A concrete header block is a masonry unit laid with its short end facing outward in a wall, used primarily to tie together multiple layers of masonry or to provide structural support above and below openings like doors and windows. While the term can refer to the orientation of a standard concrete masonry unit (CMU), it also describes specially shaped blocks designed to create bearing surfaces and distribute weight in load-bearing walls.
How a Header Block Differs From a Standard Block
In masonry, the word “header” describes how a block or brick is oriented. A stretcher is laid with its long face parallel to the wall surface. A header is turned 90 degrees so its shorter, square end faces outward. This positioning allows the block to span the full thickness of a wall, physically connecting the outer layer of masonry to the backing layer behind it. In traditional brickwork, headers used this way are sometimes called throughstones or perpends.
The distinction matters because a wall built entirely with stretchers has no mechanical connection tying its front face to its back. A course of header blocks bridges that gap, locking the two layers together and significantly increasing the wall’s stability. Standard concrete masonry units are commonly available in nominal widths of 100, 150, 200, 250, and 300 mm (roughly 4 to 12 inches), with a typical nominal height of 200 mm and length of 400 mm. The actual dimensions run about 10 mm smaller in each direction to account for mortar joints.
Supporting Weight Over Openings
One of the most common uses for header blocks is creating structural support above doors, windows, and other wall openings. Every opening in a load-bearing wall interrupts the natural path that weight follows from the roof and upper floors down to the foundation. Without a horizontal support spanning that gap, the masonry above would collapse inward.
Header blocks solve this by acting as a beam across the top of the opening. They take the weight of everything above and transfer it sideways to the solid masonry on either side, which then carries it down to the foundation. This system works the same way whether the opening holds a window, a door, or a pass-through. In some installations, headers are also placed below an opening to further distribute the load, reducing the stress on the opening itself.
Specially shaped blocks designed for this purpose include lintel blocks (also called U-blocks or channel blocks), which have an open channel along the top. This channel allows horizontal rebar to be placed inside and filled with grout, creating what is essentially a small reinforced concrete beam within the wall. High lintel versions with a nominal height of 400 mm are available for spans that need extra depth and strength.
Headers vs. Lintels
Headers and lintels serve similar roles, but they aren’t interchangeable terms. A lintel is a beam placed across the top of an opening to carry weight from above. It can be made from steel, precast concrete, stone, or reinforced masonry. Headers also span openings, but contractors can install them both above and below an opening to share the load more effectively.
Lintels offer more design flexibility. They come in various profiles and materials, and architects often choose them for their visual contribution to a facade. Headers are more utilitarian, typically appearing in a single standard shape. In practice, many masonry walls use both: a header course to bond wall layers together and a lintel or lintel block to handle the concentrated loads over large openings.
Bonding Patterns in Masonry Walls
Beyond structural support, header blocks play a major role in the visual patterns of masonry walls. The arrangement of headers and stretchers defines some of the most recognizable bond patterns in construction.
- Header bond: Every brick or block in every course is laid as a header, showing only the short face. This creates a distinctive grid of small squares across the wall surface.
- English bond: Alternating courses of all stretchers and all headers. This is one of the strongest patterns for load-bearing walls because every other course ties the wall together across its full depth.
- Flemish bond: Each course alternates between stretchers and headers within the same row. It’s visually appealing but slightly weaker than English bond for structural applications.
- English garden wall bond: Three rows of stretchers followed by one row of headers. This reduces the number of expensive header units while still providing periodic structural ties.
- Flemish garden wall bond: Three stretchers followed by one header in each course, balancing aesthetics with economy.
The choice of pattern affects both the wall’s appearance and its structural integrity. Walls that need maximum strength, like retaining walls or heavily loaded bearing walls, typically use more frequent header courses.
Reinforcement and Grouting
In reinforced masonry construction, header blocks and other CMUs work together with steel rebar and grout to form a composite structure far stronger than the blocks alone. For load-bearing walls, rebar is typically placed in every other masonry core. Tie rods anchoring the wall to the foundation should be set at least 6 inches into the concrete footing before it cures.
The grouting process depends on the size of the block cores. Cores wider than 4 inches call for coarse-aggregate grout, while cores under 4 inches use fine-aggregate grout. When header blocks are used to form lintels over openings, the horizontal channel is filled with grout around horizontal rebar, creating a reinforced beam that can span several feet without additional support.
Strength Requirements
All concrete masonry units, including header blocks, must meet minimum compressive strength standards. The current ASTM C90 specification, updated in 2014, requires a minimum net area compressive strength of 2,000 psi when used with Type M or S mortar. Earlier versions of the standard allowed 1,900 psi, but research by the National Concrete Masonry Association on prism strengths led to the increase.
Depending on the application, blocks with much higher ratings are available. Compressive strengths for CMUs range from 1,700 psi at the low end up to 4,500 psi for high-performance units. The strength you need depends on the loads the wall will carry, the height of the wall, and whether it serves as a bearing wall or simply an enclosure. Header blocks used in structural lintels over wide openings or in heavily loaded bearing walls generally need to be at the higher end of that range, since they concentrate load transfer into a relatively small cross-section.