Knauf vs Rockwool

Thermal Performance

 

There are two key considerations when looking at thermal performance: 1. Thermal conductivity of the insulator, and 2. How the performance of the insulator may change over time – this is referred to as thermal drift.

Both brands offer strong thermal conductivity ratings:

• Rockwool thermal conductivity: typically around 0.034–0.040 W/mK
• Knauf thermal conductivity: typically around 0.032–0.044 W/mK

On paper, Knauf would appear to achieve a slightly better thermal performance per millimetre of thickness, however, when you consider thermal drift, Rockwool performs better.

What is thermal drift?

All insulation materials experience some degree of performance reduction over time. This can happen because of how the material is made, exposure to moisture, or natural movement within the building. This gradual decline is known as thermal drift, and it results in the R-value reducing (the measure of thermal resistance).

Knauf insulation is lightweight, soft, and doesn’t hold its shape too well (especially with rolls). Over time, it will sag or compress, leading to gaps in the insulation where heat will escape. Knauf also has a very open fibre structure, which means that if it becomes damp, the thermal performance will significantly drop, as moisture displaces the air pockets that are crucial to insulation.

On the other hand, Rockwool is tough, rigid, and dense. It’s designed to bounce back to its original shape even after compression, and thanks to its rigid structure, it stays in place without sagging. Because stone wool is naturally water-repellent, it doesn’t readily absorb moisture, making it far more resistant to thermal drift and a better choice for thermal performance.

Why are you insulating your home?

It’s important to ask yourself this question as it will help you find the products you actually need. The most common reason people use insulation is for thermal performance, but there are other reasons as well, such as acoustic performance or fire resistance.

If you’re insulating just for thermal performance, you would be better off using a different brand with a better thermal conductivity rating, as it allows you to achieve the same target U-values with thinner boards. Some of these include:

• Celotex insulation (thermal conductivity up to 0.022W/mK)
• Ecotherm insulation (thermal conductivity up to 0.22W/mK)
• Kingspan insulation (thermal conductivity up to 0.019W/mK)
• Recticel insulation (thermal conductivity up to 0.022W/mK)

*For reference, these are previous thermal conductivity ratings:

• Rockwool: typically 0.035–0.040 W/mK
• Knauf: typically 0.032–0.044 W/mK

Using two insulators alongside each other

The alternative brands mentioned above are made from high-performance PIR, which is incredibly thin, yet highly effective for thermal performance.

This narrow thickness means you can use them alongside Knauf or Rockwool, so you can reap the rewards of two insulators. This is often done so you can achieve target U-values for energy efficiency, while also improving fire safety and noise reduction.

 

Fire resistance

For fire performance, Rockwool is the better option.

Both brands have the same fire rating of Euroclass A1, meaning they do not contribute towards the spread of fire or toxic smoke. However, unlike Rockwool, Knauf is not 100% fireproof and will melt in extreme temperatures.

This is why Rockwool is the superior choice. Because it’s made from volcanic rock, it doesn’t melt and can handle extremely high temperatures of well over 1,000°C. This is why it’s relied on in environments where fire-safety standards are in the highest demand, such as partition walls and ceilings.

Sustainability

While sustainability doesn’t impact the performance, we understand that it’s an important factor for many customers.

Knauf is produced using a high percentage of recycled glass (often up to around 80%) and is manufactured with its ECOSE® binder, which is bio-based and designed to reduce environmental impact. For more details, please visit Knauf’s website.

Rockwool is made from naturally occurring volcanic rock, which is durable and recyclable. For more information, please visit Rockwool’s website.

Cost

The upfront cost is most often the biggest deciding factor, but it shouldn’t be the only one. The long-term costs often outweigh the initial investment.

Upfront costs – Price per Square Metre

• Knauf insulation ranges between £2-30/m²
• Rockwool insulation ranges between £5-30/m²

Long-term costs

Whilst Knauf will cost you less money in the short-term, if you have the space for it, Rockwool will be more cost-effective in the long run due to its superior resistance to sagging, moisture and thermal drift.

No matter which brand you choose, you will save money on your energy bills, with reductions of up to 50%, which can save the average home anywhere from £300 to £500 a year.