If you have been battling with a rotting, slippery timber patio for years, you are likely wondering if you can simply rip up the old wood and install premium composite decking in its place.
The short answer is yes. Upgrading to composite decking saves you from the nightmare of annual sanding and staining, provides incredible resistance to rot and insects, and gives you a stunning, modern finish.
However, you cannot simply lay composite boards over a failing foundation. Here is our professional, step-by-step tradesman guide to successfully upgrading your old timber deck to composite.
Step 1: Remove the Old Wood Decks
Removing the old wooden deck boards is the first stage of the upgrade.
- The Tools: You will need a heavy-duty pry bar (crowbar) and a drill/impact driver to back out any stubborn, rusted screws.
- The Goal: You must strip the deck completely bare so the underlying timber joists are fully visible.
Step 2: Inspect (And Upgrade) the Subframe
In our experience, many customers try to reuse their existing timber subframe to save on costs when upgrading. We completely get it, but you must never save money at the expense of the project’s safety and lifespan. You cannot lay a 25-year composite board on a subframe that is about to fail.
- The “Screwdriver Test”: Before deciding to keep the old frame, you must ensure it is safe. Take a standard flathead screwdriver and physically poke the timber joists and support posts. If the wood feels soft, spongy, or crumbles under the pressure, wet rot has already set in. Any cracked posts or rotting joists must be replaced immediately, or your new deck will inevitably fail in the future.
- The 300mm Rule: Older timber decks were often built with joists spaced at 400mm (16 inches) or even 600mm apart. Composite decking requires a strict 300mm joist spacing. If your old joists are too far apart, you will need to purchase extra C24 treated timber and install new “in-between” joists to bring the spacing down to 300mm.
- Treat and Protect: If you cut any new timber during the rebuild, you must treat the exposed ends with a cut-end wood preserver. Finally, apply waterproof Joist Tape over the top of every timber joist. This stops rainwater from sitting on the wood and prevents future rot.
Step 3: Install Your Composite Decking
Once the subframe is upgraded to 300mm centres, passes the screwdriver test, and is protected with tape, you can begin laying your boards.
- The Fixings: Unlike traditional timber, you do not screw directly through the top of the board. You will use a hidden fastener system. Starter clips are used to lock in the very first board, and T-Clips are used to secure the rest of the deck.
- Expansion Gaps: As you lay the boards, the T-Clips will automatically create the perfect 3mm to 6mm side-to-side gap. However, wherever two boards meet end-to-end, you must manually leave a 5mm to 6mm expansion gap to allow the plastic polymers to expand in the summer heat without buckling.
Step 4: Cover the Edges
To achieve a professional, high-end finish, you must hide the exposed cut ends of the composite boards and the ugly timber subframe underneath.
- Fascia Boards: The easiest method is to run a vertical composite fascia board around the perimeter of the deck to hide the timber framework.
- Picture Framing: If you want a truly premium look, you can install a “Picture Frame” border using a contrasting colour. Just remember, this method requires you to build extra joist support around the perimeter of the subframe first!
Conclusion: A Permanent Upgrade
Replacing your tired, high-maintenance timber with composite decking is one of the smartest investments you can make for your garden, but ensuring you pick the correct type of composite board for your project is important. By taking the time to properly inspect your old joists, reinforcing the spacing to 300mm, and using hidden fasteners, you can easily transform a rotting patio into a luxury, fit-and-forget outdoor living space.
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