Cavity wall diagrams: What is a Cavity Wall? Construction and Advantages of Cavity Walls

What is a Cavity Wall? Construction and Advantages of Cavity Walls

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  • What is a Cavity Wall?
  • Construction of Cavity Walls
  • Advantages of Cavity Walls

What is a Cavity Wall?

Cavity wall is constructed with two separate walls for single wall purpose with some space or cavity between them. These two separate walls are called as leaves of cavity wall. The inner wall is called as internal leaf and outer wall is called as external leaf. Cavity wall is also called as Hollow wall.

For non-load bearing cavity wall, two leaves are of equal thickness or sometimes internal leaf with more thickness is provided. The cavity size should be in between 4 to 10cm. The internal and external leaves should have at least 10 mm thickness. The two leaves are interconnected by metal ties or links as shown in above figure.

Construction of Cavity Walls

In general, cavity wall doesn’t require any footings under it, just a strong concrete base is provided on which cavity wall is constructed centrally. Two leaves are constructed like normal masonry, but minimum cavity must be provided in between them. The cavity may be filled with lean concrete with some slope at top up to few centimeters above ground level as shown below.

Weep holes are provided for outer leaf at bottom with an interval of 1 m. Normal bricks are used for inner leaf and facing bricks are used for outer leaf. Different masonry is also used for cavity wall leaves. The leaves are connected by metal ties or wall ties, which are generally made of steel and are rust proof.
The maximum horizontal spacing of wall ties is 900mm and maximum vertical spacing is 450mm. The wall ties are provided in such a way that they do not carry any moisture from outer leaf to inner leaf. Different shapes of wall ties are shown in below figure.

For half brick thickness leaves, stretcher bond is provided. And for one brick thickness or more thickness, English bond or Flemish bonds type constructions are provided. While laying bricks, care should be taken without filling the cavity with cement mortar.
To prevent mortar dropping in cavity, wooden battens are provided in the cavity with suitable dimensions. These battens are supported on wall ties and whenever the height of next wall tie location is reached, then the battens are removed using wires or ropes and wall ties are provided.

Two leaves should be constructed simultaneously. Spacing should be uniform and it is attained by predetermining the location of wall ties. Damp proof course is provided for two leaves separately. In case of doors and windows, weep holes are provided above the damp proof course.

Advantages of Cavity Walls

Following are the advantages of cavity wall when compared to solid walls.

  • Cavity walls give better thermal insulation than solid walls. It is because of the space provided between two leaves of cavity walls is full of air and reduces heat transmission into the building from outside.
  • Economically they are cheaper than solid walls.
  • Moisture content in outer atmosphere is does not allowed to enter because of hollow space between leaves. So, they also prevent dampness.
  • They also act as good sound insulators.
  • They also reduce the weights on foundation because of their lesser thickness.
  • Outer Efflorescence is also prevented.

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A Detailed Study on Cavity Wall

A cavity wall is the construction of two walls with some gap instead of a single-wall for a purpose. Different types of cavity walls such as brick cavity walls, block cavity walls, etc. can be observed in the construction.

A cavity wall is thinner when compared with normal walls as two walls are constructed apart with a gap. Further, a cavity wall can be called as a hollow wall due to the existence of a gap between the two walls.

Purpose of a Cavity Wall

Cavity walls are constructed only special purposes only. Generally, we construct solid walls without having a gap as there is no such requirement always.

You could understand the uses when you read the advantages and disadvantages of these types of walls.

Use as a Sound Barrier

Large noise becomes a big issue for the functionality of the building. For example, if we operate an office with high noise, workers cannot work freely due to the noise.

How does the noise generate?

In buildings, usually, we install generators to the power supply or to uses it as an alternative source of power. Further, it is used when there is a failure in power.

A generator produces very high noise when it operates. It is very difficult here.

Nobody likes to listen to the noise.

So we construct cavity walls as a sound barrier.

When there is an air gap, it is very difficult to sound to travel as the medium changes. Further, depending on the requirement of the project, insulations are also used to improve the efficiency of the system.

Use as a Thermal Insulation

There should be a medium to heat to transfer. Creating an air gap reduces and the air gap acts as an insulation. Especially, when we need to maintain the heat, need to avoid heat transfer, etc. we could construct cavity walls as appropriately.

Use to Prevent Dampness

Cavity wall work as a barrier to transfer the moisture into the building. Providing the air gap between the walls avoid it as it is difficult to wall to transfer dampness through the air.

Economical Construction

Construction of a solid wall to resist the issues discussed above is costly.

We have to construct thick solid walls for this purpose. For example, if we need to avoid dampness, we have to have a fairly higher thickness and it could be much higher than the normal wall.

If we construct a cavity wall, there is a considerable saving of materials as we construct the cavity walls with thinner brick or block walls.

Properties of Cavity wall

Properties of the cavity wall are discussed in relation to its uses as they are connected. Further, studying the relevant properties is quite important in the special construction of this nature.

Brick cavity walls are quite common in construction. Further, blocks are also used in construction now.

Thermal Properties

Energy-efficient of a building is very important today as we try to develop sustainable constructions. Unless we heading to a green area, there would be an environment for future generations.

Therefore, we must save energy as much as possible.

A cavity wall is a good option for that. It reduces thermal conductivity and reduces heat load. Further, it reduces the rise of the heat or the temperature inside a building when the outside is hotter.

The energy required to cool the building will be less comparatively. Therefore, there will be saving.

It works in opposite directions also. If outside is cooler and if we need to retain the internal heat, the cavity wall could provide the solution.

Structural Capacity

There is an attention to the structural properties of the cavity walls due to the less thickness of the individual walls. However, When they are tied to each other, load resisting capacity increases.

When the cavity walls are used as load-bearing walls, special attention shall be made on the load-bearing capacity of the wall.

The strength of the brick/block and the motor are the factor affecting its load-bearing capacity mainly. They shall be checked adequately.

Further, construction work shall b supervised to maintain good workmanship.

Fire Resistance of Cavity Walls

Having created an air gap between two brick walls, improve the fire resistance of the cavity walls. Generally, it reduces the transfer of the heat due to the air gap.

Therefore, it as good resistance to the fire.

Resistance to the Moisture Transfer

As discussed above also, the cavity wall has good resistivity to the moisture transfer.
Even though one wall absorbs the heat, it won’t transfer to the other wall due to the gap between the walls.

The air gap significantly reduces the transfer of dampness through the wall.

Advantages of Cavity Wall

  • Cavity walls can be used as thermal insulation. It reduces the heat transfer considerably.
  • Higher fire resistance
  • Sound resistance. Sound waves travel faster through the solid wall. The cavity wall obstructs it.
  • Less transfer of moisture or less dampness
  • Economical to construct than a solid wall that builds achieve the same properties
  • Less weight and it reduces the structural cost.
  • It improves energy efficiency in a building. When we airconditioning a building, heat transferred through the soil walls needs to be considered. However, the cavity wall reduces it considerably.

Disadvantages of Cavity Wall

  • Construction supervision shall be done actively.
  • Skilled labors should be used
  • If the mortar falls into the gap, it shall be clean. If there will be a considerable amount of mortar fill, the performance will be reduced.
  • The collection of the motor between the wall will increase the dampness.
  • Proper insulation method shall be adopted at openings
  • Cavity walls are less stiff compared with solid walls. The structural settlement could crack the walls
  • Necessary stiffeners shall be provided the avoid cracking due to thermal actions.
  • Concrete lintel beams could be provided wherever necessary.
  • Wider beams are needed to be constructed.
  • Thermal bridging issues
  • The air gap needs to be adjusted based on the requirements of the insulations. Or the thickness of the insulation will be limited to the available gap of the wall on an occasion where it is required to provide insulations.

Cable laying inside hollow walls

Igor Ivantsov

Today, in new and reconstructed buildings, structures in the form of a frame made of special metal profiles (less often – from a wooden bar) are widely used, on which plasterboard sheets are fixed on one side (if it is a finishing wall panel) or on both sides (if it is a partition) (dry plaster). Due to their brittleness, surface wiring, pre-drilling holes and concealed cabling in cavities require extra care. The use of traditional tools (chisels, drills) can lead to cracks and violation of the sealing of the edges of the panels. A special tool allows, even after the repair is completed, to quickly and accurately mount hidden wiring through small holes and install terminal blocks for it.

The simplest task is to make mounting and installation holes in drywall. Round holes of small diameter are made with a wood drill, and larger ones with an annular cutter. In most cases, this is enough for laying cables, protective sleeves and installing sockets for hidden wiring. If the hole has a complex shape, then it is easier to make it with a small hand hacksaw. Such a hacksaw has a sharp tip, which allows, without using drilling, to carefully prepare the starting hole, and then cut out the desired configuration along the contour.

Do not forget that the manufacture of any opening must begin with checking the place for the presence of frame elements or electrical wiring lines. The inexpensive device used for this – the heterogeneity detector – should become the “best friend” of the installer. It allows you to determine the type of inhomogeneity (wiring, metal, wood) behind drywall or other non-conductive sheet material, as well as its location and size.

Harvesting cable routes in the frame elements before installing drywall sheets is also not a very difficult operation. Channels in frames for laying embedded pipes of cable ducts or rigid sleeves inside partitions are made using special long (up to 1 m) large-diameter drills (up to 130 mm). To make holes of complex shape (for example, curved along the longitudinal axis), a cutter is required. The design of such drills and cutters takes into account the possibility of metal (nails, screws, etc.) getting on the working edges. Special, “cunning” drills allow you to expand the hole in the wooden frame without removing the wiring laid through it.

Much more difficult is the installation of cables in operated premises or where repairs are not completed, but the walls are fully assembled. The choice of a tool for making hidden wiring inside hollow walls depends on the direction of the route (horizontal or vertical), the location and material of the frame, the presence and type of sound / heat insulating filling of the cavities. When performing work, you have to direct the cable in the right direction, determine the location of the frame, drill holes in the frame inside the walls, etc. The complete set, the use of which guarantees cable laying in any situation, consists of a long small metal chain, a magnetic catcher on a flexible rod, fiberglass rods with a set of interchangeable tips (magnetic catcher, magnetic tip-indicator with a short chain, Z-shaped and V-shaped hooks), a set of flexible drills with a guide, a compass and a heterogeneity detector. Having such a set, the installer will easily master a number of tricks that allow him to “travel” inside the walls in any direction without damaging them.

Hooks are used for pushing (Z-shaped) or retracting (V-shaped) wires. If connectors are already installed on the wires, they are pre-protected with a tight cable stocking of a suitable size.

A metal chain, together with a magnetic catcher or a wire hook, is used to cut vertical channels inside hollow walls from the top hole to the bottom (best results are achieved with a chain with ball links). If the frame does not have horizontal elements and the wall cavities are not filled, then it is not difficult to lower the cable down from the ceiling to the level of the outlet. To do this, it is enough to drill an inlet at the top strictly above the installation hole for the socket, lower the metal chain from above and grab it with a magnetic catcher or hook through the bottom hole. Then the cable or ultrasonic device with a flexible rod is pulled in with the help of this chain.

If the upper and lower holes should be on different sides of the wall, but on the same vertical, then the operation is performed in two steps. First, the upper hole is drilled, and an ultrasonic device with a magnetic indicator and a chain is lowered into it to the desired height. Then, on the other hand, using a compass, the location of the magnetic indicator is determined, after which the lower hole is marked and made. It should be noted that the compass can also react to other metal elements inside the walls (fasteners, frame, etc.). It is easy to distinguish a magnetic indicator, since it has two poles, the location of which is known – the compass needle will change its readings as it moves along the indicator.

Hole markings made on one side of the drywall wall can be transferred using hardened steel wire with a diameter of about 1 mm. An even piece of wire of the desired length can be clamped into an electric drill chuck and drilled through the wall. The resulting hole is so small that the decorative coating will not be damaged.

It is possible to prepare a channel between holes located at a significant horizontal distance from each other using an ultrasonic device with a short chain as a tip. The ultrasound is introduced in the required direction through one of the holes and picked up by the magnetic catcher through the other.

If the wall cavities are filled, then a fiberglass rod with a short chain is the only tool with which you can prepare the channel. It combines the advantages of a rigid ultrasonic device (it can be directed in the right direction and pushed with considerable effort into a small space between or through a cavity-filling wall with sound / heat insulating material) and a metal chain that is easily picked up by a magnetic catcher. The position of the chain can be easily determined by using a tip with a magnetic indicator.

Since the resistance of the filler material will not allow high positioning accuracy of ultrasonic testing, it is better to prepare the channel from top to bottom along the frame element or from bottom to top along the plane of the wall panel. In the first case, positioning is provided by the frame element. In the second, the upper hole behind the false ceiling is made in the place where the position of the magnetic indicator will be detected using the compass.

It should be noted that similar techniques are used in the vertical passage of hollow (wooden) floors.

If the cable route must cross the ribs of the frame, the only way to get the job done is directional drilling with a flex drill. The drill is inserted into the starting hole (15-20 mm) and guided in the right direction using a special tool. Typically, holes are made from the location of the terminal block to another block, junction box or plinth. At the end of drilling, the cable or sleeve to be laid is fixed with a cable stocking to the hole in the drill tip that has appeared on the other side of the wall and is pulled in the opposite direction. This technology makes it possible to harvest channels in any direction. It should only be remembered that when drilling any frame, burrs remain, and the cable should be laid in a protective sleeve.

Some types of flexible drills can be used not only in wood and/or metal frame structures, but even in concrete and masonry walls. Since in the latter cases the amount of friction of the drill shank in the hole is quite large, it is protected with a special anti-abrasive stocking. The diameter of the channel prepared using flexible drills can reach 25 mm, and the length can be up to 2 m (up to 4 m if an extension is used).

Installation of hidden wiring between the electrical box-plinth and built-in sockets or switches, as well as connection of sockets installed above the plinth is not possible without making holes in the internal space of the partition through the lower supporting element of its frame. A special flexible drill with a mandrel allows you to perform this operation quickly, even without removing the baseboard. Then a bar with a short chain is inserted into the hole, which rises to the level of the socket, after which it is removed by a magnetic catcher.

Article published with permission from LAN Network Solutions Magazine, No. 07-08 2001

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