What is under the boards: deck substructure

Everyone shops for a deck by the board. Merbau or composite, the colour, the look. But the board is the finish. The deck is the frame underneath it, and that frame is the part a cheap quote goes quiet on. It is also the part most likely to fail first. Here is what is under the boards, and why it decides whether your deck lasts.

What the substructure is

Under every deck is a hidden frame that holds the whole thing up. From the ground up, it is the footings, the posts, the bearers, the joists, and where the deck meets the house, the ledger board and its flashing. Get that frame right and the deck stays flat and quiet for decades. Get it wrong and the deck sags, bounces, or lets water into your wall, no matter how good the boards on top are.

The parts, from the ground up

• Footings. Concreted holes that carry the load into the ground, dug to depth for the height and the soil. The higher the deck, the more load through them, so they are sized, not guessed. Pads sat on the dirt are the first thing a cheap quote does instead.
• Posts. The uprights that stand on the footings and carry the frame, sized for the height. H4-rated where they go into the ground, so they do not rot out early.
• Bearers and joists. The horizontal frame the boards screw to. Joist spacing is the quiet number that matters most: spread them out and the deck flexes, and composite needs them closer together than timber.
• Ledger and flashing. Where the deck bolts to the house, the ledger carries the load and the flashing keeps water out of the wall. Bolt a board straight on with no flashing and the wall behind it rots.

Why the cheap quote goes quiet on it

You cannot see a footing once the deck is down. You cannot see the joist spacing or the flashing either. That is exactly why they are the first things a cheap quote shrinks, because no one walking the finished deck will notice, until the deck starts to move. A lump sum for "the deck" with no word on the footing depth, the joist spacing or the ledger flashing is not a saving. It is a bet that you will not ask.

The boards on top are the part everyone looks at. The substructure underneath is the part that decides whether the deck is still flat in ten years. It is the deck. The boards are the finish.

Why it is the part we warrant

We name the footing depth, the joist spacing and the ledger flashing on the quote in plain numbers, so there is nothing hidden, and you can compare us to the next quote on the part that actually holds the deck up. Then we warrant it: ten years on the footings, bearers and posts, in writing. We back the substructure because it is the part that matters and the part we build properly, every job.

How we build the substructure at Deckline

We dig and concrete the footings to depth, set the posts plumb, and space the bearers and joists for the board and the height, closer together for composite, so the deck stays flat and never bounces. We flash the ledger properly where it meets the house. The depth, the spacing and the flashing go on the quote in plain numbers, and the footings, bearers and posts carry a ten-year written warranty. That is the part you never see, done right.