Arbordeck blog

Don’t Let Wood Rot Wreck Your Deck Foundation

As you dream of summer in the garden, consider how a new deck might add to the enjoyment of longer days in the sun. Imagine a lovely extension of your home in the perfect colour, featuring sleek rails and sophisticated lighting. The roses are in full bloom and the air is fragrant and warm.

It’s enough to make you want to ring up your builder straight away!

But hold up. Before you plan your dream deck, think practically about the long-term use of this outdoor space. If you’re investing in this home improvement, you want it to last.

Water can undermine a deck in as little as eight years, because wood that gets repeatedly wet will rot and deteriorate. Even if you choose composite deck boards — often warrantied for 25 years — the substructure or foundation, those beams and joists that hold up the deck floor — are made of wood. Don’t let dry rot, fungus, mold or mildew break down your wood and compromise the structural integrity of your deck.

Joist & beam tape

To stop rot, you must stop the water. Think about it: every time you have a downpour, gallons of water are seeping between your deck boards onto your deck’s beams and joists. Additionally, we can put plants out on the deck or let leaves accumulate, which further holds in moisture. We don’t intend to damage our deck with a lovely potted clematis, but that’s just what can happen.

Fortunately, you’re in the perfect position to stop the rot during the construction phase. It’s then that you can cover the beams and joists with the waterproofing power of a high-quality flashing tape for joists and beams, such as Trex Protect.

Trex protect on top of timber joists.

Adding a butyl flashing tape on your deck foundation creates a moisture barrier. Choosing butyl over asphalt-based tapes allows the tape to endure through higher temperatures. Butyl also installs better through a wider range of temperatures.

The tape comes in two widths, 40 mm x 20 m for joists and 100 mm x 20 m for bearers, and is backed with a 20-year warranty. The cost is relatively minimal. An average-size deck, measuring 3.5m x 7.5m, will require about 6 rolls of 50mm x 20m Joist Cap Tape and one roll of 100mm x 20m Bearer Cap Tape.

Choosing the right materials

Of courses, the wood you choose for your deck foundation also matters. Use rot-resistant, treated wood to reduce the risk of break down.

Also, consider composite decking, which is made of recycled plastics and wood fibers. With composite boards you can reduce the ongoing maintenance needs of sealing and staining. As mentioned previously, most composite decking materials come with a manufacturer’s warranty. Choose a trusted decking supplier such as Arbordeck to source your deck dreams.

Watch for dry rot

If you already have a deck, be sure to check it often for wood rot. Even with a new deck, take a look around at least once a year.

Pay special attention to the ledger board, which is installed against your house. A failing ledger board may require the deck to be rebuilt, as this is critical to the integrity of your deck.

Rotten joists


Rot often appears as spongy or discoloured wood that flakes off or falls apart when wet. Use a screwdriver to test for soft spots. Pay special attention to these problem areas:

  • Where wood contacts the ground
  • Greyish mold or darker-looking wood
  • Insect damage, which could be a combination of pests and rot since dry rot attracts termites
  • Water sources such as leaky plumbing, failing gutters, sprinkler system problems, and anything else that can cause water to pool
  • Also, be sure to look at any adjacent areas if you find rot
  • If in doubt, call a professional to do an inspection

What to do about rot

If you discover dry rot on your deck, take immediate action. Call a professional and get an estimate. Or if you’re handy and the damage is not extensive, follow these general guidelines for DIY repairs:

  • Remove hardware. Take out any screw, nails or fasteners.
  • Remove and replace any rotten beams and joists. Be sure to reinforce any wood that is soft or discoloured.
  • Remember to cover new beams and joists. Before replacing decking boards, cover joists and beams with butyl tape.
  • Support the joist. Install a reinforcing joist if needed.
  • Install deck boards. If you need to replace damaged decking boards, try to match the wood type. Be sure to seal any new boards.

Don’t skimp on your deck’s foundation. Being proactive today will make a difference tomorrow and for seasons to come. With the right wood protection, you can breathe easier and enjoy your garden oasis a lot longer.

Now, you can get back to dreaming of summer days and sunshine on your deck!

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