Redecking Over an Under-Deck Drainage System with 24″ × 24″ Hardwood Deck Tiles

A real-world deck project showing how to reuse existing 16″ O.C. framing, improve layout support for 24″ tiles, and choose hardwood details that perform better in restricted-airflow builds.

Hardwood deck detail showing drainage clearance and airflow beneath Garapa deck tiles and Ipe perimeter boards

Project snapshot

Deck size: approx. 20 ft wide × 14 ft deep
Existing framing: joists at 16″ on center (reused where sound)
Condition: under-deck drainage system already installed
Deck surface: 24″ × 24″ Garapa deck tiles with hardwood perimeter detailing
Key challenge: restricted airflow beneath the deck surface

Why airflow matters when a drainage system is installed

There are many cases where a customer has an existing deck system built with joists spaced at 16 inches on center, but also has an under-deck drainage system installed. While these systems do a good job managing water below the deck, they also reduce airflow. As we know, when using hardwoods (or really any decking material), reduced airflow can compromise longevity. Ipe Wood Decking in particular, limited airflow can increase the likelihood of cupping.

If you want a deeper explanation of the airflow issue, plus how it relates to moisture balance and cupping, reference this guide:
Ipe & Hardwoods: Drainage & Cupping.

This deck project is a great real-world example. The deck measured roughly 20 feet wide by 14 feet deep. The existing joists were in fairly good condition and spaced at 16 inches on center. An under-deck drainage system had been installed below the framing, and this is where the project began.

What was found during tear-off

As the previous pressure-treated deck surface was removed, it became clear that the drainage system had accumulated years of debris and buildup from not being regularly cleared. It is also worth noting that this type of drainage system hangs below the joists, which offers slightly better airflow than membrane-style systems that sit directly against the decking. Even so, the combination of restricted airflow below and direct sunlight above would have created a high risk of cupping if traditional hardwood deck boards were used across the entire surface.

Because of those conditions, Garapa Deck Tiles became the natural solution for this deck project.

Adjusting 16″ O.C. framing to support 24″ × 24″ deck tiles

Before 24″ × 24″ deck tiles could be installed, the framing had to be adjusted so each tile would land properly on joists.
Converting an existing deck framed at 16 inches on center to accommodate 24-inch tiles requires adding joists, but not nearly as many as most people expect.

A design schematic is included showing that over a 20-foot span, only five additional joists are needed to create the correct layout.
For this project, five pieces of Heritage 2×10 deck framing were added:
Heritage 2×10 Deck Framing.

Because these joists would be exposed to reduced airflow, the homeowner opted for a higher-performing framing material.
The existing joists were assumed to be an older, no-longer-available CCA-treated product, making the upgrade even more appropriate.

Diagram showing how to add joists to convert 16 inch on center framing to support 24 by 24 deck tiles

Installing the Garapa deck tiles for access and serviceability

Once the new joists were installed, the framing system was properly configured to support the 24″ × 24″ tile layout. The deck plan was designed so full tiles could be used throughout the field and across the majority of the deck surface.

The Garapa deck tiles were fastened using 2-1/2 inch stainless steel GRK trim head screws. Wherever possible, screws were slipped between the surface planks of the tile, fastening the underside cross members directly into the joists. This keeps the fasteners nearly invisible from above.

In a few locations, where the direction of the tiles relative to the joists did not allow fastening through the underside members, trim head screws were installed through the surface boards. Even in those cases, the fasteners remain extremely discreet.

This fastening approach also serves an important functional purpose. Because the tiles are screwed down rather than permanently fixed, individual tiles can be removed easily to access the drainage system below. That makes it simple to spray out and clear the drainage system as needed, which helps protect both the structure and the drainage components long term.

Perimeter detailing for irregular shapes and restricted airflow zones

As shown in the photos, the deck includes a bay window that introduces a non-rectangular condition. Along the perimeter of the deck, and especially where the bay window projects outward, traditional hardwood boards were used to create a clean picture-frame finish and handle the irregular geometry.

In these areas, Ipe Decking was selected specifically in a profile designed for restricted airflow. The material used was Ipe 1×6 (Bottom-Grooved).
The bottom relief grooves help manage moisture movement in reduced-airflow environments by balancing moisture exposure and reducing the tendency to cup.

Since deck tiles are about 1-1/2 inches thick and Ipe 1×6 boards have a net thickness of about 3/4 inch, furring strips were installed on top of the joists to bring both surfaces to the same elevation. For this build, Cumaru 1×6 boards were ripped in half and used as furring strips:
Cumaru 1×6 Solid Decking. These strips created a finished face width of roughly 2-3/4 inches and lifted the Ipe perimeter boards to match the tile height.

The Ipe perimeter boards were fastened using T-15 brown-headed stainless steel screws. These are corrosion-resistant, discreet, and visually intentional. Like the deck tiles, this fastening method also allows boards to be removed later if access to the drainage system is ever required.

Special attention was given to board spacing and corner details throughout the project. Spacing was kept consistent not only along straight runs, but also through corners and transitions, which helps the entire deck read as intentional and well-planned rather than patched together.

Finishing details that make it look natural and intentional

At all cut ends, the boards were lightly rounded using a 60-grit orbital sander. This step was done to mimic the subtle 1/8 inch roundover found on the factory edges of both the deck tiles and the decking boards. The result is a uniform appearance where cut ends blend seamlessly with milled edges, avoiding the sharp, unfinished look that often gives away field cuts.

These small finishing details matter, especially on a tile-and-board hybrid layout where the eye can quickly spot inconsistencies.

Stair treads using solid Ipe 1×6

The hardwood design elements were carried through to the stairs, where solid Ipe 1×6 (Solid) was used as stair treads. These boards were not bottom-grooved, since the staircase has open airflow and is not subject to the same cupping risk as the main deck surface.

Using solid boards here keeps the look consistent while matching the performance requirements of an open-air stair assembly.

Wrap-up: a smart layout for restricted-airflow decks

In the finished photos, you can see that the deck tiles span the full width and depth of the deck wherever possible.
Ipe boards were used around the perimeter and near the house where cutbacks and irregular shapes occur.
This combination allows the deck to perform well in a reduced-airflow environment while still delivering a clean, refined appearance.

This deck project is a strong example of how to design with airflow in mind when an under-deck drainage system is present, and how to accommodate 24″ × 24″ deck tiles when existing joists are placed at 16 inches on center.

If you have questions or want help planning an optimized hardwood deck system for similar conditions, feel free to reach out.
We are always happy to help.