How to Determine Deck Framing Lumber Sizes: A Complete Guide

Just like any other woodworking project, it’s crucial to start by considering the size of your lumber from hardwood stores. This is essential for ensuring that all the pieces fit together perfectly, just like a puzzle.

However, many people may find this task challenging. One of the main difficulties lies in selecting the right size, type, and quality of lumber. It’s important to not only focus on dimensions and visual appeal but also choose wood that is resistant to rain and weather conditions.

But don’t worry! Figuring out the appropriate lumber for framing a deck doesn’t have to be complicated. The key is to first understand the roles of different structural components and how they transfer loads to the supporting footings.

If you want more in-depth information on this topic, check out our comprehensive guide to choosing deck framing lumber.

Importance of Having the Right Tools

Now that you know about selecting the perfect lumber, let’s talk about another crucial aspect of woodworking: having the right tools.

Whether you’re a professional woodworker or someone who enjoys DIY projects, having high-quality tools is essential for creating outstanding and visually pleasing pieces.

But what tools do you need? And how can you get them? In this article, we will cover everything you need to know about woodworking tools, including:

1. The essential hand tools every woodworker should have
2. Must-have power tools for more efficient work
3. Tips on acquiring tools without breaking the bank

So before we dive into the main discussion, make sure to check out our guide on woodworking tools and familiarize yourself with them.

How to Determine Deck Framing Lumber Sizes

Understanding Deck Framing Design

A deck frame is a raised wooden platform supported by beams and posts. It consists of the following components:

1. Joists: Horizontal 2-by lumber that forms the main framework of the deck.
2. Beams: Horizontal supports that carry the weight of the deck and transfer it to the posts.
3. Posts: Vertical supports that hold up the beams and distribute the load to the footings.
4. Footings: Concrete bases that anchor the posts in the ground.

Joist Framing on Small vs Large Decks

On a small deck, the beams are sometimes incorporated into the joist framing. This means that the joists rest directly on top of the beams.

On larger decks, however, separate beams are used to support the joists from underneath.

Understanding Rim Joists and Ledger Boards

The rim joists are the outermost joists that make up the perimeter of the deck frame.

If the deck is attached to a house or building, one of the rim joists is replaced by a ledger board. This board is fastened to the house framing and serves as a connection point for attaching the deck to the building.

In terms of size, the ledger board is typically made from lumber that is similar in size to the other joists (e.g., if you’re using 2-by-8 joists, then use a 2-by-8 ledger board).

Consistency in Joist Sizing

When it comes to choosing lumber sizes for your deck frame, it’s generally best to keep things simple and consistent:

• Use the same size lumber for all your rim joists, ledger boards, and interior frame joists.
• If you decide to use 2-by-8 joists for your rim joists or ledger board, then use 2-by-8 joists for the rest of the frame as well.

Understanding Joist Sizing

The size of your deck’s joists depends on two factors:

1. Spacing: The distance between each joist.
2. Length: The distance that the joists span from one end to the other.

Minimum Joist Size

According to building codes, the minimum size for deck joists is typically a 2-by-6 lumber.

• Spaced 12 inches apart, these 2-by-6 joists can span up to 11 feet 7 inches without additional support.
• This means that if you have a small deck with short joist spans, using 2-by-6 joists may be sufficient and cost-effective.

Factors Affecting Joist Size

However, for larger decks with longer joist spans, other factors come into play:

1. Structural Integrity: Longer spans require bigger and stronger joists to ensure structural integrity and prevent sagging.
2. Additional Materials: Using smaller joists might seem cheaper initially, but it can lead to more expenses in terms of extra materials such as joist hangers, bolts, and concrete footings.
3. Labor and Installation: Building a deck with smaller joists may also require more labor-intensive tasks like digging and pouring additional footings.

Using Joist Span Tables

To determine the correct size for your deck’s joists based on spacing and length, you can refer to joist span tables specifically designed for different types of lumber.

Here’s an example of how to use a joist span table:

1. Look at the chart provided below (specifically designed for southern yellow pine or similar strength woods).
2. Find the row that corresponds to your desired spacing between joists.
3. Locate the column that matches your joist length.
4. The intersection of this row and column will give you the recommended joist size.

Example Scenario

Let’s say you have the following deck specifications:

• Joist spacing: 16 inches apart
• Joist length: 12 feet (144 inches)

Based on the joist span table, a 2-by-8 joist would be the logical choice as it can span up to 12 feet 10 inches at this spacing.

However, if your joists were 15 feet long instead, then you would need to use 2-by-10 joists, which can span up to 16 feet 5 inches.

Keep in mind that with these larger spans, no additional support is required under the joists. In contrast, using smaller 2-by-6 joists would necessitate the inclusion of a beam with support posts and footings beneath it.

Understanding Beam Sizing and Post-Spacing

Beams play a crucial role in supporting the weight of the deck and transferring it to the posts and ledger board.

Similar to joists, the size of your beams depends on two factors:

1. Joist Span: The distance that the beams will span between supporting posts.
2. Post Spacing: The distance between each post along the beam.

Minimum Beam Size

According to building codes, the minimum size for deck beams is typically a double 2-by-6 lumber configuration. This means using two pieces of 2-by-6 lumber fastened together.

Factors Affecting Beam Size

When determining the appropriate beam size for your deck, consider these factors:

1. Joist Span: Longer spans require larger beams to support the joists adequately and prevent sagging.
2. Post Spacing: Wider spacing between posts allows for larger beams since there are fewer points of support.

Using Beam Span Tables

To determine the correct size for your deck’s beams based on joist span and post spacing, you can refer to beam span tables specifically designed for different types of lumber.

Here’s an example of how to use a beam span table:

1. Look at the chart provided below (specifically designed for southern yellow pine or similar strength woods).
2. Find the row that corresponds to your desired joist span.
3. Locate the column that matches your post spacing.
4. The intersection of this row and column will give you the recommended beam size.

Example Scenario

Let’s say you have the following deck specifications:

• Joist span: 10 feet
• Post spacing: 8 feet apart

Based on the beam span table, you have two options:

1. Use a 4-by-8 beam with posts spaced 8 feet apart.
2. Use a 4-by-12 beam with posts spaced 12 feet apart.

The choice between these two options is significant, especially if you need several beams for your deck’s design.

On a large deck, using the 4-by-12 beam will save you the labor and cost of pouring additional footings and installing more posts. If the height of your deck allows for it, this can also create more open space underneath for a patio or storage area.

Understanding Post Sizing and Placement

Posts are essential components of your deck’s structure as they provide vertical support for the beams and transfer the load onto the footings.

The size and placement of your posts depend on two factors:

1. Beam Size: The dimensions of your beams, which are determined by the joist span and post spacing.
2. Deck Height: The distance from the ground to the top of your deck’s surface.

Beam Size and Post Spacing

The distance required between posts depends on the size of your beams:

• A 4-by-10 beam that supports a joist span of 12 feet requires posts no more than 9 feet apart.
• If your beam is around 9 feet long, then two posts will be sufficient for proper support.
• If your beam is 12 feet long, then three posts are needed to ensure stability.

Deck Height and Post Size

The height of your deck above the ground level also influences the size of your posts:

• For decks below 6 feet in height, you can use 4-by-4 posts.
• For decks that are 6 feet or higher, you’ll need to use stronger 6-by-6 posts.

Using Post Sizing Charts

To determine the correct size for your deck’s posts based on beam size and deck height, you can refer to post-sizing charts specifically designed for different load areas.

Here’s an example of how to use a post-sizing chart:

1. Look at the chart provided below (specifically designed for southern yellow pine or similar strength woods).
2. Identify the load area by multiplying the spacing between posts by the spacing between beams.
3. Determine if your deck’s height is below 6 feet or 6 feet or higher.
4. The corresponding value in the chart will give you the recommended post size.

Example Scenario

Let’s say you have the following deck specifications:

• Beam spacing: 10 feet apart
• Post spacing: 6 feet apart

Based on the given specifications, you can calculate the load area by multiplying the beam spacing (10 feet) by the post spacing (6 feet), resulting in a load area of 60 square feet.

Next, determine the height of your deck. If it is below 6 feet, you can use 4-by-4 posts. However, if it is 6 feet or higher, you will need to use stronger 6-by-6 posts for added stability.

Refer to the post-sizing chart for southern yellow pine or similar strength woods. Find the load area value of 60 square feet and locate the corresponding recommended post size based on your deck’s height.

Following these steps will ensure that your deck is properly supported with posts of the correct size and spacing, ensuring its structural integrity and safety.

How to Choose The Right Lumber Type

Determining the lumber size also has a lot to do with choosing the right kind of lumber for your deck. Lumber types used in deck construction generally fall under either of the following categories:

• Pressure Treated Lumber, which is usually pine or fir. These are treated with chemicals to make them extremely heat-resistant. This makes it ideal for warm countries. This type of lumber is also the least expensive, but take extra care in choosing to ensure that the lumber you get is free of loose knots.
• Naturally Resistant Species, which can usually be cedar, redwood, and cypress. These are resistant to rotting and insects. To retain the natural beauty of the tree source, you can seal or stain the wood before using it to build your deck. If you have the budget for more expensive but also more durable options, meranti, cambara or Ipe are great choices.

Putting it All Together

It might seem overwhelming at first, but in practice, it is not hard at all. Decide what size deck you want to build.

1. Determine the joist lumber that requires the least amount of support for the size of the deck.
2. Choose beams, post spacing, and post sizes.

Determining the lumber to use is one of the first steps in estimating deck building costs.

Let’s look at two examples.

Deck one – 24 x 10 feet

If the deck only extends 10 feet from the house, there’s no need to use 2-by-10s for joists.

• According to the Deck Joist and Joist Sizing Chart, 2-by-6 joists on 16-inch centers will span 9 feet 9 inches.
• Our joists are just 9 feet 7 1/2 inches long. We add in 1 1/2 inches for the ledger thickness, and another 3 inches for the rim joist which will act as our beam. This brings the total span to exactly 10 feet. So we can use 2-by-6 joists.

Next, let’s figure out the right beam size that can support the deck with the fewest number of footings. Since our joist span is 10 feet, we can determine that a:

• 24-foot long beam
• 4-by-12 dimensions

This beam with posts spaced 12 feet apart will be able to support our joists.

We’ll need:

• 3 posts
• 3 footings

Here’s how they should be positioned:

• One post on the left side of the deck
• One post in the middle, 12 feet from each end
• One post on the right side

The size of these posts is determined by two factors:

1. The load area
2. The deck height

In this case, the beams are 10 feet apart (ledger to beam = 10 feet) and the distance between the posts is 12 feet.

So our load area is:

10 x 12 = 120 square feet

According to the chart, we’ll need 6-by-6 posts regardless of how high the deck is.

Deck two – 12 x 12 feet

Based on the joist chart, we can use a 2-by-8 joist to span 12 feet without needing additional center support.

• One beam along the front of the deck will be sufficient since we don’t require a center support beam.

According to the Deck Beam and Post Spacing chart:

• A 4-by-8 beam supporting a 12-foot joist span should have posts spaced no more than 7 feet apart.
• For our 12-foot width, we can use a 4-by-8 beam with three posts and footings spaced 6 feet apart.

Our load area is calculated as 6 x 12 = 72. Based on this:

• We can use 4-by-4 posts for decks that are lower than 6 feet.
• For decks higher than 6 feet, we should use 6-by-6 posts.

Final Thoughts

A deck is a wonderful addition to any home, especially when it offers a beautiful view of your garden. It’s like having an outdoor room that seamlessly connects with your indoor living space.

You have the freedom to customize your deck based on your preferences: create a cozy seating area, decorate it with lush green plants, or even turn it into an open-air entertainment center with a TV and speakers for movie nights under the stars. Just make sure to shield your electronics from rain and dust!

However, keep in mind that having stylish deck furniture may attract unwanted guests such as birds and critters who see your deck as their new hangout spot. Instead of resorting to drastic measures like getting rid of them yourself, consider using professional bird control services to keep them away.

Additionally, if you often have visitors over, your deck can serve as a welcoming space to host and socialize with them. Taking all these factors into account, the tips provided above should assist you in creating a well-designed and functional deck.

Remember, the foundation of a good deck lies in selecting the right type and size of lumber. This ensures that you’re constructing something durable and long-lasting. So go ahead, and embark on your deck-building journey with confidence!

FAQs (Frequently Asked Questions)