How to Build Storage Under Your Deck

What do you do with the area under your deck? Nothing will grow there, except for a few weeds. Some people keep the area covered with mulch, so it isn’t a muddy mess, then they forget about it. Wouldn’t it be nice to make that space useful? Well, what about making the space into a storage area for your stuff?

If the ground under your deck is relatively level and at least five feet between the ground and the deck floor joists, then converting the area under the deck into storage space is a project worth considering.

Here, we will briefly discuss what you should consider before attempting to convert the area under your deck into a storage area, as well as some ideas about how you might undertake this project.

Determine Your Deck’s Condition

It does not make sense to invest time and money on the area under a deck that is unsafe, or in poor condition. If you’re unsure about the state of your deck, call in a qualified building inspector to give you an expert assessment.

A professional may be willing to provide some informal feedback about your storage space project, and about what you might do to improve the condition of your deck. An assessment of the condition of your deck can be useful, even if you decide not to proceed with your deck storage project.

Settle on a Storage Plan

Your next task is defining your objectives for the storage area under your deck and identifying issues that might limit what you can do. Here are some questions to ask yourself:

1. What do you want to store under your deck?
2. What conditions do those items need to preserve them in good condition? For example, do they need to be in a dry area, or can they withstand limited exposure to water?
3. Are you concerned about theft?
4. Does your neighborhood have restrictive covenants that might impact your project?

Now that you’ve checked out your deck’s condition and determined what you want to store in the under-deck area, it’s time to decide on options that will suit your needs.

Option #1: Deck Storage for Items That Can Withstand Moisture Exposure

This is a low-cost project, but it’s DIY friendly and suitable for storing items under a deck that can stand exposure to moisture.

If the headspace beneath your deck is limited, and if you need to store stuff like gardening tools and supplies or materials that can be protected in bags or containers, this storage project will work well for you.

If these machines can be protected with tarp covers, your new storage area could also house a lawnmower or garden tractor.

Project Conditions:

1. The height under the deck is five feet or more.
2. The ground under the deck is reasonably level and can be sloped at least ¼ inch per foot to drain water.
3. The ground around deck post footings will not be disturbed by the project.
4. No equipment is under the deck, such as an air conditioning condenser, a gas meter or an electricity meter, an electrical panel, or the septic tank.
5. No vents or exhaust duct terminations are under the deck, such as a vent serving a high-efficiency furnace or a clothes dryer exhaust duct; a bathroom exhaust duct termination is okay.

Project Steps:

1. Grade the area under deck to slope about ¼ inch per foot toward a drainage point (usually where the door will be located), extend this area about three feet beyond the deck on the side where the door will be located, compact disturbed soil with a hand tamper.
2. Cover the graded area under the deck with geotextile fabric.
3. Spread a 4-inch thick layer of crushed stone on top of the geotextile fabric.
4. Compact the stone with a hand tamper.
5. Build a frame to support the lattice using preservative-treated lumber (usually 2 x 4) to support the frame on concrete blocks where necessary.
6. Install the lattice on the frame according to the lattice manufacturer’s instructions.
7. Build at least a 3-foot wide door using the lumber and the lattice.
8. Install the door using the hinges and latch.

Option #2: Build a Semi-Dry Storage Area

This is a medium to high-cost project that will protect from water intrusion into the storage area and provide some security against theft. The cost and level of water intrusion protection will depend on the water drainage system you select.

The skill level required will also depend on your selected water drainage system. Some systems require a contractor trained on how to install the water drainage system. Other systems may be suitable for someone with intermediate DIY skills. A two-person or more crew is recommended.

This storage area is appropriate for storing things such as gasoline-powered equipment, lawn and garden tools and supplies, and leftover materials from other projects, including some wood if the materials are protected from water intrusion. Do not store wood on the storage area floor if you live in a termite country in most of the United States.

Water Drainage Systems Include Installing:

1. A waterproof membrane that is designed for pedestrians walking on top of the deck.
2. A flexible membrane above the deck floor joists and below the deck floorboards.
3. Various systems that are designed to be installed under the deck floor joists.

The waterproof membrane system is for those who want a completely dry area under the deck that might be suitable for finished interior space. This system is for newer decks that are safe and in good condition. A contractor should install the membrane per the manufacturer’s instructions. This is the highest cost system. An example is Duradek.

The flexible membrane system is for those who want a mostly dry area under the deck. This system is for a new deck or for a deck that is being renovated because the membrane must be installed before the deck floor is installed. Someone with intermediate DIY skills may be able to install these systems per the manufacturer’s instructions. An example is Trex RainEscape. This is a medium-cost option.

The under-deck system option is for those who want a primarily dry area under the deck. This option can be installed under an existing deck that is safe and in good condition. Someone with intermediate DIY skills may be able to install these systems per the manufacturer’s instructions. This is a medium-cost option. An example is Zipup.

When deciding which system is best for you, you should consider that the flexible membrane and the under-deck systems require that you keep your deck clear of debris that could fall between the deck boards. This debris can block the water drainage and cause the water to back up into the house, and cause significant damage.

Project Conditions:

These are the same as Option #1, or as required by the water drainage system manufacturer’s instructions.

Basic project steps:

1. Complete steps 1, 2, and 3 in Option #1.
2. Install the water drainage system per the manufacturer’s instructions.
3. Build a frame to support the siding using preservative-treated lumber (usually 2 x 4).
4. Support the frame on concrete blocks where necessary, be sure to keep wood that is not preservative-treated at least six inches above the soil.
5. Install the corner boards and the siding on the frame per the siding manufacturer’s instructions.
6. Build at least a 3-foot wide door using the lumber and siding
7. Install the door using the hinges and latch
8. caulk and paint the corner boards, siding, and door per the siding and paint manufacturer’s instructions.

Every Deck is Different

Each deck is different, each area under the deck is different, and each house is different. The devil, it is said, is in the details, and the details about how to convert your deck into a storage area will be different for every situation.

This article assumes a do-it-yourself project and assumes a safe deck, in good condition, with many years of service life remaining. If the deck needs to be replaced, many more opportunities are available. Designing and building a storage area under a new deck is the ideal situation and is a project that is well worth considering because it can add as much or more value than the cost.

Note that a building permit may be required for these projects in some jurisdictions. Check with your building department about their requirements.