Just like traditional wood decking, composite decking should overhang the edge of the deck. The decking overhang creates consistency in the overall deck appearances and hides many inconsistencies between the decking and deck’s substructure. Also, composite decking overhang helps to increase the life of the deck by diverting water.
Overhanging composite decking is an important element to the deck’s design for aesthetic reasons and protection of the deck’s substructure. Most composite decking should overhang the deck’s substructure ¾” (18mm) but may be limited to only a 1/2″ (12mm) or as great as a 1 ½” (38mm).
Unlike wood decking, composite decking overhang is determined by the manufacturer’s, which varies between brands and composite decking lines.
Let’s start there. What are the manufacturers ‘ limits to composite decking overhang?
There are two areas of composite decking with overhang limitations, the ends and the edges. Which are not always the same. This is especially true with scalloped decking boards.
For consistency, whichever is the smallest between the two, you will want to overhang the decking. Overhanging both the front and sides of the deck consistently.
Allowable Composite Decking Overhang by Brands
|Brands||Board Edges||Board Ends|
|DuraLife||2” (50mm)||2” (50mm)|
|Calimboo||5/8” (15mm)||5/8” (15mm)|
|Envision||Not Permitted||Not Permitted|
|Moisture Shield||¾” (18mm)||1 ½” (38m)|
|Trex||¾” (18mm)||½” (12mm)|
|TimberTech||1” (25mm) non-scalloped||1” (25mm|
|Verandadeck||1 ½” (38m)||1 ½” (38m)|
Why Overhang Composite Decking?
There are two big reasons to overhang composite decking.
Aesthetics and Structural
Overhanging deck makes your deck look better and increases the life of the deck.
This is done in a number of ways.
Structural Reasons to Overhang Composite Decking
First, hanging the decking past the edge joist, water is lead off and away from the joist. Limiting water exposure helping to keep your substructure dry and rot free.
It may not seem like much, but it does make a difference. Especially if you install composite fascia board to the rim joist. Without the decking overhanging the fascia board, water becomes trapped between the rim joist and the fascia board.
Trapped water is rot water.
I have torn many decks apart, and whenever you have two boards sandwiched together, the chances of rot is almost guaranteed. As water becomes trapped between the boards with nowhere to go but feed the fungi eating away at the joist.
Overhanging the decking acts as a mini roof shielding the micro gap between the material. Diverting the water off the deck and joist preventing rot.
“Do not surface-fasten within 1-1/2 in. (38.1 mm) of the end of a board or within 1 in. (25.4 mm) from the side of the board.”Fiberon Decking
Not all composite decking requires as much room from the ends of composite boards for fasteners but still. Overhanging the decking past the last joist provides more material between the end of the board and the fastener. Which is a good thing.
Increasing the distance from the end of the board will minimize the cracking of boards. Both during construction and those cold winter days when the boards shrink, puling against the fasteners and stressing the decking around it.
Aesthetics Reasons to Overhang Composite Decking
Yes, a deck provides a room to enjoy the outdoors, but we all want it to look good. It’s the little details that make all the difference in appearance.
Overhanging decking is one of those little things with many benefits in appearance.
Covering Fascia Board with Overhanging Decking
One way is covering over the composite fascia board. This keeps water out from behind the fascia board and hides the joint where the composite and wood meet. Giving the deck a nice clean look. Nothing but decking. Not an ugly joint filling with dirt as you lean on the railing looking down.
To do this, you need a minimum decking overhang of the composite fascia, which generally is 9/16″ (14mm) to ¾” (18mm)—depending on the fascia used. Aesthetically you want at least enough to cover the top of the fascia board.
But as my shop teacher taught me.
“Flush is hard. Intentional reveal is better.”
This is so true in so many construction applications, including decking overhang. Decking installed flush with the end joist highlights construction issues.
For example, if your joist bows slightly at the deck blocking, even only a 1/8″ (3mm). It’s noticeable. That little bit of joist sticking out past the decking makes it look really amateur. But if the decking overhangs ¾” on the ends and then narrows even to ½” in the middle. With overhang, you won’t notice it. Out of sight, out of mind, but in a good way.
Matching Stair Nosing Overhang
I don’t know why, but stairs just look better with nosing. That little overhang also shortens the run why maintaining the tread size.
Keeping that overhang consistent with each step, including the top step, the deck’s edge improves the look of the deck.
“The overhang of the stair tread is not to exceed 3/4”Trex Decking
Not all composite decking has the same nosing limits as Trex, but you do want to be consistent. If the deck has stairs, plan the same overhang for the decking on the deck. You will thank me later. It’s one thing that you can’t place, but it looks odd if the stairs and deck overhang don’t match.
Limitations with Composite Decking Overhang
With wood decking, I like to overhang the decking between 1″ and 1 ½” (25-38mm). A nice two to one ratio. 4 inches of material supported by the substructure with the rest cantilever off the deck. The same thing you do with deck joists.
But the same is not always true with composite decking. Only DuraLife composite decking allows such a significant overhang.
“DuraLife™ Natural Grain Collection decking should NOT extend more than 2″ (51 mm) beyond the framing in any direction.”DuraLife
Most are limited to 1″ (25mm) or less, with ¾” (18mm) being the most common.
With scallop boards limiting overhang even more. Scallops boards are becoming more common in an effort to reduce costs by reducing material. In the field, scallop effect little. The decking can still span 16″ (400mm), looks the same as a solid board from the top but costs less. But on the edge of the deck, it makes a big difference. With minimal edge material, there is little to support the decking overhanging.
TimberTech going as far as to say no overhang for many of their popular scalloped boards.
“All scalloped, PRO Terrain, EDGE Prime, and Reliaboard, can only be cantilevered on the ends.”TimberTech
This is not good for the health of the deck, but not all hope is lost.
One option is to picture frame the decking with a solid stock composite deck board, which allows for cantilever. A little more costly but provides material to be supported by the joist.
Not ideal, but another option is to support the edge of the decking with the fascia board. Not ideal in that fascia board is not structural and is not designed to be stepped on. Which is what you are doing each time is step on decking supported by composite facia board.
This isn’t a significant concern with a deck with railing, which will have minimum stress on overhanging decking. With the railing prevents foot traffic except by the stairs. And those times that your kids climb over the railing to get unto the deck. I have even seen an adult or two do the same.
So, with a railing around the deck’s perimeter, the picture frame decking is largely cosmetic. With no foot traffic, you can a little push of the rules a little more. Your call, but it will save you a little money and make your deck look better.
Conclusion of Composite Decking OverHang
Overhanging composite decking will improve the look and life of your deck. But unlike traditional wood decking, how much you can overhang is not consistent between boards. Always check with your decking manufacturer and the specific line of decking.
But as much as possible, incorporate it into the deck’s design. It’s good for the deck and good for you.