Do you want to boost your home’s living space by adding a deck but don’t want to hire someone for the work? Building a deck isn’t as difficult as you may think. With a few basic guidelines, beginners can learn deck construction. The first step is to plan how the deck will look. Here’s where you’ll run into the question, what is better, deck board overhang or flush?
Building practices say deck board overhang is better than flush. The overhang helps your deck look stunning and last longer. Both the stair nosing and deck boards overhang to protect the substructure. The overhang also protects the decking, especially if it’s wood.
The amount of overhang you need varies. Most boards overhang the substructure between ¼ to 1 ¾”, depending on the material. In this article, I’ll show you why overhanging decking is better and how much overhang is best.
Is It Better to Have Deck Board Overhang or Flush?
Deck board overhang is better than flush edges, according to decking industry professionals. There are several reasons to go for overhang over flush. But you have many options. Ultimately, it’s your choice. The decision depends on your taste, the building codes in your location, and the decking material.
Why is Overhanging Decking Ideal?
Overhanging is good practice in deck building. Deck board overhang protects the materials, and it also looks nice. The construction is easier for beginners to build a deck that’s pleasing to the eye.
The main reason is that the overhanging boards protect the substructure of your deck. It also contributes to safeguarding the joists and the decking material itself, especially if it’s wood. Wood is the most common choice because pressure-treated lumber is excellent for combating persistent moisture damage and decay.
Wood decking may split from the ends due to moisture or dryness and weaken over time. The material’s elasticity becomes shot, and the wood may even start to pull apart around the screws without cracking. However, overhanging wood deck boards add wood between the screws and end grain, keeping the fibers in place after fastening, and prevents splitting later.
An outdoor deck is exposed to rain and snow, so keeping moisture from becoming a problem is critical. Overhang deck boards allow moisture to divert from the wood before causing damage. The water can’t pool or sit and rot the joist rim or framing. Instead, it’s redirected away from the gaps to keep water from building up.
Overhanging deck boards boost the appearance of particular materials as well. Composite fascia and other types of composite material look better with overhanging. Fascia board edges can be unsightly, but the overhang covers this unattractive feature and prevents the material from rotting from rainwater.
An overhang enhances the look of a deck overall. Many people prefer the appearance of overhanging deck boards because it’s aesthetically pleasing. The overhang runs across the top of the band joist, hiding it from view.
If you have stairs leading to your yard, the overhang will also help with a smooth transition between decking and stair nosing. Stair nosing is a requirement. The nosing on your stairs creates more tread. Keeping the overhang on the deck edge consistent with the stair nosing improves the overall look.
Decking overhang has few limitations worth considering. Some people, for example, may not like seeing the end grain along the deck edge. However, composite decking also features ugly ends too, and there are options to solve issues with end grain.
Benefits of Deck Board Overhang
- Protects the joists and substructure
- Wicks moisture away from the deck
- Keeps wood and fascia in better condition
- Blends in with stair nosing
- Appearance is better
- More straightforward for beginners
- Visible endgrain
- Unsightly decking ends
Why Not Flush the Edges?
Appearance is always a matter of opinion. Some people prefer the edge of the deck to sit flush with the rim board and hide the wood grain behind a fascia board. So why is it better not to flush cut the edges?
It’s difficult to flush cut the edges of certain materials, including wood or composite planks. Composite materials are tougher to cut than wood. Plus, their exposed ripped or crosscut edges are not very appealing. Without sharp equipment and plenty of practice, you’re unlikely to produce a smooth edge.
Making the edge flush is extremely difficult with wood too, even though it is what most people use for their decks. Wood contracts and expands with temperature changes and moisture, so the result often looks sloppy after a year or two. With an overhang, the final deck takes on an intentional appearance.
Flush cut ends don’t project past the rim or band board and can allow moisture to seep or pool under the ends. Use of a fascia board to hide the end grain also collects water and can accelerate rot. However, there are a few options to hide the cut grain without making the edges flush. We’ll discuss those more in-depth below.
Another issue is that the joists become more visible from above if you have the edges flush. Each joist should be straight before screwing them into place. If the decking doesn’t overhang, you could stand on the deck and look down to see the joists. An overhang allows the decking to have a beautiful, clean straight edge because the joists stay hidden.
How Much Overhang Should a Deck Board Have?
The decking should overhang the joists between ¼ and 2 inches beyond the end joists and rim board. The amount of overhang you should leave depends on your deck board materials:
- Most wood decks: ¼” to 1 ¾”
- Composite decking: 1½”
- Picture frame deck: 1”
How much overhang you include depends on your materials and if it requires picture framing. Composite decking has unsightly edges and many people want to hide the end grain, so picture frame decks are popular. They hide the rim and finish the deck with clean lines.
Composite decking requires picture framing to clean up the ends. Wood decks could go either way, depending on your preference. Picture frame decking does have limitations, though.
With composite fascia, the overhang must extend at least 1 ½” past the unfinished rim to allow space for the picture frame. Some people leave up to 2 ¾” of overhang before installing the fascia. Otherwise, the deck has a weak spot that bends under your weight when you step down.
The rim joists are responsible for supporting more expensive materials or composite decking without scallop grooves. They help a picture frame stay strong under pressure and have a more distinct visual appearance.
Stair nosing plays a role in the amount of overhang you include as well. Some states or regions limit the stair nosing to 1”, which is the reference you’d use to create consistent decking. If you’re making a picture frame deck with fascia, the initial install of composite decking would cover the rim board and overhang the decking 1 ½” to leave room for the 9/16” fascia board. The result is a 1” overhang finish that’s safe and visually appealing, and matches the stair nosing.
Wood deck boards are the easiest to work with for both beginners and pros. You can adjust the overhang to suit your preferences. Make sure the deck board overhang matches the stair nosing.
How Far Can Deck Boards Overhang the Joists?
No matter what material you select for your decking, the overhang should never extend more than the ⅓ the width of the board. The greater the distance from the fasteners and support, the more likely the ends will bend or splay. Additionally, they may not look as appealing with your choice of railing either.
Most deck board overhangs are a minimum of ¼”. Less than that for the overhang, and there really isn’t one, and the structural integrity of the deck will suffer. If you’re unsure how far the deck boards should overhang, check with your local building department for acceptable guidelines.
You also want to limit joist overhang to a 2-1 ratio, especially with the overhang on stairs. The goal is to have enough material to keep the stairs or the decking edge from pulling up and off when someone steps on the edge. Industry code provisions in America allow cantilevers to extend ¼ of the joist’s backspan, meaning the total space depends on your material. Southern pin 2x10s that are 16” and span 12 feet can cantilever up to three feet, for example.
For the best results, allow a foot of overhand per two feet of support deck. Support the boards by limiting how much decking will overhang. Never overhang the edge of your decking more than a third of the material. That means standard 5.5” decking may have up to 1 ¾” of overhang.
Can Composite Decking Overhang?
Composite decking can overhang, but the material has limitations. The overhang may reduce the amount of kick damage to the boards. However, the material may not be as sturdy as lumber when it comes to the amount of weight it can support along the deck’s edge. For this reason, composite decking tends to have either an inch of overhang, or it sits flush with fascia installed to frame (and cover) the edges and ends.
If you choose to go with composite decking, check the material’s allowable overhang. Trex is a popular composite material with a maximum overhang of 102mm or around 4 inches. Between one and two inches of deck board overhang is ideal when you attach an outer fascia board, or at least 1 ¾” to 2 ¾” of overhang before installing the fascia.
Best practices go with overhang due to the structural benefits. Depending on the type of material you use to make your deck, the overhang is easier, especially for your first time. Beginners can build a great looking wood deck using the overhang.
What are your experiences with deck board overhang? Have you ever made a flush, picture frame deck? Share your experiences with decking in the comments. If you found this article helpful to your deck building project, please share it with your friends and family.