The Complete Guide to Adding Gravel Under a Deck

Decks are a great addition to any home, providing a space for outdoor entertaining and relaxation.

However, decks can also be susceptible to damage from moisture and insects. One way to protect and improve your deck is to install a gravel bed under it. Gravel helps with drainage, prevents moisture from building up under the deck, and can deter weeds from growing under the deck. If you have a high deck, adding gravel under your deck can also create a great space for storage and other uses (interestingly, these are some of the same reasons why you should get a gravel base for your above-ground pool).

Should I put gravel under my deck?

The short answer is: Yes, gravel or crushed stone is usually the best material for under a deck. We recommend ¾” clean stone as the best all-around gravel for under your deck.

Exactly what type of rocks you put under your deck will depend on several factors:

1. What under-deck problem(s) you are trying to solve?
2. How high is your deck?
3. What kind of budget do you have?

Overall, though, installing a gravel bed under your deck can extend its lifespan, increase its usefulness, and keep it looking its best for years to come.

Reasons to put gravel under a deck

There are several reasons to consider adding gravel or crushed rock under your deck. These include:

Weed control

Few things make a deck look more neglected than a mess of weeds under it. (And God forbid that some of those weeds poke up through the cracks in the decking!) A gravel pad with a landscape fabric beneath it will ensure that the area under your deck remains weed-free.

Erosion control

Depending on the slope beneath your deck, the size of the gaps in your decking, and the amount of rainfall you receive, erosion can be a real concern. There are examples of decks with bare ground beneath that have lost up to 12” of topsoil due to erosion (like this video). Adding gravel under your deck will allow water to drain while keeping the soil in place.

Drainage

Speaking of drainage, a gravel bed under your deck can help with that too! Gravel drains much more quickly than some other materials, such as mulch. A gravel bed keeps water from draining too quickly but doesn’t retain unnecessary moisture either.

Aesthetics

Adding gravel or crushed stone under your deck creates a nice, clean look. Rather than bare dirt or patchy lawn growth, make the area beneath your deck look orderly and intentional. While plain crushed rock is typically the most affordable option for under a deck, there are other options with more aesthetic appeal. These include river rock and colored landscaping stone, to name a few.

Usability

This is probably the single most-overlooked benefit of adding gravel under your deck. For high decks in particular, the space beneath them often goes to waste. Adding a gravel pad under your deck provides an excellent space for storage. It can even serve as a low-cost patio area in some cases!

What type of gravel should I put under my deck?

We recommend ¾” clean crushed stone as the best type of gravel for under a deck. Crushed stone is both affordable and easy to get. We like the ¾” size because it drains well, is easy to install, and locks into place when tamped.

To answer the question of “what kind of rock goes under a deck” more broadly, here are the primary categories:

Crushed stone

This is most often crushed limestone. Natural crushed limestone is bluish or grayish in color. It’s also possible to get crushed landscaping stone in other colors, though these are typically more expensive and only used for aesthetic value.

As mentioned above, we typically recommend ¾” clean crushed stone. In general, we find larger sizes of crushed stone to be harder to spread under the deck and less useful as a storage area (you can also add a top layer of turf through our artificial installation services). Small gravel sizes can be scattered or washed from under the deck too easily. Avoid crushed stone that includes the “fines” or stone dust (such as “crusher run” stone), as it will not drain as well.

River rock

Unlike crushed stone, which has uneven edges, river rock is completely smooth and generally round. “Egg rock” (so-called for its oval shape) is one subset of river rock that is often used under decks.
River rock is popular in landscaping applications for its beautiful, clean look. However, it does tend to be more expensive than crushed stone (costs 2x-3x higher according to Fixr). Due to its smooth edges, river rock will not lock into place when compacted. This makes it less suitable for creating a stone pad storage area beneath a deck.

Pea gravel

Pea gravel is essentially the smaller cousin of river rock. Pea gravel tends to be cheaper than river rock, making it more affordable for under a deck. However, its smooth edges mean that it also will not compact tightly for under-deck storage uses. Pea gravel may also be harder to keep in place if the area under your deck is sloped.

Alternatives to gravel under a deck

In addition to gravel/crushed stone, there are several other materials that are often considered for use under a deck. These include:

Dirt

Some folks consider clearing or spraying the vegetation under their deck and just leaving bare dirt. Unfortunately, any weeds that were present under the deck are likely to come back sooner or later. Plus, bare dirt is more prone to erosion, so this method is not recommended.

Mulch

Mulch is a common landscaping material and it’s often considered for use under a deck. It’s appealing for its low cost and generally attractive appearance.

However, there are also a few downsides. As an organic material, mulch will eventually decompose and need to be replaced. It won’t prevent erosion in the same way that gravel will and it’s not as good at keeping weeds down in the long-term.

In dry regions, mulch can pose a mild fire risk when used under a wooden deck. Mulch can also provide an inviting space for pests like termites.

Sand

Sand is not an ideal material for under a deck. It presents the same erosion concerns as bare dirt. Plus, sand creates an inviting space for animals to defecate under the deck…not exactly the smell you want wafting up during a barbecue!

Rubber mulch

Rubber mulch is popular for its weather resistance and because it’s made from recycled materials. It’s available in a classic black color or dyed in various shades.

Rubber mulch is known to give off a strong synthetic odor during warm summer months, meaning it’s not the best option for under a deck.

Glass mulch

Glass mulch or “recycled glass gravel” is another recycled material used in landscaping applications, such as under a deck. Aesthetically, it’s one of the most striking options.

On the downside, glass mulch is much more expensive than traditional crushed stone. It’s also not an option if you’re planning to use your under-deck area for storage.

Pavers/Concrete

Pavers and concrete are some of the most durable options for under a deck. They are stable, beautiful, and virtually weather-proof.

Price is the main reason why many people don’t choose this option. A concrete pad or a paver patio are both significantly more expensive than adding crushed stone or gravel under a deck.

All in all, we find gravel to be the best material under a deck in most cases thanks to its durability and cost-effectiveness.

Planning for gravel under your deck

There are several ways to go about laying gravel under a deck. The method you choose, however, will depend on a few key considerations:

Pre-construction vs post-construction

It’s much easier to add gravel under your deck before it’s built, especially if your deck is close to the ground!

If your deck is not constructed yet, you can add gravel under the deck area but leave spaces for the footers. Fill in these spots after the footers are installed and the deck frame is built, but before the deck boards are in place.

If your deck is already constructed and is lower than shoulder height from the ground, you’ll need to plan for getting the gravel under your deck. Besides shoveling gravel under the deck by hand, one idea is to use a sled with a rope to drag stone under a low deck.

High vs low decks

As mentioned above, the higher your deck is, the easier it is to add gravel under it. Plus, the area under high decks can be used for storage space or even for a gravel patio area.

Consider whether the area under your deck could be used in some way. If so, it will affect what type of gravel you use under your deck, as well as how you install it.

Leveling gravel under a deck vs spreading gravel “on-grade”

The simplest way to add gravel under your deck is to spread it “on-grade”, meaning you don’t level the area before adding gravel. This method is much faster but leaves a higher risk of gravel washing out over time. The more sloped the area under your deck is, the higher the risk of washouts if the gravel is spread “on-grade”.

Under high decks, leveling the ground before installing gravel is a great way to create more usable space under the deck. We recommend installing a treated lumber perimeter under the deck around the area where the gravel will be installed. This perimeter not only keeps the gravel contained but can also be used as a sort of retaining wall to level the area under the deck.

To level the area under your deck, you have three choices:

Build up to level

In this scenario, the perimeter functions as a retaining wall to raise the low side of the area to the same height as the high side. This is the easiest method in most cases.

Dig out to level

With this method, the high side of the area is dug down to the same level as the low side. In this case, the perimeter functions as a retaining wall to support the ground outside the dug-out area.

Combination

It’s also possible to dig out the high side and build up the low side for a final grade between the two extremes.

The choice between these options really comes down to whether you want the finished gravel area to match the highest or the lowest area under your deck. It’s also possible to use a combination of the two methods if you want the finished gravel area to fall between the highest and lowest points.

How do I put gravel under a deck?

The steps we recommend for putting gravel under a deck are similar to the steps for installing a shed foundation. We recommend that you review that more detailed guide before starting your project.

This method is most useful for high decks where the area beneath the deck is intended for use.

1. Build a perimeter

After deciding whether you want to build up or dig out to level, determine the grade of the area under your deck. It’s easiest to find grade using a laser level as detailed here, but you can also use a string level.

If there is still topsoil in the area, remove several inches until you reach firm, undisturbed soil.

Start at the lowest point of the area and add pressure-treated lumber around the perimeter of the area. In most cases, we recommend using pressure-treated 4×6 lumber, turned on edge so a 4” side is pointing up. Once the first course of lumber extends around the site (or is completely below ground on one end, begin the second course of lumber. Continue with as many courses as needed to level the area under the deck.

We recommend fastening the corners of the lumber with 4” exterior wood screws, plus adding screws “toenailing” each course together if there are multiple courses. For maximum longevity, you should also drill through the lumber and add 24” stakes of ½” rebar every 6’-8’ around the perimeter.

We find that ensuring a level and durable perimeter is the key to creating a long-lasting gravel area under a deck.

2. Add weed barrier

We recommend using a heavy-duty stabilization fabric/weed barrier under your deck. A heavy-duty woven fabric will help to stabilize the gravel area under your deck, in addition to preventing pesky weeds from cropping up. You should always use a woven weed barrier to allow proper water drainage.

Staple the edges of the fabric to the inside of the wooden perimeter. Some folks also add landscaping staples, but we find that those aren’t needed once the gravel is in place on top of the fabric.

3. Spread the gravel

As mentioned above, we recommend ‘3/4” clean’ crushed limestone as the ideal material for under a deck.

There should be a minimum of 4” of crushed stone under all parts of the deck. Extra gravel could be needed to bring the area under the deck up to level.

4. Compact the gravel

This is an optional step, though highly recommended. We include it as a standard part of every gravel pad that we install.

Compacting the stone under your deck will help to lock it in place and will create a stable base for any objects you might wish to place on it (such as storage containers, grills, or seating).

For a more detailed explanation of these steps, be sure to review our step-by-step guide to installing a gravel pad.

Other FAQs about “under-deck” areas

Here are answers to several commonly asked questions about the areas below home decks:

What do I do with the area under my deck?

As detailed earlier, there are various ways to make the area under your deck useful. Some of our favorites include:

• Storage – At a minimum, you can add several storage cabinets on top of the gravel under your deck. If your deck is high enough, you could even add an entire storage shed!
• Patio area – Creating a patio under your deck gives you a shaded place to relax on sunny days. A level gravel pad is a budget-friendly way to make an outdoor hangout area. Concrete or pavers are other (more expensive) options.
• Outdoor kitchen – Moving your grill under the deck means you can cook in the shade. Of course, you’ll want to be always aware of the potential fire hazard when operating a grill near a wooden structure like a deck.
• Add landscaping – While you may want to keep weeds down, there’s no reason you can also do some intentional planting. Adding some landscaping rocks or shade-loving plants (even in planters) is a great way to spruce up the area under your deck.

Use your imagination, but don’t let a perfectly good space go to waste!

What can I put under my deck to keep it dry?

Gravel is a great option for keeping the ground under your deck dry since it drains quite well. However, many folks are also interested in keeping water from running through their deck in the first place. To answer the question “How do I keep water from running under my deck?”, an under-deck ceiling/drain system is your best bet. There are numerous systems designed specifically for under-deck drainage, including:

• Trex® RainEscape®
• ZipUP® UnderDeck®
• UpSide® Deck Ceiling®
• Etc.

Once you’ve finished the gravel area under your deck, it can make sense to consider waterproofing the deck ceiling as well.

Do I need gravel under a floating deck?

Whether you have a traditional backyard house deck or a floating deck like a pool deck,  it’s a good idea to add some type of gravel underneath for stability and drainage. In many cases, the floating deck is built on deck blocks, which are in turn placed on a bed of compacted gravel. Below is an example of a floating deck foundation that our company built.

Should you put landscape fabric under a deck?

Yes, it’s a good idea to always add a woven weed barrier or landscape fabric under a deck. This will:

• Prevent weeds from growing under your deck.
• Stabilize the ground beneath the gravel under your deck.

We include woven stabilization fabric as a standard part of every gravel pad that we install. Make sure the material you use is woven so water can drain through it.

In summary, adding gravel under a deck is one of the best ways to prevent erosion and weed growth and to create a stable, usable area for storage and more.

Our service area covers much of the northeastern and Mid-Atlantic USA. If you’re interested in professional gravel pad installation, you can learn more here or request a free quote here.