Why timber frame houses are more earthquake resistant than concrete or brick houses

Timber frame houses are sometimes said to be too light to be strong. And yet, being light comes with a number of advantages: simpler and cheaper foundations, thinner walls which means more usable space for the same built-up area, better behaviour during earthquakes. Romania is a country with a high seismic risk and we have very unpleasant memories of such events. It is therefore not surprising that when people decide to build, they are interested in making their homes as earthquake-resistant as possible. Wood, which is elastic and lighter than ordinary building materials, has the capacity to make houses with this structure earthquake-resistant.

How the earthquake acts on the house

Earthquakes occur because of geological phenomena. They have a central point, called the epicentre, from where shock waves propagate so that the earthquake is felt far away from the area where it occurred. These seismic waves cause the earth to move and with it, houses start to move. The movement of the earth acquires a certain acceleration which, together with the weight of the house (its mass, to be precise), forms the seismic force of inertia acting laterally on the walls. It is the most important force acting during an earthquake and the most dangerous. As a result, the walls collapse and the unsupported ceiling collapses.

The action of seismic force occurs on any building, regardless of the material it is made of. This is why houses are designed with this in mind. The earthquake resistance of residential and commercial buildings is regulated by Seismic design code P100issued by the Ministry of Development, Public Works and Administration. According to these regulations, the elements of the resistance structure and their positioning are calculated so that the building's response to earthquakes is optimal.

A timber frame house is 3-4 times lighter than a concrete or brick house

The stability and strength of a building is given by the mechanical strength of the material it is made of. Wood has mechanical strength comparable to that of common building materials. For example, spruce wood has a compressive strength of 24 N/mm², slightly higher than ordinary brick or concrete, while oak is the same as high-strength concrete, with a compressive strength of 50 N/mm². In the case of industrialised wood, such as LVL or laminated beams, the compressive strength is even higher.

Wood, however, has a lower specific weight than the building materials mentioned above, and the difference is significant. For example, dry spruce wood has a specific weight of 405 kg/m³, whereas the specific weight of normal concrete is 2200 kg/m³. This means that a wooden building element is much lighter than a similar one made of concrete or brick with comparable compressive strength. The weight of the building elements is added to the total weight of the house, which means that a timber-framed house with the same mechanical strength as a concrete or brick house is much lighter. Experts say that a wooden house is 3-4 times lighter than a concrete or brick one.

The seismic force acting on the house is directly proportional to the weight of the house, and the greater the weight of the house, the greater the force. As a timber-framed house is lighter than a concrete or brick house of the same strength, you will be subjected to less seismic force in the event of an earthquake.

Wood can warp without affecting its strength

Mechanical strength is not the only property of wood that has an impact on earthquake resistance. Its elasticity, malleability and hardness are also important.

The natural ability of wooden buildings to return to their original form after an earthquake has made them a popular choice in regions prone to seismic activity. Some centuries-old wooden buildings have remained standing after major earthquakes, while modern reinforced concrete buildings have suffered significant damage. As an example, the oldest wooden building in the world,a 5-storey pagoda in seismically active Japan is over 1000 years old.

The elasticity of the wood that forms the structure together with the fasteners - screws, metal connectors, fasteners - gives the building the ability to deform and then return to its original shape, thus cushioning the force of the earthquake. The force dissipates and the building remains standing.

The malleability and hardness of wood are also important in the event of an earthquake. Wood has the ability to withstand lateral seismic forces without being damaged, and being a hard material makes it resistant to knocks or friction without giving way.

It is clear and proven that a wooden building is much more resistant to earthquakes than a concrete or brick one. Recent test have shown that a timber-frame building of up to six storeys can withstand a magnitude 7.5 earthquake with very little damage. In our country you cannot make wooden buildings that high, the regulations still do not allow more than 3 levels (ground floor and 2 floors). But if you want a new house, consider this option, as earthquake resistance is not the only advantage of houses on wooden structure.