Choosing PVC Decking for a Renovation: What to Check First

Evaluating Your Existing Deck Frame: A Structural Overview

Before considering any new decking material, a thorough inspection of your existing deck frame is essential. This includes examining the posts, beams, joists, and ledger board for any signs of damage, rot, or instability. Even if the current decking appears sound, underlying structural issues can compromise the safety and longevity of your renovated deck.

PVC decking, while lighter than some hardwoods, still requires a robust and level substructure. Any sagging, warping, or deterioration in the existing frame will need to be addressed. This might involve replacing individual components, reinforcing sections, or even rebuilding parts of the frame.

Joist Spacing and Load Bearing for PVC Decking

A critical factor for PVC decking installation is the joist spacing. Most PVC decking products specify a maximum allowable joist spacing to ensure proper support and prevent deflection.

Your existing deck frame's joist spacing must match or exceed the requirements of your chosen PVC decking. If your current joists are spaced wider than recommended, you will need to add sister joists or install blocking to create the necessary support. Failing to do so can lead to a bouncy deck, board deflection, and potential warranty issues. PVC decking from manufacturers like Azek and TimberTech Azek is 100% synthetic, meaning it has no wood fiber to swell, stain, or rot, but still needs proper structural support.

Ledger Board and Fastening: Ensuring Connection Security

The ledger board, which connects the deck to your house, is a primary concern in any deck renovation. Inspect it carefully for rot, insect damage, or loose connections. The ledger board must be securely fastened to the house's rim joist or band board, typically with appropriate lag screws or through-bolts, and flashed correctly to prevent water intrusion into the house structure.

If the ledger board is compromised, it must be replaced. Proper fastening and flashing are not just for structural integrity; they are crucial for preventing water damage to your home and are often mandated by local building codes. Do not assume an old ledger board is adequate for a new decking material without a thorough inspection.

Considering Ventilation and Drainage Underneath

PVC decking, being a non-porous material, requires proper ventilation beneath the deck surface. Adequate airflow helps prevent moisture buildup, which can lead to issues with the substructure and potentially create an environment for mold or mildew. Ensure that your existing deck design allows for sufficient air circulation.

Additionally, assess the drainage around and under your deck. Standing water or persistently damp conditions can accelerate the deterioration of wood framing, regardless of the decking material. If your renovation includes enclosing the space under the deck, special attention to ventilation and drainage becomes even more critical.

Worked Example: Assessing a 10x12 Foot Deck Frame for PVC Decking

Imagine you have an existing 10-foot by 12-foot deck frame, currently decked with pressure-treated lumber, and you wish to upgrade to PVC decking. Here's a hypothetical assessment:

You notice some minor surface checking on a few joists but no significant rot or insect damage. The ledger board appears securely fastened and flashed.

This immediately flags an issue.

You'll also need to ensure these new joists are properly connected to the ledger and rim joist.

This will need to be corrected by shimming or planing before installing the PVC, as PVC boards will conform to an uneven surface, resulting in an unlevel finished deck.

This example illustrates that even a seemingly sound frame can require significant modifications to meet the specific requirements of new decking materials like PVC.

Before you order

• Is the existing deck frame structurally sound with no signs of rot, insect damage, or significant deterioration?
• Is the ledger board securely attached to the house with proper flashing and free from damage?
• Are the joists, beams, and posts level and plumb, without significant sagging or twisting?
• Is there adequate ventilation and drainage around and under the deck structure?
• Are there any local building codes or permit requirements for renovating a deck that need to be considered?
• Have you accounted for the cost and labor of any necessary frame modifications (e.g., adding sister joists, replacing beams) in your renovation budget?

Confirm installation details, approved uses and warranty terms in the current instructions for the exact product and profile. Your installer should verify the substrate, structure and applicable project requirements.

Questions to help you decide

Keep planning your project