this guide, a higher R-value indicates a stronger resistance to heat flow, but this is only one factor to consider when making your decision. Other factors such as thermal conductivity, moisture and fire resistance and UK building regulations will all contribute to whether you achieve the best results.
Who Decides The Value Needed For A Project?
The value you need depends on your project and can be determined by your architect or designer, but is predominantly decided by the Building Control to ensure that the building meets the UK Building Regulations. The higher the insulation’s value, the greater its resistance to heat flow. This also makes it easier to achieve the required thermal performance.
At Trade Group, we supply a wide range of high-performing insulation products with great R-values, including PIR insulation boards, mineral wool loft roll and specialist thermal solutions. When choosing the right insulation products, make sure you choose Trade Insulations.
