What Is the Difference Between Hollow and Solid Composite Decking?

Composite decking comes in two structural types: hollow and solid. Both are made from the same blend of recycled wood fibers and plastic polymers. The difference is internal. Solid boards are dense throughout with no cavities. Hollow boards have chambered channels running through the core.

This single structural difference affects weight, cost, strength, installation, and long-term performance. Choosing the wrong type for your project can lead to unnecessary expense or performance issues.

This guide compares hollow and solid composite decking across every factor that matters. It includes specific numbers, real trade-offs, and clear recommendations for different project types.

Quick Comparison Table

Prices reflect U.S. national averages as of 2025.

Understanding the Two Structures

Solid Composite Decking

Solid composite boards are dense from edge to edge. There are no internal voids. The board feels heavy and substantial, similar to a hardwood plank.

This density gives solid boards higher bending strength and better resistance to point loads. Heavy furniture, hot tubs, and high foot traffic are all handled without concern. Solid boards also produce less noise when walked on. They feel firm and stable underfoot.

The trade-off is weight. A single 8-foot solid composite board weighs 18–28 pounds depending on width and thickness. Carrying and positioning these boards during installation is physically demanding. Most installers recommend having at least two people for solid board projects.

Solid boards also expand and contract more with temperature changes than hollow boards. This is because they contain more material. In regions with extreme seasonal temperature swings, proper expansion gaps are essential.

Hollow Composite Decking

Hollow composite boards have internal chambers separated by structural ribs. These ribs maintain strength while reducing material use by 30–40%.

The result is a board that weighs roughly one-third to one-half of a solid board of the same length. An 8-foot hollow board typically weighs 8–14 pounds. One person can carry and install hollow boards without a helper.

Hollow boards also expand and contract less than solid boards because there is less material to respond to temperature changes. This makes them more dimensionally stable in climates with hot summers and cold winters.

The downsides are lower load capacity, a slightly hollow sound when walked on, and visible cavities at cut ends that require end caps for a clean appearance.

Detailed Comparison

Cost

Hollow composite decking costs 25–40% less than solid. The savings come from reduced material use during manufacturing.

For a 200-square-foot deck using mid-range capped boards, the material cost difference is roughly:

However, hollow boards often require closer joist spacing (12 inches vs. 16 inches). This means more joists and more labor for the subframe. The additional framing cost typically adds $300–$600 to a 200-square-foot project. This partially offsets the material savings.

Bottom line: Hollow decking still costs less overall, but the gap narrows once framing is included.

Strength and Load Capacity

Solid boards are stronger. They handle heavier point loads and wider joist spans without flexing or sagging.

Recommended maximum joist spacing:

For decks that support hot tubs, heavy planters, outdoor kitchens, or frequent large gatherings, solid boards are the safer choice. Hollow boards are perfectly adequate for standard residential foot traffic, light furniture, and normal use.

Weight and Installation

Hollow boards are significantly easier to handle. At 8–14 pounds per 8-foot board, one person can carry, position, and fasten them without fatigue. This makes hollow decking ideal for DIY projects.

Solid boards at 18–28 pounds per board are manageable but tiring over a full deck installation. Professional installers can work with either type efficiently. For homeowners doing it themselves, the weight difference matters.

Both types cut, drill, and fasten the same way using standard woodworking tools. Hidden clip systems work with both hollow and solid boards that have grooved edges.

Thermal Expansion and Contraction

All composite materials expand in heat and contract in cold. Solid boards expand more because they contain more material.

In regions with temperature swings of 80°F or more between summer and winter (such as the Midwest or Northeast U.S.), solid boards may expand up to 6 mm (¼ inch) per 12-foot length. Hollow boards typically expand 3–4 mm over the same length.

Both types require expansion gaps during installation. Follow your manufacturer’s specifications exactly. But hollow boards are slightly more forgiving if gaps are marginally undersized.

Sound and Underfoot Feel

Solid boards feel and sound more like natural wood when walked on. The dense material absorbs vibration and dampens footstep noise.

Hollow boards produce a subtle drumming sound, especially when the deck is elevated above the ground with open airspace below. The effect is more noticeable with hard-soled shoes. Most homeowners describe it as minor, but it is perceptible.

If your deck is built close to the ground with minimal airspace underneath, the sound difference between hollow and solid is negligible.

End Appearance and Water Management

Solid boards have a clean, finished look at cut ends. No additional treatment is needed. This is an advantage for stair treads, border boards, and any visible edge.

Hollow boards expose the internal chambers at cut ends. Without end caps, these openings look unfinished and allow debris, insects, and water to enter the core.

Water management is critical for hollow boards. If water enters the chambers and cannot drain, it pools inside. In freezing climates, trapped water expands as ice and can crack the board from the inside. To prevent this:

• Always install end caps on every cut end
• Ensure boards are installed with a slight slope (1/8 inch per foot minimum) so water drains through and out
• Avoid fully sealing both ends of a board — leave the lower end open or use vented caps to allow drainage

Solid boards eliminate this concern. No internal cavity means no trapped water.

Durability and Lifespan

Both hollow and solid composite boards last 25–30 years when properly installed and maintained. The lifespan depends more on whether the board is capped or uncapped than on whether it is hollow or solid.

Capped hollow boards with a polymer shell resist moisture, stains, and UV fading nearly as well as capped solid boards. Uncapped hollow boards are the most vulnerable to moisture absorption through the exposed core and cut ends.

For maximum longevity, choose capped boards regardless of hollow or solid structure.

COOWIN offers both hollow and solid composite decking in capped configurations. All boards feature a co-extruded HDPE shell for superior weather protection. Request free samples of both types to compare weight, texture, and feel side by side.

Capped vs. Uncapped: A Separate Decision

Hollow vs. solid and capped vs. uncapped are two independent choices. They create four possible combinations:

For most residential deck projects, capped hollow offers the best balance of performance, weight, and cost. For premium projects, heavy-use areas, or commercial applications, capped solid is the top choice.

Which Type Should You Choose?

Choose hollow composite decking if you:

• Are working with a limited budget
• Plan to install the deck yourself (lighter boards = easier handling)
• Have a standard residential deck with normal foot traffic
• Live in a climate with wide temperature swings (less expansion)
• Need to install on an existing subframe with closer joist spacing

Choose solid composite decking if you:

• Want the firmest, quietest underfoot feel
• Plan to place heavy items on the deck (hot tubs, outdoor kitchens, large planters)
• Prefer clean edges without end caps, especially on stair treads
• Are you building a commercial or high-traffic deck
• Want to avoid any concerns about internal water accumulation

Not sure? Contact COOWIN’s team for project-specific recommendations. COOWIN manufactures both hollow capped boards (CO-02) and solid capped boards (CO-03) to suit different project needs and budgets.

Final Thoughts

Hollow and solid composite decking serve different priorities. Hollow saves money and makes DIY installation easier. Solid delivers a firmer feel, better load capacity, and cleaner edge details.

Neither type is universally better. The right choice depends on your budget, who is doing the installation, what the deck will support, and how important the underfoot feel is to you.

For most standard residential decks, capped hollow boards offer excellent performance at a lower cost. For premium builds, high-traffic decks, or areas with heavy loads, capped solid boards are worth the investment.

Frequently Asked Questions

Is hollow composite decking strong enough for residential use?

Yes. Hollow composite decking is engineered for standard residential foot traffic, outdoor furniture, and normal use. It performs well when installed on joists spaced 12 inches on center. It is not recommended for hot tubs, heavy outdoor kitchens, or commercial applications where point loads are high.

Does hollow composite decking feel bouncy or flexible?

There can be a slight flex between joists, especially if joist spacing exceeds the manufacturer’s recommendation. At the correct 12-inch spacing, most homeowners report that hollow boards feel stable and secure. The flex is minimal and comparable to standard wood decking on the same joist layout.

Do I need end caps for hollow composite decking?

Yes. End caps are essential. They prevent debris, insects, and water from entering the hollow chambers. They also give cut ends a finished appearance. Most manufacturers include end caps with their hollow board products or sell them separately.

Which is better for a pool deck, hollow or solid?

Solid is generally the better choice for pool decks. Pool areas see frequent water exposure, heavy foot traffic, and wet conditions that increase slip risk. Solid boards eliminate any concern about water pooling inside the board. They also handle the weight of pool equipment and heavy foot traffic better.

How much weight can hollow composite decking hold?

Load capacity depends on joist spacing and board dimensions. At 12-inch joist spacing, most hollow composite boards support 250–400 pounds per square foot of distributed load. This is more than adequate for residential use. Always check the manufacturer’s specific load ratings and span tables for your chosen product.

Does hollow composite decking last as long as solid?

When both are capped and properly installed, the difference in lifespan is minimal. Both types last 25–30 years. The capping layer is a bigger factor in longevity than the internal structure. Uncapped hollow boards have a shorter lifespan because moisture can enter the exposed core more easily.