How Much Does Under-Deck Drainage Cost? [2025 Data]
For a 12’ by 20’ deck, it costs $7,700 to install under-deck drainage. Your price will depend on the size of your deck, and costs commonly range between $5,100 and $8,000. It’s best to call a pro for an accurate quote.
Under-deck drainage costs anywhere from $1,500 to $10,400. For a 240-square-foot deck, most people pay around $7,700 for drainage systems. However, the size of your deck will significantly affect your costs. You can expect to pay $21 to $43 per square foot for materials and professional labor.
Under-deck drainage is used on second-story decks to prevent water from leaking down onto the area beneath it. Installing this type of drainage system will keep the space dry, so you can add lighting, storage, furniture, or even an outdoor kitchen.
Under-Deck Drainage Cost Factors
Several factors impact the cost of under-deck drainage, including your deck’s size, the materials used, and labor prices in your location. Here’s an overview of the main factors.
Deck Size
Your deck’s size greatly affects the cost of under-deck drainage. For materials and labor, installing this type of drainage system runs between $21 and $43 per square foot. Here’s how much it would cost to add under-deck drainage for various deck sizes.
| Dimensions | Square Feet | Average Cost |
|---|---|---|
| 12x12 | 144 | $3,030–$6,200 |
| 12x16 | 192 | $4,040–$8,260 |
| 12x20 | 240 | $5,040–$10,320 |
| 14x20 | 280 | $5,880–$12,040 |
| 12x24 | 288 | $6,050–$12,390 |
| 16x20 | 320 | $6,720–$13,760 |
| 20x20 | 400 | $8,400–$17,200 |
Materials
Prices also depend on the materials you choose. For example, Trex RainEscape is a well-known under-deck drainage system. It includes a range of products, such as trough panels, downspouts, caulk, and tape. According to the company, the Trex under-deck drainage system costs $6 to $8 per square foot.
However, prices will vary if you buy your own materials instead of purchasing a kit. The cost to build a DIY under-deck drainage system depends on the specific materials you choose. Fiberglass, galvanized steel, and plastic are a few options to consider, all of which vary in price.
Prep
While some people choose to install drainage when building a second-story deck, you can also add a drainage system to an existing deck—either above or below your deck joists.
Installing a drainage system above the joists is more complicated and time-consuming. Your pro will first need to remove the deck boards and railings, which requires additional time and increases your costs.
Labor
Labor accounts for a significant chunk of the cost to install under-deck drainage. On average, a local deck builder will charge between $15 and $35 per square foot for their services.
Under-Deck Drainage Ongoing Costs
An under-deck drainage system doesn’t require much upkeep, but there are a couple of ongoing costs you could face after installation.
Maintenance
After installing your drainage system, it’s important to take care of it as part of your routine deck maintenance. You can perform annual deck inspections on your own, but if you notice any leaks or backed-up water, bring in a pro to fix the drainage system.
Repairs
Like the other parts of your deck, your under-deck drainage system may require repairs from time to time. The price depends on the specific issue, but on average, deck repairs cost $870 to $3,470.
DIY Under-Deck Drainage Installation vs. Hiring a Pro
If you have some experience with home improvement projects, you could install your own under-deck drainage system. Since the materials cost $6 to $8 per square foot, you’d spend between $1,440 and $1,920 to set up a drainage system on a 12’ by 20’ deck. You’ll also need a few tools, including a caulk gun and utility knife. By doing the work yourself, you could save a couple thousand bucks in labor costs.
Still, hiring a pro is worth the expense. With an expert in charge, you’ll get high-quality work and faster installation. Plus, you won’t have to worry about removing the deck boards and railings, buying the right materials, or putting the deck back together when you’re done (if you’re installing an over-the-joist system).
Cost of Common Under-Deck Drainage Add-Ons
If you’re adding a drainage system to an existing deck, it’s a good opportunity to tackle other deck-related projects, too. Here are a few common add-ons to consider:
Staining a deck costs $550–$1,250
Sealing or waterproofing a deck costs $500–$1,400
Deck refinishing costs $900–$2,720
Deck painting costs $500–$2,000
Installing outdoor lighting costs $2,000–$6,000
Building an outdoor kitchen costs $6,300–$26,900
How to Save Money While Installing Under-Deck Drainage
Adding an under-deck drainage system can get pricey—especially when you hire a professional. However, there are a few possible ways to cut costs on this project, including:
Doing your own prep work: You could reduce labor costs by preparing the deck for installation before your contractor arrives. For example, you could clean up leaves and debris from the deck or move any outdoor furniture so that they can get straight to work. If you’re comfortable with it, you could even remove the deck boards and railings, but be careful not to damage them.
Planning your project for the off-season: For decking pros, work often slows down in winter, and contractors may offer lower prices then. By scheduling your project during the slower season, you could get a better deal.
Shopping around: It’s a good idea to request quotes from at least three professionals before hiring someone. This helps you compare pricing and ensures you’re paying a fair rate.
How Angi Gets Its Cost Data
Home is the most important place on earth, which is why Angi has helped more than 150 million homeowners transform their houses into homes they adore. To help homeowners with their next project, Angi provides readers with the most accurate cost data and upholds strict editorial standards. We extensively research project costs to develop the pricing data you see, so you can make the best decisions for you and your home. We rely on reputable sources, including the U.S. Bureau of Labor Statistics, academic journals, market studies, and interviews with industry experts—all to ensure our prices reflect real-world projects.
Want to help us improve our cost data? Send us a recent project quote to costquotes@angi.com. Quotes and personal information will not be shared publicly.
Frequently Asked Questions
If you want to use the space beneath your second-story deck, then yes, an under-deck drainage system is worth it. Having a drainage system in place lets you run power to the area, so you can install a ceiling fan, lighting, TV, or other appliances to create a comfortable outdoor living space.
Yes, it’s possible to add under-deck drainage to an existing deck, but it may require some prep work. Many drainage systems sit on top of the deck joists, so you’ll need to remove the decking boards, railings, and other structures before installation. To avoid this, you could install a below-the-joist drainage system instead.
If you’re starting from scratch, you’ll spend between $9,600 and $14,400 to construct a 12’ by 20’ (or 240-square-foot) deck. However, the cost to build a deck depends on a few factors, including the decking material, the deck type and location, and the price of labor in your area. Adding an under-deck drainage system to a 240-square-foot deck costs $7,700.
