The short answer
Good capped composite decking typically lasts 25 to 30 years, and leading brands give warranties of 25 years or more. Treated softwood usually lasts 10 to 20 years. In practice, the frame underneath and how the deck was built decide how long it really lasts.
Composite decking costs more to fit than timber, so how long it lasts is really a question about value. Spread over its life, a deck that lasts three times as long can work out cheaper, even before you count the weekends not spent sanding and staining.
How long composite decking lasts
Good-quality capped composite boards are commonly expected to last 25 to 30 years, a figure HomeBuilding quotes from the decking firm Ultra Decking. Warranties back that up:
| Brand | Warranty (residential) |
|---|---|
| Millboard | 25-year limited structural warranty (some installations 10 or 12 years) |
| Trex | Up to 50-year limited warranty, 25 or 50 years depending on the colour |
Warranties vary by product line and installation, so read the terms for the exact boards you’re quoted. Most cover the boards against rotting, splitting and structural failure, with separate, shorter cover for fading and staining.
How that compares with timber
| Decking | Typical lifespan |
|---|---|
| Capped composite | 25 to 30 years |
| Treated softwood | 10 to 20 years, depending on care |
| Hardwood | Longer than softwood with regular care |
Timber’s lifespan depends heavily on maintenance. A softwood deck cleaned and treated every year or two in a sunny spot can last well; the same deck in a damp, shady corner and left alone may start to rot within a decade.
What really decides how long a deck lasts
The frame underneath
The boards can be guaranteed for decades, but they sit on a frame. If the frame is treated timber, it needs to be graded for ground contact, kept off wet ground and ventilated, or it can rot long before the boards wear out. Aluminium or composite joists cost more but remove that risk. Ask what the frame is made of and how long it is expected to last.
How the ground is prepared
A level, well-drained base with a weed membrane stops the frame sinking and keeps it dry. Poor groundwork is one of the most common reasons decks fail early.
Following the maker’s instructions
Composite expands and contracts with temperature. Joist spacing, gaps between boards and the fixings used all need to follow the maker’s instructions. Get them wrong and boards can buckle, and the warranty may not apply.
Board quality
Capped boards with a solid core generally last longer and resist staining better than cheaper hollow or uncapped boards.
Care
Composite needs little care, but a wash twice a year keeps algae and stains from building up. Our cleaning guide explains how.
Does composite decking fade?
All composite boards change colour a little in the first weeks and months outdoors, as the surface weathers in sunlight. Capped boards settle quickly and then change very slowly; cheaper uncapped boards can fade more noticeably and unevenly. Most warranties cover fading and staining separately from structure, often for a shorter period, so check both. Lighter, mid-tone colours tend to show fading and dust less than very dark ones. If you are adding boards later, for example a step or an extension to the deck, expect a slight difference in shade at first while the new boards weather in.
Signs a composite deck is reaching the end
- boards sagging or bouncing between joists, often a frame problem
- cracks, splits or swelling at board ends
- deep scratches through the protective cap
- heavy fading that cleaning does not improve
Often only the frame or a few boards need replacing, not the whole deck.
Is composite worth it for the lifespan?
If you plan to stay in your home for ten years or more, composite usually makes sense: one deck instead of possibly two in timber, and far less maintenance along the way. If you’re moving soon or working to a tight budget, a well-built softwood deck can still be good value. Our composite vs wood decking guide compares them side by side, and the decking cost calculator shows what each would cost for your size.
What to ask an installer
- Which boards, which range, and what warranty, in writing?
- What is the frame made of, and how long should it last?
- Will the installation follow the maker’s instructions, so the warranty stands?
- What guarantee do they give on their own workmanship?
If you’re planning decking in Sheffield, the quote form takes two minutes and the installer can answer these at the visit.