How to Lay Decking

Installing a deck is a fantastic way to bring new life, style, and purpose to your outdoor space. With an attractive selection of styles, colours, and materials available to purchase, it’s never been easier to create a deck that perfectly suits your tastes and your garden. Whether you’re an avid DIYer ready to tackle the project, or a homeowner who’d just like to save a little money, building your own decking area is simpler than you may think.

Table of Contents

• What Do You Need to Lay Decking?
• How to Plan a Decking Project
• How to Prepare the Ground for a Deck
• Can I Join my Deck onto my Property?
• Can I Build a Deck Directly on the Ground?
• How to Assemble the Sub-Frame
• How to Lay Timber Decking Boards
• How to Lay Composite Decking Boards
• Additional Q&A
  • How Far Apart Should Decking Boards Be?
  • Can I Lay Decking on Sand?
  • What are the Grooves on Decking For?
  • Are Decking Boards Reversible?
  • Is it Better to Nail or Screw Deck Boards?

What Do You Need to Lay Decking?

• Your chosen decking boards
• Tape measure
• Appropriate PPE
• Builder’s line
• Club hammer
• Spirit level
• Quick-drying concrete (concrete method)
• Brick Trowel (concrete method)
• Damp-proof course (concrete method)
• Gravel
• Weed control fabric
• Edger
• Spade/Shovel
• Pencil
• Decking joists
• Coach screws
• Coach bolts
• Drill
• Sockets
• Appropriate cutting tools – Jigsaw, Mitre saw, Panel Saw, Circular Saw
• Workbench/work surface
• Sandpaper/sander
• Paint brush
• End grain protector
• Wood oil/stain/treatment

How to Plan a Decking Project

The very first step in any successful DIY project is proper planning. One of the first decisions you’ll have to make before laying a deck is deciding where it should go. There are many different factors to consider, including sunlight exposure, privacy, maintenance, aesthetics, water run-off and more. To ensure you’ve chosen the best spot for your decking, take a read through our handy checklist of planning tips below:

• Different areas of your garden will be exposed to varying levels of daily sunlight. It is recommended to avoid building in heavily shaded/damp areas, as deck boards laid under these conditions will require more maintenance and may not last as long.
• If you are constructing your deck next to a property, you must ensure that it is 150mm below the damp-proof course and that no air bricks are covered.
• Plan your deck so that the fall of the frame is 1:100 and runs away from the direction of the property. This will help with water run-off and prevent your deck surface from getting too slippery.
• Make sure to carefully plan out the area and dimensions of your deck before beginning construction. This will help to limit the need for board cutting and minimise wastage.
• Evaluate the positioning of your deck in terms of privacy. Do you want neighbours to easily overlook your decking spot? Or would you prefer your deck to be more secluded and private? If you are using your deck to surround a hot tub for example, consider how the raised height of the deck may impact its visual exposure.
• A good way to visualise the best spot for your decking is to set up garden furniture in the area that it will be placed.

Health & Safety

As with any DIY project, the most important thing should always be the safety of yourself and those around you. We’ve outlined the key safety advice that you should bear in mind when carrying out your deck construction:

• Always ensure your deck boards are firmly secured when sawing/drilling.
• Do not use any power tools if you aren’t confident and comfortable doing so.
• Equip yourself with the appropriate PPE. This includes suitable protective clothing, safety goggles, safety gloves, a dust mask and potentially knee pads. Goggles should always be worn when drilling or sawing and a dust mask should always be worn when cutting with a jigsaw or sanding the ends of wood boards. Protect your hands with safety gloves when handling/moving the deck boards or applying any kind of wood treatment.
• Having a second person on hand can be practical for heavy lifting.
• When using specialist wood treatments or wood preservers, always read and follow manufacturer’s instructions & guidance.
• Never burn offcuts of treated timber – if you unsure of the safest disposal method, ask for professional advice from your local disposal centre.

How to Prepare the Ground for a Deck

Before any deck boards can be laid, you must first prepare the area of ground for construction. This involves shaping and marking out your deck coverage as well as carefully levelling out the ground surface. To prep the area for decking correctly, utilise the following method:

1. Shaping & Marking

Using your tape measure, measure out the ground site according to your plan. Take your time with this to ensure optimum accuracy in dimensions. Then, hammer a peg securely into each of the four corners and run a builder’s line from each of the four pegs. This should create a clear map to help you visualise your decking area.

2. Clear the Area

Fully clear the area within the builder’s line, moving away all plants, rocks, weeds, and debris. Then, using an edger, cut into your lawn and bring up the loosened turf with a spade or shovel. Continue this across the entire decking area until you are left with only the bare earth beneath.

3. Check the Levelling

To ensure optimum results for your decking finish, you must ensure that the ground surface is completely level before commencing construction. Using one of your deck boards with a spirit level positioned on top, move around the area checking that the ground surface is level. If it is not, fix any unevenness and re-measure with the spirit level.

Can I Join my Deck onto my Property?

If you plan to build your deck so that it joins directly onto your house, you will first need to fix a wall plate (or ledger board). To do this:

1. Using a pencil, mark a vertical line onto the wall at the point of which the end of the wall plate will be placed against. This basically marks out the corner point of your deck.
2. If there is a window sill or step within the area you wish to build your deck, take a deck board, and position it level with the lowest part of sill/step. Mark a small line beneath the board, then move the board down 10mm to create a gap for expansion. Mark a level line across this point using a spirit level as a guide. Extend this line across the entire span of the decking area.
3. Cut the joist to length, making sure to sure to accommodate any obstacles (such as pipes) within the cut. Carefully measure 100mm inwards from one of the joist ends, make a mark, then draw a straight vertical line down from it.
4. Measure 50mm from the top of the line and 50mm from the bottom, creating marks for the pilot holes to be drilled later. Repeat at 600mm intervals across the entire length of the wood. When you reach the end of the wood, measure another 100mm inwards and mark.
5. Using a 6mm drill bit, drill pilot holes into the previously marked spots.
6. Position the wall plate so that it sits in line with your pencil marked line and use a spirit level to check it is completely even. Also make sure to double check that the deck board can fit beneath the window sill before fixing the wall plate.
7. Firmly secure or hold the wood in place, then drill guide holes into the wall using a 7mm masonry drill bit. Move the wood away and drill fully into the walls to finish the holes.
8. Push 6mm x 10mm screws through the holes in the plate and position washers (galvanised or plastic) on the end. There must be a 10mm gap between the wall plate and the wall so use enough washers to accommodate. Tighten the screws into the plugs first by hand, and then secure fully using a drill.

Can I Build a Deck Directly on the Ground?

The simple answer to this question is yes, although it can have an effect on the durability of your deck boards. You typically have two options when it comes to building a deck on grass or soil: laying directly onto the earth or building on top of concrete pads. In this section, we will talk you through the two methods so you can decide which may be more practical for your outdoor space.

Method One – Laying Directly onto Ground:

The first method is pretty quick and easy. If you want to lay your deck directly onto the ground, first cover the entire area with a layer of weed control fabric. Then, add a 40-50mm depth of gravel on top of the fabric and even out across the space.

Although this method is very simple and convenient, it can lead to some issues with longevity and maintenance after installation. When laying directly on the ground, you may find that your decking is more at risk of moisture absorption which in turn creates more strenuous maintenance and could even result in a level of damage that requires replacement.

Method Two – Concrete Pads

To increase stability and optimise the lifespan of your deck, you may find it more beneficial to add concrete pads instead. When placing concrete pads, it is vital that they are positioned correctly and completely square for the deck joists. The last thing you want is to realise your deck is wonky after installation. To prevent this, you will first need to square the site:

3-4-5 Triangle Method

The 3-4-5 triangle method allows you to easily form perfect right angles at each corner. The method basically says that say a triangle has 3 sides measuring 3,4 and 5m in length, a perfect right angle should form where the shortest sides meet.

How to Square: Step-by-Step

1. Timber Profiles

To ensure total accuracy when setting out the sub-frame for your deck, it is recommended that you construct timber profiles. To do this, simply cut three 600mm lengths of 22mm x 100mm wood per profile, then cut two of the three pieces for each at one end to form stakes. Next, secure the third piece of each with nails to join the top end of the stakes with nails.

2. Builder’s Line

After removing the existing pegs and builder’s line, secure two profiles into the ground at each corner of the site. Make sure these are positioned around 450mm from the excavated soil area with the crosspiece centre parallel with the perimeter.

Run a builder’s line from each profile and tie taught. Hang a line level from the centre of the string and hammer the profiles into the reading shows completely level.

3. Checking the Lines

To double-check that the lines cross directly at the corners, lay a joist along the edge of the excavated area. Then, place a spirit level vertically against it at its corner and adjust the lines until they cross directly above the corner of the excavated area.

4. Measure & Adjust

Carefully measure out, then apply masking tape 900mm from the corner on one line and again 1200mm on the other. If the diagonal distance is 1500mm, the corner is a perfect right angle. If it isn’t, make the correct adjustments, opening up or closing the angle until perfect.

5. Perfectly Level

When you are sure that all of the lines are level and square, pencil mark the string’s position on each crosspiece, then make a small saw cut at the mark. Tie the builder’s line in line with this cut to finish.

Adding the Concrete Pads

With the site squared, it is now time to add the concrete pads. To do this:

1. Work out the positioning of the pads and dig holes around 150mm square and 150mm deep at 2m intervals around the deck area.
2. Fill the holes to just above the ground level with quick-drying concrete. Check that the pads are level with a spirit level and straight edge. If uneven, use a brick trowel to level off whilst the concrete is in a semi-dry state.
3. Wait for the concrete to harden, then cover the entire area with weed control fabric and add a layer of gravel 40-50mm
4. Cut out squares of damp-proof course and position between the concrete and deck joists.

How to Assemble the Sub-Frame

Whether you are using timber or composite decking boards, a sub-frame will need to be assembled. Here’s how to do it:

1. Dry Run

The very first step we suggest is to map out a dry run of the decking first to ensure the plan of the area fits practically with the boards. Place down the joist frame, then position the deck boards on top, making sure to leave the correct expansion gaps.

2. Measure & Cut

With the dry run complete, carefully measure up your deck frame and cut to size. Take your time with this to ensure optimum accuracy and clean results.

3. Mark & Drill

Draw two pencil lines on each end of the two outer joists as a guide for the coach screws. Make sure the marks align with the centre of the adjoining outer joist. In total, you should have eight pencil marks when finished.

Using a flat wood bit, drill into each of the marks to the depth of the screw’s head. The recesses should be wide enough so that a ratchet or socket attachment can tighten.

4. Pilot Hole

Using a drill bit that is thinner than the coach screw’s shank, line up the adjoining outer joists then drill a pilot hole through the very middle of the recess. This should go from the outer joist into the adjoining outer joist, creating a guide for the screws to fit into.

5. Tighten & Secure

Tighten and secure the coach screws into place using a drill driver and socket attachment or socket and ratchet.

6. Inner Joists

The final step is to secure the inner joists. You can simply repeat the same process as previously mentioned to fix the coach screws through the frame into the ends of the inner joists.

How to Lay Timber Decking Boards

Step 1: Position the First Board

The first step to installing your new timber deck is positioning the first timber board.

Where Do You Start When Laying Decking?

Position your first timber board in one corner of the sub-frame so that is lays across the inner joists in the opposite direction. Make sure the board is completely flush with the frame.

Place end to end joins between the deck boards so that they sit halfway across an inner joist. This will allow both boards to be secured firmly into the joist for optimum deck stability and strength.

Mark a cutting line as appropriate across the end of the board and cut carefully down to size, remembering to allow for 3mm of expansion whilst measuring.

Step 2: Secure to the Joists

Now its time to fix your first row of timber boards into place. To ensure your deck is robust and sturdy, you will need to secure the boards with two decking screws at every joist along the sub-frame.

Measure and mark out the screw spots first. These should sit a minimum of 15mm from the end of the board and 20mm from the outside. To prevent the timber from splitting, first drill a pilot hole on each mark using a drill bit that is thinner than the screw’s shank.

Then, screw the decking screws into the pilot holes to secure the first row to the joists.

Step 3: Second Row

Continue laying and fixing boards to create the second row of your decking. Remember to incorporate expansion gaps of the relevant sizing whilst doing so. Staggering your boards will give your deck a more robust structure and creates a clean and classic look. 

Step 4: Continue Installation

Repeat the fitting method described above to complete the rest of your timber deck installation. Always remember to include the appropriate gaps for expansion across the entire deck!

Step 5: Smooth, Preserve & Finish

If you are left with any rough cut ends, use sandpaper or a sander to smooth down to the perfect finish. Once smooth, apply an end grain preserver to protect the ends of the timber from rot and decay. You may also use a stain, oil, or wood paint to enhance the protection of your new deck even more.

How to Lay Composite Decking Boards

Step 1: Start Clips

Beginning in one corner of the frame, secure start clips along one edge of the outer joist. These should each be centred. Fix the start clips into place using screws and appropriate drill bit.

Step 2: Push & Secure

Carefully push the grooved long edge of one composite board into the start clips, ensuring it is perfectly straight and firmly fitted. Then, slide the hidden fastener into the grooved edge.

Step 3: Semi-Fix

Semi-fix with screws, aligning the screw hole in the fastener with the middle of the joist and screwing halfway downwards. Don’t fix all the way tight just yet. Repeat along the board’s full length at every joist.

Step 4: Second Board

Push the second board into position, fitting the fasteners into the groove. Follow the above method once again to semi-fix the fasteners on the other side of the composite board, remembering now to tighten all the way. After this, you can then completely tighten the screws of the first row of fasteners.

Step 5: Continue Installation

Continue installing the composite boards, repeating the above steps, securing each row after the following board has been pushed into place.

Step 6: Installing the Final Board

Fascia Board Fixing – To install the final deck board so that it sits flush with a fascia board, first pre-drill holes at an angle through the grooved edge of the board through into the outer joist. Then, attach the fascia board so that it is flush with the deck and screw to secure.

Overhang – To install for an overhang, pre-drill pilot holes at a 45° angle upwards through the deck from the outer joist. Place the final board into the fasteners so that it overhangs the outer joist without exceeding 13mm and secure with composite deck screws.

Additional Q&A

How Far Apart Should Decking Boards Be?

Customers often ask us if they should have a gap between their decking boards, and the answer is always yes. Decking boards will shrink and expand over time, often due to fluctuating temperatures or weather conditions, and the gap you leave between the decking boards will prevent this from damaging the structure of your deck. Gauge or screws or off-cut pieces of wood can be used to ensure that all the gaps are evenly spaced for a clean finish.

Timber decking boards require a 5-8mm expansion gap along the length of the boards, and a 3mm gap at the ends of the boards. For composite decking boards, we’d advise leaving a gap of 6mm along the length, and 3mm along the ends. If you find that the end row of decking boards overhangs, you may need to reduce the expansion gaps. Bear in mind for composite decking projects, it may not be possible to alter the gap, so the size of the outer frame may need to be adjusted instead.

Can I Lay Decking on Sand?

Yes, you can lay decking on sand. The method is very similar to laying decking on grass or soil. Click the link to jump back to our section on the best way to do this. Can I Build a Deck Directly on the Ground?

What are the Grooves on Decking For?

The grooves in decking boards are designed to move water away from the decking area, as well as improving airflow and the stability of the deck. These factors are vital in ensuring the safety and longevity of your deck. You could also consider laying the decking boards at a slight angle to further help with drainage.

Are Decking Boards Reversible?

Another question our customers often ask is which way up they should lay their decking boards. Although decking boards are technically reversible, and can be installed with either side facing up, it’s generally recommended to lay them ridge side down. This is because these grooves help to move water away from the deck, and if they’re facing up, moisture may collect and lead to water damage, rot, and more.

Is it Better to Nail or Screw Deck Boards?

Generally, screws will perform far better than nails in decking installation. Screws have good tensile strength and are less likely to pop or move out of place, creating a more secure and robust fit for your deck boards.

Thinking of Starting Your Own Decking Project?

If you’ve been inspired to give laying your own decking a go, take a look at the high-quality range available on our website. We’ve got premium composite decking boards from top manufacturers such as Composite Prime, along with all necessary fixings, flashings, and balustrades.