Building a House with Thermoblock

Although thermoblock arrived on the Spanish market around the 1990s, this ceramic brick has not become popular until recent years, when building regulations have become much stricter in terms of energy efficiency, making this large-format block with excellent thermal properties a piece with many competitive advantages compared to traditional brick.

In this article, we analyze the pros and cons of thermoblock, when it is worth using, and when it is possible to use it as a single leaf without a second insulation layer. We assess technical advantages and compare costs and construction times against other traditional methods.

Manufacturing Process

Its manufacturing process begins with crushing the clay, which is ground and kneaded, and to which lightening additives are added to form the mixture that will be poured into extrusion molds. Once formed, the pieces are left to dry before being placed in the kiln for firing at over 850°C.

This is a manufacturing process similar to that of any ceramic material (bricks, tiles, vaults, etc.) except for the addition of granular components to the clay mass during dosing and kneading.

Upon reaching these very high temperatures, the granular components that had been added to the clay disappear, leaving a void in their place, which will reduce the material’s density. At the same time, it provides a fine porosity homogeneously distributed in the ceramic mass in the form of visible macropores, giving the thermoblock the characteristic dotted appearance. [1]

Types of Blocks

To build a house with thermoblock, we have many types of pieces of different sizes that by definition are always larger than the gero, the basic perforated brick used mostly for raising walls. However, unlike the gero, which is characterized by its systematization—that is, all pieces have the same dimensions and can be modified on-site—thermoblock blocks respond to a system designed to resolve each specific situation with a special piece. For this reason, conventional base pieces are replaced at singular points by corner pieces, T-wall junctions, lintels, or joints, because their specific geometry makes on-site modification very difficult.

In the case of conventional thermoblock base pieces, the largest surface face—the one that is perpendicularly perforated—has constant dimensions of 30 × 19 cm with different types depending on thickness, which can vary from 14 to 29 cm.

There are also complementary pieces: the half piece, vertical and horizontal modulation piece, termination piece, corner piece, 135° angle piece, patching piece, and lintel piece. The latter, the lintel piece, is the most different from the rest as it is U-shaped to be placed around the beam or structural support piece of a window opening, so that it is visible both inside and outside. [2]

These pieces are characterized by their special perforation, not as in the case of the gero, where all holes have the same square, circular, or diamond shape. These are cells with a specific geometry, designed to offer good thermal performance and improve transmittance.

In recent years, traditional thermoblock blocks have evolved to the ECO1, ECO2, and ECO3 thermoblock range, which features an interior cell geometry that allows transmittance to be reduced even further, minimizing thermal bridges. In this range, only variations around the base piece of 24 or 29 cm are marketed. [3]

Structural Performance

Thermoblock has high mechanical resistance, exceeding 12.5 N/mm². For this reason, it can function both as a facade enclosure and as a structural load-bearing wall in buildings up to 3 stories. However, we must consider that due to its internal geometry, it has lower compression resistance compared to conventional gero. Therefore, in very heavy structures, it is necessary to distribute loads very well, because it has less resistance to point loads.

A very relevant advantage is that it allows avoiding the use of reinforcement in the wall. Reinforcement consists of corrugated steel bars or specific geometry metal pieces that are placed horizontally in the continuous joints between courses when building walls of ceramic pieces, remaining embedded in the mortar. Although not established as mandatory by the Technical Building Code in Spain, the practice of reinforcing between courses is common in load-bearing walls of ceramic pieces, except for gero walls—perforated brick—or thermoblock.

Its function is to resist tensile stresses, exactly opposite to those resisted by stone or ceramic pieces or mortar itself, which resist compression. For all this, in the case of building a wall with another type of conventional ceramic piece, the structure must be reinforced at least every 3-4 courses to compensate for both types of stresses.

Avoiding this reinforcement thanks to thermoblock not only allows us to save material and reduce costs and time, it also allows us to avoid using a material—steel—which is considered today as one of the three materials with the greatest impact on the planet, along with plastic and cement. [4] Recently, increasing attention is being paid to products or construction systems that dispense with metallic materials in order to avoid the conduction of electromagnetic fields.

Thermal Performance

One of the main reasons for deciding to build a house with thermoblock is its good thermal performance. The energy efficiency that thermoblock manufacturers boast about is closely related to its technical improvements over conventional ceramic blocks, specifically two characteristics: high thermal inertia and reduced transmittance.

Thermal Mass

Thermal inertia is the ability of a material to remain stable at a certain temperature, whether cold or hot. Materials with high inertia work well in climates with thermal variations between day and night, as they allow a lag of several hours from when they absorb energy until they release it.

In the case of facades finished with thermoblock:

In winter, the material accumulates daytime solar radiation and releases it during the night, when it is most needed because the environment has cooled.

In summer, the material absorbs heat and releases it at night, when we can ventilate effectively and cool the environment because the outside temperature has dropped.

A facade executed with thermoblock blocks has three times more thermal inertia compared to a wood fiber facade, the typical construction solution in the USA.

Transmittance

Another characteristic of building a house with thermoblock is the transmittance of the material itself, which is defined as the amount of energy that passes through a body per unit of time.

Thermoblock blocks, both conventional and the ECO line, enjoy low transmittance due to their lightening, but not enough to allow thermal performance and comply with energy efficiency regulations with a single-leaf wall, always requiring an insulation layer unless special insulated blocks are used—which are not yet manufactured in Spain.

Recently, in Germany, a new line of high-performance ceramic blocks called Poroton has been developed, filled with rock wool or expanded glass, both ecological insulations. [5]

This technology allows achieving very good transmittance, around 0.22-0.26 W/m²*K, so it is an element that can be used as the sole structural and enclosure element, remaining exposed without the need to add an insulation layer, because the pieces are directly insulated from within.

In the case of opting for a solution that incorporates insulation in the block itself, we must consider that if we leave an exposed finish on an unrendered wall of thermoblock blocks, air tightness problems may appear—that is, the dwelling may have leaks and its energy efficiency may be reduced.

The Technical Building Code (CTE) favors the option of preventing users from intervening in the regular air renewal in their homes, so it requires very high airtightness, with minimum ventilation flows in habitable rooms ranging between 4 and 10 l/s depending on the use of each room, a condition impossible to achieve with a single-leaf Poroton wall without rendering on either face. To meet this requirement, an exterior render, interior plastering, or vapor barrier will be necessary. [6]

All this allows eliminating thermal bridges, points with more complex construction situations where poor resolution can imply higher transmittance—that is, heat escapes at these points—such as junctions of facades with slabs or window openings.

Acoustic Properties

Building a house with thermoblock can help us meet the acoustic insulation needs of our dwelling, both in facade solutions and interior partitions. Thermoblock walls improve their performance by 2 dB compared to others of equivalent mass, since porosity reduces the modulus of elasticity of fired clay, while increasing damping.

The requirements of the Technical Building Code (CTE) regarding acoustic insulation in Spain require insulation between 30 and 47 dB of airborne noise in activity rooms in residential use, values that vary depending on the day noise index, L_d. [7]

The values of a single-leaf thermoblock wall depend on its thickness, and range between 46.5 and 52 dB, the latter at a thickness of 29 cm, being more insulating the greater the wall thickness. [8] Another option is a mixed solution of heavy leaf with light leaf and an addition of mineral wool acoustic absorption insulation, which can guarantee values of up to 70 dB.

Building a House with Thermoblock

When building a house with thermoblock, we must consider, in addition to the characteristics and properties of the material itself, the variety of construction solutions that this system offers.

Bond Pattern

Bond pattern in architecture consists of the arrangement of small-format building materials for the formation of a wall. The most conventional bond is known as stretcher bond, where the pieces of the upper course are placed centered over the vertical joint of the immediately lower course.

In the case of thermoblock blocks, a new characteristic comes into play: the tongue-and-groove system between block and block, which involves recesses and projections only on the sides of the piece that assembles with adjacent pieces without mortar. In this way, both faces of the wall are flat and the vertical joints between pieces draw a zigzagging geometry. This offers an improvement at the mechanical, thermal, and acoustic levels.

To execute the bond, an amorphous binding material is used—mortar—which is based on a mixture of cement, water, and aggregates. There are two assembly options: interrupted joint or thin joint. The first consists of placing two strips of mortar in the horizontal joint between one course and another with a central interruption of 3 cm, which allows generating a small interior air chamber that helps interrupt transmittance, always higher at joints.

The thin joint involves applying a thin layer of adhesive mortar, which due to its chemical characteristics only works on rectified thermoblock blocks, in which the finish is previously abraded so that it has minimal tolerance. This second option offers two advantages: reducing water use and a large amount of mortar, but it is true that it requires prior treatment that consumes energy.

Construction Solutions

At the level of construction solutions, it is evident that manufacturers pursue a block that allows resolving all requirements with a single-leaf wall visible on both faces, but this is still an anecdotal situation, which can work in very specific situations such as greenhouse-type interior patios where the facade is complemented by a glazed roof that, combined with the wall’s transmittance, allows reaching the transmittance standards required by regulations.

Below, we analyze two possible construction solutions that meet CTE requirements and what each entails.

Advantages of Building a House with Thermoblock

All the characteristics that have been mentioned throughout the article usually represent benefits of thermoblock over traditional masonry block. Thus, building a house with thermoblock implies improvements at the thermal level, since we manage to improve inertia and reduce transmittance—although we do not eliminate the need for insulation—; at the structural level, since we avoid the need for reinforcement; and at the acoustic level, since we achieve greater insulation due to its greater porosity.

All this is also complemented by reduced cost and shorter execution times, due to steel savings, less need for mortar, and reduction in the number of pieces and therefore labor, being of larger dimensions.

Furthermore, considering sustainability criteria, thermoblock not only allows working with passive strategies such as thermal inertia, but also technically improves what is already a completely natural material with a millennial tradition.

All this is reflected in its EPD (Environmental Product Declaration), which measures the equivalent consumption of kg of CO₂ per ton of product. In the case of thermoblock, this value reaches 254 kgCO₂ per ton of product. [9]

Although one of the greatest drawbacks to reducing this impact lies in the need to have kilns at temperatures over 850°C, a temperature that is still difficult to achieve through renewable sources. This is undoubtedly one of the greatest challenges for construction in the coming years, both for the manufacture of ceramic blocks such as thermoblock and for the manufacture of other materials such as cement or steel.

The Spanish ceramic sector is one of the largest European producers and a reference for other countries in fields such as innovation and industrial technology. Hispalyt, the Spanish Association of Manufacturers of Fired Clay Bricks and Tiles, groups together about 100 ceramic product manufacturing companies, representing 85% of the sector’s production. This association also ensures the correct transmission of information to customers, architects, and suppliers, requiring, for example, that all thermoblock manufacturers have the EPD, documentation that is not yet mandatory in Spain. [10]

The fact of having an important tradition of local manufacturing companies in our country leads us to raise the debate about the need to import insulated blocks from Northern Europe, as is the case with Poroton. Although it is a block that improves the qualities of national blocks by incorporating insulation in the block itself, we must consider that it is an imported product that requires adding the ecological footprint of its transport to the final balance of its installation.