Insulating with cellulose

Paper flakes or cellulose insulation is a bio-ecological insulation material. With a thermal conductivity coefficient ( = λ-value = lambda value) between 0.035 and 0.04 W/mK, this insulation belongs in the same category as mineral wool or polystyrene products. In terms of renewability and recycling, cellulose insulation also scores much better.

Paper flake insulation is made from old, unsold or incorrectly printed newspapers. Paper fibres are extracted from these during the production process. These fibres hook into each other and take the form of elastic flakes that feel a bit like cotton wool. Between the hooked fibres are small air pockets. It is these hollow spaces of stagnant air that make cellulose an insulating material.

You can find this insulating material in two forms. The most common form is the 'loose' paper flakes. These are blown into hollow compartments (such as between rafters and lattices). Inside, they form a continuous layer and encapsulate all shapes and penetrations. This way, you avoid cracks and crevices that lead to energy losses. In addition, you can also buy cellulose compressed as a thick mat. Like mineral wool, this mat can then be sandwiched between the rafters of your roof construction, for example.

Ecological

Paper flake insulation is labelled "ecological" for several reasons. Firstly, the raw material of paper, namely wood, is regrowable and therefore basically inexhaustible. Cellulose in mat form also needs support fibres to achieve good rigidity and mechanical resistance. These are usually natural fibres such as hemp.

Secondly, cellulose insulation gains additional advantages because it is largely a recycled material. Wood - and thus paper - is also a store of CO2. The longer we keep this CO2 in circulation, the longer it takes for it to re-enter the atmosphere.

In addition, when you work with blown-in cellulose flakes, as you do at 't Centrum, you not only create a seamless insulation layer without cracks and crevices, but you also do so without loss and cutting residues during installation.

The paper flakes can also be reused again in a subsequent project when the building is demolished, even if it has completely different dimensions and complex shapes. They can also be added back to the production line. In other words, they can be used in a circular way.

Finally, the cellulose flakes used have another ecological edge. The cellulose used in 't Centrum is produced in Belgium, resulting in limited transport distance. In addition, the raw materials are sourced locally within an average radius of 257 km. The production energy is very low (among the lowest in the insulation materials sector) and is produced using 100% green electricity.

Circular cellulose in 't Centrum

At 't Centrum, cellulose is blown into the prefabricated timber frame walls.

"Cellulose is in itself a recycled product. That is also placed loose (blown in) so that it is also removable, reusable and recyclable," explains Dirk Verbeeck, architect at Kamp C. "But in 't Centrum, circularity is also secured at element level. The prefabricated facade part, including the cellulose, is a standard element and can be integrally reused in a new building."

Cellulose chosen only for ecological and circular properties?

Above, you already read that cellulose insulation stands its ground among conventional insulation materials in terms of lambda value. But there is more:

1. Good moisture control against building damage and mould: Cellulose insulation material can absorb up to 20% of its own weight in moisture without losing its insulating properties. This makes cellulose very suitable for temporarily storing and evacuating existing moisture from the construction elements (or any unwanted and absolutely avoidable moisture infiltration). The moisture in the construction is thus well regulated. This reduces the risk of mould and rot in the construction. However, despite cellulose's ability to absorb and release moisture well, it is not recommended to use cellulose insulation in wet building elements (e.g. a cavity wall).

2. Fireproof: Even though paper fibres are the raw material of cellulose insulation, it does not immediately catch fire. Cellulose insulation is more comparable to a phone book than to paper in case of fire. Moreover, a protective charred crust forms on the cellulose. This charred layer thus provides protection for wooden structures, allowing wooden beams to emerge from the fire unscathed. This is further enhanced by additional additives that act as fire retardants.

3. Pest resistant: The dusty nature of cellulose insulation and the additives are annoying and therefore repel pests and insects. Its elasticity and structure are also unattractive to rats and mice.

4. Soundproofing: Cellulose insulation, like all mat-like materials, has a good sound attenuation index of ± 50 dB. Therefore, it can be used in roofs and partitions to dampen ambient noise. Because cellulose insulation is not pressure-resistant, it can be used in hollow wooden floors but you are not going to prevent impact noise with it. For that, other materials are used for floating floors.

5. Protection against summer heat: In winter, cellulose insulation retains heat well and in hot periods it keeps it out longer. Phase lag means how long it takes for the (outside) temperature to penetrate an insulation material. For example, with cellulose insulation, for the same thickness of insulation, it takes considerably longer than, say, glass wool, for the heat/cold to reach the inside of your house. In other words, with cellulose, summer heat does not penetrate until the outside temperature has dropped, and night ventilation can be actively used. Of course, there is a note to this: the effect is smaller than that of good shading, avoiding cracks and crevices, ... Also, during heat waves when the temperature remains very high at night, the effect is somewhat smoothed out.

6. Versatile: Cellulose insulation can be used for interior and exterior insulation in new buildings and renovations. It is suitable for roofs, walls and (attic) floors. In 't Centrum, cellulose is used for prefabricated timber frame walls.

7. Environmentally friendly and sustainable: As cellulose insulation material is largely manufactured from waste newspaper and the number of additives is very limited, the environmental impact during the production process is minimal and a lot of waste and new material is saved. We discussed the other ecological advantages above.

Other insulation materials for specific applications

The insulation on the outside of the skirting in 't Centrum in the wet zone is extruded polystyrene foam from Jackon. This is also 100% reusable due to the system of processing.

For roof insulation, we need a pressure-resistant material in 't Centrum. This does reduce the choice of materials quite a bit. For the roof, we therefore use pressure-resistant rock wool insulation (Rockwool Caproxx). "The first choice was wood fibre insulation but this was no longer available due to the corona crisis," explains contractor Joeri Beneens. The circular principle of Rockwool is mainly its processing. That loose-fitting insulation is perfectly reusable. With any other pressure-resistant board material, it would have been just the same. But (pure) rockwool is also recyclable and of mineral origin. Under the office terrace, rock wool is not sufficiently pressure-resistant and Foamglas was chosen. This is made of 60% recycled glass.

Due to the loose insulation and roofing, a ballast layer is provided. This will also protect the roofing from direct solar radiation, which also improves summer comfort.

Acoustic insulation is of less importance with roofs. It does help against airborne noise. But acoustics is especially important between 2 building layers in connection with impact sounds.

The floor insulation in 't Centrum consists of shells, the layer of Ecoshells is 60 cm thick. Because the shells themselves do not have a very good insulation value, you have to apply a greater thickness of them.