Building a Composite Deck with Benches Creates an Outdoor Gathering Place

Building a composite deck with benches offers seating matching the deck.

A composite deck with benches built in lasts through rainstorms and prevents ruined cushions and damaged furniture.

When one of my friends upgraded to a nicer home, he found himself with an unexpected problem. One of the biggest selling points of the house was the screened-in pool in the backyard. But the layout of the rear patio was so awkward that it was impossible to put his patio furniture anywhere under the cover of the roof without blocking the rear door of the house. A few rainstorms later, and the cushions on his patio chairs became something no one wanted to sit on.

The situation led to several get-togethers where guests sat on folding fabric chairs or on the ground. His guests, including myself, were okay with it, but his wife found it embarrassing. It was, after all, their next level house and not their starter home. Eventually, the solution they hit upon was building a composite deck with benches. This would not only take care of the seating problem but also cover up the 1980s-era textured patio with something more contemporary.

Positioning Deck Benches

When you’re building benches into your deck project, the first step is to decide where they will be located. The biggest concern in positioning is that they don’t interfere with passage in and out of the home. A bench blocking the door isn’t seating, it’s a trip hazard. The same goes for a bench that interferes with walking around the deck. Avoid irritating situations that will make you regret building immovable seating by placing benches to the side of any doors or any stairs leading off the deck. Also, allow 30 inches of space between the benches and walls or any other structure to leave a clear walkway. The next step is deciding how you’re going to hold the bench up.

Building Bench Supports into Deck Substructures

Composite is a more flexible material than wood and does not provide enough support on its own to hold a person up. This means that composite benches will need to be solidly supported by a wooden subframe. The wood posts holding up this subframe cannot be anchored directly to the composite, but should be anchored beneath the surface, either to the ground or to the deck’s substructure. Composite material then goes over the wood to match it to the deck’s surface. Composite deck railing posts, for instance, are often wood covered with a composite post sleeve.

Posts made out of four-by-four lumber are the standard timbers that provide the vertical supports for most decks. They’re also a fairly standard support for benches built on decks. There are three different types of posts that can be used for a built-in-bench on a deck:

  • Substructure posts are the very same posts that hold the deck up in the first place. In a bench, they’re cut above the surface at an appropriate height for the seating. The difficulty with these types of posts is that they may not line up or be spaced appropriately for a bench unless they’re on the perimeter. However, it is possible to use one of these deck substructure posts in combination with a post anchored by a different means.
  • Dedicated posts are posts put in place solely for the purposes of holding a bench up. They are rooted in the ground the same way as substructure posts, but are there solely to support the bench. The advantage of these is that they can be placed conveniently for bench building and are strong enough to hold several seated persons. The disadvantage is that they’re overkill and a waste of material. On a deck with space for use beneath, they’ll be in the way.
  • Short posts are dedicated posts that don’t run all the way to the ground. They are instead attached directly to the joists and beams underneath the deck with additional wood to hold them tight. A four-by-four post inserted between joists spaced 12 or 16 inches apart will need to be tied directly to the substructure through additional two-by-sixes running between the joists.

On ground-level decks, or when laying composite decking over a concrete porch, posts for benches can simply be anchored to the ground beneath or to the concrete. Since the deck is so low, this method won’t waste material, and since there is no room beneath the deck, these posts won’t be in the way.

Covering Built-In Benches with Composite

It is possible to build other types of benches using means of support other than two four-by-four posts. A storage bench, for instance, can be a box of two-by-four or two-by-six lumber that is secured to the deck joists with screws and covered with composite boards. This style of bench will still have to be anchored to the deck’s substructure, though, rather than simply resting on the composite’s surface.

No matter what style the bench is, when one is built onto a composite deck, it will need to be covered with the same material as the deck in order to create a unified appearance. There are a few different ways to do this. The surface of the deck seat is best made out of the same deck boards as the surface of the deck. Posts can be covered with composite sleeves or painted to cover the raw wood and match the color of the composite. The two-by-sixes that make bench backs can be covered with composite soffit board trimmed to fit. The precise details vary with the type of bench, the type of deck, and the options available through the composite manufacturer, and the ultimate choice will be up to the homeowner or builder.

Building a Composite Deck with Benches

When it came time to build my friend’s deck, we laid out the plan for the benches first. These were relatively simple backless benches with two posts centered directly beneath the seat on either end. The posts for these benches were simply four-by-fours attached to the concrete with a post base and some wedge anchors. These were cut off at 19 inches above the planned surface of the deck. Standard seat heights are around 20 inches, and this dimension left room for installing a composite surface later on. Once all the bench posts were in place, we built the rest of the deck’s substructure and laid the composite decking. Only then did we turn our attention back to the bench.

Constructing the actual bench itself started with cutting matching composite sleeves for the posts. We cut these about five and a half inches lower than the top of the post we’d already cut. This would allow us to install the two-by-six framing that would support the seat of the bench above the composite sleeve. We sandwiched the top of each post with two-by-sixes cut to 15½ inches in length placed center on the posts. The exterior framing of the bench was then added to the bench by nailing two-by-sixes cut to seven feet in length to the ends of the two-by-sixes sandwiching the post. In turn, these long two-by-sixes were boxed in by more two-by-sixes, and two-by-six blocking was added every 12 inches off center. This completed the framing for the bench, and it was time to add the composite. The seat was made of deck boards cut to slightly overhang the edge on every side. Composite fascia was then added to the exterior surface of the outward two-by-fours to completely hide the wood of the bench from view. The result was a bench that almost seemed to be floating above the surface of the deck, and which completely matched the deck beneath it.

The benches I helped my friend put together were backless benches, meant for casual seating. Adding a back to the bench makes it harder to conceal the wood beneath and it was important to my friend that none of the wood show. We also opted not to add a two-by-six on top of the framing and underneath the composite seat, because it could be seen between the composite boards of the seat by anyone sitting down on it. This made it important to find a rigid, high-quality composite that wouldn’t flex when someone sat on it.

Infinity decking from Fortress Deck fit the bill. Infinity decking is a bamboo-based composite with a stronger structure than the typical wood-plastic composite. The extra rigidity and density of these boards helps prevent flexing underfoot when used on a deck’s surface and under rear ends when used as a bench seat. It’s also engineered to resist UV, moisture, and other outdoor threats. A unique, slightly rubbery capping around the board gives each board a natural matte texture and color. Contact Fortress Deck to find out more or request samples, or check out Fortress Building Products’ other beautiful and durable outdoor products.

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