Fire Risks and Sheep’s Wool Insulation (Critical Points)

A photograph of sheep's wool insulation in a roofspace. There is a fire extinguisher symbol at the bottom of the image and the words "Fire Risks and Sheep’s Wool Insulation" across the top in white on a red background.

Insulation is an essential component in homes to reduce energy needs and provide a more stable atmosphere.

However, the insulation type also contributes to fire risk, as some materials are more flammable than others.

So, what are the fire risks when it comes to sheep’s wool insulation?

Sheep’s wool insulation isn’t flammable, and it’s naturally fire resistant up to temperatures of 1,040°F (560°C). Sheep’s wool is a good insulation choice because it’s safe to handle and resistant to fire. Additionally, sheep’s wool resists mold, dampens sound, and is highly durable.

Sheep’s wool is suitable for home insulation because of its longevity, performance, and fire resistance.

In this article, I’ll discuss flammability and fire risks for all insulation and then discuss key points of wool’s fire-resistant properties.

Havelock Wool is one of the top sheep’s wool insulation companies in the world. For a detailed review of them, read our article “Havelock Insulation: A Review Of Their Wool Insulation.”

How Fire and Flammability Affect Insulation

A picture of a worker installing spray foam using a spray gun between rafters in a roofspace. There is a black-on-yellow flammable warning sign overlain.
Spray foam can present a fire risk. However, sheep’s wool insulation is naturally fire-resistant.

The primary purpose of insulation is to stabilize temperature within spaces by preventing heat from escaping in or out of that space. Insulation keeps rooms warm or cool by trapping energy in one place.

However, a concern with insulation is that it can trap heat so well that it becomes a fuel source during fires. Because of this concern, most insulation is treated with flame-retardant materials that self-extinguish or slow the flame rate during a fire.

Different insulations have varying flammability, resistance to fire, longevity, and cost.

Flammability and fire resistance both contribute to an insulation’s fire risk:

  • Flammability refers to how likely a material is to ignite.
  • Fire resistance is how efficiently that material maintains its structural integrity in the presence of heat.

For example, a highly flammable material that’s also resistant to fire will ignite easily but also extinguish quickly. One that isn’t flammable but is not resistant would be difficult to ignite, but once burning, it will degrade quickly.

The best insulation materials are not flammable and very fire-resistant, as shown below:

Insulation TypeFlammabilityFire-ResistanceLongevity
WoolVery LowVery HighHigh
Fiberglass/Mineral WoolLowHighHigh
Polyurethane FoamHighLowHigh
CompositeVery LowVery HighVery High

In general, the less flammable a material is, the more fire-resistant. However, each material’s structural makeup and use of fire retardants will determine how it’ll respond to a fire.

How Fire Resistant Is Insulation?

An insulated roofspace with rafters and roofing membrane visible. There are cartoon flames overlain.
Some types of insulation are more flammable than others. Sheep’s wool is naturally fire resistant and a good choice for home insulation.

All insulation is treated with fire-retardant chemicals to prevent it from spontaneously igniting. However, some materials are more flammable or fire-resistant than others.

The most concerning materials are polyurethane (PU) foam and cellulose.

Cellulose is made with treated recycled paper, while PU foam is spray-on plastic insulation. These materials are highly flammable without chemical treatment and prone to ignite in intense heat.

These materials have highly porous surfaces, which provide ample surface area for fire to spread once it ignites. The use of fire retardants slows their ignition but doesn’t prevent these materials from catching light if a fire spreads within a building’s walls.

Additionally, heavy use of chemicals leads to increased smoke and hazardous gasses when these materials catch fire.

Wool, fiberglass, and composite insulation are much less flammable while providing adequate resistance to fire. These materials are much less likely to ignite and are structurally more resistant to high-heat conditions than PU foam or cellulose.

Of these materials, sheep’s wool provides the best fire resistance for its price over other insulation types.

How Fire Affects Sheep’s Wool Insulation

A photograph of sheep's wool with a symbol indicating fire resistance with an arrow and some stylized flames.
Sheep’s wool insulation is highly fire-resistant; more so than cellulose and spray foam, both of which are popular insulation choices.

Sheep’s wool is a popular organic alternative to other insulation types because of its resistance to fire.

According to Sheep Wool Insulation, sheep’s wool has the following fire-resistant properties:

  • Wool will not ignite until it reaches 1040°F (or 560°C).
  • Wool is self-extinguishing because of its limiting oxygen index (~25.2).
  • Wool has a higher fire resistance than cellulose or PU insulations.

Additionally, most sheep wool insulation is treated with fire-retardant chemicals to increase its resistance to fire.

Does Wool Catch Fire Easily?

Wool doesn’t catch fire easily. Wool is naturally fire-resistant and isn’t flammable, making it one of the safest insulation materials for your home. Additionally, wool is very durable, so it should last for a long time.

How Flammable Is Sheep’s Wool?

Sheep’s wool isn’t flammable. Sheep’s wool insulation requires temperatures exceeding 1040°F (560°C) to ignite. Compared to PU foam or cellulose, which can ignite when exposed to a local flame, Sheep’s wool smolders in the presence of fire and is naturally self-extinguishing.

Is Sheep’s Wool Insulation a Fire Risk?

A sheep viewed from the side. It has a cream-colored fleece, black legs and a black face. There is a cartoon flame with a red circle around it and a diagonal red line across it.
Sheep’s wool is not a fire risk, so you can rest easy if you’re using sheep’s wool insulation in your home.

Sheep’s wool insulation is not a fire risk and is much safer than other insulation types. This insulation type has a limiting oxygen index of 25.2, making it very safe for homes.

The limiting oxygen index (LOI) measures how much oxygen (by %) a material requires to ignite. Air has 21% oxygen, so materials with LOIs of 22 or greater will not ignite directly and require extreme heat to catch aflame.

Sheep’s wool won’t start or contribute to a fire unless that fire exceeds 1,000°F (538°C) and is already present.

Final Thoughts On Fire Risks and Sheep’s Wool Insulation

Insulation is vital in homes to reduce energy consumption and stabilize ambient temperatures.

However, many insulations can also contribute to fires if exposed or if temperatures exceed a specific limit.

Of the various insulation types, sheep’s wool is a popular alternative that is exceptionally fire-resistant and durable in high heat.

When considering fire risks for insulation, cellulose, and PU foam are the most concerning insulation types.

Sheep’s wool is a natural material, and you might have seen it used by animals for their nests, making you wonder whether using sheep’s wool in your home might attract vermin. Luckily for you, we’ve written an article about that, which will answer all your questions. Read it here: Birds And The Bees: How Animals Like Your Wool Insulation.

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