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CLT Sound Insulation

CLT Sound Insulation

Cross laminated timber  or CLT as it is also known is growing in popularity as a building material. It has many features that appeal to an architect when designing a building.  Some of these features include

  1. Strength and Durability: CLT panels are incredibly strong and can be used as load-bearing elements in buildings. They have high tensile and compressive strength and can support significant loads.
  2. Sustainability: CLT is considered an environmentally friendly building material because it is made from renewable resources – wood from sustainably managed forests. It has a lower carbon footprint compared to concrete and steel.
  3. Speed of Construction: CLT panels are prefabricated, which means they can be manufactured off-site and then transported to the construction site for assembly. This can significantly reduce construction time and labour costs.
  4. Lightweight: Despite its strength, CLT is relatively lightweight compared to traditional construction materials, making it easier to handle and transport.
  5. Fire Resistance: CLT has good fire-resistant properties. The thick layers of wood char slowly and in the event of a fire, provide some protection to the structural integrity of the building.

CLT panels are flat structural elements composed of glued wood sheets to form oriented wooden layers: each single panel is composed of three or more layers.


Does CLT need insulation

Yes , CLT needs insulation to improve its acoustic performance.

To understand why we need to look back at point 4 in our list of features of CLT. Due to its lack of mass CLT is not as effective as concrete or masonry, in insulating impact and airborne noise.

This means that noise from inside and outside the building can more easily penetrate through the walls, floors, and ceilings made of CLT. To address this challenge, designers and builders need to consider incorporating additional layers of sound insulation for areas that require high levels of noise isolation.


Less Mass – Less Sound Insulation

As stated earlier due to its strength CLT can serve as load-bearing elements in buildings.

CLT is being used instead of concrete in the construction of floors and also as the main material in the construction of walls. While its strength make it a suitable material to be used, the acoustics of the material let it down.

Less mass means both impact and airborne soundwaves can pass through structures made of CLT easier than more traditional materials that have  more mass.

Let’s compare the sound reduction index (R) for airborne sound insulation and the impact sound pressure level (Ln,w) for impact sound insulation between a 150mm concrete slab weighing 391 kg/m squared and a 175mm thick CLT panel weighting 88 kg / meter squared

  1. Airborne Sound Insulation (Rw):
    • Concrete Slab (150mm, 391 kg/m²): Concrete slabs typically provide good airborne sound insulation due to their mass. Depending on factors like the composition of the concrete and construction details, you might expect an Rw value of around 45-55 dB or higher.
    • CLT Panel (175mm, 88 kg/m²): CLT panels can provide some airborne sound insulation, but they are generally not as effective as concrete due to their lower mass. You might expect an Rw value of around 35-45 dB or so for a CLT panel of this thickness.
  2. Impact Sound Insulation (Ln,w):
    • Concrete Slab (150mm, 391 kg/m²): Concrete slabs are typically poor at reducing impact sound transmission. Depending on the exact composition and construction, you might expect an Ln,w value of around 78 dB or higher.
    • CLT Panel (175mm, 88 kg/m²): CLT panels do not perform as well as concrete in impact sound insulation due to their lower mass. You might expect an Ln,w value of around 87 db for a CLT panel of this thickness.

These are rough estimates, and the actual performance of these materials in a specific project can vary based on factors such as building design, construction techniques, and the surrounding environment. The overall point is to reach the levels of insulation you get with a concrete floor for both impact and airborne sound insulation you need to add to the mass of your CLT installation.

The same is true in the construction of walls and so some form of acoustic insulation is necessary.


Acoustic Floating Floor

One building method often used when looking to increase sound insulation for a floor made of CLT is the addition of an acoustic floating floor.

An acoustic floating floor is a specialised construction technique designed to minimise airborne and impact sound transmission between floors.

Unlike traditional acoustic floors, which are directly connected to the structural base, an acoustic floating floor is intentionally decoupled or isolated from the floor’s foundation. This decoupling is achieved by utilising resilient under screed acoustic insulation materials and specific installation methods, allowing the floating floor to operate independently.

At the core of an acoustic floating floor is a resilient underlayment, which serves as a crucial element forwhat is an acoustic floating floor sound insulation. This underlayment is typically composed of materials with high-density, visco-elastic properties that absorb and dissipate sound vibrations. It effectively disrupts the transmission of airborne and impact noise by converting the sound energy into minimal heat energy. Products such as Grei – Underscreed Impact Sound Insulation, Upgrei – Acoustic insulation for high thickness floating floors or Roll Acoustic Under Screed Insulation from the Isolgomma range have these properties and meet all government regulations in the UK

This approach allows you to enjoy all of the benefits of CLT while also ensuring it meets the acoustic insulation requirements of the building.


CLT Walls

clt sound insulationOn an acoustic level, CLT walls are affected by their relative weight, so they need intervention to improve their acoustic characteristics.  A product such as Rewall 40 wall soundproofing is ideal to provide the acoustic insulation needed for CLT walls.

Its low thickness allows for application even in situations where space is limited and in renovations works as well.

The panel actually has high thermal as well as acoustic insulation properties, is practical to install and environmentally friendly because it is produced from recycled and regenerated materials.

clt acoustic insulation using trywall insulation



Another great product to improve the acoustic (and thermal) insulation of CLT walls as well as lightweight stud walls is Trywall from Isolgomma.

Trywall is a 48mm thick laminated panel consisting of 3 layers. The central panel is made of high density rubber with a thickness of 8mm and a density of 800 kg/m³. On either side of it are two panels of polyester fibre of 20mm thickness each and a density of 60 kg/m³.


Finally when using CLT panels we must look at the X, T, and L-shaped junctions in CLT structures. These refer to the various ways these panels are connected or join together at different angles. These junctions are crucial for transferring loads and providing stability to the structure.


CLT Junctions

Depending on the purpose of the building you may need to consider the acoustic performance of these junctions to minimize sound transmission between spaces.

Buildtec Acoustics recommend Joinwood CLT Acoustic Bearing Strip  to solve this issue. It is a decoupling element for the reduction of lateral noise transmissions in Cross Laminated Timber (CLT) structures. Made to be resistant to compression means it maintains its excellent elastic properties. This will dampen the transmission of vibrations inside the CLT structure.

We have years of experience working with professionals to maximise the insulation of building using CLT. If you have any questions do not hesitate to call us on 07553 473877 or email us info@buildtecacoustics.co.uk.

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