Elevated Garage Concrete Floor System Options

While elevated residential garages with usable spaces below are popular, constructing high performing and durable structural floor systems is challenging. Our two favorites are prestressed concrete planks and corrugated metal decking with cast-in-place (CIP) concrete. Each system offers advantages that can meet unique project parameters.

Prestressed concrete planks are ideal as they can sustain water and salt runoff from vehicles. Reinforcing steel in the planks is the only metal, and is it well protected within the concrete plank. Planks are usually topped with a durable cast concrete finish that can protect the plank, and durable epoxy finishes waterproof the system. Fabrication of the planks occurs in a controlled, indoor environment that leads to high quality. But to be cost-effective, the planks need to be a standard, rectangular shape. This option has a higher cost, as it also requires expensive transportation and a crane to install.

CIP concrete with corrugated metal decking provides greater design flexibility, making it ideal for buildings with unique architectural shapes and features. But the metal decking is susceptible to corrosion, so maintaining a watertight finish is essential. Construction of this floor system requires less coordination because the metal deck acts as permanent formwork for concrete, reducing the amount of temporary shoring. However, the process is labor intensive due to onsite concrete placement.

 

 

 

 

 

 

 

 

Custom Architectural Shape

 CIP concrete with corrugated metal decking was utilized for this building, which features a second story garage and unique footprint. Sections of CIP concrete and decking are supported by steel drop beams strategically arranged to fit the building’s geometry. This floor system was selected because it was more cost-effective than custom-shaped precast planks.

Utilization of Both Systems in One Design

Precast planks were determined to be the best option for this second-story garage, allowing for large spans without requiring posts in the space below. A sloped concrete topping was added on top of the planks to provide drainage. CIP concrete with a metal deck was used near the stairs, as these smaller areas were most cost-effective to construct with CIP concrete rather than precast planks.

Concrete Patio in a Flood Zone

Concrete planks can also be effectively used in exterior patio deck applications. In this case, the architect wanted a concrete patio design feature. However, the house had to be built on piers due to coastal flood zone restrictions, so a concrete slab on grade was not an option. Steel beams were used as an alternative to a frost wall, providing support for the edges of the planks and spanning the gaps between the piers.

Choosing Between the Two Systems

For the two-story garage shown below, it was not initially clear which floor system would be most cost-effective. Structural concepts were developed for both systems, and they presented similar solutions as both were able span the footprint without introducing posts in the space below. Ultimately, the client selected CIP concrete with metal decking (Option B) because it proved to be most cost-effective.

Full Height Concrete Wall Connection for Elevated Garages

These details were for a two-story garage built into a steep slope. The elevated concrete floor was supported by full height concrete walls acting as retaining walls. A 3” concrete reveal was incorporated to protect the wood wall plate from water damage.

 

Ali McNamara, E.I.T.

Olivia Caron, E.I.T.