I. Introduction
Openings in walls, such as windows and doors, play an essential role in the design and functionality of buildings. However, their presence can affect the structural integrity of a wall, especially in terms of its strength and stability. Proper design and construction of these openings are crucial to ensuring that the walls retain their load-bearing capacity. In order to prevent weakening the structure, regulations often restrict the size of openings, particularly in solid and cavity walls, to maintain stability.
This article explores the various aspects of openings in walls, focusing on the components that make up these openings, such as jambs and heads, as well as the types of lintels and arches used to support the wall above the openings. Emphasis is placed on the importance of ensuring the strength and stability of the wall, which must be preserved even with the introduction of openings for doors and windows.
II. Parts of Openings in Walls
When considering openings in walls, there are several parts to take into account that contribute to the structural integrity of the wall. The key components of openings include the jambs, the head (or lintel), and the surrounding brickwork. These parts need to be designed with precision to ensure that the stability of the wall is not compromised.
Jambs of Openings
Jambs are the vertical sides of the opening. In solid walls, the jambs of openings can be either rebated or plain. Rebated jambs are typically used for larger openings or frames, offering both functional and aesthetic advantages. For example, rebated jambs help protect the window or door frame from weather exposure, while also providing a more polished appearance compared to plain jambs. The rebated jamb includes various components such as the inner reveal, outer reveal, and threshold.
The reveal refers to the visible thickness of the brickwork at the jambs, with the outer reveal typically being half the width of the wall to ensure good bonding. The inner reveal, on the other hand, corresponds to the thickness of the wall itself. The depth of the rebate can vary between half or a quarter of the wall width, depending on whether the frame is designed to hide or expose more of the window or door.
Additionally, the bonding at rebated jambs plays a significant role in maintaining the wall’s stability. Just as in corners and quoins, bricks at the jambs must be cut to achieve a proper overlap for bonding. In particular, cut bricks, like beveled closers, are used to prevent vertical joints from weakening the structure. These cut bricks should be incorporated at the jambs to ensure that the wall above the opening remains securely supported.
Head of Openings in Solid Walls
The head of an opening is the horizontal section of the wall above the opening, which needs to be adequately supported to maintain the overall strength of the wall. This support is typically provided by lintels or arches. These structural elements transfer the load of the wall above the opening to the jambs on either side.
Lintels, which are horizontal support beams made of materials such as stone, timber, steel, or concrete, are essential for distributing the weight of the wall. If properly installed, lintels ensure that the load above the opening is transferred efficiently to the surrounding brickwork. Similarly, arches, which are curved structural elements, can also distribute the load effectively across the span of the opening. Both lintels and arches work by creating an arching effect that transfers loads away from the central opening.
III. Jambs of Openings in Walls
Jambs are not merely aesthetic components but play a vital role in maintaining the wall’s strength. As mentioned earlier, the jambs of an opening can be rebated or plain, and each design has its purpose in terms of both functionality and appearance.
Rebated Jambs
Rebated jambs offer both practical benefits and aesthetic value. These jambs are designed with a notch (or rebate) to accommodate the window or door frame. In contrast to plain jambs, rebated jambs help protect the frame from weathering and provide a cleaner, more attractive finish. They also allow for a deeper, more secure integration of the frame into the wall.
The depth of the rebate and the method of bonding used at the jambs are important for ensuring the overall stability of the wall. The reveal at the jambs should be carefully designed to match the thickness of the wall and provide a strong bond. The outer reveal should typically be half the wall width, and the depth of the rebate is often a quarter of the wall’s thickness. By using special brick types, such as cut bricks and beveled closers, the structural integrity is maintained by avoiding vertical joints that could otherwise weaken the wall.
Bonding at Rebated Jambs
To ensure a robust bond at the jambs, bricks should overlap by a quarter of their width, a technique that is common at angles and quoins in brickwork. To prevent continuous vertical joints from weakening the structure, specially cut bricks such as beveled bat and king closers should be used at the jambs.
IV. Head of Openings in Solid Walls
The head, or the top section, of the opening, is critical for ensuring the strength and stability of the wall above the opening. The proper use of lintels or arches at the head prevents the wall from collapsing under the weight of the brickwork.
Lintels and Arches for Stability
Both lintels and arches distribute the weight of the wall to the jambs on either side of the opening. In cases where solid brickwork exists over the opening, the introduction of a lintel or arch supports the weight of the upper wall. The arching effect that occurs when the brickwork above an opening is removed shifts the load to the sides of the opening. A well-placed lintel performs a similar role by carrying the load above and transferring it efficiently to the jambs.
Lintels in Solid Brickwork
Lintels are crucial for supporting the weight of the wall above an opening. A lintel is typically a single piece of material, such as stone, timber, steel, or concrete, that spans the opening. The material used for the lintel must be capable of withstanding the compressive forces exerted by the wall above it. When choosing the right lintel, factors such as the width of the opening, the type of wall, and the amount of load to be carried must all be considered.
V. Types of Lintels
There are various types of lintels used in wall construction, each with its advantages and limitations. These include timber lintels, concrete lintels, prestressed concrete lintels, boot lintels, and steel lintels. Each type is chosen based on factors such as load-bearing capacity, durability, cost, and fire resistance.
Timber Lintels
Timber lintels were commonly used in the past to support openings in solid brickwork. However, their use has decreased due to their limited fire resistance and vulnerability to decay when exposed to moisture. Timber lintels were replaced by more durable materials such as concrete and steel.
Concrete Lintels
Concrete lintels are strong, economical, and versatile, making them a popular choice in modern construction. Concrete is particularly effective at resisting compressive forces, though it has low tensile strength. To address this, steel reinforcement bars are embedded in concrete lintels to enhance their tensile strength. Concrete lintels can be cast in-situ or precast, with the latter being more convenient due to faster installation.
Prestressed Concrete Lintels
Prestressed concrete lintels offer additional strength through the pre-stressing of concrete. These lintels are commonly used for internal openings and are available in composite and non-composite forms. Composite lintels work best for smaller spans, while non-composite lintels are used for larger openings and heavier loads.
Steel Lintels
Steel lintels are also used to support openings, particularly for non-load bearing and load-bearing walls. They are available in a variety of sizes and can be hollow or solid. Hollow steel lintels are often filled with concrete to enhance their load-bearing capacity.
VI. Brick Arches for Openings in Walls
In addition to lintels, brick arches are commonly used to span openings in walls. Arches distribute loads efficiently and have been used for centuries in both residential and industrial construction.
Semicircular Arch
The semicircular arch is one of the most efficient and aesthetically pleasing types of arch. It is commonly used for small openings such as windows and doors. The arch distributes the load directly to the bricks on either side of the opening, making it an elegant and structurally sound solution.
Rough and Axed Arch
Rough and axed arches are constructed using wedge-shaped mortar joints or uniform wedge-shaped bricks. These arches are typically used in situations where a more rustic appearance is desired, or where precision cutting is not necessary.
Other Types of Arches
Other arch types, including segmental, flat chamber, flat gauged chamber, and two-ring arches, offer different aesthetic and functional benefits depending on the specific requirements of the opening and wall construction.
Conclusion
The design and construction of openings in walls require careful consideration of various structural elements, including jambs, lintels, and arches. By selecting the appropriate materials and construction techniques, it is possible to maintain the stability and strength of the wall while providing necessary openings for windows and doors. Proper attention to these elements ensures that the integrity of the building is preserved and that the openings perform their intended functions safely and efficiently.