When building a deck, you need to give it a base, regardless of if you want to build a raised or ground deck. I wanted to build a deck but was unfamiliar with the ground preparation that I needed to do before building the deck. I knew it had to be rocks or gravel, which made me wonder what size gravel to use under my deck?
If you build a raised or ground deck, you need to prepare the ground before building the deck. The last preparation step is laying a gravel bed or rocks under the deck. The correct size of gravel you need to lay under your deck is 3/4-inch to 1” washed, and clean crushed gravel spread out evenly.
There are various things you have to do before you build your deck, and one of them is laying a bed of gravel. I was unsure of the size of gravel I needed and how thick it needed to be as the gravel serves an important purpose when preparing the ground for a deck. After thorough research, I wanted to share the information I found in this post.
What Size Gravel To Use Under Deck?
There are many sizes of gravel, also called crushed stone, that you can find, but only a few are the correct size to use as a subfloor when preparing the ground for a deck you will build. You need to consider certain factors when deciding on the right size of gravel to buy to use under your deck.
What Type Of Deck Are You Building?
You need to consider the type of deck you are building when choosing the size of the gravel you will use. If you are building a ground deck, you can use the finer gravel but in a thicker layer so it can still serve its purpose. So using 1/8-inch as a subfloor would work well.
When you use the 1/8-inch gravel screening, you will need to add at least a 4-inch leveled-out layer so it can still drain properly and keep the ground stable.
If you want to build a raised deck, you need to use the bigger size gravel as you won’t have the deck’s weight to help compact the ground and keep it even. So using the 3/8-inch washed gravel or stone will work as it has the added weight you need. It’s best to lay a bed of gravel that is at least 4-inches thick and leveled out when you use the 3/8-inch washed gravel.
The Type Of Gravel You Want To Use
There are two types of gravel experts agree are best to use if you are using it as a subfloor for your deck. Both use different sizes and shapes of gravel but can be utilized for the same purpose.
When you choose to use crushed stone, you need to remember that crushed stone is gravel with jagged edges and might be uncomfortable to walk on, so experts suggest using this type of gravel when you have a ground patio, so it has a level, well-draining subflooring.
It will also benefit you to use garden fabric that won’t puncture when the weight of the jagged edges of the gravel is on top so the ground moisture won’t seep in. If you choose washed crushed stone/ gravel to use under your patio, the best size is ¾-inches to 1-inch.
If you choose pea gravel as a subflooring for your deck, you will get smooth-edged pea-sized gravel that will work well for raised beds as it comprises pea-sized rocks and stones that are softer on the feet and easier to walk on. While pea-sized gravel works well to keep the garden fabric and your feet safe, it is not great when it comes to drainage.
Because the stones and rocks are only pea-sized, they retain water longer than other gravel. They do dry eventually, but it can be an issue if you use them under a ground deck made from wood. Pea gravel ranges in size from 1/8-inches to ¾-inches.
What Does The Size Of The Gravel Determine?
The gravel size you use will affect how long your deck will last and how well the ground will stay stable in harsh weather conditions. Some of the other things the size of the gravel has an impact on are:
The size of the gravel directly impacts the drainage ability of the gravel. The smaller gravel tends to hold moisture longer, which is an issue if your deck is on the ground and made from wood. It could become a bigger problem if the weather persists, as water retention can cause the ground under the gravel to liquefy and shift, especially if the garden fabric has been torn.
The Weight And Amount
The size of the gravel also directly impacts the amount you will need. In severe weather storms, the gravel has to weigh enough to keep the garden fabric from lifting up or pulling away from the subbase. It also needs to be thick enough to keep the subbase from shifting in severe weather.
So if you use the smaller-sized gravel or stone, you need to spread a thicker bed that will weigh enough to keep the subbase stable. In the end, it will cost more because you will need to buy more to make up the correct weight and thickness.
Ease Of Maintenance
The gravel size will only be an issue in maintaining your deck because the jagged edges can make it uncomfortable and unsafe to walk on if you choose a size that is too big. Smaller-sized gravel makes it easier to maintain your deck because it doesn’t have sharp edges and evenly distributes the weight so you won’t hurt, sprain an ankle, or cut yourself.
If you’re looking for how many beams you should use in your deck you can check out Do decks need beams on our site here.
It is important to choose the correct size of gravel to use under your gravel as it directly impacts the durability of ground decks, the maintenance, and the amount of gravel you need to buy.
If you are not sure of the right size to get, you can always use ¾ inches to 1 inch for crushed stone and 1/8-inches to ¾-inches for pea gravel.
Which ever size you go for it pairs well with Wood decking which you can read more about here.