Fireproofing wood structures – What you need to know

Timber is one of the oldest known construction materials. When harvested from well-managed forests, it’s one of the most feasible and sustainable building resources available. The wood in question is characterised by a very high strength to weight ratio and can transfer both forces of tension and compression. In a construction setting, timber is utilised for an assortment of structural forms such as columns, beams, girders, trusses and systems like piles, deck members, railway sleepers and in formwork for concrete. If damaged, timber structures can easily be repaired, reshaped or altered.
Perhaps best of all though, when appropriately treated, detailed and built, timber structures can be profoundly sturdy, durable and beautiful. Around the globe, there are numerous examples of timber used as the primary building material, achieving an aesthetic look which steel or concrete cannot achieve.
But as you would expect, the Timber of today, is not the same as the timber of yesteryear, with technology making it an even better material than before. Broad and extensive research over many years has resulted in the discovery of timber and its reconstituted and engineered products with well documented evidence of structural design and service performance. We are specifically talking about Cross Laminated Timbers.

Why Construction is using more Timber

As you will undoubtedly know, there has been a renaissance of timber structures in recent years. Driven by a renewed focus on environmentally sustainable development with lower energy demands and aesthetic goals, timber has become a brilliant building material again.
Construction with timber offers economic, performance and environmental points of interest not ordinarily found with other construction materials, plus timber is adaptable and versatile. Its proven record for safety is evidenced and likewise demonstrated by its utilisation in private developments as well as in some of today’s most innovative non-residential architecture.

Until recently however, the inability to fire rate timber meant it could not be readily used (in the construction of new buildings, not older buildings where were already erected) as the structural elements. There were limitations in building guidelines and regulations in many countries, particularly for taller structures.  However, through technology, extensive testing, novel fire design concepts, ideas and products have been created which mean timber can be again used for structural elements.

In other words, improved knowledge in the fire design of timber structures, combined with specialised fire protection of timber structures, permits the safe utilisation of timber (CLT as one example) in a wide field of construction applications. The outcomes have been building code relaxations introduced in recent years and some magnificently designed buildings.

Aside from the environmental and aesthetic aspects already discussed, it is worth noting timber has various inherent attributes that make it an ideal construction material. These include high strength to weight ratio, its noteworthy durability record, performance and good insulation properties against heat and sound. It also draws aesthetic benefits from its natural growth such as grain patterns, tones and colours not forgetting its availability in many species, sizes, and can be cut to different shapes.

However, despite its advantages and appeal, as we mentioned, there are some critical aspects – namely safety in case of fire – which need to be considered. These are structural adequacy and fire hazard properties. A word of warning, this part gets a little more technical, so if you need help understanding it, please get in touch with our team who can help you.

Structural Adequacy

The ability of a load bearing element of construction to support a load when tested in accordance with AS1530.4 is referred to as structural adequacy. This standard sets out test systems and criteria for the assurance of fire-resistance of components of building construction. It alludes to the capacity of a structure to keep its stability and load bearing capacity during a fire, while keeping its ability to resist the transfer of flames and hot gases from one part to another.  With appropriate insulation, it should be able to contain temperatures and stop heat transfer between zones for a pre-determined period of time.

Fire hazard property

The Building Code of Australia (BCA 96) contains different measures relating with the performance of materials when exposed to fire. These deemed-to-satisfy provisions require certain materials or assemblies to be non-combustible or have nominated fire hazard properties. With respect to timber, it lists and records the different timber species available alongside their hazard indices (Ignitability, Heat Evolved, Smoke Developed, Spread of Flame and so on) for the different structural components inside each building classification.

Additionally, the BCA contains information on: (a) natural (solid) timber and lists test results on samples of a number of natural timber species according to AS 1530.3. (b) Data on manufactured products for example, factory produced wood based products, hardboard, medium density fibreboard (MDF), particleboard and plywood assessed by AS 1530.3.

However, since products may widely vary in composition periodically and between manufacturers, (raw materials plus additives), specific indices should be validated by the manufacturer of the particular named or branded products and/or a registered testing authority Certificate of Accreditation.

Use of Fire Rating Paints for Timber

With the BCA requiring builders use a fire rated paint on all structurally exposed elements (wood or steel) to ensure the structure can withstand the effects of fire as long as possible, it is essential you use a product which gives you the required protection.

Easy to use and quick drying products such as AITHON PV33 are recommended for fireproofing wood structures used on the interior. Like all intumescents, when exposed to fire, the product swells to form a protective char more than 3cm thick. This foam car acts as an insulating layer between the timber and flame and has been shown to be resistant to more than 1000°c. In our experience, the novel gel properties in the AITHON PV33 basecoat and the advanced AITHON F3 finish coat, are unmatched as a decorative and protective finish.

However, it is not just possible to protect new structures, with Aithon suitable as a fire protective coating on older and even heritage listed buildings. For existing buildings where you wish to apply a protective coating, we encourage you to get in touch with our team first so you understand the impacts and can ensure the product is suitable for use.

In technical terms the AITHON PV33 framework can be utilised on timber and wood derivatives with minimum thickness of 10mm and a density equivalent to or greater than 390kg/m³, which compares favourably with other systems and flame retardants which may require coatings at least 20mm thick. It also achieves a Euro-Class B s1 d0 reaction to fire (accepted as an equivalent performance to UK, Class 0 by United Kingdom Building Regulations).

In general, AITHON PV33 framework provides an unrivalled finish and is one of only a handful of products to benefit from the stringent European Technical Assessment (ETA) process. It is utilised all through Australia, Europe, and the World on small and large prestigious projects.