PVC vs composite decking
PVC and composite are sold side by side and look similar in a showroom. They are different materials with different failure modes. PVC will not absorb water or grow mould; it also moves about twice as much as composite and is less stiff.
What is actually different
| Composite | PVC | |
|---|---|---|
| Core | Wood flour + plastic binder | 100% plastic (cellular PVC) |
| Water absorption | Low, but the core can take on moisture at cut ends | None |
| Mould and mildew | Possible on organic residue | Very unlikely |
| Thermal expansion | ~1/16″ per 12 ft per 20°F | ~1/8″ per 12 ft per 20°F |
| Stiffness | Higher | Lower — 12″ centres common |
| Material cost | $6–12 per sq ft | $9–16 per sq ft |
| Colour depth | Multi-tone, streaked | More uniform, fewer variegated options |
Expansion is the installation constraint
PVC moves roughly twice as much as composite. On a 20 ft run across a 40°F seasonal swing, that is close to a quarter inch more movement than composite — and it has to go somewhere.
What that means in practice:
- End gaps are mandatory, not optional. Most manufacturers specify 3/16″ to 1/4″ at each end, and more on long runs or in full sun.
- Do not butt boards tight hoping the gap will close. It closes in winter and buckles in summer.
- Picture-frame borders pin the field. A border restrains expansion, so the field boards need their gaps computed from the border, not from the deck edge.
- Run boards the long way where possible, so the movement happens at fewer joints.
Heat and stiffness
PVC runs hotter than composite in the same colour because it has more air voids and lower thermal mass. A light-coloured PVC board still reaches 140°F+ in direct summer sun. Dark PVC is the worst combination on the market for bare feet.
Stiffness is the other half. PVC requires 12″ joist centres in most systems and 12″ at 45° regardless of board thickness. If your frame is already built at 16″, PVC means adding joists.
When PVC is the right answer
- Pool decks and docks. Chlorine and salt water are where PVC's zero absorption matters most.
- Deep shade. Composite in permanent shade grows mould on pollen and dirt; PVC does not feed it.
- Coastal high-humidity sites where the deck never fully dries.
- Anyone who will never clean it. PVC is the most forgiving surface when neglected.
Skip PVC when the budget is tight, the deck is small, the frame is at 16″ centres, or you want a variegated wood look — composite does that better and cheaper.
What this comparison will not rank
- It does not rank brands. Board construction varies more within each category than between them.
- It does not cover fasteners. Both need hidden clips rated for the material; using composite clips on PVC is a common and expensive mistake.
- It does not include the frame changes in the cost — add 8–12% for the extra joists PVC usually needs.
- It says nothing about resale value. That is a local market question, not a material one.
Questions people actually ask
Is PVC decking better than composite?
It is better in wet and shaded conditions, because it absorbs no water and does not support mould. Composite is better on cost, stiffness and colour variety. Neither is better in general.
How much does PVC decking expand?
About 1/8 inch per 12 feet per 20°F swing, roughly double composite. Manufacturers specify end gaps of 3/16 to 1/4 inch for that reason.
Can PVC decking be installed at 16 inch joist spacing?
Rarely. Most PVC systems require 12 inches on centre, and 12 inches at 45 degrees regardless of board thickness. Confirm against the specific product's span table.
Does PVC decking fade?
It is very resistant to fading compared with early composites, but it can chalk and scratch. Surface damage is more visible on PVC because the colour runs through the whole board rather than sitting in a cap.