Most of us judge windows and doors on looks, energy efficiency, or cost. Fire safety rarely crosses the mind, but it should. When uPVC (unplasticised PVC) is exposed to intense heat or flames, it doesn’t just melt. It can release toxic fumes, and in a fire, it’s often smoke, not flames, that causes the greatest harm.
Independent research shows that when PVC burns, it releases gases including carbon monoxide and hydrogen chloride, along with thick, harmful smoke. In some conditions, dioxins and other hazardous chemicals can form too. These fumes spread quickly, especially in enclosed domestic spaces.
A study on PVC materials found that under flaming conditions, smoke was produced much faster and in much higher quantities than in non-flaming scenarios. Real-world incidents, including the well-documented Garnock Court fire in Scotland, showed uPVC frames melting, contributing to the spread of heat, smoke and fumes.
Surprisingly, no. uPVC doesn’t ignite easily and often self-extinguishes once the heat source is removed. But “hard to ignite” isn’t the same as “harmless in a fire”. Once exposed to high enough heat, uPVC decomposes and releases toxic smoke that can rapidly fill a room.
Because not all window materials behave the same in a fire.
Timber, especially high-performance timbers like Accoya, behaves very differently. Instead of melting, it chars, forming a protective layer that offers valuable extra minutes of structural stability. In an emergency, those minutes matter.
At GBS Joinery, this is exactly why we take our responsibility seriously. Our team advises customers based on safety, longevity and integrity, not shortcuts. It’s part of our core values of Trust, Care and Excellence — principles that guide every decision, every installation, and every detail of our craft.
This isn’t about fear. It’s about awareness and informed choice. Every material has pros and cons, and uPVC certainly has benefits in terms of cost and maintenance. But when it comes to fire behaviour and toxic emissions, it’s important to understand the full picture.
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