Building a prefabricated ecological house

When it comes to reducing construction costs, many of our clients arrive looking to build a prefabricated ecological house.

Is a prefabricated ecological house really cheaper? Perhaps the question we should ask ourselves first is why prefabricate at all.

Starting from the premise that the concept of an ecological and prefabricated house is somewhat contradictory—since an ecological house requires adaptation to the climate and environment, along with a bespoke design—it is true that to save costs and time, we can prefabricate certain parts of our home.

Again, we must ask a new question: to what extent can we prefabricate? Obviously, if we buy a wooden house transported on a truck, this would be a fully prefabricated module, but within the concept of building a prefabricated ecological house, there are many levels of prefabrication.

What is a prefabricated ecological house like?

At Slow Studio, when we conceive an ecological house, the first thing we consider is that it must be fully adaptable; that is, our house types are not completely closed, but rather a base upon which we can work to ultimately adapt the design entirely to the environment.

In fact, in our studio, we propose ecological wooden houses and ecological masonry houses, understanding that the masonry house is built on-site while the wooden house is partially prepared in a workshop—that is, a part is prefabricated.

Prefabricating allows us to save time and costs; so far, so good. However, we must not forget that an ecological house is a lifetime investment. While it is true that the budget is a limitation for many clients, it is not the only factor to consider.

The materials and the construction system we use will determine the comfort, efficiency, and health of our home, and consequently, the energy expenditure and the quality of the indoor environment.

If we want to achieve an efficient and healthy home, it is important not to settle only for a house that fits our budget, as today it is possible to achieve healthy and efficient homes at a reduced cost if the architectural team has sufficient expertise to allocate our budget to those items that are truly important.

Let us look in detail at the options we have for building a prefabricated ecological house and what results we should expect from each of them.

Materials for building a prefabricated ecological house

Prefabricated ecological masonry house

While the concept of masonry is inherently related to manual labor, we could speak of the construction of a prefabricated ecological house where the load-bearing walls are made of concrete, while the floor structure or the roof itself is made of prefabricated wood from a workshop.

In fact, at the studio, we are applying this system to a home in Vallromanes where the budget is tight but where, for technical and energy efficiency reasons, we are interested in solving the roof using a continuous wooden structure prepared in a workshop, while the walls are prepared on-site.

In this type of construction, the thermal inertia of the exterior walls is utilized, which collect heat from the sun (it is important to orient the house well) and store it to release it later into the interior of the house.

In summer, the operation is similar, but the heat dissipated at night is extracted through natural cross-ventilation via openings in courtyards or different facades.

This is one of the reasons why courtyards appear in many of our projects; it is precisely to take advantage of the thermal inertia of the masonry walls and use it to our advantage by dissipating or storing the heat from the walls depending on the time of year.

Materials for building a prefabricated ecological masonry house can range from classic exposed ceramic brick to coated hollow clay blocks or, in the case of tight budgets, concrete blocks that can even be left exposed or painted white on the inside.

Sometimes it is not just a matter of budget but of taste. There are clients who prefer houses with a more finished look, in the sense that they want plastered interior walls, and other clients who prefer to leave the bricks exposed even if they are concrete blocks, achieving an austere but very authentic appearance.

Regarding finishes for building a prefabricated ecological masonry house, this will depend on the client’s budget. At Slow Studio, we usually propose double-leaf ventilated facades—one interior and one exterior—but if the budget does not allow it, we can finish the masonry wall with an ETICS system, coated with mortar.

Prefabricated ecological steel and concrete house

At the studio, we rule these out completely, basically for two main reasons:

– Concrete does not breathe.

Concrete is a closed-pore material, so it acts as an insulator and waterproofer without allowing the construction elements to breathe. Thus, it is a material that does not help absorb or release water vapor and, therefore, does not regulate indoor humidity levels.

– Steel interferes with the Earth’s magnetic field.

Steel is a material that involves a high energy cost in its extraction and manufacturing and contains materials such as copper, zinc, tin, or lead in its alloys—materials that are very harmful to health.

Apart from these drawbacks, steel has ferromagnetic characteristics, which means it can alter the Earth’s natural magnetic field. These alterations represent an imbalance factor for the cellular polarization of the human organism; therefore, in the construction of a prefabricated ecological house, it is highly recommended to avoid or minimize the presence of this material.

Furthermore, it is also necessary to take into account that most prefabricated ecological house projects found on the market have energy efficiency problems, as they usually resolve construction details in a way that thermal bridges appear at many of the junctions.

Prefabricated ecological wooden house

In this type of house, everything is an advantage and, although the price may be slightly higher than a masonry house, this is compensated by the increase in long-term energy efficiency, as well as the reduction in construction time.

– High efficiency.

Firstly, it is essential to highlight the high energy efficiency of wood as a construction material. In addition to being a natural, ecological, and renewable material, it allows for the construction of breathable, well-insulated houses with airtight enclosures and great thermal comfort.

This will allow you, if you choose to build a prefabricated ecological wooden house, to considerably reduce spending on heating and cooling, which is the largest portion of a home’s energy expenditure.

– Fully natural and sustainable product.

Wood is a natural material with a negative ecological footprint; that is, wood absorbs more CO₂ during its growth process than during its logging and transformation into construction material.

Furthermore, it is a renewable material as it continues to grow and will always be available to us.

In a project for the construction of a prefabricated ecological wooden house, it would be important to control its origin, extraction, and sustainable management; therefore, it is advisable to check that the wood we use has FSC certification (certified by the Forest Stewardship Council).

– Possibility of working with locally sourced raw materials.

More and more national companies are researching the properties of wood, and sawmills are working with wood from local forests. Some examples are the company Egoin in the Basque Country or Fustes Sebastià in the Pyrenees.

– Reduction in construction times.

The construction of a prefabricated ecological wooden house allows for a considerable reduction in on-site assembly times since, while the parts are being prefabricated in the workshop, it is possible to move forward with other construction phases such as excavation and foundations.

Similarly, when these parts arrive at the site, it will be very easy to fit and join them due to the perfect control of details in the workshop.

We are talking about a wooden house being assembled in the workshop in about two months while the foundations are prepared on-site; once the assembly is ready, in just over a week, the structure of the house is ready at the construction site, pending the completion of interior and exterior finishes. This type of construction is very suitable when there is a hurry, such as in the case of adding floors onto existing homes.

– High control of details in the workshop.

Thanks to laser cutting, which allows for millimeter control of the junctions between parts, a high quality of construction details is achieved with impeccable and fully airtight joints and junctions.

Furthermore, workshop work is much faster and more effective, as it is carried out by professionals specialized in working with prefabricated wooden structures using specialized machinery.

– High airtightness of the enclosures.

Finally, thanks to the millimeter control mentioned, it is possible to guarantee a structure with airtight joints and connections that achieve, in this way, unbeatable thermal performance.

It is very important to take this aspect into account, as high airtightness of the enclosures will prevent energy losses and, therefore, reduce heating costs.

Prefabricated ecological CEB house

Perhaps a final note on the construction of a prefabricated ecological house would be the use of Compressed Earth Blocks (CEB), as an alternative to rammed earth walls.

The CEB system is an evolution of the traditional adobe brick still widely used in South American or Asian countries, which in our latitude are prepared in factories with strict resistance and durability controls. An example of production and marketing is the company Cannabric.

In this sense, we could say that the CEB is a prefabricated clay piece that we apply on-site, although the construction process subsequently remains a manual or artisanal process of wall assembly; again, as in the case of a prefabricated ecological masonry house, the CEB wall can be combined with a wooden structure for floors and the roof.

Before finishing, we wanted to review the steps for building a prefabricated ecological house because, although building with prefabricated or semi-prefabricated systems as seen in the previous points can save costs and time, there are some construction steps that we will have to follow regardless of our choice and that are important to keep in mind.

5 Steps to build a prefabricated ecological house

1 Find a plot of land

Firstly, it is necessary to acquire a plot of land. To find it, you can opt for different routes. On the internet, there are many pages through which you can contact sellers.

If you prefer to go hand-in-hand with a trusted agent, you can contact a real estate agency, or it is common for architectural firms to know an associated real estate agent who guides their clients in the purchase of the land.

In any case, when you face the choice of a plot of land to build a prefabricated ecological house, it is important that you take two key factors into account:

In any case, if you are in the land search phase, we recommend that you review our post on how to search for land, where we tell you the key points to consider when selecting a plot.

2 Contact an architect

Yes! 100% recommended.

Although it seems that to build a prefabricated ecological house we can contact a prefabricated house construction company directly, it is important to be wary of the salespeople who sell these types of houses and who often have technical deficiencies; instead, value construction with an architect specialized in energy efficiency and healthy homes.

A very common mistake is to contact a builder first to assess the construction cost, but it is important to keep in mind that every plot, every location, and every family has very particular needs whose cost is impossible to predict without a prior project.

The most common scenario is that if you contact a prefabricated house construction company first, they will present you with the construction price of a standard house and will not give you the price for the foundations; this is because they do not know the composition of the subsoil of your land and the location of the resistant substrate.

As always, if you want to build a prefabricated ecological house, it is important that the team of professionals has knowledge of sustainability, energy efficiency, passive climate control systems, bioclimatic housing, or natural materials.

3 Design the house

The design phase of the house is a very beautiful process in which you, as clients, can take an active part.

It is very likely that you have ideas and concerns that you want to share and implement in the design; that is why it is important that you have previously selected an architect who, in addition to having experience in the sector, has human quality and facilitates communication and teamwork.

Sometimes prefabricated house companies have closed designs to which we must adapt. A house for a lifetime should be much more than a distribution plan and must adapt to the needs of each family.

Furthermore, to develop a bioclimatic design, it is very important to take the land and its surroundings into account to decide how to orient the home and make the most of solar energy. It is also interesting to propose water reuse systems and create semi-outdoor spaces, such as porches or galleries.

Green roofs or the use of natural materials will also make your home a healthier and more pleasant space by having better regulation of indoor humidity and a healthy indoor environment.

4 Finance the construction

Regarding financing, many clients wonder if it is possible to apply for a mortgage to build a house. The answer is a resounding yes!

The type of mortgage for building a home is different from one for purchasing, but it is also feasible. In this case, the bank will provide the money as the work progresses.

In any case, it is always advisable to have savings, as we must take into account that today the bank will ask us for 20% of the total to positively assess the financing of our home.

5 Build a prefabricated ecological house

Once everything is ready, only the construction remains. Here another agent appears: the construction company.

As mentioned in previous points, it is very important to reach the selection of the construction company with a prior project or alongside an architect with technical judgment to ensure that the project is carried out appropriately.

What we always advise is that once the design project has been completed, a tender for builders be held and the prices of each of the items be compared, whether through prefabricated systems or manual masonry.