If you're planning to install an under-deck drainage system for your deck, understanding the total cost is an essential step. Beyond the cost of building the deck itself, the drainage system will require some budget as well. A common question is: How much does an under-deck drainage system really cost?
In this blog, we’ll walk through the costs for two different deck sizes—20'x20' and 16'x20'—and explain the role of each product involved in the system. By the end, you’ll have a better understanding of the materials, their functions, and how to estimate the costs for your own deck drainage project.
1. The Role of Each Product
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Waterproof Membrane: The waterproof membrane is the core of the drainage system. It covers the underside of the deck, ensuring that water doesn't seep through to the deck or the ground below. The membrane effectively directs water to the downspouts and drainage system, preventing water accumulation and decay.
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Downspouts: Downspouts collect the water from the deck surface and guide it to the drainage system, directing it out of the deck area. The number of downspouts typically matches the number of joist spaces (one downspout per joist), ensuring that water can flow freely and preventing pooling.
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Waterproof Tape: Waterproof tape is used to seal the seams and edges of the waterproof membrane. It ensures that water does not leak at the junctions of the membrane, making the entire system waterproof. This is essential for maintaining the system's overall effectiveness.
2. Material Costs
Let’s break down the costs of the materials:
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Waterproof Membrane: A 50-foot roll costs $63. Each roll covers 50 square feet, making it ideal for large areas beneath the deck.
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Downspouts: Each downspout costs $35. These downspouts are installed at drainage points to collect and direct water away from the deck.
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Waterproof Tape: Each 50-foot roll costs $12.99. The tape is used to seal the edges and seams of the waterproof membrane, ensuring that the system is completely watertight.
3. Cost Estimate Based on Deck Size
Now, let’s estimate the cost based on two different deck sizes, assuming a 16-inch joist spacing (which means one downspout per joist):
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20'x20' Deck:
This deck has an area of 400 square feet, and with 16-inch joist spacing, you will need 20 downspouts.-
Waterproof Membrane: You’ll need 8 rolls to cover the entire deck, which costs $520 ($65 x 8).
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Downspouts: You’ll need 20 downspouts, and at $35 each, the total cost for downspouts is $700 (20 x $35).
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Waterproof Tape: You’ll need 2 rolls of tape to seal the seams, totaling $23.98 ($11.99 x 2).
Total Cost:
Waterproof Membrane ($520) + Downspouts ($700) + Waterproof Tape ($23.98) = $1,243.98 -
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16'x20' Deck:
This deck has an area of 320 square feet, and with 16-inch joist spacing, you will need 16 downspouts.-
Waterproof Membrane: You’ll need 7 rolls, which costs $455 ($65 x 7).
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Downspouts: You’ll need 16 downspouts, and at $35 each, the total cost for downspouts is $560 (16 x $35).
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Waterproof Tape: You’ll need 2 rolls of tape to seal the seams, totaling $23.98 ($11.99 x 2).
Total Cost:
Waterproof Membrane ($455) + Downspouts ($560) + Waterproof Tape ($23.98) = $1,038.98 -
4. Cost Per Square Foot
Here’s the breakdown of cost per square foot for each deck:
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20x20 Deck:
Total cost $1,243.98 ÷ 400 square feet = $3.11 per square foot. -
16x20 Deck:
Total cost $1,038.98 ÷ 320 square feet = $3.25 per square foot.
5. Summary
Installing an under-deck drainage system provides a long-term solution for managing water beneath your deck. While the installation cost depends on the deck size and design, based on our calculations, the total cost for a 20x20 deck is approximately $1,243.98, while a 16x20 deck will cost around $1,038.98. The cost per square foot ranges from $3.11 to $3.25.
If you’re considering installing an under-deck drainage system for your deck, this cost estimate should help you prepare your budget and ensure you have enough funds to cover all the necessary materials and installation. If you have any other questions, please feel free to contact us at support@emayuu.com.