Know all the facts when considering using a composite decking board

In this blog we delve behind the glossy marketing claims and discuss some of the issues with composite decking products which are not well documented. These include slip risk over time, why they are not as sustainable as many believe when looking at the whole life cycle, static shocks, the requirement for a more substantial sub structure, disclaimers on product guarantees and insufficient fire ratings when looking at the present advice.


Slip Resistance

Deck boards will be safe in dry conditions, but have the potential to be slippery when wet which could lead to personal injury and potential insurance claims. The most common hazard on deck boards is standing water after rainfall. Deck construction design and regular maintenance can aid surface run off but will not remove the hazard altogether so the potential risk will always be there if using boards without non-slip inserts. For a surface to be deemed to have a low slip potential, a pendulum test value (PTV) of 36 or above needs to be achieved on the Stanley pendulum test (BS7976). 

Many composite deck boards will achieve an initial PTV above 36 in wet conditions, however almost all will be below a PTV of 45. These ratings are achieved on brand new boards straight from the production line in controlled testing facilities. The slip resistance of boards will reduce over time due to wear and tear and as the deck is exposed to the different elements over time. Therefore composite boards are likely to become slippery after a number of years.

This is a big problem as it would be reasonable to expect your deck to last for twenty years. By choosing a board which has only been tested for an initial slip resistance, you are gambling on how long that deck will stay safe. Will it be 2, 3, 5 years? You could have a surface which has the potential to be a slip risk for over 75% of its service life.




The above photo is of a composite deck at a major visitor attraction in the UK. Slip risk needs to be considered at design stage, especially in areas of high footfall and on decks that will be used all year round in all weather conditions. The HSE estimates that slips and trips occur for 1/3rd of all accidents so you should ensure the boards are fit for purpose for the whole life span of the product.

As safety is a critical factor we would recommend a product with non-slip inserts. Our deck boards with non-slip inserts will achieve a minimum initial PTV of 85 and are guaranteed not to fall under a PTV of 55 for ten years giving real peace of mind. We re-tested our boards which had been in situ at the Eden Project for over ten years which is one of the busiest visitor attractions in the UK. The boards we sent to testing had been exposed to extremely high footfall with over one million people walking over them each year. Even after this level of use they still achieved a PTV above the initial PTV of every composite deck board on the market.  

Plastic content - Look at the whole product life cycle

Most composite products use recycled plastic polymers within their products. Polyurethane or HDPE (High-density Polyethylene) are plastic polymers which are used globally in a variety of products such as plastic bottles and unfortunately we often see them littering our lands and oceans. By re-using them in decking products the plastic content can have another use. Sounds great. Right? But what happens after the useful service life of the deck board? 

A composite deck board should provide a useful service life of between ten and twenty five years and although the deck boards may have deteriorated during it's service life and needs replacing, the polymers within the boards are still very durable and the boards are likely to last for hundreds of years after it's useful service life. 

A small number of composite manufacturers in the UK can recycle old composite boards in their manufacturing process, however the number of boards that actually go through this process is unfortunately negligible. Roughly speaking, a composite board will be 45-50% polymer and 45-50% wood content as well as containing colour additives, UV protectors, resins and fire retardants (not in all products though). As the two materials have been mixed together in the production process and with no way of easily separating the materials they cannot be recycled at a waste management centre. Polymers which haven't been mixed with other materials can be easily recycled and used again in other products. The options left for composite decking are leaving them in landfill for hundreds of years taking up space or to burn them with other waste which will release a huge amount of questionable gases into the atmosphere.

Plastic polymers are petroleum based products which require a high energy input in the production process. That coupled with the fact the polymers can no longer be recycled at waste management facilities which could then potentially be recycled over and over again if managed correctly, the sustainability credentials which are marketed are questionable as they only focus on one aspect of the product life cycle.

On the other hand, timber will grow in sustainable forests and take carbon out of the atmosphere as well as releasing oxygen as the trees grow. Roughly speaking, one tonne of carbon is stored in every cubic metre of timber. The forests also support whole ecosystems with a wealth of wildlife living within them. Every part of the supply chain is audited annually by third party accreditation schemes giving assurances to the end user that the timber is sustainably sourced. The energy required to manufacture the products is far less and every part of the tree can be used for some form of product. In managed European forests, five saplings are planted for every tree that is harvested. The expected service life of timber products varies from 15 years for treated softwood to 60 years for accoya or some hardwood species. At the end of their service life they can be used for biomass heating or re-used in other timber products such as chipboard or animal bedding. 

When looking at the whole life cycle, it is much more sustainable to choose a timber option which in many cases will match or better the product performance of a composite product. In the years to come there will be a much greater focus on the whole product life cycle and how we can move away from a consumption economy to a circular economy and re-use our resources. Composite products should be avoided if you want a product which can move into the circular economy in twenty years time.


One consideration which is often overlooked as it is very rarely mentioned in product literature is that composite decking does generate static electricity and can give users of the deck a very painful shock. The issue of static build up is increasing in the UK as our summers are becoming dryer, hotter and longer reflected by the record temperature in the UK of 38.1C recorded in June 2019 at the Botanical Gardens in Cambridge.

Static electricity occurs when there is an imbalance of electric charges. Composite decking is an insulating material because of the high levels of polymers within them. As a result of this, composite decking will gain a positive charge as energy is transferred to it (from the sun heating dust particles which are sitting on the deck). Once a person walks over the deck or pulls up a chair on the deck causing friction, this energy is then transferred causing a shock. 

Composite decks can be treated with an anti-static solution to remove this issue. The problem is that they need to be re-applied after every rainfall as this removes the solution. Therefore the maintenance team could be re-applying the treatment indefinitely which is not cost effective or practical. 

Recommended joist spans

As there are a number of different manufacturers there is a wide variety of composite products. They can be hollow or solid boards and vary in thickness between 20 and 35mm. They all have different recommended joist spans - the distance between each joist supporting the deck boards underneath to ensure the deck isn't springy under foot.

The sub structure is an important part of a decked structure as this is the part that gives the deck it's strength and is often made from structurally graded timber to ensure that it can support the expected load of the deck. A hidden cost of composite deck boards is often the sub structure. Due to the high plastic content, the recommended joist centres tend to be much narrower as they are not as strong as timber options. Recommended joist centres of 300mm is not uncommon for composite boards.

When compared to our bamboo product which has a recommended joist centre of 462mm, you will need to use over 1/3rd more joists. This will have an impact on both material costs and installation times. We would recommend considering all elements of a deck including deck boards, joists and fixings to get a truer reflection of how much the whole system will cost rather than the deck board itself.

Product Guarantees

It is reasonable to expect a 25 year guarantee to deliver just that. Especially if it has been heavily featured in a product's marketing material. However certain conditions or disclaimers are often inserted, so do check the small print on what is actually covered.

Many composite manufacturers state a guarantee period of around 20-25 years but then reading closer, this is only applicable for certain applications. Residential and commercial warranties are common place for composite products. But what actually counts as a residential or commercial project is often left out. Is a residential warranty for a person's home? Can the same residential warranty be applied to a residential development even though there maybe 100+ apartments on the scheme? Does that count as a commercial project given the value of the development? Under closer inspection, it gets very grey, very quickly.

Furthermore, many guarantees we have seen use a sliding scale so as the years go by the value of the refund or replacement you are entitled to is significantly reduced. These work by offering a full refund in the event of product failure in the first few years. After the initial time period where a full refund can be claimed, the value eligible to be claimed is reduced. After as little as ten years, the entitled refund is less than half the original purchase price. Getting into the final years of the guarantee, the entitled refund is so small, it is practically worthless. Be sure to read the small print before purchase for peace of mind.

Fire ratings

For decking products which will be used on high rise buildings such as balconies and terraces there is growing focus on fire performance. Following the Hackett Review in the wake of the Grenfell Tower tragedy the building regulations were changed meaning that products used on the façade of buildings over 18 metres (cladding and balcony components such as decking) need to achieve a minimum fire rating of Euroclass A2-S1, D0. This classification means that fires are unable to spread across the outside of a building making it much safer for residents.

In the wake of recent fires on buildings under 18 metres in height using Euroclass D fire rated materials, the CTI (Confederation of Timber Industries) have advised that all products used for cladding and balconies (deck boards) should achieve a Euroclass B fire rating in addition to a fire risk assessment.

The majority of composite products only achieve a Euroclass D rating so in the event of a fire, the products will not perform as well as a Euroclass B rated product. There are some composite products on the market which achieve a Euroclass B rating but these are very costly as fire retardants needs to be added to the boards. Timber products such as Redwood, thermowood and accoya can achieve this rating by sending the timber to a specialist fire treatment facility which can upgrade a Euroclass D rated product to a Euroclass B rating. Our Bamboo range achieves a Euroclass B rating without the need to send the boards for external fire treatment. Euroclass B products will offer a much more robust performance in the event of a fire when compared to standard products and will give peace of mind to residents and developers alike.


I hope this blog gives you food for thought and enables you to make a more informed choice when considering a decking product. We have a range of timber products at different price points which will out perform the composite alternatives and will not have any of the issues highlighted in this blog. Gripsure also offers a CPD on timber decking for specifiers which gives an overview of all the products on the marker. If you have any queries or would be interested in a CPD then feel free to get in touch with me to discuss further.

Tom Anderson -



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