How Much Does a 16×20 Composite Deck Cost?

Quick Answer: A 16×20 composite deck (320 square feet) in the Oswego and Fox Valley area typically costs between $22,000 and $45,000 fully installed, including materials, labor, permit, standard railing, and a basic stair run. Mid-grade composite with standard composite railing lands in the $22,000 to $30,000 range. Premium capped composite with upgraded railing (cable or upgraded profiles) runs $30,000 to $45,000+. Complex designs, multi-level configurations, or significant elevation add further.

Why 16×20 Is a Popular Size

At 320 square feet, a 16×20 deck is a genuinely functional outdoor living space. It accommodates:

A full outdoor dining set (6 to 8 people)
A separate seating / lounge area
Space to move between zones without feeling cramped

This size is large enough to entertain comfortably and small enough to be cost-effective for most homeowners. It’s one of the most common sizes we build across Oswego, Aurora, and the surrounding Fox Valley communities.

Breaking Down the Cost Components

Footings and concrete: A 16×20 deck typically requires 6 to 8 footings. Each is augered to 42 inches (frost line), concrete poured, post base set. Concrete and footing labor is a meaningful cost component.

Framing lumber: Posts, beams, rim joists, and interior joists at 12-inch on-center spacing (required for composite). On a 320 sq ft deck, this is a substantial amount of pressure-treated lumber.

Composite decking boards: 320 sq ft footprint requires approximately 350 to 380 sq ft of actual board material accounting for cuts and waste. Board cost depends heavily on the product tier chosen.

Railing: A 16×20 deck with railing on three sides has approximately 56 linear feet of railing. At composite railing pricing, this is a significant line item. Upgrading to cable railing on a 56 linear-foot run adds several thousand dollars.

Stairs: One standard stair run is typically included in base estimates. The cost depends on height and width.

Permit: Required in Oswego and surrounding municipalities. Based on project valuation – a few hundred dollars for this project size.

Mid-Grade vs. Premium: The Actual Difference

For a 16×20 deck, here’s what the composite material tier choice means in practical terms:

Mid-grade capped composite (Trex Enhance Naturals, TimberTech PRO Legacy):

25-year warranty on fading and staining
Fully capped, performs well in Illinois conditions
Solid appearance and durability
Total project range: $22,000 – $30,000

Premium capped composite (Trex Transcend, TimberTech PRO Reserve):

25 to 30-year warranty
More realistic grain pattern and color variation
Better heat performance in some product lines
Total project range: $28,000 – $38,000

Premium composite + upgraded railing (cable, glass, or decorative aluminum):

Railing upgrade adds $3,000 to $8,000+ depending on system
Total project range: $32,000 – $45,000+

Important Considerations

Design affects cost. A straight rectangular 16×20 deck is more efficient to build than one with a bump-out, diagonal board pattern, or picture-frame border. Design choices are worth making with full awareness of their cost implications.

Elevation matters. A 16×20 deck that’s ground-level is less expensive than the same size elevated 6 feet above grade. Taller posts, more robust framing, and more railing linear footage all increase cost with height.

Our full cost guide for composite decks in Oswego and Aurora covers all the cost factors in detail.

Compare 12×12 composite deck cost if you’re deciding between sizes.

Is the cost worth it vs. wood? We do the honest math on that page.

What to Do Next

A 16×20 deck is a significant project and a significant investment. You deserve a contractor who shows up, gives you a real number, and builds it right. That’s what DDT does.