Garage Concrete Reinforcing Requirements

Garage foundations with block stem walls use upright reinforcement.bricklayer,mason image by Greg Pickens from Fotolia.com

Reinforcing garage concrete floors requires estimating the amount of weight the concrete is expected to bear. Garage floors built primarily for automobiles and light pickup trucks need minimal reinforcement, while those that must support heavy equipment such as bulldozers fare better with heavy reinforcement. Another consideration for reinforcing the garage concrete is the weight that will bear on it from the building’s structure. Consult an architect or engineer for reinforcement instructions for your particular garage and location.

Considerations

Garage concrete reinforcement is used in footers, stem walls and slabs. The foundation’s design determines where to place the reinforcement and what type of reinforcement to use. For example, a foundation that uses a footer, stem wall made of concrete blocks and slab poured to the blocks, would usually use two reinforcing bars in the footer, upright reinforcing bars every 3-feet in the block stem wall, and a grid made of reinforcing bars in the slab. Another factor to consider is the weight the floor will need to support. Residential garages perform well with slabs designed to handle 50 pounds per square foot, while garages for equipment and repairs will perform best with slabs that will handle 100 pounds per square foot, according to “Basic Engineering for Builders.”

Many counties, cities and states specify the type of reinforcement to use in building foundations and how to install it. There are, however ,differences based on the types of soils, the soil conditions, the expected depth of frost and the garage use. Another aspect of reinforcement is the strength of the concrete. Local building codes often require 4000 psi concrete, itself an expression of reinforcement. Within the slab, many codes require at least wire mesh with a 6-inch by 6-inch grid. Others may require #4 rebar (1/2-inch diameter) laid in a grid that is 18-inches by 18-inches, or even 2-feet by 2-feet. In all cases the reinforcing material has to be prevented from being near the bottom or the top of the concrete. Reinforcement sitting below the concrete does no good, and when it is too close to the top, changes in temperature and moisture leads to spalling, where the concrete flakes at the surface.

It is common practice to place two #4 rebar in the footer, near its center. Use rebar chairs (steel supports) of the correct height to hold the rebar in place. Install two upright #4 rebar every four feet in a poured stem wall and attach two continuous #4 rebar to them, spaced vertically every 12 to 18 inches. For stem walls made of block, install upright rebar every 3 feet in the cells. Reinforce slabs with 3000 to 4000 psi concrete and 6-inch by 6-inch woven wire mesh or #4 rebar laid out in a grid 2-feet by 2-feet. Keep the reinforcement in the center of the slab using chairs.