How Does Wood Fibre Perform In A Fire? – Can I Just Ask? – Ep.8

It’s one of the first questions that comes up whenever we talk about wood fibre insulation: how does it perform in a fire? The short answer is – surprisingly well. While it’s true that wood burns, wood fibre behaves in a very specific and useful way during a fire, offering passive protection with a remarkably low toxic load. Here’s what you need to know.

If you’d rather hear Andy and Chris talk through the ideas in this article, you can watch Episode 8 of Can I Just Ask? below. 👇

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Understanding Fire Behaviour in Building Materials

When considering insulation for timber-frame buildings, fire performance is a top concern. Organic, wood-based materials tend to raise eyebrows—but the reality is far more reassuring than many assume.

Wood fibre insulation, like all timber products, is combustible. However, its fire behaviour is predictable and slow-burning, with a distinct advantage: it chars. This charring layer insulates the material beneath and can slow the spread of fire, protecting structural elements for longer than many synthetic alternatives.

In contrast, some widely used insulations – such as PIR and certain mineral wools – may release highly toxic gases when exposed to high heat. PIR, for instance, can emit cyanides, while binders in some mineral wools can produce hydrochloric acid gas. Wood fibre, on the other hand, gives off minimal toxic fumes during combustion, especially when compared to these synthetic options.

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Not Just About Combustion—But Toxicity Too

In a fire, smoke inhalation is often more dangerous than flames. That’s where wood fibre shows its worth. Unlike plastics and many foamed insulations, wood fibre doesn’t produce a cocktail of carcinogenic or corrosive gases. Even under incomplete combustion – where carbon monoxide can be an issue – it’s still less hazardous than synthetic counterparts.

This matters not just for building occupants, but also for firefighters. Studies have shown that firefighters face significantly higher cancer rates, partly due to prolonged exposure to the toxic by products of modern building materials. Choosing low-toxicity insulation like wood fibre is one way to reduce that burden.

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Predictable Performance, Useful Protection

Wood fibre insulation typically holds a Euroclass E fire rating in isolation – lower than non-combustible materials, but far from inadequate. When integrated into a build-up with other materials, performance improves dramatically.

For example, internal wall linings using wood fibre can achieve a B classification when tested as a complete system. And when used structurally, wood fibre can contribute to timed fire ratings of up to 90 minutes, offering robust passive protection with no added chemical flame retardants.

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Fire Ratings: More Than Just a Letter

Fire performance is typically assessed in three ways:

1. Individual material classification – how a product burns on its own. Wood fibre is Class E.
2. Surface lining classification – how materials behave when used as linings. Combinations can raise wood fibre to Class B.
3. Elemental fire resistance – the timed rating of an entire wall or roof build-up (e.g. 30, 60, or 90 minutes).

With the right design, wood fibre can meet or exceed standard regulatory requirements for fire resistance – even in demanding applications.

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Beyond the Flames: Rethinking Fire Safety

There’s a tendency to assume that using non-combustible insulation will preserve a building during a fire. The reality is more sobering. After a serious fire, most interiors – regardless of what they’re made from – are stripped back to the bones. The key, then, is not preventing all damage, but slowing fire spread and reducing the harm caused during those critical minutes.

Wood fibre won’t stop a fire, but it will buy time – without filling the air with noxious chemicals.

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Explore Timed Wall Build-Ups with Wood Fibre

We’ve developed a range of timed build specifications that demonstrate how wood fibre can be used to meet 30-, 60-, and 90-minute fire resistance ratings in real-world wall and roof systems.
👉 See our timed wood fibre build-ups here.