Is Your Subframe Subpar?

How to build the best base for your composite decking…

One of the major draws of composite decking is its longevity. But your composite deck is only going to last as long as the subframe that supports it. If you cut corners with the subframe, you aren’t doing your new deck justice. Here’s how to build a robust subframe that will keep your decking safe and supported for as long as you need it.

Prepare the foundations

If you want your deck to last as long as possible, it’s not recommended that you build it over soft ground. If this can’t be avoided, ensure you prepare the ground properly.

Mark out where you want to lay your deck and dig down to a depth of 5cm. Line the ground with landscaping fabric and lay gravel on top. If your ground is particularly soft it’s wise to place paving stones in each corner and halfway along where each joist will be. This will help preserve the deck.

Ideally, you will have a solid foundation under your deck. If this is concrete, make sure it’s at least 10cm thick. Patios and concrete foundations should be placed at a gradient sufficient enough to encourage water to run away. We recommend a gradient of at least 1 in 100 (1%).

Build a subframe

We recommend using treated C24 timber. You can use other materials, but they may expand and contract with temperature changes and this will result in the structure warping over time. For this reason, timber is the best choice.

Once you have constructed your timber subframe, you need to place the timber joists. Mark out the positioning as per the advice in the installation instructions for the decking you’ve chosen, if using our HD Deck® then the requirement is that the joists are fit with 300mm centres. Measure your joists and cut them accordingly.

How to protect your timber joists

Timber isn’t without its pitfalls. All wood is porous and vulnerable to damage from moisture and wood boring insects. Whilst composite decking is mostly impervious to bad weather, the UK’s harsh, wet winters can wreak havoc with your timber subframe. Nobody wants a soggy bottom… So the best way to avoid rot and damage to your timber joists is to use joist tape.

You can buy tape alongside your composite decking boards. The tape can be used to fully wrap the joists or you can lay strips across the top and the edges of the timber. Our HD Protect™ tape is not only perfect for the job, but it’s the only tape you can use with your composite deck that won’t invalidate your warranty. You can buy it from many of our stockists, including Amazon. 

Hand the job over to a professional

We’re not saying your DIY skills are questionable. But we are saying that the best way to ensure your deck outlives its warranty and needs minimal maintenance is to ensure a problem-free installation. Sometimes, the only way to ensure this is by hiring a professional installer.

A composite deck is a premium product that provides a quality finish that has the promise to last decades. Make sure the subframe measures up. Find an installer here.