Building an eco-friendly timber house

Although timber construction is not common in Spain, the truth is that wood is one of the most sustainable building materials, as it is fully renewable.

By an eco-friendly timber house, we mean a house whose structure and envelope (walls and roofs) are built entirely in wood and that also operates with high energy efficiency.

In other sections, we will see that it is also possible to use wood for the structure of a straw-bale house, for example, or as a material for windows and doors in an eco-friendly home.

In addition, the use of wood in construction is very common for floors and ceilings in conventional homes; however, in this section we will focus on using wood as the main construction system for an eco-friendly home.

Wood is a highly flexible building material, with a wide range of construction details that allow it to adapt to many different situations. Let us see how to build an eco-friendly timber house.

Timber house designs

A timber house can vary greatly in design, from modern timber homes—where the wood is worked with mechanised cuts that give it a uniform appearance—to traditional techniques for building rustic timber houses, following construction systems that are centuries old.

Unlike concrete, which requires a certain curing temperature, wood is a “dry” building material that allows building at any time of year and in any climate, which makes it a material used at all latitudes, although it is more common in cold countries where the use of mortar or concrete is not usual due to low temperatures that prevent the water-based mix from bonding properly.

Structure

Wood is considered a lightweight building material with good compressive strength and outstanding tensile strength (resistance to bending). For this reason, timber design makes it possible to create very large, open-plan spaces in which timber beams support the weight of the roof. The greater the depth of the timber beam, the longer it can span, and therefore the larger the open-plan spaces we can achieve.

Nowadays, wood (especially in central and northern European countries) is supplied prefabricated using lamination techniques, joining several layers of wood that are glued in different directions to increase strength and thus achieve robust structures that are every bit as good as steel structures.

If we want to achieve eco-friendly construction, it is important to control the origin of our timber and the lamination manufacturing process so that the adhesives do not compromise indoor air quality.

Construction

Timber houses are built using a main structure of timber posts and beams. This initial structure is infilled with timber frames that will support the walls, which can either be made of timber panels or filled with straw bales.

The timber structure is extremely flexible and can accommodate a wide variety of wall-envelope construction systems; however, it should be borne in mind that timber houses have low thermal mass, which means it is not a material with the capacity to store heat. This can be an advantage in climates or areas with little sun or with very cool breezes.

If our house is well insulated, even with low thermal mass it will be able to respond very effectively—with an appropriate heating and cooling system—to any variation in outdoor temperature.

In any case, we can always increase the thermal mass of timber by incorporating concrete slabs or ceramic walls.

Insulating a timber house

Normally, insulation in a timber house is placed between the structural elements. In this regard, it is worth remembering the insulating capacity of air and distinguishing between different types of insulation that are more or less compressed, and different levels of airtightness in the walls of our timber house.

The most effective timber construction is the passive house, whose walls and envelope are completely sealed against air leakage, so we will need mechanical ventilation to renew the air in the home. In this way, we reduce heating and cooling needs to a minimum.

In a passive house, with a small heat/cooling fan we can heat or cool our home with an energy use on the order of 1 to 10 compared to a conventional home.

Waterproofing a timber house

It should be borne in mind that waterproofing timber can act as a vapour barrier and cause condensation inside the home; therefore, the use of a breathable membrane that allows moisture to dry out is recommended.

Durability and insect attacks

Wood is an organic material that deteriorates with water and sun. Correct detailing—especially those that prevent exposure to rainwater—is essential to keep it in good condition.

However, it should also be borne in mind that water can reach the timber through condensation, when water vapour passes into the interior of the walls, for example due to an incorrect insulation solution or excessive sealing that does not allow the walls to breathe and, when there is a high temperature difference between inside and outside, produces condensation.

As for insect attacks, it should be noted that the main enemy of wood is termites, and therefore the timber in structures, walls and roofs must be protected against this dangerous pest. Termite protection is carried out in two steps: first, physical preventive protection, and second, chemical protection, which can be preventive and also used as a treatment once an infestation has been detected.

As termites attack from the ground, the best preventive strategy is to design the house to prevent termites from entering from the ground, as well as to provide inspection hatches that allow us to check for possible pests.

In any case, it is advisable to apply preventive chemical protectants to prevent termite attack, especially on the structural elements of our home.