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» Build a Backyard Play Structure

How Did I Do It? > Parenting & Kids > Build a Backyard Play Structure
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What cures summer boredom better than a backyard play structure? Sure it is tempting to just buy a kit – but who wants a fort exactlylike everyone else? With this project you get more fort for less money than a kit (the lumber and hardware was less than $800 – most kits are more than $1000).

This project covers all the details – from plan drawings to site preparation to filling the sand box. With some help, the construction can be finished in about 3 days. The inspiration for the general design came from a friend who built a similar structure last year. It was simple yet still something to provide hours of fun for the kids. I made a big change in the roof design, tweaked the dimensions to suit our needs, and added the rope swing at the request of my oldest daughter.

Fort plan drawings - click to see all views
Fort plan drawings - click to see all views

Backyard Fort Plans

The plan was to use 4×4 for all of the posts, 2×6 for the roof and outer edges of the main floors, 2×4 @ 12" for the floor joist, 2×4 for the rail, and 2×8 for the outer edges of the steps. The supply list details all lumber and hardware required.

The main floor areas are 6 feet by 8 feet (joists running 6 feet). The steps are 32 inches square. We choose not to bury the posts in the ground. They rest on 12" round concrete pads which provide adequate stability. The lower floor is about 12" off the ground and has a sand box in the middle (the floor is hinged like a trap door).

The second floor is about 6‚½ feet off the ground. The exact height of the second floor was determined by planning the first step 18 inches off the ground and each step 12 inches above the previous one. To better fit in the area, we ended up rotating the main structure such that in the view above, you would be looking at the 8 foot width. A project like this requires major preparation. After the plans were finalized, we started preparing the area in the back yard.

We have a large boulder near the well that was already breaking up the grass, so we staked out an area – irregular pentagon in shape. It was placed between sprinklers so they could be realigned with the edge of the play area.

Sod Removal and Site Prep

The next step was to remove the sod. Technically this is optional as the structure can be built right on the grass – but that really increases the maintenance. Don’t even think about doing this with a shovel. It is totally worth $46 to rent a sod cutter. This is a very bulky machine. I was able to fit it in the back of a minivan with the seats removed, but it was very difficult to get it in and out. It took about an hour to do 1000 square feet.

Sod cut out - click to see large view
Sod cut out - click to see large view

First make a pass around the perimeter with the sod cutter to provide nice clean edges. Then go back and forth in one direction. Finally, to help in removing the sod, cross-cut in the other direction. Without a doubt, the most labor intensive aspect of this project was pulling up the sod. Wet sod is much heavier, but dry sod tends to break up – at least for a loose root system.

This was a good time to prepare the foundation. The round concrete pads were positioned and squared (by measuring the diagonals). I then dug a shallow hole and back filled with a couple inches of pea-stone gravel. It is important these are all level. To accomplish this I used a 2×4 as a straight-edge and placed the carpenter’s level on the 2×4. I then dug small holes and back-filled with the gravel to provide some drainage for the 4×4 posts that will support the steps (indicated with the arrows). These locations were approximate and actually needed to be moved later anyway.

Foundation - click to see large view
Foundation - click to see large view

To prevent the grass from growing into the play area 3 rolls of plastic edging were installed. I used the edge-trimmer attachment to my Mantis tiller to create a slot in the ground for the border. Unfortunately I punctured a few holes in some sprinkler pipe that was too shallow. After getting that repaired we were ready to move on.

Border edging - click to see large view
Border edging - click to see large view
With the border in place, we were ready for the base material. We selected raw wood chips as it did not make sense to spread premium mulch. Planning for 3-4 inches deep would require about 7 cubic yards. It is significantly cheaper to purchase this amount in bulk rather than in bags. The downside is that they dumped it about 80 feet away on the driveway. By the time we got it all moved down the grass had greened up.

Woodchips - click to see large view
Woodchips - click to see large view

The amount of lumber required for this project was too large for my utility trailer (or most small pickups). So another delivery was scheduled. Fortunately they had enough sense to drop it on site! A detailed cut list explains how all of the lumber was used. Very little was wasted and it really paid off to have good planning so I did not have to run back a million times to get another piece of lumber. All lumber is pressure treated to withstand the weather.

The camera was away on vacation during the main construction, so there are not any in-progress pictures to cover the building of the play fort. The majority of the construction took place in 2 very full days. I purchased a new framing nail gun to use on this project – without which the project would have taken at least twice as long. So, to get started, I laid two 4x4x14 on the ground, about 8 feet apart. I measured and marked the location for the top of the cross members.

The lower cross member is a 2x6x8 and the upper is a 2x6x10 – the extra length is used to hang the baby swing from. Each end extended beyond the post by 1.5 inches so that in the end, the total outer dimension will be 8 feet. One nail was initially driven through each joint to allow the structure to be squared once it is raised up.

Before lifting the frame up, I nailed a 2x4x8 to the edge of one side to be used as a brace while it was standing alone. Once it was lifted up, a second brace was added to the other side so it would not fall either direction. Then, I repeated the process for the other side. With both frames standing up precariously, I quickly added the 2x6x6 on the ends. I first nailed the lower boards, and then the upper. If you are doing this alone, it helps to tack on a quick scrap upon which the board can rest while you nail it in. These end boards are actually 5’9" long so that the outside dimension will be an even 6 feet.

At this point, each joint is still connected with a single nail. This makes it much easier to move the frame around to make it plumb and square. In making it square, not only do the posts need to be square with the cross members, but the 6×8 rectangle also needs to be squared by measuring the diagonals. Once it is, I added additional nails in each joint as well as one 4" lag screw.

This is also a good time to add the corner bracing on what will become the upper floor. Each corner takes two 2x4x24" mitered at 30‚° on one end and 60‚° on the other and one 2x4x36" mitered at 45‚° each end. The 30‚° is flushed up to the bottom of a cross member with the other end covering the end of the post. The 36" brace is attached to two cross members.

The 24" braces are also attached to the cross members with a flat metal bracket and 1" deck screws.

The steps are added next, which is involved enough to get its own page. To install the top floor, first attach the 2×4 joist hangers to the long 2×6 cross members. Measure 12" centers and use a piece of scrap to gauge the hanger (width and depth) as it is attached with 1" deck screws. Measure and cut the 2×4 joists and install, attaching again with screws.

The 8 foot 5/4×6 decking will cross the joist. But first, use 2×4 scraps (or cut ends from the decking) to install cleats at the post locations. The decking can then be installed.

The decking is quick and easy to install. Simply lay one down one side and go crazy with the nail gun. Start each additional board with about a 1/2" gap. Shoot a nail at each end to make sure it is parallel and then nail the interior. With the top floor attached, the rails can be installed. Nail 2×4 horizontal members 32" above the decking, using a level. The vertical members are nailed to the 2×4 at the top and the 2×6 outer floor joist at the bottom. Use a short 2×4 scrap to evenly space the balusters.

The ceiling is framed by attaching two 2x6x8’s near the top of the posts. Then bevel the end of 8 2x6x8’s. Two of them are attached the other direction to neat the top of the posts, above the first two. The remainder are attached to the top of the first two with rafter hangers. Attach two 2x6x12’s to each other with screws along the length. Drill a hole in one end and secure the 8" eye bolt through the hole. Then attach this to the top of the rafters in the center.

The rope is secured to the eye bolt. It is difficult to secure a large rope with a knot, so I used two U-bolts which clamps the rope tightly.

The steps are constructed in sections, from top to bottom before any decking is added to the top or bottom levels.

To begin, attach two 4×4 posts (a – 114") to the inside of the top and bottom level 2×6’s. The objective is to make each step 32×32 inches. This is accomplished with careful planning and arrangement of the posts and 2×8’s that make up the box of each step. The plan used in this design incorporates a combination of 2×8’s that are 29" and 33.5" long (technically 34" is needed, but 33.5" makes it easier to cut the 8 foot lumber). The base of each post consists of a scrap piece from the decking or 2×6.

Step 1 is constructed by marking 12" down from the top floor on the posts added above. One of the other 4×4 posts (b – 102") is held in place while a 2×8 is nailed first to the secure post and then rotated in place with the aid of a level and nailed to the second post. This process is repeated on the other side and then a 2×8 is nailed to secure the both posts b.

Step 2 is constructed by marking 12" down from the top of step 1 and following the same procedure to first connect post b with post c (90"). Post c is then secured to the corner post.

Step 3 follows the same procedure using two posts d (78").

Step 4 uses post e (66") and is also attached to post b.

Finally, step 5 is created with two posts f (~18"). They do not protrude through the top of the step. Before adding the decking (which will be 5 32" pieces per step) install support cleats as needed at the posts. Also, using joist hangers and 2×4’s, add a single support joist in the center of each step perpendicular to the planned orientation of the decking. After the decking is applied, attach the rails and balusters as before.

Here is another view of the steps. The lower floor is framed with a 4×4 foot (interior dimension) hole where the sandbox will be.

Before the decking is added, supports for the trap door are needed. First attach temporary cleats 1.5" down as shown below. Then rest (do not nail) two 2×6’s (cut to allow about 1/4" gap on each side) on the cleats evenly spaced. (Lesson learned: the 2×6’s were quite dense causing the door to be heavy for small children – 2×4’s would have sufficed.) Here is a detailed image.

The decking can now be added as before. Use the full length boards now – the door will be cut out later. Use 4 – #12 1.75" wood screws to attach each deck board to each 2×6. Use a straight edge and a marking pen to mark the inside of the box on the secured decking. Cut along the marks with a circular saw with the depth carefully set to just barely go through the decking.

Mark the positions of the hinges so the hinge joint is centered over the cut and the 2×6 support. (Plan ahead and don’t drive any nails or screws to interfere.)

Using a router with a 3/4" bit, route down about 3/8". Use a chisel to clean out the edges and work around obstacles. The hinges can then be attached with #12 1.75" wood screws.

Next, set the depth on the circular saw as deep as it will go. Cut through the 2×6’s in the center (or at the gap closest to the center). If the saw does not cut through, use a hand saw to finish the job. Open the doors and remove the temporary cleats that were supporting the 2×6’s. Using two spare balusters, attach them to the ends for support when the doors are closed (as indicated with the yellow arrow below).

Some trimming of the 2×6’s may be needed to allow unobstructed opening and closing of the trap doors. Finally, create the box using 1/4" plywood and fill it up with sand. This design required about 1/2 cubic yard. The swing is constructed by laying two 4×4’s cut to length on the ground. Use the bracket (from a purchased swing set kit) to align the posts. Cut two 2×4’s to length for cross braces. Measure down the side of each 4×4 to insure each 2×4 is attached at the same place on each and will be horizontal when the structure is raised up. After the 2×4’s are attached, secure the metal brace with screws.

The swing support beam is a 10 foot 4×6. You can use a longer length if desired. Carefully measure and pre-drill all necessary holes. With the help of a friend raise the ‘A’ frame structure up into place. If you don’t have any friends, then use scraps to hold it in place. Attach a temporary cleat or permanent bracket to the post of the main structure at the correct height. This will support the beam while it is being attached to the structure and ‘A’ frame. With the beam in place, attach the metal brackets supplied in the swing set kit.

And last, but certainly not least, the slide. It is recommended that the slide be purchased to correctly match the height of the second floor.

After the wood has had a chance to season and adjust to the environment, apply a coat of Thompson’s deck sealer. Follow the manufacturer’s directions. It is easiest to apply with a garden sprayer.

Now just sit back and enjoy the pleasures of a playground in the convenience of your own backyard. Just remember, the neighborhood kids may not be the only visitors. We often found the local wildlife hanging out here in the morning too.

Download Backyard Fort Plans in PDF Format.

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