How timber structures handle fire

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Timber Structures

Timber structures are experiencing a revival for a variety of reasons. It is not only visually attractive but also versatile and sustainable. However, there are still people remain hesitant to build timber structures because of the misconception they have about how timber handles fire. They may feel that it proves to be less safe in the event of fire exposure.

Fortunately, as time and technology change, everything else changes with it. Furthermore, many studies have been made and tests have been done to improve the comfort and safety of consumers.

This blog will help you understand timber in timber structures handle exposed to fire and what is done to minimize damage and maximize safety.

What happens with timber while it burns?

  • Firstly: heat energy is transferred into the timber resulting in an increase in temperature within the material.
  • Secondly: When timber is exposed to fire and the temperatures reach 100 degrees, moisture starts to vaporize resulting in dehydration.
  • Thirdly: When temperatures reach above 200degrees, the timber starts to have paralysis or combusts, in other words, flammable gasses are released. 
  • Finally: Char oxidation occurs. This is when a char layer is formed to protect the timber core while the timber starts losing some of its mass.
Fire Test
Fire test

Testing timber for fire tolerance

David Barber from Arup specializes in the fire safety of mass timber buildings. He works with researchers, architects, and developers in the fire safety of timber structures. According to Prof. Walls, he initiated a test that involved burning a SA Pine Beam.

Barber used a SA Pine square beam of the following size: 130mm in width and 720mm in depth. The top side was covered with insolation while the other three sides were exposed to the fire for a period of one hour.  The results indicated that there was enough timber left which had enough strength to hold a load. The measurement of the left-over timber was 32mm in width and 671mm in depth.


MASS TIMBER CAN TAKE THE HEAT. The above test proves that it is possible to achieve these goals. Making timber structures much safer.

Timber exposed to fire forms an insulating layer delaying the outbreak of heating of the core of timber below. This means that IF a timber structure collapses in the event of a fire, it is not necessarily the timber that burns out. This conclusion should completely eliminate the misconception people have about how timber tolerates fire.

We cannot prevent fire from causing damage to any structure and these events happen unexpectedly. However, we can minimize damage by taking the correct measures from the start. When the fire is active, what we are essentially trying to achieve is the following:

  • We need to ensure that no one gets hurt or dies in a fire.
  • We need to be able to prevent the fire from spreading thereby ensuring the surrounding buildings are safe from the fire.

Safety measures for Timber structures

Just like any other building structure, a timber structure should be built according to the national standards and regulations provided and the correct timber material should be used. If not, you may run into some problems that could be prevented in the event of a fire. These are only two of many factors that need to be taken into consideration:

Rules and regulations

After attending a webinar (Talking Timber) and listening to Professor Richard walls, Fire Engineering Research Unit from the University of Stellenbosch, among other speakers, we concluded the following:

Structural Engineers should design according to SANS 10160 (The basis of STRUCTURAL DESIGN AND ACTIONS FOR BUILDINGS AND INDUSTRIAL STRUCTURES) regulations which include “Accidental design situations” such as exposure to fire and the actions required in such situations.

South Africa’s National Building Regulations (NBR) of SANS 10400 B states that “All buildings must have a strong, serviceable, stable and durable design.”  The code addresses the following to ensure safety as far as possible:

  • Stability, Strength, and Structural Resistance

The structure needs to be able to carry the load capacity for a fair amount of time.

  • Integrity

Smoke and flames should not be able to pass through the slabs.

  • Insolation

There is a limited amount of heat allowed to pass through the slab which is an average temperature of 60 degrees Celsius and a maximum of 80 degrees Celsius.

Fire Safety
Fire Safety

Safety measures in the design process of timber structures

Structural Designers should consider the following aspects to understand the fire risks in structures in the event of a fire when designing a structure:

  • Compartmentation

When a structure is built with many small compartments, all openings/penetrations in the walls should be fire rated.  Doors, pipes, electrical conduits, and wet services should also be fire rated.

  • Evacuation

Evacuation routes should be carefully laid out to ensure an easy and safe escape.

  • Active protection

This refers to systems that can be triggered by a human, electrical or mechanical response. This includes detection systems, sprinklers, and fire extinguishers.

  • Passive protection

This includes systems that are permanently put in place to prevent the spread of smoke and fire. An example is an Intumescent paint which is a product that expands and provides a protective layer to underlying materials when heat is detected.

  • Flashover

The potential for a flashover should be taken into consideration. A flashover is when a fire in a room spreads very rapidly through the air because of intense heat.

Structural Timber
Construction Timber

Correct timber for strong timber structures

Timber homes have become more than just timber that has been stacked together to form a square building. Its versatility has become more and more recognised over time. Furthermore, architects and interior designers have more opportunities to expand their creativity by building more beautiful and safer timber homes.

With graded, you can be sure that it holds all the necessary qualities a structure should have to consider it safe and strong. At Sabie Poles, we provide all these products to individuals and on a wholesale basis to timber merchants all over Southern Africa. We supply SABS-approved S5 graded construction timber.

Graded Structural timber will most often be seen in roofs and ceilings to give strength and provide a basis for the roof rests. Timber beams are also used for the strength of windows and doorways. The timber is also used to build timber structures.

Additionally, timber profiles or mouldings such as cladding, decking, flooring and ceiling enhance timber buildings.

*Tip: Cladding can also be used as an extra safety measure against fire in a timber structure. “Beams or columns made of steel and wood with fire protection cladding can withstand fire and smoke for at least 30 or 90 minutes longer. This ensures that life-saving escape and rescue routes are kept clear for those people and the fire brigade.” – CWS Fire Safety

We have the following sizes of CCA S5 Graded Construction Timber available at Sabie Poles:

  • 38mm x 76mm x 3.6m / 6m / 6.6m
  • 38mm x 114mm x 3.6m / 6m / 6.6m
  • 38mm x 152mm x 3.6m / 6m / 6.6m
  • 38mm x 228mm x 3.6m / 6m / 6.6m
  • 50mm x76 mm x 3.6m / 6m / 6.6m
  • 50mm x152 mm x 6.6m
  • 50mm x228 mm x 6.6m
  • 76 x228 x 6.6m

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