How to Build Floating Decks

  • 01 of 10

    Materials Needed for the Project

    Floating decks (image) are an alternative for DIYers who want to build but lack the skills.
    Floating decks are a great option for DIYers who have big plans -- but not the big skill set to match. David Beaulieu

    "Floating decks" are so called because, rather than being attached to a building as are standard decks, they are just "floating" free out there, all on their own. Not only are they easier to build than standard decks, but they are also less scary to build for DIYers. Here is why:

    When you attach a deck to a building, you need to gain access to solid wood. This requires removing the siding of your house in that area (that is, if your house is covered with clapboard, vinyl siding,...MORE aluminum siding, or beveled wood). For the non-carpenter, removing your house’s siding is a pretty scary proposition. Let’s face it: Most of us take a “Leave well enough alone!” attitude towards our houses. We do not want to take the chance of screwing up something.

    Enter floating decks, which, as independent structures, obviate any need to mess with your home's siding.

    Tools and Supplies for the Job

    • Concrete deck blocks
    • Circular saw
    • Carpenter's square
    • Carpenter's level
    • Drill and drill bits
    • Exterior screws
    • Extension cord
    • Chalk line
    • Mini-mattock or other small digging tool
    • Scissor jack (optional)

    Pressure-Treated Lumber Required to Build a Small Floating Deck

    For a longer-lasting deck, use pressure-treated lumber. Here is what you will need: 

    • 10 2x4s 8 feet long
    • 2 2x4s 10 feet long
    • 18 decking boards 10 feet long, 5/4" thick, 5.5" wide
    • Scrap lumber for shims, guides, etc.

    Before you buy any materials for the floating deck, however, I suggest you draw up a simple plan for it.

    In addition to being a floating deck, the sample structure on which this tutorial is based is a relatively easy type to build for two additional reasons:

    1. It is small.
    2. It stays close to the ground. 
    Continue to 2 of 10 below.
  • 02 of 10

    Lay Concrete Deck Blocks to Support the Small Deck

    Picture of cement deck blocks.
    Easy to situate as needed on your site, cement deck blocks provide the foundation for floating decks, as shown in this picture. David Beaulieu

    The floating deck in this project will stand just 9 inches off the ground. Concrete deck blocks (sometimes called "cement deck blocks") can be used to support such a short floating deck.

    The dimensions of this small deck are approximately 8 feet x 10 feet. Such a small deck really only requires nine concrete deck blocks (eight spaced evenly along the perimeter -- including one at each corner -- and one in the middle, under a joist).

    You might wonder, "What's the purpose of such a...MORE small deck? Why bother building it at all?" So let's discuss the site on which this small deck was built. You might have a similar problem area on your own landscape that cries out for a small deck.

    As you exit the front door of the house in question and stand on the front step, a wooden privacy fence that separates the house from the neighbor's stands not quite 9 feet away on the right. Meanwhile, a large Eastern white pine tree, standing 14 feet away, dominates the area immediately in front of you and slightly to the right.

    Have you ever tried to grow grass or perennial flowers under a tall pine tree? Then you know that most plants just do not grow well under large trees: the pine tree simply drinks up most of the available water with its massive root system.

    Consequently, prior to building the small deck, the area was just dirt and weeds -- a "problem area." Building a small deck here transformed the area into one that is usable.

    So how do you begin? Well, the area was already level, so we simply had to lay down some concrete deck blocks, as shown in the picture. As said above, the deck will stand 9 inches high, and about 4 of those inches are from the deck blocks we used. The height of this small deck is similar to that of the front step (which it abuts), so the foot-traffic transition from front step to deck will be a smooth one.

    Continue to 3 of 10 below.
  • 03 of 10

    Draw a Plan for the Small Floating Deck

    Picture: corner of deck frame.
    Check with a carpenter's square to ensure the frame corner is a right angle, then screw the boards together. David Beaulieu

    Unless you studied drafting in school, the prospect of drawing up a plan for your small deck may seem daunting. It should not, though -- not in the least. All you need is a simple guide that will help you plan your project. Such deck plans are very doable for the do-it-yourselfer.

    With pencil, paper and ruler ready, just draw lines to represent, two-dimensionally, where the frame and deck joists will be going. There is no need to include the decking boards in your drawing, as the idea of the plan...MORE is to guide you through the process of laying out the underlying structure. Your small deck plan will also help you determine how much lumber will be needed (and what lengths you need), so other than checking on local building codes, drawing a plan for your small deck should be the very first thing you do.

    Indicate dimensions on your plan as you draw in the lines. Using the numbers from this sample project, you'd indicate a width of 96 inches in your plan, and a length of 117 inches (the small deck in this project is not quite 10 feet in length). Joists will be 16 inches on center; you will be doubling up on the joists at the two ends ("double headers"), so that means you will draw in ten joists in all.

    Why bother drawing such a simple plan? Well, if you don't work with lumber that much, it's very easy to overlook something that a carpenter takes for granted. For example, although the width of this small deck will be 96 inches, you will not be cutting your joists to a length of 96 inches. Why? Because 3 of those inches are accounted for by the 117-inch 2x4s that form two sides of the frame. Remember, a 2x4 isn't truly 2 inches thick, it's really 1.5 inches thick -- which, multiplied by 2 (one on each end), comes to 3 inches. The double headers at the two ends will be the same length as the other joists (that is, they run inside the 117-inch 2x4s.

    That is the beauty of drawing a plan for your small deck: You can indicate all of this "tricky stuff" in black and white and keep the visual representation right in front of you, rather than relying on instinct or on memory.

    So in all, you will be cutting ten 2x4s to a length of 93 inches, and two to a length of 117 inches. Together, these twelve 2x4s compose the frame and joists for the small deck and form the underpinnings upon which you'll be attaching the decking boards.

    Begin the process of assembling the frame by forming a right angle (check with a carpenter's square) between a 117-inch 2x4 and a 93-inch 2x4, then fastening them together with two screws using your drill (picture). Pre-drill to avoid splitting. Repeat the process at the other three corners, until your rectangle is complete.

    Continue to 4 of 10 below.
  • 04 of 10

    Keep the Deck Square

    Image: man using a carpenter's square to check that a deck corner is square.
    Along with a carpenter's level, a square (picture) is one of the tools you can't do without when building a deck. David Beaulieu

    With the rectangular frame assembled, begin attaching the joists, 16 inches on center. Support each joist temporarily with whatever you have handy (spare concrete blocks, scrap wood, etc.) and fasten it to the frame using two screws. Continue to check that your work is square, using a carpenter's square (picture).

    When the internal joists are in place, go back and add a second joist on each end, to form a "double header," giving you extra support at the ends.

    Note that, at this point...MORE in your floating deck construction, there is no need to restrict the deck frame to what will be, eventually, its proper location on the concrete deck blocks. The frame-and-joists structure you are assembling will be light enough to enable you to rearrange it on the deck blocks later, at your leisure. At that point, you will start checking for levelness, something you need not worry about yet. Right now, you should be concerned with getting everything square (photo).

    This freedom to move the frame as needed while you work comes in especially handy if your deck is located in a tight spot. For instance, in this sample project, it would have been difficult to drive screws into the side of the frame that will abut the privacy fence, because there is not much room to work in there. So it was fortunate that this was not required.

    In the next step it will be time to place the frame-and-joist structure into its final position on the concrete deck blocks. It is only at this stage that the floating deck really seems to take shape.

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  • 05 of 10

    Keep the Deck Level

    Photo: check for level on your deck as you proceed.
    Check to see if the deck frame is level as you proceed. To make changes, adjust your blocks. David Beaulieu

    Now that you've assembled the frame and attached the joists to it, it's time to place the structure on the deck blocks and adjust, as necessary, to achieve levelness (picture). Make the rounds at each deck block, checking for level as you go with a carpenter's level.

    If you find you're up too high somewhere, remove the deck block and dig out a bit of soil. A mini-mattock comes in handy for this task, but you may use any small digging implement. Replace the deck block and check...MORE again with your carpenter's level. Repeat until you get it correct.

    Conversely, if you're too low somewhere, lift the deck frame and insert a "shim" between it and the deck block, thereby raising the level of the deck frame in that spot. Scrap lumber can function as a shim.

    You actually don't want the deck to be completely level in every direction. Build in a 1/4-inch slope in one direction (away from the house), to promote drainage.

    Incidentally, months after the floating deck is completed, the ground under it may "settle" in places, meaning your deck won't be level anymore. Not to worry: Once again, inserting a shim here or there (as described above) should do the trick. This is one of the virtues of small floating decks: they give the novice the flexibility to go back and make adjustments later, with relative ease.

    Continue to 6 of 10 below.
  • 06 of 10

    Shim the Floating Deck As Needed

    Image: Shims can be used to level your deck, where needed.
    Here a 2x4 serves as a shim to raise the level of the deck. David Beaulieu

    The picture here shows the support provided for the floating deck at its very middle. The level had to be raised, so a scrap 2x4 was used as a shim between the deck block and the joist. A larger floating deck would have required multiple internal supports.

    Speaking of support, perhaps you are wondering, "Where are the bridges?" A "bridge" is a short piece of wood placed between joists, perpendicularly, to provide extra support. For as small a floating deck as this one, bridges...MORE were deemed unnecessary.

    Continue to 7 of 10 below.
  • 07 of 10

    Attach the Decking Boards

    Image: screw your decking straight by using a carpenter's square or similar guide.
    Apply two deck screws at each juncture. Align screws using a guide or carpenter's square. David Beaulieu

    Beginning at one end, start attaching the decking boards to the joists (as mentioned earlier, this will mean proceeding width-wise in the sample project). Apply two screws at each juncture.

    Before attaching the first decking board, check (with the carpenter's square) that it is laying square on the frame. If you begin askew, then all of the decking will end up askew.

    To line up the screws accurately on the first decking board, it helps to use something long and straight as a guide -- something...MORE that will extend a few feet onto the joist. Using the guide as a "sight," you'll be able to position the screws so that they'll come down right in the middle of the underlying joist (picture).

    Where the floating deck abuts the house, the ends of the decking boards will be flush with the side of the outer joist. At the opposite end, don't worry for now about how much of the decking board hangs over: It will be trimmed at the end, leaving a 2-inch lip.

    Continue to 8 of 10 below.
  • 08 of 10

    Continue Attaching the Floating Deck Boards, and Decide on Spacing

    Deck building image: checking screw alignment with a carpenter's square.
    For the remaining decking boards, you can check screw alignment with a carpenter's square. David Beaulieu

    After you have your first decking board in place, you won't need to use the long guide any more for screw alignment -- simply use the carpenter's square (photo) to line up your screws. The screws should run at an angle perpendicular to the lengths of the decking boards.

    As you proceed into the interior of the deck, you'll have to decide whether you wish to space the decking boards or not. There are two schools of thought on this:

    1. One school uses spacers, which establish "gaps"...MORE of a predetermined distance between the decking boards right from the get-go.
    2. The other school wants as tight a fit as possible when attaching the decking boards, anticipating future shrinkage.

    You can use anything as a "spacer," as long as you're consistent about it.

    If you side with school of thought #1, remember to figure in the width of the gaps when you're calculating dimensions for your floating deck.

    The pro who built this floating deck subscribes to school of thought #2. But one of the challenges of achieving a tight fit between decking boards is created by warping

    Continue to 9 of 10 below.
  • 09 of 10

    Straightening Warped Wood

    Image: using a jack to fix warping on deck board.
    A challenge of achieving a tight fit between decking is created by warped boards. Fix it with a jack. David Beaulieu

    As I said in the prior step, one of the challenges of achieving a tight fit between decking boards is created by the presence of warped wood. Undaunted by the challenge, the pro who built this deck revealed a great tip for dealing with such warped boards when attaching your decking, using a scissor jack (you may well have one stored away in your car). Here's how:

    1. Set the warped decking board in place.
    2. Begin by screwing it down at one end.
    3. Move over to the next joist.
    4. Using two screws, attach a...MORE scrap block of wood to that joist, a foot or so down the joist from the warped decking board.
    5. Wedge the scissor jack in between this block and the warped decking board (photo).
    6. You may need to have a helper push against the warped wood further down its length.
    7. Tighten the scissor jack.
    8. When you're satisfied that the fit is tight enough, screw down the warped decking board.
    9. Repeat along the other joists to finish securing the warped board.
    10. Repeat the whole process, as necessary, with the rest of the decking.

    Save your best decking board (that is, the one least warped) for the end, since it will be more difficult at that point to straighten out warped wood (you wouldn't be able to secure the scissor jack easily).

    Continue to 10 of 10 below.
  • 10 of 10

    Completing the Floating Deck Construction: Will You Need to Rip Saw?

    Picture shows how to rip saw a board.
    When you rip saw a board, you cut along its length, not across it. David Beaulieu

    When the pro who did this job neared the end of the floating deck construction, he faced a bit of a problem after laying the penultimate decking board. A small space remained that still had to be covered with decking -- yet a full decking board would be too much for the space (only so much "lip" can be allowed to hang over the edge, unsupported). So he had to rip or "rip saw" the final decking board, meaning he had to cut it lengthwise (as opposed to across).

    The picture here...MORE shows how to rip a decking board, should you need to do so, yourself. First, to stabilize it, temporarily screw the decking board down to the overhang that you'll be trimming off shortly (see below); it doesn't matter if you damage this overhang, since you'll be removing it anyhow. Carefully measure where you'll need to be cutting the decking board, and mark accordingly (the chalk line may come in handy here). A metal guide (see picture) can be used to guide you as you make the cut with your circular saw.

    If you wish to ensure that you will not have to bother rip sawing the final decking board to make it fit, try this tip:

    At the very beginning of the project (even before you set the deck blocks down), after you have raked the ground on the site so as to make it approximately level, lay out all the decking boards you wish to use -- right there, on the ground. Abut them, side by side, just as they will appear when the floating deck is completed.

    Now measure the width of this "faux deck." Once you have that measurement, you can "work backwards" to figure out what the exact dimensions of your frame should be, to incorporate precisely this number of decking boards (plus the 1-inch lip on both ends). That way, you obviate any need for rip sawing, which can be a somewhat intimidating operation for the beginner.

    You may be wondering, "Well, why not just multiply the width of the decking by the number of boards used, instead of going through all that?" But you've hit precisely upon the problem: the decking is approximately, 5.5 inches wide, but only approximately. Each board is a fraction off, and those fractions add up quickly. So it really is easier to lay the boards out and just measure the whole thing, if you're intent on avoiding any rip sawing.

    But back to the project.... After the last decking board was in place, the pro trimmed off the excess on the deck board ends on the side opposite the house. He wanted a 2-inch lip here, which was marked by snapping a chalk line; he ran the circular saw along this chalk line to complete the floating deck construction.

    This floating deck was built in July. By October, the lumber had had time to dry out some, at which point a coat of water seal was applied to conclude the project.