How to Build an Under Deck Storage Shed


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Enclosing the space under the deck is a great idea to make more storage. When you think about it, it’s a shame that this space is just going to waste. It’s also a wonder that more people don’t think about making this a usable space. If you enclose the space under your deck, you might just start a trend in your neighborhood, and make your neighbors wonder, “Why didn’t I think of that”?

As with any building project, check with your building inspector and homeowners’ association, if applicable, before starting this project. There may be some regulations as to what you will use for siding and flooring, or you may need a building permit. Homeowners’ associations especially may insist that the same siding be used on the enclosure as was used on the house, or that it at least be painted to match.

Be aware that not all your extra stuff can be put under your deck. For instance, firewood or other flammable objects are not a good idea and may actually not be permitted to be so close to your house. Scrap wood or leftover paneling is not a great choice for storing under a deck because of possible termite problems.

Can You Put a Shed Under a Deck?

You certainly can put a shed under a deck. The higher your deck is raised off the ground the more room you will have to do this. If you have a deck extending from a second floor, you can have a full-sized shed under your deck. However, even if you only have three or four feet to work with, the space can still be enclosed for storage.

You will have enough room for boxes, tools, summer playthings such as pool toys, and even your walking lawnmower. You already have your vertical supports built, it just needs some kind of flooring or base to keep moisture from seeping out of the ground into your things plus some siding with an opening. This would be a fine way to use any siding leftover from your house. If your deck is too low there are other ways to store things, read my article How Do You Build Storage Under a Deck? for more information.

How Do You Waterproof Under a Deck for Storage?

Of course, the boards on the floor of your deck are spaced a little bit apart to allow rainwater to drain off between the boards. If you want to make use of the space underneath, however, that’s going to cause a problem. Some people choose to just let the water drip down, using plastic tarps to protect their storage items. Of course, there has to be a way to let the water drain out from under whatever siding they use for the enclosure unless lattice is used.

This is feasible depending on the type of items to be stored. If you’re storing mostly things such as garden hoses, plastic pool toys, kayaks or other plastic items, this will work. Your lawnmower and garden tools can also be kept in such a space if protected by plastic. Other things, such as those kept in storage boxes, might get too damp with a dirt floor.

If you haven’t yet started building the deck itself, you might investigate some of the drainage systems that are made for just this plan. There are membranes made to fit over the joists but under the top boards. They form troughs between the boards that actually act as little downspouts, channeling water off the edge of the deck.

If your deck is already in existence, there are systems that use plastic or corrugated aluminum panels to catch water draining down between the deck boards and channel it to the edge. Some are even custom-made to the size of your deck, and the panels lock together to form joints that are leak-proof. These systems are installed with a slight incline to encourage water to flow away from the house, so it doesn’t just sit there in the panels.

Some systems also include downspouts to which the water is channeled. If your deck is high enough, you can actually install a regular shed with a slightly sloped flat or pitched roof that will take care of the water problem. For more information on drainage read my article What’s The Best Way to Add Drainage Around a Shed?

How Do You Install Under Deck Drainage?

For the panel systems, you can have them professionally installed or buy a kit and install it yourself. Some systems require professionals to install. If you choose to do it yourself, you’ll need some cutting tools, a tape measure, safety glasses, a level, and a drill. You may need a helper as well.

The kit you buy should include installation instructions and a list of the tools you’ll need. Some hardware and perhaps sealant may be provided with the kit, or the instructions will tell you what kind you will need to purchase.

Basically, you install blocks at each corner of the underdeck, using a level to form the slight drop you will need. A horizontal board goes against the house to be used to attach support beams while using the lower edge of the deck for the other end of the supports. If your kit features a gutter and downspout system, flashing for these will be next. The panels are attached to the joists. Everything is sealed to be watertight.

If you don’t want to buy a kit, you can buy some plastic or fiberglass corrugated panels. If you like plastic, tell the supplier how you plan to use them so that he can guide you to the type of plastic you need to withstand the weather for years. When installing, you can use shims or blocks at the outer edge to give you a slope. Having a slope of 1 to 1-1/2 inches is sufficient. What you use to create the slope will be determined by the length of your deck.

Using screws with neoprene washers to fasten the panels to your supports will help keep it watertight. If possible, investigate roofing screws made for installing metal roofing, as they have the same purpose. You’ll need some type of sealant at the places the panels join.

You can let the panels extend out from the deck a bit at the end to drain water off the deck and have it land on the ground away from your shed siding or install a gutter at the end with a downspout to channel the water away. Some choose to install the gutter on the inside of the main deck supports to keep it out of sight.

There are also rubber flanges available to keep water from going between the deck boards. They come in different widths to accommodate different board spacing. One brand has horizontal flanges on the end. A slot is milled into the ends of the deck boards with a router or dado blade.

Then the end flange is pounded into the end of the boards with a mallet, and the rest of the rubber strip is inserted between the boards, leaving a little space at the top so that the rubber strips can act like little gutters to drain the water away.

One thing that needs to be tended to with any of these drainage systems is keeping the deck clean. Any debris, such as small twigs, tree catkins or pine needles, can get between the deck boards and into your drainage system, causing a possible blockage. Cleaning it out would involve a lot of flushing, but even that may not get rid of some of the debris.

Do You Need Ventilation Under a Deck?

If you put in a panel drainage system under the deck, you won’t get as much moisture condensing under the deck board and joists. However, you still have the problem of moisture seeping up from the ground and looking for a place to go. Putting in some kind of flooring system will go far to prevent this, many people use lattice panels for the siding, which provides plenty of ventilation.

If you need more security so that it’s not so obvious that items are being stored under the deck, some landscape fabric attached to the inside of the lattice panels will hide your items and still let in some air. Additionally, you can install some air vents in solid walls. The more airflow, the less likely you will end up with a mildew problem.

How Much Height Is Needed to Build a Shed Under a Deck?

Some people build storage under their decks with a little as three feet of clearance. If you have a hard time kneeling or squatting down and getting back up, you’ll need enough room to at least stand up and walk, even if it means bending over.

How much height you’ll need is really at least partially dependent on how much height you’ll need to get around under there. Also, what you plan to store in it will affect how much height you need. If you want to store bicycles or a riding mower, you’ll obviously need more space.

Keep in mind that a drainage system under the deck flooring will take up a little headspace as well as the flooring you choose to use. If you don’t have enough height for an enclosure, you can build a frame and mount some large drawers into the space. This will be a great place to store all kinds of smaller things that just keep piling up in the house.

Do I Need a Floor for an Under Deck Shed?

Some choose to leave the floor as bare dirt, leaving either a drainage system under the deck board to protect the items. It would be a good idea to install some kind of floor, if for no other reason than to keep moisture from seeping up through the ground and condensing inside your enclosure. There are different options available.

Installing a vapor barrier is necessary as the first step for most solutions. Putting some kind of flooring over the vapor barrier will help keep the plastic from being perforated after years of use. Plastic interlocking tiles are made in many designs and sizes specifically to use as flooring.

However, most types, if not all, are perforated, which is why you need the vapor barrier to be installed first. Artificial deck turf is another option. The artificial grass is short enough so that it won’t interfere with getting items in and out. It will also provide a softer surface in case your shed is short enough to necessitate some crawling around at times.

Some people build an actual solid wood or plywood floor for their items. If this is your choice, it’s best to use a vapor barrier underneath and build your floor raised up a few inches. You want to protect this flooring and joists from moisture and insects just as you would when building a free-standing shed. Read my article What Are the Strongest Shed Floor Materials to Use? for more information on shed floor options.

How to Build an Under Deck Storage Shed

First of all, if your deck isn’t new, you’ll need to check the condition. If it’s showing obvious signs of age or deterioration or is unsafe, it’s not worth the time or expense to build something underneath. Since you’ll need to use the outer support posts as outer framing for your siding, these need to be set solidly and be in good condition.

One way to build a good foundation is to grade the area underneath the deck. Use a level to create a slope about an inch for every four feet toward the side where you plan to put the door, extending the slope about three feet past the intended wall.

Tamp the soil down, then put down some sort of landscape or geotextile fabric. Spread a two-inch layer of crushed stone on top of the fabric, tamping it down solidly, then spread another two inches of gravel and tamp that down.

Next, install whatever water drainage system you plan to use. As noted above, you can use corrugated plastic or fiberglass panels. Any wood materials should be pressure-treated to withstand moisture. The more moisture protection you can provide the better.

You can use the deck joists or add additional supports, as long as you make sure that you have a slope to the front of the deck for the water to run off. Shims can be used to help or wood blocks if needed, depending on the length of your deck.

Putting in a gutter system with a downspout will keep water from just pouring off the end of the deck and will protect the wood there. It will also keep the siding from being constantly splashed with mud during rainstorms. The guttering can be installed just behind the support posts to keep it invisible, with the downspout tip sticking out from under the wall.

Put in additional vertical support posts to attach to whatever siding you choose to use. Using concrete blocks underneath these posts would be a plus. Put in a header to connect your supports all around the three sides. 2 x 4s can be used for both the top frame and additional posts.

Some people also put in a bottom board to make a complete frame, but it’s not absolutely necessary, especially if you’re using lattice for siding. If you do build a complete frame, try to keep the bottom boards raised up a bit to let water any water drain out. Even with a system to keep water from flowing down between the deck boards, rain doesn’t always fall straight down and can be blown into your storage area, especially with lattice walls.

Make sure to have a framework for your door. It probably should be put on one end of the deck rather than the front. This keeps people from being tempted to try breaking in and also makes a more pleasing appearance. The door should be at least three feet wide. Depending on the materials you use for siding, you could use a panel for a door using simple hinges.

Be sure to include some sort of accommodation for a padlock. There are lock assemblies that feature a hinge on the long side that swings back over the hinge itself when it is locked. This keeps people from simply unscrewing the lock system to get in.

The siding can be the same as used on your house, plywood or lattice. Lattice panels are popular and come in either wood or plastic. While the plastic is impervious to rot, if you need or want to match the color of your house, you may opt for the wooden lattice so that you can paint it to match your home’s siding. Be sure to get pressure-treated lattice if you chose to use the wooden type. Both types are easy to cut to size and install. For information on inexpensive siding options check out my article What is The Cheapest Siding For a Shed?

Conclusion

Utilizing the space under your deck will provide great storage space. If your deck is tall and large enough, using this space for storage may mean that you don’t have to have a separate shed, which would be a plus if your backyard space is small.

Building this storage is one of the easier construction projects you can plan around your home and will make it even more attractive. It may even be an added attraction to potential buyers when it is time to sell. Why not investigate the possibilities and keep that space from going to waste?

 

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