what size screws for decking

3 min read 26-12-2024

Choosing the right screws for your decking project is crucial for its longevity and safety. Using screws that are too small can lead to loose boards and potential structural failure, while screws that are too large can cause splitting and damage. This guide will help you determine the ideal screw size for your decking needs.

Understanding Decking Screw Types and Sizes

Decking screws are specifically designed for outdoor use, offering superior resistance to corrosion and rot. Common materials include stainless steel, coated steel, and composite materials. Size is expressed in gauge (thickness) and length (inches). The gauge number is inversely proportional to thickness—a smaller gauge number means a thicker screw. For example, a #8 screw is thicker than a #10 screw.

Common Decking Screw Sizes:

Length: Screw length is determined by the thickness of your decking boards and the type of joist or support structure beneath. Generally, you want the screw to penetrate at least 1.5 inches into the supporting joist for adequate holding power.
Gauge: Common gauge sizes range from #8 to #10. #8 screws are suitable for thinner decking boards, while #10 screws provide more holding power for thicker boards.

Choosing the Right Screw Length:

The length of your screws depends on several factors:

Decking Board Thickness: Measure the thickness of your decking boards precisely.
Joist Depth: Measure the depth of your joists or support beams.
Desired Penetration: Aim for at least 1.5 inches of penetration into the joist.

Example: If your decking boards are 1-inch thick and your joists are 2x6 (approximately 1.5 inches deep), you’ll need screws at least 2.5 inches long (1 inch + 1.5 inches).

Screw Head Types:

Flat Head: Offers a low profile, suitable for flush installation and preventing tripping hazards.
Bugle Head (Pan Head): Provides a slightly countersunk head, allowing for a recessed look and better water runoff.
Waisted Head (Oval Head): Offers a combination of a countersunk head with a slightly raised center for a more decorative look.

What Size Screws for Different Decking Materials?

The best screw size also depends on the type of decking material:

1. Wood Decking (e.g., Cedar, Redwood, Pressure Treated Pine):

For most wood decking applications, #8 or #10 screws, 2.5 to 3.5 inches in length, are suitable. Always check the manufacturer's recommendations on your specific wood species and board thickness.

2. Composite Decking:

Composite decking materials often require specialized screws designed for their unique properties. These screws usually have a coarse thread to improve grip and prevent stripping. Always check the manufacturer's recommendations for your composite decking brand. The specific screw type will depend on the composite material's density.

3. PVC Decking:

PVC decking needs screws specifically designed for plastic. Using standard wood screws can cause damage. These screws typically have a self-tapping design.

How to Avoid Common Mistakes:

Pre-drilling: Pre-drilling pilot holes is almost always recommended, especially for hardwoods. This helps prevent splitting and ensures a cleaner installation. Use a drill bit slightly smaller than the screw shank diameter.
Using the Wrong Type of Screw: Using standard screws instead of decking screws will compromise durability and may lead to rusting or rot.
Overtightening: Overtightening can strip the wood or break the screw.

FAQs:

Q: What is the best type of decking screw?

A: Stainless steel decking screws are generally recommended for superior corrosion resistance. Coated steel screws offer a more affordable option but may require more frequent replacement.

Q: How many screws per board?

A: The number of screws needed per board depends on the board length and spacing of your joists. A general guideline is at least two screws per joist.

Q: Can I use shorter screws than recommended?

A: No, using shorter screws can compromise the structural integrity of your deck. Always use screws long enough to provide adequate penetration into the joists.

By carefully considering the factors outlined above, you can confidently select the right size screws for your decking project. Remember to always consult the manufacturer's recommendations for your specific decking materials and choose quality screws for a long-lasting and safe deck.