WHAT IS THE R-VALUE?*
R-value is a score that shows how good a material is at stopping heat. If it has a high R-value, it's great at insulation. So, when you're insulating a building, aim for materials with a higher R-value because they keep the heat in better. Paying attention to the R-value when choosing insulation materials for your home is a smart move. A higher insulation R-value usually means a higher price point as well. Pleas note, R-value only applies to specific materials, not to systems, factors such as effects of temperature, ageing, and exposure to moisture can change the R-value of insulation product and reduce the overall insulation of a structure.
R-VALUE CALCULATOR
The R-value is determined by factors such as thickness and thermal conductivity. When calculating the R-value of an insulation product, you don't need any specialized calculators; just divide the thickness of the material by its thermal conductivity, usually found on the information label.
R-Value = Thickness (m) / Thermal conductivity (W/mK)
Units: m2K/W
If you want to calculate the R-value for multiple partitions, it's as straightforward as adding the R-value of each material in a given cross-section. However, if this seems too complex for you, you can use an online insulation calculator. By entering a few details, you can find the proper thickness of insulation needed for your house.
DOES DOUBLING UP INSULATION DOUBLE THE R-VALUE?
Generally speaking, increasing the thickness of insulation can indeed increase its R-value. The R-value is a measure of a material's thermal resistance, and typically, by increasing the thickness of insulation, you also enhance its ability to block the flow of heat. Doubling the thickness of insulation can result in a similar doubling of the R-value, especially if the layers consist of identical materials with similar thermal properties. However, it's important to note that the effectiveness of insulation depends on various factors, including the type of material used and its thermal conductivity.
Please note each additional layer contributes less to the overall insulation effectiveness compared to the previous layer. The exact impact of doubling up on insulation depends on various factors, including the specific materials used and their interactions.
WHAT IS A GOOD R-VALUE FOR INSULATION?
In the insulation industry, premium R-values are exemplified by phenolic boards from leading manufacturers like Xtratherm (Unilin) or Kingspan, reaching an impressive 7.85m²K/W. These materials represent the epitome of insulation excellence and are highly sought after for their superior thermal performance.
When determining the ideal R-value, the focus shifts to the roof, a critical area for minimising heat loss. Adhering to a stringent standard, roofs are expected to meet a U-value of 0.16 W/m²K. Consequently, a recommended R-value for effective insulation surpasses 4.54m²K/W. For those inclined towards a more unconventional approach, a still viable option would be 4.15m²K/W.
Walls also play a pivotal role in maintaining thermal comfort. A commendable R-value for walls is approximately 3.30m²K/W, setting a benchmark for creating a snug and energy-efficient living environment. These high R-values are indicative of top-tier insulation materials that should be prioritised when seeking optimal thermal performance in building insulation projects.
In the United Kingdom, a reliable R-value typically falls around 4.15m²K/W, but for an added layer of security, it's advisable to target values above 4.54m²K/W.
A good R-value in insulation comes with a thicker insulating material:
Phenolic board: 1x120mm
PIR rigid board: 1x140mm
EPS Polystyrene: 1x190mm
Tab.1 Good R-value vs Insulation thickness
WHAT INSULATION HAS THE BEST R-VALUE?
The best insulation, when it comes to R-value, is the one that gives you the highest number while using the least amount of material. To see which insulation tops the R-value chart, it's like having a face-off among different types available in the UK. We've got phenolic contenders from Unilin and Kingspan, PIR options from Celotex and Recticel, polystyrene choices from Jablite and Stylite, and mineral wool selections from Knauf.
As depicted in the diagram, phenolic boards provide the most elevated R-values, with PIR boards coming in a close second. On the other hand, both polystyrene and mineral wool exhibit the lowest R-values, indicating comparatively lower thermal insulation effectiveness.
Pic. Insulation with high R-value
WHAT IS A GOOD R-VALUE FOR EXTERIOR WALLS
Considering the limitations imposed by insulation thickness in the UK, the top choice for external wall insulation is Kingspan Kooltherm K5. Its chemical composition and manufacturing technology ensure the highest R-value per thickness. The most commonly selected thickness for insulating external walls in this case is 70mm. A 70mm thickness provides an R-value of 3.50m2K/W, which is the highest achievable with a single-layer insulation material for external walls.
However, if thickness is not a constraint, one could consider EPS polystyrene with a thickness of 200mm, offering an impressive R-value of 6.60m2K/W, one of the highest available in the market.
WHAT IS THE R-VALUE OF 100MM CELOTEX?
In the UK, the space for insulation is usually between 50 to 150mm, with 100mm being a common choice. Knowing the R-value is crucial. Unilin PIR and Celotex PIR are popular for their ease of installation and cost. A thickness of 100mm gets you an R-value of about 4.50m2K/W, hitting a sweet spot for effective insulation. It's essential to note that going thicker than 100mm doesn't bring as much additional benefit in insulation systems.
WHAT IS THE R-VALUE OF KINGSPAN?
R-value changes based on how thick the insulation is. For Kingspan phenolic boards, the thermal conductivity is always the same at 0.018 W/mK, the lowest and best in the UK. Because this value is always steady, and for Kingspan, it's the lowest, you can be sure that their insulation always has the best R-value, ranging from 4.10m2K/W to 7.15m2K/W.
So, in simple terms, Kingspan's insulation is the best because it has the lowest thermal conductivity compared to other brands, ensuring it consistently has the highest R-value, ranging from 4.10m2K/W to 7.15m2K/W.
R-VALUE INSULATION COST
The thicker the insulation, the better the insulation quality indicator, known as the R-value. Unfortunately, with thicker insulation material, the cost goes up because more material is needed to make it. Insulation materials with the best R-values, like phenolic boards, will be the most expensive, while solid PIR boards are a bit more affordable. On the other hand, materials like EPS or XPS are cheaper but require a thicker layer of insulation to achieve the same R-value.
For example, to achieve the same R-value at 6.30m2K/W, a phenolic board will cost around £53 per square metre (with a thickness of 120mm), while a PIR Rigid board will cost £28 per square metre (with a thickness of 140mm). On the other hand, if we opt for expanded polystyrene, we need to consider costs of around £42, but that's with a thickness as much as 190mm.
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