How To Stay Dry On Your Patio Below Your Deck

Elevated decks are a trendy way to create more accessible access points to your home, create beautiful vantage points, and expand your outdoor living space.

However, one thing many builders forget about is water drainage – and the results could be a very wet patio underneath that spoils your living plans for that area. 

How To Stay Dry On Your Patio Below Your Deck

If you want to build a deck over your patio (or perhaps, another lower deck), then you need to figure out how to waterproof that space so you can keep it dry and use it in the future – but how? 

Here are some ideas and methods you can use to help keep the patio below your elevated deck nice and dry! 

Why You Should Waterproof Your Under Deck Space

First, let’s take a look at the major reasons why you should consider waterproofing the space under your elevated deck.

Some people may assume that waterproofing the space under the deck is an optional step that can be skipped in order to save time and money, but this is not the case.

There are two major reasons why every elevated deck should include a water drainage system to help keep the space underneath dry and moisture-free. 

You Gain Additional Outdoor Space

The first reason is that by keeping your patio dry, you can transform that space and increase the use of the area.

Some people turn that space into an outdoor living area with furniture. Some turn it into an outdoor bar space, others an outdoor dining area – whatever you desire.

Because the area is safe from exposure to water and moisture, you can add electrical lighting, ceiling fans, and even televisions. (Did you know a fan is one of the best ways to clear your outdoor space of mosquitosOpens in a new tab.?)

Alternatively, some people turn the space into a storage area or garage where you can store motorcycles, bikes, tools – anything you don’t want in your house but can’t be left outdoors where they can corrode or become ruined due to the elements. 

If you have a patio beneath your deck, this is likely your top reason why you want to waterproof your under-deck space – so you can actually continue using the patio as you did before. 

It Will Improve Your Deck’s Life Cycle

Most deck frames are made from wood, which means that trying to keep the deck frame dry is a major concern for most people. 

As exposure to moisture and water encourages rot, causing fungi to grow on your deck’s beams and joists, eating away at the nutrients and strength within the boards.

Over time, your deck’s substructure will start to rot and become very unsafe to use.

Stopping water and moisture from reaching the wooden substructure of your deck is one of the best ways to save you from the huge cost of replacing the deck beams and joists.

As a result, it’s valuable to waterproof your deck’s substructure – even if you have no plans to use the space underneath! 

Methods For Keeping Your Under Deck Space Dry

So, it’s important that you keep the space under your deck dry and moisture-free – but how? 

Here are some of the most popular methods people choose when adding water drainage systems to their elevated decks! Check them out and find the right method that suits your project’s needs! 

Install Deck Membrane With Downspouts

One of the easiest methods for waterproofing areas of your deck is simply installing a deck membrane with downspouts as your deck waterproofing solution.

This method involves adding a plastic membrane over and between the bays between your deck’s joists.

This will create troughs that capture any water or moisture draining underneath the deck’s floorboards, so it does not drip through to the patio below. This keeps the below patio space dry and moisture free. 

However, that water still needs to go somewhere – and so every under-deck membrane water drainage system should include downspouts. 

Downspouts direct the water from the membrane troughs down to a gutter and then away from your patio space.

Without downspouts, the water will splash all over the gutter and onto the patio. Not to mention getting the beam and joists wet.

With the membrane installed over your deck’s joists, they too, are protected from water dripping between teh decking.

TKeeping them nice and dry, reducing the chances of rot growing over the wooden substructure of your elevated deck, and ruining the support and strength of the beams and joists. 

This is why the deck membrane method is a popular choice for waterproofing patios – because it also provides great protection to your deck’s substructure and improves its durability so you can save more by extending the deck’s life cycle. 

Check out our full comparison of two popular underdeck drainage systems: DEK Drain, Trex RainEscapeOpens in a new tab.

How To Stay Dry On Your Patio Below Your Deck

Under Deck Ceiling Drainage Systems

The previous method involved adding a waterproofing system above and over the deck’s joists – but what do you do if your deck is already built? 

The next best method for waterproofing the space under your elevated deck (if it’s already built) is to add an under-deck ceiling drainage system.

Instead of relying on troughs created by plastic membranes, this method uses panels made from either plastic or corrosion-resistant metals (for example, aluminum) to catch and drain the water away from your patio space.

Creating a leakproof while finishing the deck’s ceiling above. Improving the look of the patio space below. 

Including downspouts will help direct the water away from your patio space, making the space even more enjoyable.

In a way, it’s very similar to the previous method, except that the water is caught below the deck’s joists rather than above it. 

This doesn’t protect the deck’s joists from moisture but does create a dry space under your deck.

Where you can add ceiling fixtures like lighting and fans. 

But most importantly, a dry space where you can set your chair up outside.

Best Under Deck Drainage System: UnderDeckOpens in a new tab., DrySpaceOpens in a new tab., DEK DrainOpens in a new tab., Zip-Up UnderDeckOpens in a new tab.

Use Flanges Between The Deck Boards 

This method for waterproofing the space underneath your deck is popular with both elevated decks above patios and with regular-height decks due to how it also protects your deck’s substructure from rot caused by moisture.

This makes it an affordable alternative option for both the membrane method and the deck ceiling method. 

It works by adding deck flanges in between each of your deck’s boards, acting like mini-gutters that capture and divert any water that collects on your deck’s surfaces.

Because deck flanges are made of flexible rubber, they provide a watertight seal so no water can drain past them.

Preventing the rain from falling between the gaps in the decking. While still allowing the boards to expand and contract with the seasons.

They’re a great choice for composite and PVC decks as flanges are already pre-made to fit into the grooves of composite and PVC boards.

They are also easy to install as they are made from rubber, so they can be smacked into the gaps between the boards by using a mallet. 

Flanges are not a great choice if building with wood decking as they do not have grooves cut into them.

Plus, wooden deck boards will absorb moisture and water and carry it down through to the joists, rendering the flanges useless.

This means that this method is best used on composite or PVC elevated decks and not decks that use wooden boards. 

Popular Flanges Brands: Dexerdry 

In Summary – Which Method Works Best For You?

So, there are a lot of options open to you if you want to make your patio space beneath your elevated decking nice and dry for living use.

However, which method works best for you all depends on the type of decking you have above. 

Most people with composite or PVC decking opt for installing flanges as they are more affordable and easy to install.

For wooden elevated decking, installing a membrane drainage system is the best option, while some people also add panels to give their patio a nice ceiling. 

Of course, it is possible to use all three together, but that’s overkill and could eat unnecessarily into your budget.

So, take a look at the options above, consider what you want to get out of your patio, and choose the best method for your type of decking. Good luck! 

Ryan Nickel

A Red Seal carpenter, passionate about building decks to be enjoyed.

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