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Can You Screw Down Composite Decking

There are many reasons why people choose composite materials for their decking construction projects. One of its advantages is the ease of installation. Similar to wood, there are many options for how to install composite decking. It’s a matter of choosing which one you prefer. Usually, the first method that comes to mind is simply screwing into the boards. But the question is, can you use screws to install composite decking?

It is not advised to screw or drill directly through hollow composite decking boards. You can only drill through solid composite decking (must be pre-drilled). You should also check with the manufacturer on how they recommend fixing their composite boards to the subframe or joists underneath your decking area to ensure any warranty is not void.

Always Ask the Manufacturers

If you are building a composite deck, it is best to read all the instructions and guidelines supplied with the boards. If you have questions, it is best to contact your supplier or the manufacturer for correct advice and guidance on the types of screws recommended for the decking boards purchased.

Hidden Fastening Systems

Composite boards are not designed to be screwed directly into, as they usually have a channel running down the side of the board to fit a clip. These spaces make it possible to use hidden fastening systems. The hidden fastening system is a clip that fits into the grooves, which is then screwed into the joists. People who use these can have the benefit of not having any visible screws on their decks. They can also be easily removed without damaging the decking boards, please note our reference in easily removed is using the ultra clip or a plastic clip. This is the most aesthetically pleasing method and the safest, as it will not damage the structural integrity of your boards later.

What Screws Should You Use for Solid Composite Decking?

When installing solid composite decking, it’s very important to use screws that are designed for use with composite materials. The material must be compatible with the screws that you are using in order to avoid issues such as cracking and splitting in the surface of the decking further down the line. The screws used for solid composite decking typically have a type 17 drill point to prevent splitting, with coarse thread design providing better grip and holding power in the material. You will also note that most composite screws have a reverse upper thread and a undercut head to help to prevent mushrooming. Although timber decking screws may also have a coarse thread, the design may be adapted to the specific properties of timber or composite, such as its density.

Solid composite decking will also require pre-drilling to prevent the composite decking from splitting as it expands and contracts over time. Timber decking may not require pre-drilling, depending on the type of wood and screw design.

A common issue that you see when screwing directly into composite decking is mushrooming. This is where the area around the screw head elevates, therefore creating a raised area that looks like a mushroom. By designing the screw with a reverse thread near the top of the screw, this prevents this from happening. Manufacturers also design this screw with a curved inward face, which is described as concave. The purpose of this is to achieve a smooth and flush finish, avoiding any protrusions or uneven surfaces. In summary, the concave face is used to press material down and create a level finish.

How Many Screws Should You Buy?

There is no straightforward answer to this question, as not all decking is the same. Several factors might affect how many screws you will need.

Here are a few things you should consider.

  • Deck Dimensions – First, you will need to consider the dimensions of your decking area, including the height, width, and length. The bigger and more spacious your deck, the more screws you will need.
  • Deck Board Spacing – Composite decking boards require spacing between the boards. Decking boards require space to give way for occasional contraction and expansion due to temperature changes.
  • Joist Spacing – Another crucial detail to consider is the frame. Similar to decking boards, you also need to have proper spacing, especially for the joists. In decking, it is often 300mm on-centre. The joist spacing will determine how stable the boards will be. The more space there is between the joists, the fewer screws are required.
  • Screws per Decking Board – You will also need to count how many screws you will use for each board. Most decking boards will require two screws each to secure them onto the decking joist. As for decking boards for rim joists, many recommend using at least three screws.
  • Hidden Fasteners – Hidden fasteners do not use the same traditional method of laying the decking boards. These fastening systems use clips inserted into the grooves of the deck boards. As there are several varieties of clips and fasteners, the number of screws needed can vary, but on average you will require half the amount compared to screwing the board into position.

Most professional builders estimate the number of screws by the total square metres of the deck area. For standard composite decks with 3.6m/3600mm in length and 300mm joist centres, you will need at least 100 hidden fasteners for every 4 square metres installed.

This is worked out from the boards length and the joist centre. So for composite decking with hidden clips you take the boards length 3600mm and divide by joist centre in this case 300mm = 12 clips and screws every 3.6m board.

Now if your not using clips you will need to fix the board into position using 2 screws on each joists, so again 3600mm length of the board divide by 300mm joist centre give you 12, but your using two screws when your not using clips, so double it, meaning you need 24 screws for each 3.6m board.

Based on you using screws to fix your boards into position each 3.6m board is almost equal to half a sqm, so you will need 50 screws every 1 sqm, that’s 200 screws every 4 sqm. Since most hidden clip fastener systems require fewer screws, you will need 100 screws for the same 4 square metres area.

How to Best Secure Composite Decking

1 Use The Right Screw

There are different types of screws. Depending on what you use, there will be a significant difference in performance. For instance, traditional wooden screws work well with wooden decking. However, they might not be suitable for composite decking. Composite decking screw as mentioned above require a type 17 drill point with a coarse thread design and reverse upper thread.

2 Don't Screw Down Hollow Boards

Hollow composite decking must not be screwed through from the top of the boards due to structural stability. Use the manufacturer’s approved hidden fasteners to securely fix composite decking boards to the subframe or joist underneath.

3 Thicker Screws

Screws tend to be thicker because of the threads. It makes screws stronger when it comes to holding down the decking boards and the joists. However, this thickness has its downsides. While composites are not prone to splitting, that does not mean they’re invincible. Placing the screws improperly can damage the boards and leave lasting marks on the surface.

4 Use Hidden Fasteners

While not all people mind it, some people don’t want the look of screws on their decks. Instead, they want a seamless and smooth design. This is why hidden fasteners are a great option.

5 Screws Loosen

While not as prone as nails, screws can loosen up due to the expansion and contraction of the decking materials. This rarely happens with composite decking. If it does, it could pose a safety risk to people using the deck.

6 Pre Drill

Most composite decking materials are known to be dense and durable. Because of this, using screws to install them can be quite difficult. You might need to pre-drill the materials before you can screw them down. Doing this adds budget and time to a deck construction project.

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