How To Build A Composite Deck

Building a composite deck is among the most cost-effective ways to improve your outdoor living space and perfectly enjoy the open air. This decking is a durable, safe, and eco-friendly replacement for natural wood.

You usually need to hire a professional contractor to install Trex decking, and you may have to pay for architectural blueprints. However, we’ve gathered all the information necessary to make constructing a deck easier.

With less common knowledge about building anything besides timber decking, it can sound like a different concept entirely when it comes to composite decking. Discover your motivation and learn the main steps of the deck-building process with our instructional article.

What Is Composite Decking?

Composite decking is generally assembled from a combination of recycled wood and plastic, which are manufactured to give the appearance of wood.

The wood portion contains lumber industry biproducts, such as wood fibers, sawdust, and chips, and plastic may consist of shredded polyethylene from milk jugs and shopping bags. The resulting deck boards last longer than standard wood decking and are easy to maintain.

How much does composite decking cost?

Composite decking has a higher initial cost than other deck materials. Its installation costs about $30 to $60 per square foot, including the substructure. Materials, deck size, and labor costs are all factors behind deck pricing.

Installing the deck yourself is a great way to save on your composite deck costs. Many DIYers prefer composite decking for its longevity and efficiency. New composite material is cooler on bare feet than wood, low-maintenance, and relatively invulnerable to weather.

Following the manufacturer’s instructions when building with the composite decking material is paramount. The composite deck changes its size due to temperature. It will grow longer and shorter as temperatures rise and fall; therefore, follow correct spacing to prevent warping.

Types Of Composite Decking

  • Solid Composite Decking – Solid composite decking is solid with no material reduction designs. They look more like natural lumber. Solid composite boards are firm and durable, used often to make permanent floors for houses, offices, and hotels.
  • Hollow Composite Decking – It’s a decking that has holes inside them, making them a lightweight option for a composite deck. The holes in the decking also help it to grow and shrink smoothly. End caps are used to cover the ends of hollow boards.

  • Whatever the type of composite decking, both will give you a solid and long-lasting deck. The product must be treated with a preservative and antifungal chemical. Your timber will rot gradually when exposed to weather conditions without treatment.

Steps For Building A Composite Deck

Composite decking materials add finesse and resilience to any deck. Here’s how to install composite decking and deck railings.
A man is holding a piece of wood on a decking.

Before Starting

Before you get down to business on your new deck, look carefully at everything you will use in your deck project. Your materials will depend on the deck boards you’ll be using, but usually, you will observe that your composite decking can be established with standard woodworking tools.

Opt for lighter boards to maintain a cooler deck. The lighter the colour of your boards, the less heat they absorb in direct sunlight.

Preparing The Ground

You have to prep the site on which your decking will sit. Building your decking on level ground is vital to preventing the deck boards and substructure from being moved and subjected to buckling.

If you’re building your own deck over the lawn, outline the area with pegs and builder lines. Remove the grass and excavate the soil about 2 inches deep. Cover the area with a layer of weed control fabric to control damaging weeds from rising through to your decking boards. Then add 2 inches of gravel on top to help with proper drainage of water. Then put paving stones over the gravel, which will adequately reinforce the joists and maintain the deck. Place a spirit level to ensure the stones are all on the same level.

If you want to build your composite deck beside your house, ensure it’s not less than 6inches below the damp-proof course and that you don’t conceal any air bricks. You also have to elevate your frame away from the surface by installing it on a network of pedestals to avoid compromising the roof’s waterproof membrane.

Building The Deck Frame

Before you can lay boards, you have to build the frame. And this is done using wood.

The vital part of your framework is the bearers – the strong timbers that support the deck. They carry most of the weight from the decking and ensure your finished deck is secure and stable.

Determine Deck Spacing

  • Joist spacing – Deck joist spacing must never exceed 16 inches on the center. Local building codes may set a joist spacing. It is advisable to check in with your local building department to meet their requirements.
  • Butt-end spacing – Boards expand during the hot season and shrink during the cold season, so monitor the thermometer throughout the installation. Observe the manufacturer’s spacing specs to deter your boards from damage.
  • Edge spacing – A general benchmark with edge spacing is not to allow the spacing to be overly distant, that it is a risk, and not too narrow that debris or water to become stuck. You can use 16d nails to allocate the between-board spacing. With a hidden fastening system, the spacing is fixed for you.

Shape Your Deck Plan Using Deck Boards

Place a mock-up shape of the deck with timber or deck boards. A wood outline presents a reliable beacon for pinpointing deck footing spots and establishing post bases. You can mark the structure area by planting stakes, enabling you to take the boards out to dig holes or pour footings. Then you can easily replace your outline planks to arrange post bases or lay posts.
A man is building a deck.

Square Your Deck Frame With A Ledger Board

The best way to square a deck is to use the 3-4-5 method. Measure and mark the top of the ledger board 3 feet away from the corner. Then, on the top of the side rim joist, measure 4 feet from the same corner and mark this also. Measure between the two marks. The marks must be 5 feet apart.

Attach And Protect The Ledger

Remove the siding or cladding and expose the home’s band joist. Then verify the height of the ledger board. You have to cover any holes with back flashing. The deck ledger board must be attached to the side of the house using non-corrosive carriage bolts that pierce deeply into or through the house sill plate.

After fastening the board to the exterior sheathing, apply silicone caulk along the seam where the ledger meets the house. Then install metal flashing across the entire length of the top of the ledger. Drive roofing nails through the flashing’s top edge every 8 inches.

After adequately establishing the flashing, install the siding above the ledger as needed. Slip the siding up under the siding board above. Use the 1-1/4″ spacer board to position the siding at the correct height and drive nails to fasten it.

Use joist hanger nails to affix concealed-flange double joist hangers at both ends of the ledger and flush with its bottom edge.

Install A Diagonal Brace

If you’re installing a horizontal decking, a diagonal sway brace must be affixed to provide lateral stability and prevent the deck from rocking back and forth and collapsing. You may mount a metal “T” brace (a long metal strip) diagonally across the deck joists or attach a diagonal deck board across the bottom of the deck frame.

A diagonal decking does not need sway bracing.

Smooth Out The Joists

Most composite and PVC products are not chiselled compared to wood decking. If some of your joists are higher than others, you might have an uneven surface. You have three options to grade the joist – a belt sander, wood planer, or circular saw.
A man using a power sander to refinish a wooden deck.

Mounting The Railing Posts

For composite decks, mount the posts to the inside of the joists.

Determine The Post-Spacing

Begin by measuring one deck flank between the two corner posts and divide by the distance permitted between posts. Ensure the posts are evenly spaced. You can shift it slightly if one lays up over a joist.

Cut The Posts

Cut the railing posts to length as specified on your plan and local regulations. The bottom ends of the posts will be flush with the bottom of the framing.

Install Deck Bracing

You’ll have to use the same wood to build the frame to support the railings. The bracing extends over the spacing between joists, so measure this space and trim the wood to length. Then, position a piece of the bracing adjacent to where the post will sit and use deck screws to attach extra bracing.

Install the Posts

Start placing the posts along an end joist. Each post must lean against the joist on one side and the bracing on another. Screw a post in position, ensuring it’s plumb and extends to the bottom of the joist.

Mark The Joists And Drill The Holes

Measure and mark 1 inch from the opposite sides and 1.5 inches from the top or bottom of the joist with a tape measure. At the marks, drill holes the same diameter as the carriage bolts you will use.

Tilting the holes prevents the post from splitting along the grain lines.

Install Anchor Bracing

Affix the first anchor bracing by supporting it over the uppermost hole you drilled. Introduce a carriage bolt through it and drive the bolt in with a rubber mallet. Under the deck, fit in a washer and tighten a nut for each bolt. Fasten the other end of the anchor with screws.

Each post should have two carriage bolts, but only one anchor.

Brace The Rim Joist

Corner posts are the strongest. Add similar bracing perpendicular to the railing. Then back nailed from joist to block end and toe-nailed.
A man climbing up the side of a wooden deck fence.

Laying The Deck Boards

Once the frame is welded, you can set up the decking. Use hidden fastener clips and grooved composite boards for a more natural impression.

Hidden fasteners work best for securing composite planking and can be bought at any home improvement store.

Fasten Start/Stop clips

These clips hold grooved composite boards steady. Begin on the side nearest to the house. Use screws to attach the start / stop clips flush with the rim joist, spaced around every 16 inches.

Lay The First Board

The composite boards have grooves on their sides. The board’s groove is intended to link over the clip’s prongs. Get your straightest deck board and push it into these clip prongs until tightly secured. Make sure the overhang is no more than an inch.

Screw the special clips into the first board and the frame’s joists. Make sure the screw holes are aligned with the joists’ centers and that you utilize one clip per board at butt joints and at board ends and each joist.

To estimate the number of clips you must have, multiply the number of deck boards by the number of joists.

Install The Rest Of The Composite Decking Boards

Finishing the deck requires a pattern of boards and clips. Slice the next board on the deck, affixing the groove into the free side of the previously placed fasteners. Apply a little force to ensure that it attaches solidly. Then, put deck clips on the other side of the board, and screw them.

Repeat this process for each successive decking board until you’re left with just the final decking board to lay.

Cut Holes For Posts In The Boards

Make notches on decking boards around the posts with a carpenter’s square. Drill a hole to start, then use a jigsaw to cut the decking and work around the posts as necessary. Arrange the board onto the post.

Install The Last Board

Trim the final board if need be. Like you did on the first board, use your markings to screw your hidden clips at each end of your frame and over the frame’s joists at fixed gaps.

Set the board and secure it with decking screws. You can use identical fascia boards to cover the ends of your composite boards, though this is non-mandatory.

Trim The Boards

To cut the deck boards to length, snap a chalk line across the end joist and around the sides of the deck, so they’re level with the frame. Cut along the line with a circular saw.

If you’re establishing skirting, leave a 1-1/4-inch overhang. Skirting isn’t required, though it looks pleasant. You can trim the framing so it inclines upwards towards the deck’s surface, then sheathes it with composite boards.

Otherwise, you can trim the decking flush with the joists if you do not intend to install a skirt. On the last deck board, you’ll need to cut it to work and then cut a groove into the board with a router.

Fit The Parting Boards

Parting boards offer extra water drainage. Cut the decking to suit the parting boards in the deck’s center.

You may have to use an extra joist to brace these boards. This can be achieved by picking up a piece of lumber the same length as the deck, laying it in the gap you trim.

Secure All The Boards

Secure the parting boards stably with composite decking screws. Wield a screw to place a drainage gap.

Note: It’s better to position all the screws first because adding the clips can make you forget what you’ve already finished.

Installing Composite Railings

A house with a pricey mahogany deck and stairs.

Slide On The Post Sleeves

Cut your post sleeve to one to two inches higher than the post. You want the same height in all the post sleeves relative to the deck’s surface. Slide them on the post.

Glue Post Sleeve Collars

If you are attaching collars (decorations that sit on the post footing), you must have PVC cement to secure them. Follow the package instructions for the correct application.

Measure And Mark the Bottom Rail

Measure the length between two posts and mark both ends of the bottom rail a quarter inch shorter, keeping the baluster hole spacing level between the marks. Do the same thing on the top.

Cut The Rails To Length

If the railings are lengthy, trim them based on the lengths you got previously. You can use a circular saw to do this. Note that the bottom railing will emerge slightly shorter than the top railing.

Secure A Crush Block

Apply PVC cement to fasten a crush block centred on the underpart of every bottom rail. A minimum of 2 crush blocks are needed. This crush block supports the center of the railing. Allow the cement to cure.

Ensure the holes in the bottom rail face upwards.

Trace The Bottom Bracket

Slide the brackets and flanges onto a bottom rail. Hold it against the post as you trace the bracket, and remove the rail. Then place the bracket again in your drawing and mark its holes on the post.

Install The Bottom Bracket

Drill the holes. And when done, set the flanges on the post and fasten them with screws. Follow the same method for all the posts.

Attach The Brackets And Balusters

All you have to do is slide the rail onto the bracket. Then as a guideline, insert either end balusters in position and place the top rail.

Like you did on the bottom railing, set and trace the bracket position. Repeat the installation steps, tracing the screw holes and drilling them out. Then put the flanges.

Connect the railing to the brackets and balusters

Insert all the balusters into the holes of the bottom railing. Once fixed, put the railing onto the brackets. Give it a little push to lock them in position. Place the top caps on the posts, glue them with PVC cement, and proceed to the next railing you need to establish.

Things To Remember

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  • A building permit is not needed if your deck project is lower than two feet above grade and doesn’t have a roof. But, if your deck will include a roof that’ll be attached to your house, permits will be mandated.
  • It is necessary to work safely and avoid risks. Wear protective clothes, gloves, safety goggles, and a dust mask.
  • Let the composite boards sit in your area a day or two to acclimate to your local temperature and conditions before initiating work.
  • Don’t install your DIY deck during the cold season.
  • Composite boards must be predrilled to lessen the chance of splitting or cracking. Due to similar reasons, nail guns are not advised for building a composite deck.
  • Never use random-length boards and butt-joint them together.
  • You don’t need to adhere to one product or appearance for the entire deck. You can lay perimeter boards the same colour as the railing or opt for a different post colour.


Composite decking is a cost-effective, sustainable, rot-resistant, and long-lasting alternative to natural wood. Our tutorial presents the best procedure for installing composite decking. Hopefully, you gained some helpful advice for your composite decking project.

You may also call and hire your local builders for assistance and a better deck finish.

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