What is a Lap Splice? Length of Rebar Overlap

Definition and Guidelines for Rebar Lap Splices

rebar splice
rebar splice. Photo SpacesImages/Getty Images

What is a Lap Splice?

Reinforcing bar (rebar) comes in lengths of up to 60 feet. In theory, this would seem to obviate the need for splicing the material for all but the largest commercial projects. In practice, for any number of reasons, shipping constraints on length and efficient use of materials being two of the most common, most building projects involve extensive rebar splicing. A lap splice is the most common way of creating a single structural entity from two rebar segments.

The lap splice, as the name suggests, is created by overlapping two lengths of rebar, then wiring them together. From a structural point of view, the most critical aspect of a lap splice is the overlap length. Note, however, that overlap requirements vary with both rebar size and the specific structural application.

Rebar Splices Code Requirements

In almost every construction instance, overlap lengths are subject to local building codes. Although it's imperative to check your local code for detailed compliance requirements, most codes are derivative from the IBC (International Building Code). IBC code requirements are almost identical to ACI codes. ACI code section 318-14, which governs rebar splicing, has been incorporated without meaningful modification into the corresponding concrete section of the 2015 IBC. Therefore either the IBC code sections governing concrete or ACI 318-14, current as of 2016, provide reliable information about lap splice code requirements.

This article describes code requirements for the most common kind of lap splice, the contact splice. Note that other kinds of splices are code-compliant, specifically mechanical splices and welded splices. These splices go beyond the scope of this article. In any event, the contact lap splice is the usual rebar solution for relatively small-scale construction projects, such as residential buildings.

Overlap Requirements for Lap Splices in Masonry and Concrete

Below you will find IBC/ACI splice length requirements. Keep in mind, however, that the governing code for your project is the local building code. A few large US cities -- Los Angeles, for example -- have developed their own version of IBC codes and most inspectors will not pass a project that is IBC code-compliant if it conflicts with the local version of the code.  Furthermore, almost all US jurisdictions now require a structural engineer's approval stamp on any structural aspect of the building plan. In other words, the information below is only suggestive; the actual requirements will be specified in detail by the structural engineer in the structural plans.

The structural engineer takes into account not only the standard requirements listed here, but the many exceptions having to do with critical stress points, the different splice length requirements when connecting rebar of different diameters and requirements for staggering splices in order to avoid rebar congestion at overlap points, which can result in inadequate concrete flow into the splice area. All splice locations must be specified in the structural plans before approval.


Rebar Splices In Masonry
1500 PSI#4 21 INCHES
2000 PSI#4 18 INCHES
2500 PSI#416 INCHES
1500 PSI#5 32 INCHES
2000 PSI#528 INCHES
2500 PSI#525 INCHES
1500 PSI#846 INCHES
2000 PSI#840 INCHES
2500 PSI#836 INCHES

Rebar Splices in Concrete

  Concrete StrengthSteel GradeRebar TypeSplice Length
2500 psi60,000 #441 inches
2500 psi60,000#551 inches
2500 psi60,000#661 inches
2500 psi60,000#789 inches
2500 psi60,000#8102 inches
3000 psi60,000#437 inches
3000 psi60,000#547 inches
3000 psi60,000#656 inches
3000 psi60,000#781 inches
3000 psi60,000#893 inches

Wiring Requirements for Lap Splicing Rebar

The code requirements for the wiring material and fastening method are brief and note only that the wiring method employed should "secure" the rebar in place. The lack of specific requirements for the wiring material or specification of the wire wrapping method may seem surprising at first, but consider the wire's only purpose is to hold the rebar temporarily in place.

Once the pour is completed and the concrete has begun to harden -- within a few hours of the pour -- the wiring material has no further purpose.

These splice lengths shall not be used when you the rebar needs to be drilled into the concrete. If that's the case, the structural engineer must determine the embedded depth of the rebar and the appropriate product to anchor the rebar to the existing concrete.