There is nothing like a beautiful deck to make a home’s outdoor space usable. But what good is a deck if it's not stable?. A stable, long-lasting deck needs five vital components: posts, bearers, joists all of which comprise what is called the “frame.” And on top of the frame, of course, sits the floorboards. Let’s break down each component so you can understand what makes a stable and long-lasting deck.
Frame
What is a Frame?
The frame is the skeleton of the deck. It’s the support structure, comprised of posts, bearers and joists. The posts are the frame’s legs. They make the deck level and give it ground clearance. The bearers are the main support structures of the upper part of the deck and sit directly on the posts. The joists are the upper-most support structures that attach to the bearers and are the foundation for the deck boards.
Posts
What are Posts?
Think of posts as the legs of your deck. Posts are the vertical support structures that carry all of the deck’s weight. Usually, posts are placed on a concrete footing which adds extra stability. The most common sizes for posts are 4” x 4” and 6” x 6” but you can add a couple more inches to these being 4” x 6” or 8” x 8” posts if you are looking for extra stability and longevity.
Material of Posts
The material of your posts could affect its stability and longevity.
Cedar
Cedar wood makes for posts which are visually pleasing and emits a pleasant smell. It's also naturally insect-repelling with tannins and oils that keep insects away. The downside of cedar as a decking post is that it is expensive and requires occasional maintenance such as annually applying sealant and staining that protects against UV exposure.
Pressure Treated Wood
The next best wood option is pressure-treated wood. Pressure treated wood is widely available and affordable. It’s easy to cut and it will stay bug-free when properly oiled and stained. However, weather extremes make it contract and expand, compromising its longevity over time.
Powdered Steel
Where there are serious concerns about weather-influenced changes in wood such as warping and splitting or constant insect infestations, steel posts are a great alternative. Steel is perfect for heavy decks especially in traffic intense areas like commercial premises. Powdered steel which has a protective layer allows for the post to exist in wet and humid conditions, preventing rust.
Aluminum
Aluminum posts are a good choice that balance costs and weatherproofing. Aluminum is not prone to insect attacks or rust. Furthermore, it is also lighter and more affordable than powdered steel.
Installation of Posts
Footing: A footing is a concrete or compacted gravel mixture providing a solid anchor for the post. The footing is either cylindrical or square and is placed in a hole in the ground. Generally, the footing is created, and then the post is installed on top of the set footing. This solid base makes the post more stable and minimizes shaking, shifting or tilting of the post and deck.
Positioning: Ideally, posts should be on level ground. If it's installed on a slope or uneven ground, it needs to be positioned vertically regardless of the angle.Posts come in a variety of thicknesses and the thicker the post, the more weight it can safely bear. The typical range between post installation is 6 feet apart, using 4”x4” posts. If you are using 6”x6” posts, 8 feet apart is acceptable. If you want a more rigid deck, you can have more posts and space them closer to each other.
Securing Posts
Bolting
Galvanized carriage bolts secure the posts to the bearers (upper structure). They usually come in sizes of 5/16", 3/8", and 1/2" costing anything from 20 cents to about $3 each.
Post Brackets
When you mount the posts directly on a footing, you need a way to secure the post to the concrete underneath. This is when a contractor would use brackets. The brackets are secured both to the footing and the post with anchor bolts, providing a strong, permanent attachment of the post to the footing.
Bearers
What are Bearers?
Bearers are large horizontal beams that rest on posts and carry the deck’s weight. They are placed perpendicular to the post forming a 90° angle.Their main job is to distribute the deck’s weight to the posts. However, they also serve a secondary function of allowing proper ventilation under the deck and between joists.
Material of Bearers
As a foundational element to your deck, it's best to use high quality material. Because the bearers are exposed to the elements, building specialists recommend using H3 treated pine. H3 treatment is a procedure applied to wood to condition it against weather damage in outdoor use. It also makes the wood resistant to decay, fungi buildup and insects.
Bearer Sizing
Since bearers are the main support for the upper deck, it's necessary to use thick lumber. The most common size for bearers is 5.5”x 1.77”. However, you can use 7.48”x 1.77” depending on the joist size. If your deck is not wide, you can use 3.45” x 1.77” bearers.
Installing Bearers
Alignment
Correctly aligned bearers rest level and parallel to your home's support board (ledger). This basically means that the bearers are flush to your home, allowing for the homeowner to exit the home onto the deck and have it on the same plane as the home’s flooring. Thus, it's essential that the bearers are straight as to avoid sloping. Not only will sloping make using the deck uncomfortable, but it may also compromise the structural integrity and overall safety of the deck.
Attaching Bearers to Posts
A secure attachment of the bearers to the post is essential. A common way of securing the two together is with galvanized bolts.The most common size of galvanized bolts measure ⅜” in diameter for basic residential decks. Use bigger diameter bolts up to 9/16” for more stability in heavily loaded decks. You can also add diagonal bracing to complement the attachment, which helps to prevent shifts in the deck frame after long-term use.
Joists
What are Joists?
Joists are the horizontal beams that lie on bearers and hold the deck’s upper boards. They are usually made from the same material as the bearers being hardwood or treated pine.
Joist Placement
The average width of joist timber is between 1.5 and 2 inches while the average height is between 5.5”-12.5”. The joists can be placed on the bearers or installed flush to the bearers using a notch and bracket connecting the joists to the bearers. If placed on top of the bearer, the joists are secured in place with galvanised bolts. Spacing between each joist is about 18 inches apart depending on expected load. The correct positioning allows for even distribution and reduces sagging or warping with weather changes. Once all the joist boards are aligned and the surface is confirmed to be level, it is set for deck board installation.
Deck Flooring
Although not part of what is considered the frame, we decided to also include the essential part of a deck, being the floorboards. The floorboards are about 1 to 1.5 inches wide. The floorboards are spaced 1/8 to 1/4 inches apart for wood or 3/16 to 1/4 inch for composite boards. The spacing accommodates for expansion and contraction from weather changes.
Deck Flooring Material
You can choose from wood, vinyl, or composite decking flooring material. Pressure treated pine is most affordable, while vinyl is more expensive, and composite is even more expensive. Wood requires a lot of maintenance including regular staining and sealing. Vinyl is a great choice, but somewhat ugly and fake looking, as it is just plastic, yet it's great as it's resistant to warping, mold, and pests. Composite is often a combination of both natural and synthetic materials. It isn’t resistant to mold but does repel pests.
Deck Flooring Placement and Securing
The typical length of deck boards ranges from 8, 10, 12, 16, to 20 feet long. They are laid perpendicular to the joists. You can choose different patterns, the simplest being a straight placement. You can consider more intricate patterns for enhanced appeal. Deck boards are secured into joists using 1 inch screws or nails. You can use stainless steel or galvanized screws and nails for added protection against rust.
Common Deck Building Challenges and Solutions
Uneven Joist Heights:
Problem: Joists of varying thickness can cause misalignment. Joists with different thickness will ruin the deck’s level alignment and compromise its stability.
Solution: Get joists with equal thickness from one supplier. Place the joists on a flat surface. Use a level to confirm they have equal thickness before install.
Inconsistent Lumber Thickness
Problem: It’s common to find pressure-treated lumber with different thickness.
Solution: Inspect each component’s thickness ensuring every group's lumber has equal thickness before installation. Where there’s inconsistent thickness, use electric and manual planers to reduce excess thickness. Sand down minor thickness errors.
Warped Joists
Problem: When using lumber for decking, your frame may warp due to weather changes, especially after a long time.
Solution: Identify the warped joist. Remove the deck floor board directly above it. Wet the warped joist. Attach a strong straight board to it. Clamp together the 2 pieces and allow it to set. Once corrected, use a planer to ensure they’re level. Reinstall the decking floor board. Alternatively, you can replace warped lumber with harder wood or alternative material.
Breakdown of Deck Components and Purposes
| Component | Purpose | Properties |
| Frames | Forms the deck structure. | Stands on the posts and footing. Consists of bearers and joists. |
| Posts | The vertical support structure that raises the deck above ground. | Anchored in concrete footing. Can be made from H3 treated pine, cedar, or treated hardwood composite wood, steel or aluminum. Measures 3.5”x3.5”, 4”x4” up to 6”x6”. Thicker posts offer more stability. |
| Bearers | Primary support structure. Transfers weight to posts. | Horizontal wood boards resting on posts. Measures 5.5”x1.75”, 7.5”x1.75”, or 4”x2” |
| Joists | Secondary support structure. | Vertical wood boards that rests perpendicular to bearers. Typically measure between 1.5” and 1.75”. Spaced in intervals of 18 or 24 inches depending on expected load weight. |
A deck is a simple structure but must have all the key elements in order for it to be safe and long-lasting. Abiding by the proper measurements necessary to allow for proper load-bearing capabilities are required. Deviating from standard timber sizes and spacing can lead to a dangerous and unstable deck. If you are looking for a new deck for your backyard, call Lumina Construction today at 212-951-9163.
Frequently Asked Questions
A deck is made up of posts, bearers, joists, and floorboards, which together form the frame and create a stable, durable structure.
Deck posts can be made of cedar, pressure-treated wood, powdered steel, or aluminum. Each offers different advantages with regard to stability, longevity, and resistance to weather and pests.
Bearers rest on posts and joists lie on bearers. They both provide the foundation for floorboards and ensuring even load distribution.