How to Build a Floating Deck

In these plans, I cover how to frame a floating deck and how to install Trex composite decking. Your deck won’t be the same size as mine, but you can take the same concept and apply it to your own deck build. If you are framing the deck yourself, check out my first video on how to design a floating deck. In that video, I cover how to determine the size of your deck, direction of decking & framing, how to determine deck height, and the layout of your deck. You can find that video HERE. Below you will also find a cost breakdown as well as a list of tools and materials needed for framing and decking.

Cost Breakdown

Framing materials	$1,408
Decking materials	$4,145
Misc. fasteners & supplies	$200
Total	$5,753

FRAMING

Check out the framing YouTube video HERE

Framing Material

Treated 2’ x 8’ x 16’	https://bit.ly/3Jyn3ix
Treated 2’ x 8’ x 12’	https://bit.ly/3YM49sK
Concrete deck blocks	https://bit.ly/3lbJBw3
Paver sand	https://bit.ly/3YFD7n0
Landscape fabric	https://bit.ly/3LeIGWn
Protective joist tape	https://bit.ly/3mAnbov
3” Exterior grade deck screws	https://bit.ly/3mKDtvl
2 1/2” Exterior grade framing screws	https://bit.ly/3LzyNTt
1 1/2” (10) Galvanized nails	https://bit.ly/3JBiVhS
Joist Hangers	https://bit.ly/3YJKEkB
Corner brackets	https://bit.ly/3FhBHIv

Framing Tools

Landscaping tools
Tamper	https://bit.ly/3ngI5JB
Dry string
Metal stakes
Batter boards
4′ level
Circular saw	https://bit.ly/2Y7zPzf
Impact driver	https://bit.ly/2XBgyCB

Let’s take a quick look at the framing plan. I designed our deck in SketchUp. It’s a great tool for planning your layout and dimensions. We are digging 3 trenches, then using concrete deck blocks and paver base for the foundation of our floating deck. We will frame the deck directly on the deck blocks.

The overall dimension of our deck is 24’ 4.5”x 16’. The floating deck is not attached to the house – it’s right next to it. We’re using treated 2×8 lumber in 16’ and 12’ lengths for the framing. We’re using 16’ boards for the center joist, rim joist, and to double up the cantilevered ends. The interior joists are 12’ long and placed 16” on center with deck blocks under each joist. The center framing member has deck blocks about every 4’. Blocking will be installed in between every joist, with some additional blocking along the cantilevered ends. We’ll secure joist hangers under every joist.

In my deck design video, I go over some resources that you can use to design your deck and where you can find estimated costs, so be sure to check that video out. Depending on the size of the deck you’re going to build, your framing probably won’t look exactly like mine. So do your research and consult a professional to solidify your deck design.

I am not a structural engineer or architect or licensed contractor, so before designing and building your own deck, be sure to consult a professional to make sure your design is structurally sound.

Also, be sure to research your local building codes before breaking ground. This is important to see if you’re even allowed to build the deck and if there are any permitting requirements. Typically, if you’re building a deck below 30” and detached from the house, it doesn’t require a permit – but like I said- double-check your local building codes before you get started.

Step 1: Prep Your Area

Now that we’ve got the design down, we can break ground!

We used to have a ton of old, cracked concrete in this area, but we had a company come in and remove the concrete for us – so thankfully we only had to dig up a tiny corner of sod.

Take a rough measurement of where you want your deck to go and remove any grass or debris from the area. Home Depot or Lowes have SOD cutting tools for rent if you need to remove sod in a large area.

If you’re building a deck near your house like us, take this time to slightly grade the dirt away from the house for drainage. If you’re building your deck in your yard away from the house, that’s not something you’ll have to worry about. I used a 2×8 with a level to make sure I am slightly sloped away from the house.

Also, an important note – Call 811 before you dig to avoid hitting any underground utility lines.

Step 2: Stake out Corners & Check for Square

The next step is to mark out the corners of your deck. I used 4 metal stakes for the four corners, and I made my own batter boards to help us find our square corners.

I’m using our house as a reference point. We want the corner of the framing to be an inch away from the house. 

So, I’m placing a stake in the left corner. We wanted the end of the deck to be in line with the window, so I placed another stake 1” away from the house.

For the other two corners, since I have more space to work with, I’m placing the batter boards just outside the corners of the deck.

I tied a string from the stakes to each of the batter boards to connect every side. The string can be adjusted left and right on the batter board until your corners are square.

You can use the 3’ 4’ 5’ method to check your corners for square.

Mark on one line 3’ from the corner, mark on the other line 4’ from the center, and adjust the strings left and right until your diagonal measurement is 5’. Do this for every corner and then place a stake where your strings cross.

Another way to check that your layout is square is to take a diagonal measurement.

Step 3: Mark out Trenches

To make sure the trenches are dug nice and straight, I’m placing two stakes 12” in from each end of the deck and placing two stakes directly in the center.

I laid some scrap wood strips to make a straight line to connect my measurements. Then I used some spray paint to mark a line in the dirt as a guide for my shovel.

We need the top of our deck to be about 10” from the ground, which is a few inches lower than the patio door threshold. We’re using 2×8” lumber for our framing, which is 7 1/4” tall. The deck blocks are 7” tall, then the top decking is about 1”, so that puts us at about 15 1/2”. With this information, we know that we’re going to have to dig our deck blocks down into the ground about 5”. We will end up digging trenches for our deck blocks at about 7” to account for 2” of paver sand.

With the deck being 10” off the ground, that’s a little too tall without needing a step – your step up shouldn’t be more than 7 3/4” tall, but we’re going to be planting grass around the perimeter of the deck and adding some extra dirt so that it will only end up being a 7-8” step up.

We had to be precise with the height of our deck to fit under the door. If you’re building your floating deck away from the house, you’ll have fewer restrictions for deck height, which will make it a bit easier

Step 4: Dig Trenches for Deck Blocks

The trenches should be at least a few inches wider than your deck blocks. You don’t want to dig them too wide, or you’re going to have to fill them with extra paver base, and you don’t want to make them too narrow because you may need some wiggle room to adjust your deck blocks left and right.

I dug out the trenches using the spray-painted line as a guide for my shovel. I am digging our trenches down about 7” and then filling the trench with a few inches of paver base to keep my deck blocks from settling.

Step 5: Check Trenches for Level and Height

Once your trenches are dug, place a few deck blocks and a framing member in line with your trenches and across the trenches to check for level. It doesn’t need to be perfect now, just get somewhere close.

You also want to double-check height to see if you need to dig the trenches any lower and calculate how many inches of paver base should be laid down.

As I said, we are using our patio door threshold as a reference for height. We wanted the deck to end up a few inches lower than the patio door threshold. So, we made sure the back row of deck blocks by the house were level first and then worked our way down.

Step 6: Install Weed Barrier.

To prevent weeds and grass from coming through the bottom of your deck, stake down rows of weed barrier.

Step 7: Lay Paver Base

To keep the deck from settling, we added about a 2” layer of paver base in the trenches. After the paver base is laid, we used a tamper to tamp the paver base down.

Step 8: Measure and Mark out Joists

I am going to measure and mark out the outside rim joists and center joist. The 12’ joists will be secured in place temporarily with exterior-grade framing screws, and then we will go back and secure joist hangers to each end of every joist.

We’re using Trex composite decking, which is secured to the framing with hidden fasteners, so the fasteners won’t be visible. If you were securing your decking through the face with standard screws, you may not want to stagger your joists like this; otherwise, your screws won’t be lined up straight. Just something to think about before you start framing. 

I mentioned earlier that we’re using treated 2×8 lumber for the framing. So, I’m going to lay out 3 good 2 x 8’’s, square off each end, and then cut them to length.

I marked the joists 16” on center.

Since the joists are going to be staggered, I marked out the measurements on two of the boards, flipped my middle board over, shifted my measurements an inch and a half over, and then transferred those measurements to the next two sides.

Step 9: Level Paver Base

Your paver base needs to be level; otherwise, your deck won’t be level. I’ll be honest, this is a time-consuming process, especially with a deck this size. It takes a lot of small adjustments to get the height just right.

I started by getting the center joist level and set where I want it, then we worked out from there.

You may need to add some paver base or take some away to make your framing level.

If your deck is attached to your home or, in our case, right next to it and its boards run parallel to the house, your deck should have a slope. It’s best if your deck has a slope of about ⅛ inch per foot to ensure that water flows away from your home.

If your deck boards are running perpendicular to your house, you don’t necessarily need a slope because the gaps between the deck boards should drain rainwater enough to keep it away from your home.

If you have a floating deck that doesn’t touch your home, you don’t need a sloping deck because the direction of the water flow doesn’t affect your house.

After getting the paver base set under 4 deck blocks in each row, we filled in the rest of the trench to match.

Step 10: Layout Center and Exterior Joists

Now we can finally start framing! To secure the framing, I’m using 3” exterior grade framing screws.

With the center joist in place, we decided to install these four joists next. Our left and right rim joists are cantilevered, so we needed these 4 joists installed first to hold them up.

After those four framing members were secured, we were able to secure all the exterior framing members. We had to get a little creative with securing these with the house in the way.

As we secured each piece, we double-checked for level and adjusted the deck blocks as we went if needed.

We found it easier to assemble a few of the exterior framing pieces in the grass and then set them in place.

When installing all your joists, make sure the crown faces up.

Before going further, we took a diagonal measurement to make sure we’re still square. At this stage, we are still able to push the framing a bit to get our corners square before the framing gets too heavy.

We doubled up the joists on each of the cantilevered ends, and now we’ve got all the exterior pieces framed.

Step 11: Frame Interior Joists

Now that the exterior joists are installed, we can fill in all the interior joists.

We set the deck blocks in place first – we had to adjust the deck blocks a bit as we went so that the interior joists were nice and flush with the center and outside rim joists.

You never know if your joists are all the same height; usually there are minor differences. So, it’s better not to pre-attach the joist hangers. For now, I used 3” exterior-grade framing screws, and then I will come back and secure joist hangers in the next step.

Once again, when installing all your joists, make sure the crown faces up.

Step 12: Install Joist Hangers & Corner Brackets

Now that everything is framed, I am going back in with these Simpson Strong-Tie joist hangers for every single joist.

To secure the joist hangers, I’m using 2 1/2” exterior grade wood screws and 10d 1 1/2” galvanized nails.

For the doubled-up end joists, I used corner brackets and 1 1/2” exterior grade screws.

Step 13: Install Blocking

Adding blocking will provide additional support to your joists and help minimize bouncing in your deck. We staggered blocking in between every joist and added additional blocking at the cantilevered ends. 

Step 14: Build up Trenches with Sand

This next step is probably overkill, but we got a bunch of sand and mounded up the trenches a bit. We just don’t want to chance water pooling up near the deck blocks and our deck settling.

Step 15: Add Protective Joist Tape

Finally, we added this protective joist tape to the top of every joist to prevent water damage.

Before adding decking, you may want to consider installing some sort of mesh or fencing so that rodents can’t sneak under your deck. 

DECKING

Check out the decking YouTube video HERE

Decking Materials

Trex composite decking square edge	https://bit.ly/3FIm1y3
Trex composite decking grooved edge	https://bit.ly/3yUezw5
Trex Fascia board	https://bit.ly/40utRTI
Trex hidden fasteners	https://bit.ly/3TEgUF0
Cortex hidden fasteners	https://bit.ly/3FIdFX3

Decking Tools

Miter saw	https://bit.ly/3QQ1hZJ
Jig Saw	https://bit.ly/38MjIKv
Circular saw	https://bit.ly/2Y7zPzf
Chalk line
Rubber Mallet
Hammer
Speed square
Impact driver	https://bit.ly/2XBgyCB

This is composite decking from Trex. They have 3 different tiers of decking products. We chose the color Coastal Bluff, which is part of their Trex Enhance line in the lowest tier.

We are doing a picture frame border around the entire deck, so for that we will use the square edge boards. These boards are about 1” thick, 5 1/2” wide, and 16’ long.

For all the inside deck boards, we will use these grooved boards. These boards are the same dimension as the square edge boards.

We used 2×8’s for our deck framing, so we went with the 7 1/4” fascia board, which is a thinner material about a 1/2” thick and that will go all along the bottom of the deck.

For the border pieces and the fascia board, we will be securing that to our framing through the face with these 

Cortex hidden fasteners. They come with plugs so we can go back and plug all the holes, and they will blend right in with the deck.

Next, we have these Trex hidden fasteners which will be used to secure all the grooved boards.

These hidden fasteners sit in the grooved boards like this.

This pack also comes with start clips which will secure the first grooved board next to the border piece.

I designed the decking layout in the Trex deck designer tool. It’ll tell you how much decking to order, what size decking to order and even include which type of fasteners to use, which is very helpful.

Step 1: Add Blocking

First things first, I need to install a little bit of blocking. For the end of the deck boards to have something to screw into.

Once again, you can check out my last video on how to frame a floating deck if you plan on doing your own framing. Our joists are spaced 16” on center, which is what Trex recommends.

Step 2: Install First Border Pieces

We are starting with a 45-miter cut on each end of our left border pieces.

Our fascia board is about a 1/2,” and we want the decking to overhang that by an additional 1/2”, so we made sure to keep a 1” overhang with all the border pieces.

We dry fit the first border piece and then cut the next border piece along the house next.

For the corners to meet up perfectly, we had to cut a tiny bit of the corner.

These pieces fit perfectly, so now we are snapping a square chalk line to use as a guide. Your first couple of boards need to be nice and square because it will affect the rest of your deck boards.

We used a full 16’ board for the width of the deck, and then we will need to cut down two 16’ boards to get the length of our deck, which is 24’ 4.5.”

We’ve got our chalk line as a guide; now we’re going to secure the boards starting in the corner to make sure the joint stays nice and tight, then working our way down.

We placed two hidden screws evenly on every joist.

Some people will pre-drill holes for these types of screws, but the directions for these fasteners say no pre-drilling is required. If you have to secure the screw less than an inch from the edge, then I would recommend predrilling.

I’m using a speed square to mark where the screws need to be placed evenly.

Step 3: Install Starter Deck Board

Now that our first two border pieces are secure, we can start on our first row of grooved boards. For this first row, we will need to use those starter clips because the hidden fastener doesn’t have anything to tie into against the square edge boards.

I used a little 3/16” scrap piece of decking to space the starter clips accurately.

Once all the starter clips were secured, we placed our first grooved board.

On the house side of the deck where our border piece is secured, we made sure to keep that 3/16” spacing between the end of the deck board and the border piece. We found that using the tip of the speed square gave us perfect spacing.

This first grooved board we cut down to the exact length. All the other grooved boards we are going to leave long, and we’ll cut them all to length at the end.

Step 4: Install Deck Boards

Now we can start using the hidden fasteners.

We set the hidden fastener in place, used a scrap piece to make sure the fastener was pushed in all the way, and then tightened the screw down about halfway. You don’t want to tighten it all the way, or else you won’t be able to fit the next grooved board in there. And you want to make sure to tighten it just enough to hold the board in place, or else it could create a gap that’s too large.

**Make sure to square cut all your deck boards before installing them. You can do this quickly with a speed square and circular saw.

After a grooved board was set in place, we found it worked best for one person to screw the hidden fasteners down all the way – while the other person pressed the deck board tight into place. In some places we used a rubber mallet to carefully pound the deck board into place.

If your deck board spacing isn’t the same all the way through, make sure your hidden fasteners are secured properly.

It took a while to get a system down – but once we did, we worked fast. We were able to install all the deck boards in one day; we just had to come back and install the fascia boards and Cortex plugs.

Before going any further, we needed to finish the border piece against the house. We measured the distance to the end of the deck and added 1” (1/2” for the fascia board and 1/2” for the decking to overhang).

Now we can install the rest of the interior deck boards.

Unfortunately, at the end here we had to rip the last piece down. It was tricky to plan for a full end board because you must account for every gap, and they might not all be the same.

We measured this last board, making sure our border piece would fit with a 1” overhang.

We snapped a chalk line on the board where we needed to cut it. You could rip this with a table saw, but Devin has a steady hand, so we decided to just cut it with a circular saw.

We were only able to secure one side of the board with hidden fasteners, so we used some of the Cortex hidden screws to secure the other side of the board every 16”.

We made sure that this last deck board matched the same length as the first starter deck board.

We cut and dry fit the end border piece, making sure it has a 1” overhang, and then before securing it down, we cut all the interior deck boards down to size.

Step 5: Cut Deck Boards

We snapped a chalk line to connect the first and last deck board. This will be used as a guide for the circular saw.

We set the depth of the saw to the same exact depth of the deck boards and then made a straight cut all the way down the length of the deck. I used a blower to clear the sawdust off the line while Devin made the cut.

Step 6: Finish Installing Border Pieces 

Now that all the interior deck pieces are cut, we can finish securing the rest of the border pieces.

Just like the other border pieces, we made sure to keep that 1” overhang and about a 3/16” gap from the end of the deck boards.

We mitered the corners at 45 degrees and secured the pieces down with the Cortex hidden screws.

The deck is looking amazing, but we still have a few more steps left.

Step 7: Install Fascia Board

The next step is to install the fascia board. These are about a half-inch thick, 7 1/4” wide, and 12’ long. You can get them in different sizes depending on your type of framing.

We beveled the miter saw at 45 degrees and cut one end of the fascia board. This end will go at the corner of the deck.

I marked out where the screws needed to go – 2 screws evenly every 16”.

We made sure the fascia board was pushed all the way up to the deck boards and then screwed the fascia into the deck framing.

Step 8: Plug Cortex Screw Holes

And finally, all the holes from the screws needed to be filled with these little plugs. I couldn’t find the plugs in our exact color decking, but these were pretty darn close.

I used a hammer to tap the plug down. I tried using a rubber mallet, and it didn’t work very well. But if you use a hammer and lightly tap it, you won’t do any damage to the deck.

We are so excited to have this deck finished! We are going to stage the deck soon; we’ve got some grass to plant around the deck, and there are a few small projects I want to do before I reveal the deck completely furnished.