Common Mistakes To Avoid When Installing Composite Decking

If you are carrying out improvements on your garden, composite decking can be the perfect way to create a space your whole family can enjoy.

Decking is excellent for those that would love the versatility of a patio but have an uneven garden. It is also a fantastic idea for people that want to separate their garden into different sections.

Composite decking is a popular choice for gardens across the UK. However, if you plan to install it yourself, you should take a look at the common mistakes to avoid when installing composite decking that we have detailed below.

What is Composite Decking?

Composite is one of the most popular materials for decking because it is low-maintenance and durable. It is made from a combination of recycled plastics and reclaimed wood.

The wood and plastic composite is held together by a binding agent to create a robust and dense material that offers a number of benefits over wood alone.

Composite decking is a wonderful choice if you are looking for an eco-friendly way to enjoy durable decking. Using recycled materials minimises waste and is an excellent alternative to traditional wood decking.


Why Choose Composite Decking?

Any garden project will be an investment, and you will want to ensure you get value for money in the design and materials you use.

Here are some of the top reasons people choose composite decking boards over wood.



Wood decking has a beautiful natural finish to it that will require treatment if you are looking for a different colour. You will be able to choose the colour of your composite deck before laying it without having to do anything to it.

The composite decking available at Ecoscape offers a natural wood look and is available in a range of colours. These include;



Composite decking boards offer a hardwearing, splinter and split-proof surface. This is perfect for anyone looking for a long-lasting surface that is safe for bare feet to walk on.

Ecoscape composite deck boards come with a residential warranty of 20 years. This gives homeowners peace of mind that they will enjoy value for money.


Low Maintenance

Wood decking requires a considerable amount of care and maintenance to ensure it stays in good condition.

Wood requires protection from the elements; sealing it against the sun, wind, rain, and frost can be time-consuming.

Replacing rotten or splintering parts over time and protecting wood against pests can also take up a lot of time.

Composite decking does not have any of those problems, and the only maintenance you will need to worry about is a general cleaning and sweeping.


Slip Resistant

Wooden decking has the potential to become slippery in inclement conditions. Your Ecoscape composite deck features excellent anti-slip qualities. This makes it a great option for families with young kids that like to run about or for older people that want a secure surface to walk over.


Easy Installation

Composite decking boards are easy to install, and you will have a choice between a solid plastic or aluminium sub-frame. You can then lay the frame on concrete blockwork, plastic posts, or the adjustable pedestals that are provided.

Attaching the starter clips to the frame’s perimeter and screwing the T-clips into the frame will allow you to easily clip your decking boards in securely.

To avoid any issues when laying your composite deck, take a look at the most common mistakes to avoid when installing composite decking later in this guide.


Cost Effective

While composite deck boards are typically more expensive than traditional wood deck boards, they offer great value for money because of their durability and longevity.

Traditional wooden decking will typically last between 10 to 15 years. Composite decking can last twice as long with significantly less maintenance.

The cost and time you will have to take to maintain wooden decking should also be considered, with stain, sealant, cleaning products, and replacing worn boards all adding up.


Common Mistakes To Avoid When Installing Composite Decking

Installing composite decks is relatively straightforward, but that doesn’t mean you shouldn’t take care during the process.

Here are the most common mistakes to avoid when installing composite decking;


Weak Deck Framing

If the ledger boards are not fastened to the house correctly or with the proper hardware, you might find you have issues. Securing the deck frame correctly improves the structural integrity of the outdoor decking.

Flashing ledger boards correctly to allow for water drainage beneath is also essential.


Substandard Subframe

If you are replacing existing decking, you might think using your existing subframe could save you time.

The chances are that your previous subframe will have some wear or erosion caused by standing water at some point.

If your previous deck was timber, the subframe might not be up to the job of supporting a composite deck.

Composite deck boards are significantly heavier than timber and require additional support.

The decking joists and subframe create a structure that supports your decking. This structure is a vital part of your decking that provides load-bearing strength and prevents warping.

Another issue with using a pre-existing subframe that previously held timber decking is the joist centres can be too wide to adequately support composite decking.

Timber subframes designed for timber decking will typically have joist centres of around 500 mm.

This is suitable for timber decking that has less flex than composite decking. While composite decking has more flex because of the plastic in its composition, it is still incredibly strong.

Joists placed between 250 mm and 400 mm apart will be suitable for composite decks.

On more extended decks, double joists will provide the support needed when boards butt against one another.

This will prevent splits or slips and allow for expansion gaps between boards. It also allows the water to drain freely between the gap. Please see page 21 –


Untreated Joists

Depending on the type of subframe and joists you install for your decking, it may need to be treated.

If you have a timber subframe or joists below your decking, ensuring the timber has been treated is vital to its longevity and performance.

Timber joist ends can often be missed if they are treated after construction. When an end is butted against a wall, finished wall assembly will make it impossible to treat, but it can still be susceptible to taking on moisture and weakening over time.


Missing Lag Head Screws

Lag head screws are essential and can prevent the collapse of your decking.

If you don’t see lag head screws after the ledger board is attached, it is a good idea for a professional to resolve the issue.

They might be able to add lag head screws to your existing frame before you can carry on.


Poor Ventilation

Composite decking is great for the UK weather because of its waterproofing properties.

It is still important that the deck has a clearance of around 12 mm from the frame for ventilation and drainage.

This will help minimise the risk of mildew or mould growth.


Forgetting About a Drainage Slope

Anyone laying decking will typically be armed with a spirit level, but a perfectly level deck could prove to be problematic in the future.

Just a 1% fall will allow water to drain from the decking without making a noticeable difference to it.

While composite decking has anti-slip properties, standing water could still cause issues. Allowing water to run from the decking is vital for anyone living in the UK.


Not Allowing the Composite Decking to Acclimatise

Prior to installation, it is advised to place the composite deck in the environment it will be fitted for up to two weeks.

Different areas in the UK have different humidity and temperatures, so allowing the composite deck boards to acclimatise is recommended.

The dimensions of the composite deck boards can change in different climates, and cutting before they have settled can lead to installation problems.


Shallow Deck Footings

Laying the foundations for your decking is an important part of the process. A solid base will ensure your decking is long-lasting.

Creating a firm, level surface to lay your decking is essential, and concrete can be the perfect solution.

If you do use concrete as your base, you should ensure you have drainage to minimise the risk of water pooling.

The concrete deck footings must be below the frost line so cold weather does not damage them.


Mismatched Fasteners

Using your own parts to fit a composite deck might seem like a good way of saving money. You might have used fasteners and screws for other projects and trusted them for the job, and want to use them for laying composite decking. This should be avoided.

Composite decking suppliers will typically include everything you need. This will include deck fasteners and screws that are designed specifically for the decking you are using.

Even screws or fasteners that are close fits can result in a poor finish or affect the performance.

Composite deck boards are hardwearing and durable. However, using the wrong parts so they aren’t fitted correctly can take its toll and decrease how long they will last.

Always check the instructions and parts list that comes with your decking to ensure everything you need has been provided.


Incorrect Installation Method

When you install your composite decking, you must ensure the gaps between adjacent deck boards are no less than 5mm. Clearance between the decking and your wall should be no less than 5mm.

Incorrect installation and extending panels to the covering deck end can cause problems with gaps being filled with dirt and moisture pooling.


Ignoring Supplier Instructions

While the process of creating composite decking can be similar, products from different suppliers can have different compositions and designs.

Anyone that has worked with composite decking before might feel confident that they understand the methods that should be used for different suppliers’ materials.

Experience in laying decking can be great, but using the installation guide from the supplier is essential to ensuring your decking is laid correctly.


Using the Wrong Subframe Material

The materials you use when building a subframe will determine the stability and longevity of your composite decking.

Roof terraces will benefit from steel subframes as they are self-anchoring.

If you plan on using timber, you should use wood that can bear the weight of the decking and is suitable for the climate.

Using pressure-treated lumber for your sub-frame can provide greater longevity and durability. Pressure-treated lumber has fungal and insect resistance, and it will last longer in wet environments than regular timber. Decking tape is advised when installing a timber decking frame. At Ecoscape we have both a 54mm and 100mm deck tape available.

Plastic lumber can be a good choice for wet areas or locations with a high water table. Wood will degrade and rot over time when exposed to moisture for a significant time.


Improper Board Spacing

The spacing between decking butt-ends must allow for expansion. If boards are pressed too tightly together, and the temperature causes them to expand, it can cause them to twist, crack or warp.

The following distances should be sufficient for the preceding temperatures;

  • 5°C – A 5.5 mm gap is advised
  • 20°C – A 3.6 mm gap is advised
  • 30°C and above – A 2 mm gap is advised


The above gaps are based on a 3m long composite deck board. Please review our expansion and contraction table on page 34 in our installation guide for further information.


What Else Needs to Be Considered When Installing Composite Decking?

While we have covered the most common mistakes to avoid when installing composite decking, there are other things that need to be considered when installing your decking.


The deck size

The size and positioning of your decking are important to consider. In the UK, decking that is to be positioned more than 30 cm above ground level or that covers over 50% of the garden area must receive planning permission.

Failure to get this prior to installation can result in legal penalties, and the decking will typically have to be removed.

Always run your plans past the local planning authority and speak with neighbours who may be inconvenienced or affected by the decking to avoid complications.

The size of the deck you decide on will be down to your personal preference. Most decks tend to be wide and run along the house.

A deck that is out of proportion with your house can look out of place. One way to avoid this is by building a deck that does not exceed the size of the house’s largest room.


Ensuring your deck is safe

Safely installing composite decking should be a priority. If your new composite decking has steps leading down to your garden, installing a handrail will improve safety.

Failure to install a handrail can contravene building regulations. It is always worth checking whether your plans require handrails.


Handling and storing your decking

Storing and handling your decking before installation is an important consideration.

Keeping the boards in a dry, shaded area is important as thermal expansion and contraction in extreme temperatures effects composite products.

Composite boards should be stacked on a level, firm surface. Stacks should not exceed 3 m in height.

Boards should not be dragged or slid as this can damage the finish. Instead, they should be held at the middle and edge when transporting them.


Finding the right fixtures to compliment your new decking

Choosing the perfect deck board colour to compliment your home and garden is easy with the excellent choice of Ecoscape composite decking. But it is essential that you compliment this with the right furnishings.

You might be tempted to reuse existing garden furniture, but this can sometimes look out of place.

Repainting or getting new furniture to compliment the new decking will help to make this space the relaxing oasis you dreamed it would be.


Stopping animals from getting underneath

Allowing space for drainage is essential. Your deck frame should also provide a solid base that will last for a long time.

Unfortunately, the space below your decking can make the perfect shelter for small animals.

As well as being sheltered, animals might also find small scraps of food that are dropped and find their way between the boards.

To stop small animals nesting beneath your decking, you should block off any potential entrances.

You can face off the side of the deck with a deck board or a composite decking fascia. Other to this and a cheaper option is to use Chicken wire and mesh, it can be a great way to stop small animals and vermin from making their way beneath your new composite decking. This should also stop leaves from being blown under, which can cause issues with drainage.



Is composite decking expensive?

Making the right decking manufacturer choice will help you find the best composite decking.

Composite decking is relatively expensive compared with other decking choices, but it still offers great value for money.

Composite decking has great anti-slip properties, making it perfect for use in the UK. It is also durable, long-lasting, and low maintenance.

The following prices are averages for composite decking, and prices may vary;

  • Uncapped hollow core composite decking – £35 per square metre.
  • Solid core composite decking – £60 per square metre.
  • Capped solid core decking – £80 per square metre.
  • PVC composite decking – £40 per square metre.


Labour and installation costs will typically set you back around £200 per day for a professional. If you are not experienced with this kind of work, hiring a professional is recommended.

Poorly installed decking can be expensive to fix. If it is not fixed, it could collapse.


How long does it take to install composite decking?

Composite decking installation will typically take between 1 and 3 days. This will depend on the size of the area and the work needed to create a suitable sub-frame. Our regular trade customers allow 1 day to install 10m2.


What time of year is best to install composite decking?

Composite decking can be installed at any time of the year. This can be a bonus as professional installers are less likely to be busy during the winter. It also means you don’t have to miss out on being in your garden during construction, and your new decking will be ready to enjoy as soon as the weather picks up.


Final Thoughts

Composite decking is an excellent choice for transforming gardens into usable outdoor spaces.

The hardwearing, long-lasting decking will typically involve a great initial outlay but will last considerably longer.

You will also save time and money with composite decking as it won’t need the traditional upkeep timber does.

Installing composite correctly will play a significant part in how long it will last.

It is advised to use a professional for installing composite decking to ensure it is completed correctly. Only take this task on yourself if you are experienced.

By following the supplier’s instructions and keeping an eye out for the common mistakes to avoid when installing composite decking that we have mentioned, you should be able to enjoy a wonderful addition to your home.

Even small mistakes can compromise the finish or structural integrity of your decking. Ensuring the job is completed correctly and keeping it clean and free from debris will make sure it looks great and lasts as long as possible.

Gary is the founder and CEO of Ecoscape UK. Gary graduated from Liverpool JM University in 2007 with a 2:1 in Economics. A passion for innovation, design and sustainability, Gary has put to market numerous wpc products/systems, some of which have UK and European registered designs. Outside of work Gary enjoys spending time with his family, the great outdoors and watching Manchester United.