Rebar in Footings, Slabs and Stirrups: Spacing, Layout and Bar Bending Schedules

This guide covers where rebar goes in footings, slabs and beams, the cover and spacing rules behind those layouts, and how a bar bending schedule turns all of it into a list a fabricator can cut and bend. It picks up where our rebar size chart leaves off.

Concrete Cover: How Far Rebar Sits From the Surface

Cover is the concrete between the rebar and the outside face. It protects the steel from corrosion and fire and lets the bar bond to the concrete. Too little cover is one of the most common inspection failures. ACI 318 sets these minimums for cast-in-place concrete:

Minimum specified cover per ACI 318 for non-prestressed cast-in-place concrete. Project specifications may require more.

For estimating, cover matters because it shortens every bar. A 3″ cover on each end of a footing bar takes 6″ off its length, and on a large foundation that adds up to real tonnage.

Rebar in Footings

Continuous (strip) footings under walls carry the building load and bridge soft spots in the soil. Their reinforcement is simple, but the details are where takeoffs go wrong.

• Longitudinal bars: commonly two #4 or #5 bars running the length of the footing, 3″ clear of the bottom and sides.
• Transverse bars: wider footings and spread footings under columns get bars in both directions, forming a mat.
• Corner and intersection bars: L-shaped bars lap the longitudinal bars at corners and tees so the reinforcement stays continuous. These are easy to miss in a takeoff.
• Dowels: vertical bars hooked into the footing and extending up into the stem wall or CMU wall, tying the two together.
• Laps: wherever a bar run is longer than the stock length.

In higher seismic design categories, the International Residential Code requires reinforcement in footings and stem walls, and many engineers specify continuous bars even where the code does not. If a plan set shows “2-#4 cont.” in a footing section, that note applies to every foot of that footing type on the foundation plan.

Supporting Rebar in a Footing

Bars must be supported at the correct height before the pour, not pulled up into the concrete during placement. Use concrete blocks (dobies) or rebar chairs rated for the load. Bricks, wood scraps and rocks are common on residential sites and are often rejected by inspectors because they can crack, rot or wick moisture to the steel.

Rebar Spacing for Concrete Slabs

Slab reinforcement does two jobs: it controls cracking from shrinkage and temperature changes, and in structural slabs it carries bending loads. Typical layouts:

Typical layouts only. Bar size and spacing are set by the structural drawings.

ACI 318 also caps spacing. For shrinkage and temperature reinforcement, bars can be no farther apart than 5 times the slab thickness or 18 inches, whichever is less. For main flexural bars in structural slabs, the limit is 3 times the slab thickness or 18 inches.

Where Rebar Sits in a Slab

Rebar lying on the subgrade does almost nothing. For a slab on grade, bars should sit in the middle to upper third of the slab depth, on chairs spaced closely enough that crews walking on the mat do not push it down. In a 4″ slab, that usually means about 1-1/2″ to 2″ below the top surface. “Hooking” the mesh up during the pour is unreliable and is a common cause of cracked slabs.

Rebar Stirrups: What They Are and How to Size Them

Stirrups are bent bars that wrap around the main longitudinal bars in a beam. They resist shear and hold the main bars in position. In columns, the same shapes are called ties and they keep the vertical bars from buckling.

• Common sizes: #3 for most beams, #4 for larger or heavily loaded beams.
• Shapes: closed rectangular stirrups, open U-stirrups with a separate cap tie, and multi-leg stirrups for wide beams.
• Hooks: seismic designs use 135-degree hooks that wrap back into the beam core. Non-seismic designs may allow 90-degree hooks.
• Spacing: closest near the supports, where shear is highest, and wider toward midspan. Where shear reinforcement is required, ACI 318 generally limits spacing to half the beam’s effective depth or 24 inches.

Types of Stirrups

Estimating Stirrup Cut Length

A stirrup’s cut length is its perimeter inside the cover plus an allowance for the hooks. For estimating, a practical approach is:

Cut length = 2 x (width – 2 x cover) + 2 x (depth – 2 x cover) + 2 x hook allowance

For a 135-degree hook, an allowance of about 10 bar diameters per hook is a common estimating figure. Fabricators use exact bend deductions from their equipment, so treat this as a takeoff number, not a shop number.

Worked Example 1: Footing Rebar Takeoff

A house foundation with 150 lf of continuous footing, reinforced with 2 #4 bars continuous, 20 ft stock bars, 24″ laps, corner bars at four corners and #4 dowels at 48″ on center into the stem wall (about 3 ft per dowel including the hook).

Corner bars and dowels make up almost a third of the total here. Leaving them out is the single most common footing takeoff error we see.

Worked Example 2: Stirrups for a Concrete Beam

A 12″ x 18″ beam, 20 ft long, with #3 closed stirrups at 8″ on center, 1-1/2″ cover and 135-degree hooks.

Real beams rarely use one spacing for the full length. A typical schedule might call for the first stirrup at 2″ from the face of support, then a tighter spacing for a set distance, then a wider spacing through the middle. Count each zone separately.

Bar Bending Schedules (BBS)

A bar bending schedule lists every bar a fabricator has to cut and bend. It is the bridge between the structural drawings and the shop, and it is also the most accurate basis for a rebar estimate. A typical BBS includes:

On commercial work, the BBS usually comes with rebar shop drawings (placing drawings) that show crews where every mark goes. Errors in either document mean bars that do not fit, re-bending in the field, or a delayed pour.

Common Footing and Slab Rebar Mistakes

• Rebar lying on the ground instead of on chairs or dobies.
• Missing corner bars and dowels in footing takeoffs.
• Ignoring cover, so every bar in the estimate is too long.
• One spacing for the whole beam when the schedule has tighter end zones.
• Forgetting “top and bottom” or “each way” notes that double the quantity.
• No laps at construction joints where the pour sequence breaks a run.
• Accessories left out: chairs, bolsters, dobies and tie wire are small per piece but add up on a large slab.

Reinforced CMU walls carry their own rules for grouted cells and bond beams. Our CMU block sizes and estimating guide covers grout and reinforcement in block walls.

Get a Rebar Takeoff or Bar Bending Schedule

Design Estimation prepares rebar takeoffs, bar bending schedules and placing drawings for contractors, concrete subcontractors and fabricators across the US, with quantities by element and bar mark. Turnaround is typically 24 to 48 hours. See our rebar estimating services or send your structural drawings for a quote.