Biomaterials in architecture

The construction sector accounts for around 40% of global greenhouse gas emissions: about 30% comes from buildings’ energy use, and the remaining 10% is attributed to so-called embodied carbon, which refers to emissions derived from the extraction and production of materials, as well as their installation on site.

While buildings’ energy efficiency has been regulated for years and is the subject of ongoing investment policies in renovation and public awareness, the same is not true for material-related emissions, which to date have largely been overlooked.

The latest revision of the EPBD, the Energy Performance of Buildings Directive in the European Union, approved in March 2023, includes for the first time the mandatory calculation of emissions in the construction of new buildings—an initial step towards regulating and limiting them, already in force in several EU countries. [1]

This new regulation represents a paradigm shift: high-impact, high-ecological-footprint materials that generate high CO₂ emissions and consume large amounts of fossil fuels during production—such as concrete, steel, or plastics—are now being required to present decarbonisation plans that in practice are unrealistic or rely on technologies yet to be developed, such as carbon capture. [2]

On the other hand, low-ecological-footprint materials that have been used in construction for thousands of years and had been sidelined due to the rise of industrialised materials—such as timber, earth blocks, fibre-based insulation, or lime-based products, among others—are once again gaining ground in the market, supported by investment in innovation, start-ups, and technologies that enable large-scale use.

These low- or zero-carbon-impact materials are typically natural, locally sourced, sustainable, in many cases renewable, and ensure minimal impact on people’s health and the environment.

Undoubtedly, the transition to a decarbonised sector requires recognising the value of, recovering, and developing these materials, which must become the new conventional construction to ensure a sustainable future.

1. TIMBER

Timber has become the leading construction biomaterial in recent times. If steel was the material of the 19th century and concrete that of the 20th, timber is expected to be considered the material of the 21st century.

According to the New EU Forest Strategy for 2030 carried out by the UNECE (United Nations Economic Commission for Europe), forests would absorb around 10% of the European Union’s CO₂ emissions. [3]

Trees therefore act as natural carbon dioxide sinks. Depending on the species, timber stores around 1.6 tonnes of carbon dioxide per m³, according to a study by FP Innovations in Canada. [4]

The UNECE highlights that using timber in the construction sector reduces CO₂ emissions by 40% when used as an alternative to concrete, and by 30% compared to steel. [5]

STRUCTURAL TIMBER

Due to its many benefits, the use of timber in construction has become increasingly popular in recent years. It is the benchmark biomaterial, extremely versatile: it can be used as a structural element capable of bearing significant loads and spanning large distances, or as cladding, enclosure, flooring, or furniture. [6]

CLT

The rise of prefabrication in architecture has positioned CLT—Cross Laminated Timber—as one of the leading options when designing buildings with sustainability criteria.

CLT is a construction system obtained by stacking 3, 5, or 7 layers made of sawn and glued timber boards, arranged perpendicular to one another.

The 90-degree layering of the timber boards gives the assembly bidirectional structural behaviour, capable of adapting to a wide variety of construction needs.

The CLT cross-laminated construction system is used in both vertical and horizontal elements, from load-bearing walls of up to 14 continuous metres, to internal partitions, as well as continuous intermediate floors and roofs.

The use of CLT as a construction biomaterial is considered one of the most popular and sustainable building alternatives on the market today. As a prefabricated and industrialised system, CLT helps simplify on-site processes, reducing construction time and cost, and becoming a highly competitive option against high-impact industrialised systems such as concrete or steel.

CLT MIX

CLT is available in different versions—one of them in the form of panels, also prefabricated, which ensure improved thermal and acoustic performance.

CLT panels with thermal-acoustic insulation are a recent variation of the original construction system, based on removing the central layers of sawn and glued timber and creating a void instead, like an internal box, into which thermal-acoustic infill is integrated.

This evolution improves mechanical performance—by reducing structural weight—while also enhancing thermal and acoustic performance—by integrating insulation inside—helping design in line with energy-efficiency and sustainability principles: less raw material for better performance.

In Spain, there is a CLT Mix manufacturer that uses timber from sustainably managed Pyrenean forests. Egoin is a company founded in the Basque Country, headquartered in Biscay, and operating throughout Spain. [7]

LIGHT TIMBER FRAMING

The light timber framing system consists of installing timber studs, spaced 40–60 cm apart, fixed together with cross members—horizontal timber pieces that act as horizontal connecting elements—forming structural lattices.

It is a prefabricated system, commonly used in North America since the 19th century, also known by its English name Balloon Frame, which uses timber as a construction biomaterial.

The voids created between studs are closed by integrating insulation materials, which are then covered with prefabricated timber panels. The result is a compact, self-supporting surface capable of resolving a home’s walls, floors, and roof.

One of the main advantages of light timber framing, beyond reducing construction time, is its energy efficiency: it is a construction system that acts as thermal insulation on its own. Not only is the overall weight reduced, but it also helps eliminate additional layers in the building envelope. This material saving has a positive environmental impact, generating a minimal ecological footprint. [9]

TIMBER FLOORING

There are different types of timber floors, including floating floors, synthetic parquet, and mixed parquet, a hybrid of the previous two. The choice of the final layer that covers the floor of our home once again highlights the dichotomy between natural and synthetic.

SOLID TIMBER PLANK FLOORING

Solid timber plank flooring includes both floating timber floors and glued parquet. The timber planks used in these surface-covering systems vary and adapt to the needs of each surface to be covered.

Natural timber parquet offers greater durability than synthetic options, as any damage the timber suffers over its service life can be restored through maintenance techniques such as sanding, thereby extending the biomaterial’s lifespan.

Due to its thickness and composition, natural timber finishes provide better insulating performance, as well as greater thermal inertia that brings warmth to the home’s interior. This reduces the need to heat the space with mechanical equipment, contributing to energy efficiency.

MIXED PARQUET

Mixed parquet is a natural-synthetic flooring. It consists of a lower layer of wood particleboard and an upper layer—considerably thinner than the lower one—of natural timber.

From an aesthetic standpoint, mixed parquet offers characteristics similar to solid timber flooring, giving the space a warmer feel than a synthetic finish.

The lower particleboard layer provides strength and durability. However, as it is not a solid natural element, mixed parquet does not allow maintenance techniques that extend its life cycle—it cannot be sanded because the top layer is too thin.

TIMBER JOINERY

Timber joinery is an alternative to the more commonly used PVC or aluminium joinery—timber is a natural and renewable material, while PVC is a plastic material derived from petroleum, and aluminium, despite its recycling potential with rates close to 100%, has a high ecological footprint. [11]

Timber’s insulating properties, both thermal and acoustic, improve the home’s airtightness and add warmth to the ambience.

The thermal transmittance of timber frames performs better against energy losses than PVC or aluminium, thereby supporting the home’s energy efficiency. As a thermal break is not required—as is the case with aluminium joinery—manufacturing is simplified.

Exposure of joinery to the exterior requires specific treatment and maintenance on one of its faces. Surfaces must be nourished annually with products that protect against direct sunlight and exterior dirt, such as stains or enamels, ensuring they are hygroscopic and VOC-free in their composition.

Due to their appearance and finish, hardness, and resistance over their service life, the most commonly used timber types for joinery, both exterior and interior, are pine, oak, larch, chestnut, and iroko. However, it should be noted that not all of these timbers can be supplied by local sawmills, so it is important to check the timber’s origin. [12]

2. TIMBER DERIVATIVES

Timber is a highly versatile biomaterial that has been used in architecture for centuries. Although its most common use is structural or in finishes such as cladding, furniture, or joinery, it still has additional applications in the construction sector.

WOOD FIBRE

Wood fibre as an insulating biomaterial is made up, as its name suggests, of small wood fibres obtained from wood waste, both of natural origin through the recovery of branches, leaves, bark, or sawdust, and from recycled wood of low commercial value.

The wood fibre production process, as with particleboards, begins by shredding the wood into small particles, which then undergo thermo-mechanical treatment that allows them to be separated into individual fibres. Additives are added to these fibres to improve fire resistance and protection against insects and fungi, such as boron salts.

Wood fibre can be supplied loose, in large quantities without a specific format—commonly used for blown-in insulation—but also in panels, rigid boards with more standardised sizes that facilitate application, or in rolls for smaller spaces or less conventional shapes.

Unlike other insulation materials with a higher ecological footprint and more widely used in building construction, such as polyethylene foam or expanded polystyrene, wood fibre has positioned itself as one of the most competitive timber-derived biomaterials on the market.

In sustainability terms, it is a renewable and biodegradable biomaterial with low environmental impact. It stands out for its thermal and acoustic insulation capacity, reducing heat and noise transfer, and also offers fire-retardant properties—fire resistance—and hygroscopic properties—the natural ability to regulate indoor humidity. [14]

CELLULOSE

Cellulose is an infrequently used option, but highly effective as an insulating biomaterial. It is an alternative to wood fibre insulation, and both materials share many similarities.

Cellulose is a plant-based material; plants are mainly composed of cellulose. It is the primary molecule present in plant cell walls, and is therefore found in large quantities in timber-derived biomaterials such as paper and cardboard.

The cellulose manufacturing process is based on reusing recycled paper, specifically newspaper. The material is shredded and mixed with water, forming a pulp of paper strips from which the ink—considered an impurity—is removed, and to which additives are added to improve fire-retardant, insecticidal, and fungicidal properties, such as boron salts.

This mixture undergoes a drying and pressing process and is then cut into small fibres, resulting in cellulose-based insulating biomaterial. As with wood fibres, it is a low-impact ecological process, promoting zero energy consumption.

Cellulose insulation is an economical and quick-to-apply system, and its applications include blown-in or sprayed insulation systems, as with wood fibre.

Its breathable and hygroscopic composition, in addition to regulating relative humidity and preventing the spread of mould, helps insulate buildings from sudden temperature changes, enhancing the feeling of thermal comfort inside the home. [15]

CORK

Spain ranks second worldwide in cork production, after Portugal, especially in the regions of Andalusia, Extremadura, and Catalonia.

Cork as a construction biomaterial is obtained from the bark of the cork oak, a tree mainly found in the Mediterranean. Cork extraction is an artisanal process carried out periodically, approximately every 10 years—the time required for the cork oak bark to regenerate—until the minimum thickness required for cork production is reached.

A circular incision is made in the tree’s bark using a specialised tool until the outer layer can be removed. This first layer is known as common cork; it is the outermost layer that regenerates most frequently, i.e., the most abundant raw material and the one most commonly used.

From the deeper layers closer to the cork oak trunk, virgin cork is extracted: a higher-quality type of black cork than common cork, used in cases requiring greater strength and durability. As it is closer to the trunk, virgin cork contains less air and more resin, which gives the material greater compactness.

With both biomaterials—common cork and virgin cork—after extraction the cork is dried. To eliminate moisture, the cork is left to air-dry for a few months, and then undergoes a boiling process to remove impurities.

Cork as a biomaterial has different installation formats, from sprayed cork—applied on site with a spray gun onto surfaces—to expanded cork in prefabricated insulating cork panels, to cork underlay in rolls of thin insulating agglomerated cork, as well as loose cork—allowing air cavities to be filled with blown-in insulation or poured directly on site. [16]

3. STONE

Stone is one of the quintessential biomaterials in the history of construction. As a biomaterial that comes from the earth, extracted directly from quarries, stone does not necessarily require a massive transformation process; rather, its own properties make it a self-sufficient option capable of meeting numerous needs on its own.

Although it is not a renewable material, stone is highly durable and therefore requires minimal replacement and has a long service life. In addition, it allows pieces to be recovered for new uses, following circular-economy principles. Waste generated by stone extraction and/or processing contains no toxic substances, making it possible to reuse the waste to manufacture engineered stone (such as porcelain flooring) or to recycle it, avoiding closing its life cycle.

ENGINEERED STONE

Natural stone, despite having properties that respect the environment and people’s health, is characterised by being a non-renewable biomaterial. This has created the need to find alternative construction solutions, integrating more synthesised anthropic processes while keeping stone as the raw material.

PORCELAIN STONEWARE

Porcelain stoneware is a type of engineered stone characterised by an appearance that seeks to imitate natural stone. It is a material composed of a portion of natural raw material mixed with synthetic additives.

The production of porcelain stoneware has a certain environmental impact. For its manufacture, agglomerated stone powder is used, typically with cement, which, after undergoing a high-temperature firing process, acquires properties of strength and hardness, as well as porosity.

The stone powder used in its production comes from the recovery of stone waste, both from natural stone offcuts from the quarries themselves and from the reuse of natural stone with a previous use. Therefore, porcelain stoneware avoids the direct extraction of natural stone from quarries, which has a positive impact given that it is a non-renewable raw material.

The final appearance of porcelain stoneware resembles that of natural stone, with an irregular, handcrafted look characteristic of stone finishes. It can be manufactured in large-format slabs for full façade or floor cladding, both interior and exterior, or in smaller formats for tiling and worktops.

TERRAZZO

Terrazzo is a construction material that comes from quarry waste, reusing unusable fragments of natural stone that still retain their physical properties.

Its manufacturing process begins by crushing stone pieces into small fragments, called aggregates, generally composed of marble chips, glass, granite, quartz, etc. These minerals are mixed with a binder, usually cement mortar, which, once set, forms the terrazzo pieces, giving them high hardness and strength.

The main application of terrazzo is in tile form for flooring, or in worktops. These pieces are manufactured by pouring the mixture into moulds, which then undergo a pressing, drying, and curing process.

Its final appearance will depend on the aggregate grain and thickness, as well as their composition, which in some cases may include pieces of glass, ceramic materials, or other recycled materials that give it a more decorative appearance.

As with porcelain stoneware, terrazzo is bound with cement, which means it has an environmental impact to consider, as cement is one of the highest-impact materials in the construction sector.

NATURAL STONE

Solid natural stone is one of the quintessential biomaterials, used in construction for centuries. It is a material with a low carbon footprint and no emission of toxic gases during its production process.

Due to its durability—a long service life with minimal maintenance required—and its resistance—to weathering, temperature changes, humidity, etc.—natural stone has become a basic biomaterial used in countless works throughout history.

However, there are two important considerations to take into account regarding the impact on the environment and people’s health of using natural stone.

The first is the ecological impact on the surroundings: it is necessary to consider the landscape and ecosystem impact of quarry stone extraction, as well as water use in extraction and cutting processes.

On the other hand, it is necessary to consider that stone is a porous material, so when using it for flooring it is necessary to incorporate a protective layer that may contain volatile toxins—VOCs—that are emitted into the air and end up being absorbed by our bodies. [18]

MARBLE

Marble is a metamorphic rock formed from limestone rocks subjected to high temperatures and pressures, reaching high degrees of crystallisation. Its composition is 90% calcium carbonate.

It is one of the most valued solid natural stones on the market for its aesthetic value, with a crystalline, veined, glossy, smooth finish.

It is a biomaterial resistant to high temperatures, supporting thermal comfort and household energy savings. Marble stands out for its durability: it has a long service life that requires little maintenance, and it is also reusable and recyclable. For this reason, its most common uses are worktops or wall cladding, mainly indoors.

GRANITE

Granite is an igneous rock composed of quartz and feldspar, formed by the slow cooling of magma produced when layers of the Earth’s crust melt, which gives it a granular, textured appearance.

Its extraction process and properties are similar to those of marble, whose most common finishes are polished and glossy. However, a sealing surface treatment is often applied to prevent the emission of possible radioactive gases, characteristic of the decomposition of this type of natural stone. While studies have determined that radioactive emissions from a marble floor or worktop are not dangerous, it should be noted that the sealing product used may emit small amounts of harmful toxins into the air. [19]

Even so, granite is positioned as the biomaterial most commonly used for worktops, but due to its high hardness, durability, and thermal inertia, it is also found in interior and exterior flooring.

SLATE

Slate, like marble, is a metamorphic rock composed mainly of quartz and minerals from the chlorite group. Its appearance is characterised by dark greyish tones, a rough texture, and irregular-finish pieces.

It is estimated that 90% of the natural slate used in construction is obtained in Spain, mainly from Galician deposits. [20]

Slate as a construction biomaterial stands out for its durable life cycle, as well as for its thermal properties and resistance to weathering and sudden temperature changes, making it a suitable option for roofs and exterior façade cladding.

LIMESTONE

Limestone is a sedimentary rock formed mainly of calcium carbonate, and it may also contain traces of minerals such as clay, quartz, etc.

Unlike marble, it tends to have more uniform textures. It is a biomaterial generally found in light tones, with a porous, matte finish, and a range of textures from smooth to rough.

Due to its versatility in properties and finishes, it is used for both interior wall cladding or flooring, generally with a smooth appearance, and exterior applications in its more textured form. As a porous biomaterial—due to its hygroscopic nature—its use in walls without waterproof protection helps regulate ambient humidity.

SANDSTONE

Sandstone is one of the most abundant natural stones in the Earth’s crust, making it one of the most sustainable options in terms of the depletion of non-renewable resources. It is a sedimentary rock composed of fragments of quartz, mica, and feldspars—minerals the size of sand grains.

It is a biomaterial with hardness, durability, and porosity that are ideal for resolving hygroscopic walls. Its fire resistance allows it to be used in fireplaces.

Because it is difficult to polish, sandstone has a grainy, irregular texture due to its composition rich in sand particles. As a result, it has a colour range in tones close to beige.

C RECYCLED AGGREGATE GRAVEL