When it’s time to replace old decking, it’s tempting to think of the leftover boards as free firewood for a bonfire or fire pit. Unfortunately, this is one of those situations where the convenient option carries real risk. Most decking wood, particularly pressure treated timber, shouldn’t be burned at all, and understanding why matters for both your safety and the safety of anyone nearby.
At JPD Landscaping & Building Services, we’ve removed and disposed of old decking across South East London for over 15 years. This guide explains exactly why treated decking wood is unsafe to burn, what to watch for with hardwood offcuts, and the right way to dispose of old boards instead.
Quick Answer: Can You Burn Decking Wood?
No, you should not burn old decking wood, particularly pressure treated timber. Treated decking releases harmful chemicals when burned, and even seemingly untreated hardwood offcuts can carry risk if they’ve been oiled or treated with a finish over the years.
| Decking Type | Safe to Burn? |
| Pressure treated softwood | No, releases harmful chemicals |
| Older CCA treated timber | No, particularly dangerous, contains arsenic and chromium |
| Hardwood offcuts (untreated) | Depends entirely on whether any finish or oil has been applied |
| Hardwood offcuts (oiled or treated) | No, treat the same as pressure treated softwood |
Why You Shouldn’t Burn Pressure-Treated Decking
Most modern decking timber goes through a pressure treatment process to protect it against rot, insects, and moisture damage over its lifespan. That same chemical treatment is exactly what makes it unsafe to burn. When treated wood is burned, the preservative chemicals used to protect it are released into the smoke and ash, which can be genuinely harmful to breathe in or come into contact with.
This isn’t a minor precaution to skip if you’re in a hurry to clear old decking. The chemicals involved can cause real health problems, and burning treated wood in a domestic fire pit, bonfire, or wood burner is generally something we’d advise against entirely.
What Exactly Is in Pressure-Treated Timber?
It helps to understand what pressure treatment actually involves to appreciate why burning it is a genuine concern rather than an overcautious rule. The process forces preservative chemicals deep into the wood fibres under pressure, rather than simply coating the surface, which is why treated timber resists rot and insect damage so much more effectively than untreated wood over a long outdoor lifespan.
Modern treatments typically rely on copper based compounds, often combined with additional fungicides or insecticides depending on the specific product and manufacturer. These compounds are formulated to leach out slowly over the wood’s working life to protect it, which is a very different process to what happens when the same wood is rapidly combusted in a fire. Burning concentrates and releases these chemicals into smoke and ash far more quickly and directly than their intended, gradual outdoor breakdown, which is the core reason domestic burning of treated timber carries real risk.
The Older Timber Treatment You Should Be Especially Cautious Of
One specific concern worth flagging clearly is CCA treated timber, an older type of pressure treatment that used a combination of chromium, copper, and arsenic to preserve the wood. While CCA treatment has been largely phased out in favour of less hazardous alternatives, older decking installed some years ago may still contain it.
Burning CCA treated timber releases arsenic and chromium compounds into the smoke and resulting ash, both of which are genuinely toxic. If you’re unsure how old your existing decking is, or whether it might have been treated with an older preservative like this, it’s safest to assume it could be and avoid burning it entirely.
- Modern copper based treatments are considered less hazardous than older CCA treatments, but still shouldn’t be burned domestically.
- Older CCA treated timber carries a more serious risk, given the arsenic and chromium content, and should be treated with particular caution.
How to Tell If Your Old Decking Might Be CCA-Treated
Since CCA treated timber often looks similar to more modern preservative treated wood once it’s aged and weathered, visual identification alone isn’t always reliable. As a general guide, decking installed longer ago, particularly anything approaching or exceeding 15 to 20 years old, carries a higher likelihood of CCA treatment, since this preservative was far more widely used before regulatory restrictions tightened.
Older CCA treated timber sometimes shows a very faint greenish tint when freshly cut, even beneath a weathered grey exterior, though this isn’t a reliable enough sign to base a safety decision on alone. If you’re genuinely unsure of your decking’s age or treatment history, the safest and most straightforward approach is simply to treat it as potentially CCA treated and avoid burning it under any circumstances.
What About Untreated Hardwood Offcuts?
This is where the answer becomes less straightforward. Truly untreated hardwood, with no oils, varnishes, or sealants ever applied, could theoretically be burned more safely than pressure treated softwood. However, in practice, most hardwood decking, including species like Balau, is typically finished with an oil or protective coating at some point during its life, whether at installation or through ongoing maintenance.
If your hardwood offcuts have ever been oiled, varnished, or sealed, it’s safest to treat them the same way you would pressure treated timber and avoid burning them. The specific chemicals in oils and sealants vary, but many aren’t intended to be safely combusted, and identifying exactly what’s been used on a given piece of offcut timber isn’t always straightforward.
| Hardwood Condition | Recommendation |
| Genuinely untreated, no finish ever applied | Lower risk, though still worth caution |
| Oiled, varnished, or sealed at any point | Avoid burning, treat as you would treated softwood |
| Unknown treatment history | Avoid burning to be safe |
If you’re planning a new deck and want to understand more about how hardwood species like Balau are treated and maintained over their lifespan, our guide on the best wood for UK decking covers this in detail, which also helps explain why most hardwood offcuts carry some form of finish by the time they’re eventually replaced.
Composite Decking Offcuts: A Different Set of Risks
Composite decking presents an entirely separate concern when it comes to burning, since it isn’t simply timber with a chemical treatment applied. Composite boards are manufactured from a mix of wood fibres and recycled plastic, meaning burning them releases the same kind of harmful compounds associated with burning plastic waste generally, alongside whatever additional chemicals are used in the board’s specific manufacturing process.
Composite offcuts should never be burned domestically under any circumstances, and should always be disposed of through appropriate waste channels, ideally following any specific guidance provided by the board’s manufacturer for end of life disposal.
Why This Risk Is Often Underestimated
A lot of homeowners genuinely don’t realise burning old decking carries any risk at all, largely because a single evening’s bonfire doesn’t produce an obviously dramatic reaction, and the health effects of chemical exposure from smoke inhalation aren’t always immediately apparent in the way an acute injury might be. This gap between the invisible nature of the risk and the visible convenience of simply burning old boards is exactly why the practice persists more than it probably should.
It’s also worth noting that this isn’t only a concern for the person lighting the fire. Smoke from burning treated timber can drift into neighbouring gardens, affecting people who never made the decision to burn the wood in the first place, which is a further reason to avoid this disposal method entirely regardless of how contained the fire itself might seem.
How to Dispose of Old Decking Wood Safely
Rather than burning old decking, the safest and most straightforward option is to take it to a household waste and recycling centre. Most local councils accept treated timber at these facilities, where it can be disposed of correctly rather than ending up in a fire pit or bonfire.
- Household waste and recycling centres. This is generally the most accessible option for most homeowners, and most centres are set up to handle treated timber correctly.
- Council bulky waste collection. Some councils offer a collection service for larger amounts of waste timber, which can be useful if you don’t have easy transport for a large volume of old decking.
- Licensed waste removal or skip services. For bigger projects with a significant amount of old decking to clear, a licensed removal service or skip hire can handle disposal properly and in bulk.
Whichever option you choose, the key is making sure the timber goes through a proper waste disposal route rather than being burned, which avoids the health risks associated with the chemicals involved.
What Happens to Decking Wood at a Waste Facility
It’s worth understanding roughly what happens to treated timber once it reaches a proper disposal facility, since this helps explain why this route is genuinely the safer option rather than simply the more inconvenient one. Treated wood taken to a household waste and recycling centre is typically sorted separately from general or untreated wood waste, since it requires specific handling.
From there, it’s usually processed through controlled industrial facilities designed to either safely combust the material under regulated conditions with proper filtration, or in some cases process it for alternative uses that don’t involve combustion at all. This is a fundamentally different process to a domestic bonfire or fire pit, which has no filtration, no chemical containment, and releases everything directly into the immediate surrounding air.
Planning Ahead When Replacing Old Decking
If you know you’ll be replacing an old deck at some point, it’s worth planning disposal into the project from the outset rather than treating it as an afterthought once the old boards are already removed and piled up in the garden. For smaller projects, a trip to a local household waste and recycling centre is often perfectly manageable in a car or small trailer. For larger gardens or full deck replacements, arranging a skip or licensed waste collection alongside the installation itself tends to be the most straightforward approach, since it avoids old timber sitting around the garden for an extended period while alternative disposal is sorted out.
Many decking installers, including our own team, can also arrange removal and correct disposal of old boards as part of a wider replacement project, which removes the need to sort this out separately once the new decking work is underway.
Case Study: Safely Removing and Disposing of Old Treated Decking
One of our typical decking rebuild projects involved a customer in South East London whose existing pressure treated softwood deck, installed roughly 15 years earlier, needed removing before a new hardwood deck could go in.
Project details:
| Detail | Specification |
| Old decking type | Pressure treated softwood, approx. 15 years old |
| Garden size | 20m² |
| Disposal method | Household waste and recycling centre |
| Customer’s original plan | Considered burning old boards on a bonfire |
What we advised: The customer had initially planned to burn the old boards on a bonfire to save on disposal costs, unaware that the pressure treatment used on the original decking would release harmful chemicals when burned. We explained the risks and arranged for the old timber to be properly removed and taken to a household waste and recycling centre instead.
Result: The old decking was disposed of safely and correctly, avoiding any exposure to the chemicals that would have been released had it been burned, and the customer’s new hardwood deck was installed without any unnecessary safety risks along the way.
Frequently Asked Questions
Can you burn old decking wood?
No, most decking wood, particularly pressure treated timber, shouldn’t be burned, as it releases harmful chemicals from the preservatives used to treat it.
Is it safe to burn treated decking in a fire pit?
No, burning pressure treated decking in a fire pit or bonfire releases the same harmful chemicals as burning it anywhere else, and should be avoided entirely.
What makes older decking wood particularly dangerous to burn?
Older decking may have been treated with CCA preservatives, which contain arsenic and chromium. Burning this timber releases these toxic compounds into the smoke and ash.
Can I burn untreated hardwood decking offcuts?
Only if the wood has genuinely never been oiled, varnished, or sealed. Since most hardwood decking receives some form of finish over its life, it’s safest to avoid burning unless you’re certain of its treatment history.
How should I dispose of old decking wood?
The safest option is to take old decking to a household waste and recycling centre, or arrange a council bulky waste collection or licensed removal service for larger quantities.
How can I tell if my old decking is CCA-treated?
Visual identification isn’t always reliable, but decking older than around 15 to 20 years carries a higher likelihood of CCA treatment. If you’re unsure, it’s safest to assume it could be and avoid burning it.
Is composite decking safe to burn?
No, composite decking should never be burned domestically, since it releases harmful compounds similar to burning plastic waste, alongside chemicals from its specific manufacturing process.
Get a Free Quote for Decking Removal and Replacement
If you’re replacing old decking and need it removed and disposed of safely, JPD Landscaping & Building Services offers free quotes across South East London.
