Outdoor patio with a white stone fire pit, a white cushioned sectional sofa with patterned pillows, green plants, and a wooden fence in the background.
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DIY Outdoor Sectional Sofa with Mattress Cushions

Big box stores want thousands for outdoor sectionals that barely survive a few summers. But I am here to show you how to build a DIY outdoor sectional for a fraction of the cost. All you need is three 6×6 timbers, basic tools, and a week to build something better. A simple outdoor sectional couch that doesn’t require fancy joinery or carpentry skills to build. And the best part is, it uses mattresses as seat cushions which saves a TON of money! Let me walk you through this easy woodworking project and building plans so you can enjoy the rest of the summer on your back patio 😉 

Outdoor patio with L-shaped wooden sofa featuring white mattress cushions, brown and patterned pillows, a round stone fire pit, potted plants, overhead string lights, and a large rug on the paver floor. Trees and a fence in the background.

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  • Cost: About $850 (including mattresses and pillows)
  • Time: About a week

Background

If you have been here for a while you may recognize parts of this build from my outdoor sofa plans I originally made for the One Room Challenge when I made over the patio. I absolutely loved those sofas. But hubby and I struggled with the cushions. Outdoor cushions cost WAY too much in my opinion and as a result, I never wanted to leave them outside out of fear of having to spend hundreds of dollars more replacing them each season.

Modern outdoor patio with a wooden sofa featuring white cushions and geometric pillows, a gray and white rug, green plants, and a storage shed in the background on a sunny day.

As a result, we rarely used the outdoor patio lounging space because the cushions were always in the basement. So I knew I had to come up with a solution to fix this. 

The Solution

My outdoor sunbed was my jumping off point. Covering a mattress in a waterproof casing and then a fitted sheet worked really well and allowed me to leave it outside all the time. That solved the cushion issue. 

I also knew I wanted to keep the original design of the patio furniture because I LOVED the look. I thought about it for a long time and finally decided a sectional sofa would be the perfect fit for my mattress cushion idea.  

Things to Note

I disassembled my original sofas to build this sectional. For the purposes of this outdoor sectional build I am going to show you how to build it from scratch. That being said some pictures may seem like I skipped a step because some of my components were already assembled. 

I have also been toying with the idea of making printable outdoor sectional plans with step-by-step instructions available for purchase. I know some people find it easier to have a piece of paper in front of them while they go through the steps. If this is something you would be interested in, please let me know 😉 

Sourcing Your Lumber

First things first. In order to build my outdoor sofa, you are going to need lumber. When I originally built our patio furniture, my local hardware store did not carry the 6×6 timbers I used for the sides of the sofa aka the arms. So I purchased mine from a local lumber yard. I have since seen 6×6 pressure treated timbers at Home Depot.

All lumber sizes are noted as common sizes in inches x inches x feet.

DIY Outdoor Sectional Supply List

Note, this picture is all the wood I used to build the dining table and both of the original sofas. You will not need this much wood for this build. 

Several long wooden boards of varying sizes are stacked neatly on the floor of a garage, which has tools, metal sheets, and other materials organized against the walls.

*I used smooth sawn Douglas fir timbers. Mine were not pressure treated and I had a few pieces that produced sap the first few years. But when I built the stock tank deck I did use pressure treated wood and still had boards that sapped. So this may or may not matter, just something to note. 

**Make sure both your impact driver and your drill each have fully charged batteries and have an extra standing by if possible. You will need them.

Know Before You Build

If you are not an experienced builder you may not be familiar with wood sizing. Common wood sizes such as a 6×6 are not actually 6 inches by 6 inches, they are 5.5 inches by 5.5 inches. If you prefer a smaller size like a love seat or a single sofa, you will need to account for this in your measurements. Always double check the actual dimensions of your lumber before making cuts.

Step 1: Cut the 6x6s to Size

You will need to cut the 6x6s into 10 pieces, each 32 inches long and 6 pieces at 7 inches long. The longer pieces will be the side pieces or the sofa arms and the short pieces will be the extra seat support under the sectional. 

A garage workshop with a miter saw on a stand, a long wooden board ready for cutting, and shelves with tools, paint cans, and various supplies against the wall.

6×6 Cut list (if using the same dimensions I did)

  • Ten – 32 inches long
  • Six – 7 inches long 

Note: It is most efficient to cut four 32 inch pieces and two 7 inch pieces per 6x6x12 and two 32 inch pieces and two 7 inch pieces out of the 6x6x8. 

I used my 12 inch miter saw to cut these but the blade is not large enough to cut all the way through in one pass. So if you are in the same boat, you will have to rotate the wood until the blade goes all the way through.

Several wooden 6x6 blocks of different sizes are arranged on a table in a workshop, ready for a woodworking project. Tools and supplies are visible in the background.

Below is a video clip of how I cut ours. This will not produce a perfect cut, however, you will be doing a lot of sanding anyway if you want to achieve the same look I have.

You will not be able to make this cut with a circular saw unless you have access to a timber circular saw. A circular saw will come close, depending on the size of your blade, but even after rotating you will still have a little bit leftover that you will need to cut with a hand saw or reciprocating saw.

Step 2: Cut the 2x4s to Size

Measure and cut the 2x4s for the seat frame. You will be building two identical frames for the mattresses. I HIGHLY recommend purchasing your sofa mattress cushions before starting this step. I used narrow twin size mattresses for the seat cushions and king size pillows for the back cushions. If you choose different mattresses or pillows, you will need to adjust your measurements to accommodate the size of the cushions. This is why you should have the cushions on hand prior to making any cuts in this step.

Based on the size of my RV mattress seat cushions (75w x 30d), I cut four 2x4s to 75 inches long, four 2x4s to 27 inches long, and eight 2x4s to 72 inches long. 

2×4 Cut list (if using the same mattresses I did)

  • Four – 75 inches long
  • Four – 27 inches long 
  • Eight – 72 inches long

Step 3: Cut the 2x8s to Size

Measure and cut the 2x8s for the back supports. There are five vertical pieces and two horizontal pieces. Based on the size of my narrow twin mattress seat cushions and the overall length of the back of the sectional you will need to cut five 2x8s to 20 inches long, one 2×8 to 75 inches long with a compound miter cut (measure to the inside of the miter), and one 2×8 to 105 inches long with a compound miter cut (measure to the inside of the miter).

A Ryobi miter saw with a red blade is positioned over a piece of wood, ready to make a precise compound angled cut. The wood is marked with a red guideline. Workshop cabinets and tools are visible in the background.

2×8 Cut list (if using the same mattresses I did)

  • Five – 20 inches long
  • One – 75 inches long with a compound miter cut on one end (measure to the inside of the miter)
  • One – 105 inches long with a compound miter cut on one end (measure to the inside of the miter)

The two mitered cuts in this step will come together for the back support corner piece. Regular miter saws will not make this cut on a 2×8. You will need a sliding compound miter saw to make the 45 degree angle on a 2×8. If you do not have one, you could butt join them, it just won’t have the same professional result as a mitered corner.  

A hand holds the corner of an unfinished wooden frame with a mitered joint, resting on a concrete surface.

Step 4: Sand All the Wood Smooth

I used my orbital sander with 120 grit sandpaper on the flat surfaces of the pieces of wood and the timbers. 

An orange electric sander rests on top of large, unfinished 6x6 wooden blocks, which are placed outdoors near a white brick wall and a partially open garage.

Then I sanded all the edges of the timbers with a belt sander and 60 grit sandpaper to create a bevel. This can also be achieved with a router, but when I originally built these I did not have one yet. If you have one, it will save you a lot of time. 

A yellow Ryobi belt sander sits on a cloth-covered workbench scattered with wood dust in a workshop setting.

This is definitely the worst step. I wish I could say this was a quick sand but it was not. This part was far from fun but gave the pieces a lot more character in my opinion. If you have never used a belt sander before I highly recommend you practice on some scrap wood first. They are pretty powerful and can damage your wood quickly if you are not careful.

This is what they looked like stacked before beveling them. 

Stacked wooden beams and planks of various sizes are arranged vertically and horizontally in a workshop setting with additional loose boards in the background.

Here is what they look like after giving them the bevel. It definitely creates the higher end look like my Restoration Hardware inspiration. 

Four stacked wooden beams with visible wood grain patterns, lying on a workshop floor next to two tape measures and other pieces of lumber.

Step 5: Attaching Your Timbers for the Sofa Arms

This part is a little tricky, so pay attention. I attached the timbers for the arms with screws, but before you drill any holes, determine the orientation you want for your wood. Meaning, if not all your pieces look the same on all sides or have a blemish you don’t want seen, stack them up the way you want to see them. Then when you are satisfied it is a good idea to flip each piece upside down and number them on the bottom so you remember the order. Do not skip this, trust me, it becomes difficult to remember once you get going. 

A wooden 6x6 with four evenly spaced holes drilled in it, lying on a concrete floor scattered with wood shavings.

You will be drilling holes to attach the pieces from the bottom side of each block. This way none of the screws or holes will be seen when fully assembled.

Diagram shows labeled stacking order for left and right sofa arms, each with five blocks numbered 1-5 from top to bottom, for a DIY outdoor sofa sectional assembly. Background is a patio with a wooden fence and trees.

To begin, use the 3/4 inch spade drill bit to drill 4 staggered holes into block two about 3 inches deep (I actually measured mine every time so they would be the same). You can also put a piece of tape around the bit so you know when to stop. Remember, these are all upside down right now so you are drilling into the bottom of piece 2.

A yellow and black DeWalt power drill with a spade bit is resting on a wooden 6x6. There is a hole drilled in the wood, with more stacked 6x6s and a plant in the background.

Word of caution. These timbers are pretty heavy duty and take some serious force to drill into. Wear work gloves and hold onto your drill tight so it doesn’t pull you unexpectedly or swing around and hit you. As I mentioned above, you will need a fully charged battery for your drill as this drains the battery pretty quick.

Now stack block two (still upside down) onto block one (also upside down). Make sure all edges are lined up and it is positioned to your liking. Then use the GRK 5/16in x 5-1/8in Structural Screws to attach the two pieces. Since the holes are drilled 3 inches deep, your screw will go through block two into block one securing them together. Note, if you choose to use different screws to attach the blocks, you may have to drill different size holes. 

A girl wearing gloves and shorts uses a power drill to drive a screw into a wooden 6x6, with multiple 6x6s visible in the background.

I chose to use the GRK screws because they are an alternative to lag screws. The entire sectional is fairly heavy and lag screws are usually the best way, but because of the depth, these were a great idea and much easier to work with.

A gold wood screw lies on a wooden 6x6 near two uneven holes, with bricks in the background and a white cloth partially visible below.

I found the impact driver to work best for this part since you are driving the screw through 5 1/8 inches of wood, about 2 1/2 inches on each block. 

From a diagram perspective, this is what you are ultimately doing. 

Diagram showing step-by-step assembly instructions for a DIY outdoor sofa arm, with labeled blocks and arrows indicating the order to attach them. Instructions and website are at the top of the image.

Once you have attached block two to block one, drill your holes in block three making sure to stagger them so they DO NOT line up with the holes you drilled in block two. To avoid confusion, I only drilled holes into one block at a time and marked where they would go before drilling. 

Instructional graphic for assembling a DIY outdoor sofa sectional arm, showing step-by-step drilling guides, a profile view, and a top view with notes on hole placement and staggering. Text reads “DIY Outdoor Sofa Sectional Sofa Arm Assembly.”

Once you have drilled the holes, stack block three on top of block two and use the screws to attach them as you did above. Repeat with the remaining blocks four and five.

A stack of 6x6s on a white sheet, beside a stone wall with drills and tools on top. In the background, a metal bench frame and patio furniture are visible.

When you have attached all the arm pieces only the bottom piece (block 5) will have holes that can be seen from the underside. The top piece will not have any holes or screws visible. 

Once all the blocks are attached you can flip the arm over and repeat for the second arm. Note, this may require two people as five of these screwed together is quite heavy. 

Step 6: Build the Seat Frame

Using the wood you cut in step 2, let’s assemble the bench supports for the mattresses. Start by laying the 2x4s out in a rectangle with the 75 inch pieces on the outside of the rectangle and the 27 inch pieces on the top and bottom inside. This is to make sure you cannot see any cut ends from the front of the sectional once assembled. This is easiest with a set of corner clamps

A rectangular wooden frame is clamped at the corners on a concrete floor. Power tools, screws, and other wooden pieces are nearby, suggesting a woodworking project in progress.

In hindsight, I could have built the frames with pocket holes and mitered corners like I did for the dining table frame so no screws would be seen, but this worked just fine and kept the build simpler without the need for a Kreg Jig. But if you have one, you could definitely build it this way. 

Attach the 2x4s of the seat frame together with the 2 1/2 inch deck screws. I highly recommend pre-drilling pilot holes so you do not split the wood and have to start over. Every time I don’t pre-drill, I always regret it! I staggered the screws just a little for a stronger hold. 

Then, place the 72 inch pieces in the middle, spacing them as even as possible (about 4.2 inches). I did not actually measure this, I just eyeballed it. Screw these into the end piece on either side the same way. 

A wooden frame made of light-colored lumber lies on a concrete floor. The frame consists of two long side pieces, two shorter end pieces, and five evenly spaced vertical crossbars. Tools are partially visible in the background.

Repeat for the second seat frame. 

Step 7: Stain All the Wood

I have used my share of exterior paint and wood stain over the years and the only one that has really held up in our Colorado sun is the Cabot oil based stain I used on our shutters. So that is the stain I used on the arms and the back supports of the sofa. 

Wooden blocks and beams are drying on a makeshift table in a garage workshop. Two blue paint-stained gloves lie nearby on a white cloth. Tools and equipment are visible in the background.

And the stacks drying after their coat of stain.

Two stained wooden stacks of 6x6s drying on a covered table in a cluttered workshop, with a yellow can of Cabot wood finish nearby and various tools and supplies in the background.

Because I was using a mix of new and old wood here, I chose to stain the seat supports black and give the sectional a two tone look, similar to something you would see in West Elm or Article furniture designs. In hindsight I probably could have used the Cabot on all the parts if I wanted. 

A black wooden bed frame with four horizontal slats is drying on a tarp-covered table, supported by wooden planks, with paint marks visible on the tarp.

I applied one liberal coat to all sides and allowed 24 hrs of dry time on each side before reapplying. Both colors require two coats of stain to protect from sun and water damage, so this is definitely a multi day process. I also didn’t have enough room in the garage to do all the parts at the same time so I had to stain all the stacks and supports and then move on to the seat frames.  

Step 8: Assemble the Arms and Seat Supports 

Note, this sectional is VERY heavy! I HIGHLY recommend assembling where the sectional will sit permanently. 

A partially constructed outdoor bench with wooden ends and black slats stands on a paved patio. A wooden fence, trees, and shrubs line the backyard under a blue sky with some clouds.

For this step you will need to bring the sofa arms, the seat frames, and the 7 inch blocks to your outdoor space and lay them all out. Note, the feet will be standing vertically at 7 inches high. The seat frames will sit on top on these, (which are 3 1/2 inches) plus the thickness of the mattress (mine is 6 inches) for a total seat height of 16 1/2 inches. 

Temporarily (DO NOT attach yet), use two of the 7 inch blocks to prop up the seat frames at either end by each arm. Lay the rest of the blocks out under the seat frames with two where the seat supports meet (one in front and one in back). Then clamp the corner seat together and level the rest of the sofa out. 

A wooden 2x4 frame under construction sits on a patio. A level tool rests across the slats, and a drill and clamps are visible. The background shows grass and a round stone fire pit.

Once the sofa parts feel secure and are level, pre-drill 5 holes into the inside of the end of the seat frames, between the 2x4s, into the arm stacks. Then attach the frame to the stack with the 2 7/8 inch headlok screws. These are beefy screws and can split the wood so don’t skip the pre-drilling. 

Two yellow DeWalt power drills rest on a wooden surface near a box of HeadLOK screws. A wooden fence is in the background, and the drills are placed on a black 2x4 frame.

This is what it looks like with the screws in place. Once it is attached you can move the 7 inch block to the middle of the frame. Repeat this on the second side of the sectional. 

Black 2x4 support frames are attached to a wooden bench with a warm brown finish, sitting on a patio made of tan and brown stone pavers.

Next, you need to attach the two seat frames together where they are currently clamped. Again pre-drill four holes through the 2x4s where the frames meet in the corner. 

A yellow power drill rests on a black wooden frame being assembled on a patio made of stone pavers; bolts connect the frame pieces, with rocks visible in the background.

Then attach them together with lag bolts, nuts, washers, and lock washers. I used my impact driver with hex driver attachment. I chose lag bolts here rather than more headlock screws in case we ever need to move it and disassemble the two pieces. 

Four metal bolts with hex nuts and washers are aligned vertically on a textured, tan surface. The bolts are arranged side by side, each threaded with two washers and two locknuts.

Step 9: Attach the Feet Supports 

Attach the feet supports under the sectional. These are the six 7 inch pieces you cut in step 1. These are necessary to keep the center and back of the couch supported. I positioned mine with four in the corner making a square and the other two roughly in the middle of each of the seat frames. Note, these are standing vertically at 7 inches high. 

A wood sectional frame sits on a stone patio, viewed from above. The frame rests on wooden blocks, with a wooden 6x6s attached. Rocks and bricks line the edges of the patio.

I used 2in 1 1/2×1 3/8 in galvanized Strong Tie brackets and #10 1 1/2in Simpson Strong Drive screws to attach these to the feet and the frames. Because I spaced the 2x4s a little tight for the added weight support, I needed my right angle drill bit extender to do this. 

A DeWalt power drill with an attachment rests on black 2x4 frame near a bracket and a box of screws. The scene is outdoors, with brick paving and grass visible in the background.

Step 10: Attach the Back Supports

First, lay out the five 2x8s you cut in step 3. I did not measure the spacing on these, I just eyeballed it. 

A wood outdoor bench frame is positioned on a stone patio, with some wooden slats attached as seats and backs. The frame is L-shaped and set near a landscaped garden with trees, rocks, and grass in the background.

Then clamp each piece to the seat frame and make sure they are level between one another. 

A partially built outdoor sectional with wood framing, a yellow level placed on top, clamps securing beams, and tools nearby. The furniture sits on a paved patio, with grass and a wooden fence in the background.

Then pre-drill three holes in a triangle pattern for the deck screws to screw directly into the frame. Repeat on the remaining four vertical supports. Also, it helps to use the brown deck screws to blend in with the wood. 

A close-up of a wooden outdoor bench being assembled on a stone patio, showing vertical and horizontal wooden slats, with houses and a cloudy sky in the background.

Once all the vertical pieces are attached, clamp the long back supports (the 105 inch piece and the 75 inch piece cut in step 3) to the vertical supports and make sure they all line up and meet in the corner. 

A wooden frame is being assembled with clamps holding pieces in place. The structure sits on a brick patio near a backyard fence, with tools and greenery visible in the background.

Again, pre-drill three holes in a triangle pattern for the deck screws to screw directly into the vertical back supports. Repeat on all five of the vertical supports. 

A close-up of a wooden frame being clamped together outdoors, with rocks and a brick wall in the background. A yellow tape measure rests on the black frame.

For extra strength I also added some brackets to the corner of the back support and where the back supports meet the arm stacks. These are galvanized and did not come in brown so I spray painted them to blend in with the wood better. Spray painting is totally optional, but this is how I did it so the screws would match too. 

A can of brown Rust-Oleum spray paint, metal brackets, a painted wooden block with screws, and are arranged on a gold-textured surface.

And what the hardware looked like freshly painted.

Metal hardware pieces, screws, and brackets are arranged on a surface and a wooden block, all spray-painted brown, with the surrounding area covered in overspray.

Once the brackets and screws are dry, attach them to the sectional. Start with each end of the sofa and pre-drill holes directly into the arm stack about 1 1/2 inches down so it sits flat under the bevel and just above the bottom of the back support. Repeat this on both sides of the sectional. 

Close-up of two large wooden 6x6s joined with a 2x8 by metal angle brackets on a patio, with a potted fern and patio chairs visible in the background.

Lastly, add the larger bracket (these are the ones I used in my original build) to the inside of the corner of the back supports. Again, you will want to predrill this. 

Close-up of two wooden 2x8s joined at a corner with a brown metal bracket and several screws. In the background, there is a fence, rocks, grass, and some blurred outdoor elements.

Initially I did not add the brackets but the back supports moved a bit when we leaned on them and didn’t feel 100% secure. Now they are rock solid!

Step 11: Add Cushions and Pillows

The last part of this build is the cushions. As I mentioned above, I used mattresses as the seat cushions and king size pillows as the back cushions. I chose twin size camper mattresses that measure 75×30. They form an L and don’t require a separate corner cushion. 

Two memory foam mattresses are unrolled on a clear plastic sheet over a patterned rug and wooden floor in front of a beige couch.

You could use a regular twin size mattress, however this would create a cushion depth of 38 inches. Since I was using the 6×6 timber stacks from my original build (at 32 inches long) a regular twin would have been too deep. But you could build this larger to accommodate a regular twin. 

For the back cushions I used six king size pillows. I researched many different options, but this was the best fit I could find. And honestly, it’s very comfortable! Several times I have felt like I could sleep out here on the patio!

Both the mattresses and the king size pillows have a zippered waterproof casing on them in addition to white fitted sheets and zippered pillow cases. I chose white to avoid the sun fading any colors or patterns and so I could wash the sheets with bleach if need be. But full disclosure, I will store all the back pillows and mattresses in the basement during the colder months since we do get a lot of snow in the winter. I do leave them out in the rain though and so far so good!

NOTE: The decorative pillows I used are not outdoor pillows and I do take them inside when we are not using them. I have a console table by the patio door that I store them in, so I don’t have to go far. You can definitely use outdoor throw pillows, but I have a hard time finding ones that match my style. 

Step 12: Enjoy Your Custom Outdoor Sectional 

Finally, sit back, relax, and have a great time enjoying your backyard while lounging on your very own outdoor sectional sofa! This modern outdoor couch is the perfect addition to your outdoor area and a great way to get started with DIY. With mostly basic tools and solid wood you can have your own DIY sofa that definitely won’t blow away in the wind!

Top: a brown wood and beige cushioned outdoor sofa. Bottom: a similar DIY sofa in a backyard, styled with cushions and a fire pit. Text points to each: “the inspiration” and “the result.”

This modern design was inspired by a high end version sold by Restoration Hardware and my desire not to haul cushions in and out of the house. I used my original sofa build from years ago and reconfigured it to accommodate our current needs. The total cost to build was about $850 including the mattresses and back pillows. But the beauty is the fitted sheets and pillow cases can be removed and washed or replaced if needed without spending $500+ on new cushions alone! 

Now I have a beautiful modern sectional with clean lines to soak up the summer on my back patio. The perfect place to enjoy a glass of wine and some tasty snacks!

A cozy backyard patio with a white sectional sofa, gray chairs, a round fire pit, string lights, a patterned rug, and a planter with herbs, surrounded by trees and a wooden fence.

Stay tuned to see how we found a way to also watch TV out here under the stars! 

Cozy backyard patio at dusk with string lights overhead, a circular fire pit, Adirondack chairs, and a cushioned sectional sofa. Trees and plants surround the area.

To see an overview video tutorial, check out my outdoor sectional reel on this build. To see the rest of the DIY patio backyard space, check out my stock tank garden, built in smoker outdoor kitchen, my faux cement tile side tables, or the stock tank pool with deck. You can also make the matching outdoor dining table with Full Tutorial

Cozy patio with a white cushioned sectional, black and white pillows, fire pit, chairs, potted plant on a small table, string lights overhead, and greenery in the background.

I have to say, this was by far the best decision I have made for our outdoor space. We are out here lounging on the patio almost every night now! 

A cozy outdoor patio with string lights, a round stone fire pit, and a white cushioned sectional sofa, surrounded by trees and greenery at dusk. Pillows and potted plants add a welcoming touch.

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A cozy outdoor patio features a white sectional sofa with brown and black throw pillows, a round fire pit, potted plants, and a wooden fence in the background. Text overlay reads “DIY Outdoor Sectional Tutorial.”

This post, DIY Outdoor Sectional Sofa with Mattress Cushions, appeared first on Garrison Street Design Studio.

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