A cavity wall is a type of wall that has a hollow center. They can be described as consisting of two "skins" separated by a hollow space (cavity). The skins typically are

masonry Masonry is the building of structures from individual units, which are often laid in and bound together by mortar; the term ''masonry'' can also refer to the units themselves. The common materials of masonry construction are bricks, building ...

, such as brick or cinder block. Masonry is an absorbent material that can slowly draw rainwater or even humidity into the wall. One function of the cavity is to drain water through weep holes at the base of the wall system or above windows. The weep holes allow wind to create an air stream through the cavity that exports evaporated water from the cavity to the outside. Usually, weep holes are created by separating several vertical joints approximately two meters apart at the base of each story. Weep holes are also placed above windows to prevent

dry rot Dry rot is wood decay caused by one of several species of fungi that digest parts of the wood which give the wood strength and stiffness. It was previously used to describe any decay of cured wood in ships and buildings by a fungus which resul ...

of wooden window frames. A cavity wall with masonry as both inner and outer skins is more commonly referred to as a double

wythe A wythe is a continuous vertical section of masonry one unit in thickness. A wythe may be independent of, or interlocked with, the adjoining wythe(s). A single wythe of brick A brick is a type of block used to build walls, pavements an ...

masonry wall Masonry is the building of structures from individual units, which are often laid in and bound together by mortar; the term ''masonry'' can also refer to the units themselves. The common materials of masonry construction are bricks, building ...

History

Cavity wall construction was introduced in the United Kingdom during the 19th century and gained widespread use in the 1920s. In some early examples, stones were used to tie the two skins together, while in the 20th century metal ties came into use. Initially cavity widths were narrow and were primarily implemented to reduce the passage of moisture into the interior of the building. The introduction of insulation into the cavity became standard in the 1970s and compulsory in the 1990s.

Advantages

*Resist wind driven rain *Insulation provided by slow moving airfilms and airgap *Enables use of low cost nonrigid insulation batts

Tie types

A tie in a cavity wall is a used to secure the internal and external walls (or leaves)—constructed of

bricks A brick is a type of block used to build walls, pavements and other elements in masonry construction. Properly, the term ''brick'' denotes a block composed of dried clay, but is now also used informally to denote other chemically cured cons ...

or cement blocks. They can be made from: * Stone * Brick * Iron - prone to rusting & expanding * Stainless steel * Plastic * Elastic

Components

A cavity wall is composed of two masonry walls separated by an air space. The outer wall is made of brick and faces the outside of the building structure. The inner wall may be constructed of masonry units such as concrete block, structural clay, brick or reinforced concrete. These two walls are fastened together with metal ties or bonding blocks. The ties strengthen the cavity wall. The water barrier is a thin membrane that keeps moisture away from the cavity side of the interior

wall A wall is a structure and a surface that defines an area; carries a load; provides security, shelter, or soundproofing; or, is decorative. There are many kinds of walls, including: * Walls in buildings that form a fundamental part of the sup ...

The flashing component is important. Its main purpose is to direct water out of the cavity. Metal flashing usually extends from the interior wall through the outer wall and a weep hole with a downward curve allows the water to drain. Flashing systems in cavity walls are typically located close to the base of the wall, so that it will collect the water that goes down the wall. Weep holes are drainage holes left in the exterior wall of the cavity wall, to provide an exit way for water in the cavity. Expansion and control joints do not have to be aligned in cavity walls. In modern cavity wall construction, cavity insulation is typically added. This construction makes it possible to add a continuous insulation layer between the two

s and, vertically, through the slabs, which minimizes

thermal bridge A thermal bridge, also called a cold bridge, heat bridge, or thermal bypass, is an area or component of an object which has higher thermal conductivity than the surrounding materials, creating a path of least resistance for heat transfer.Gorse, Chr ...

Insulation

Cavity wall insulation is used to reduce heat loss through a cavity wall by filling the air space with material that inhibits heat transfer. This immobilises the air within the cavity (air is still the actual insulator), preventing

convection Convection is single or multiphase fluid flow that occurs spontaneously due to the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the conve ...

, and can substantially reduce space heating costs. During construction of new buildings, cavities are often filled with

glass fiber Glass fiber ( or glass fibre) is a material consisting of numerous extremely fine fibers of glass. Glassmakers throughout history have experimented with glass fibers, but mass manufacture of glass fiber was only made possible with the inventio ...

wool or

mineral wool Mineral wool is any fibrous material formed by spinning or drawing molten mineral or rock materials such as slag and ceramics. Applications of mineral wool include thermal insulation (as both structural insulation and pipe insulation), filt ...

panels placed between the two leaves (sides) of the wall, but many other

building insulation materials Building insulation materials are the building materials which form the thermal envelope of a building or otherwise reduce heat transfer. Insulation may be categorized by its composition (natural or synthetic materials), form (batts, blankets, loo ...

offer various advantages and many others are also widely used. For existing buildings that were not built with insulated cavities, a fibrous material, polystyrene beads, or sometimes

polyurethane Polyurethane (; often abbreviated PUR and PU) refers to a class of polymers composed of organic units joined by carbamate (urethane) links. In contrast to other common polymers such as polyethylene and polystyrene, polyurethane is produced from ...

foam can be installed in the cavity to reduce heat loss. The fibrous material often is

cellulose insulation Cellulose insulation is plant fiber used in wall and roof cavities to insulate, draught proof and reduce noise. Building insulation in general is low- thermal-conductivity material used to reduce building heat loss and gain and reduce noise tr ...

or glass wool blown into the cavity through suitably drilled holes until it fills the entire wall space. Although some foams used in the past, such as

urea-formaldehyde Urea-formaldehyde (UF), also known as urea-methanal, so named for its common synthesis pathway and overall structure, is a nontransparent thermosetting resin or polymer. It is produced from urea and formaldehyde. These resins are used in adhesiv ...

, are no longer used (some people are allergic to this material, which is very difficult to remove once inside the wall), others, such as polyurethane, have taken their place. Cavity wall insulation also helps to prevent convection and can keep a house warm by making sure that less heat is lost through walls; this can also thus be a more cost-efficient way of heating a house. About a third of the heat lost in an uninsulated home escapes through its walls.

United Kingdom

In the

United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the European mainland, continental mainland. It comprises England, Scotlan ...

, grants from the government and from energy companies are widely available to help with the cost of cavity wall insulation. The Affordable Warmth Objective (HHCRO) provides help for low income and vulnerable households to improve the energy efficiency of their properties and reduce heating bills. A large number of properties that had the insulation installed by successive UK government-backed schemes were installed incorrectly or were unsuitable for the property. Incorrectly installed cavity wall insulation (CWI) causes water to seep into a property's walls, causing structural problems and damp patches that may also manifest into mould. In some cases, the damp and mould resulting from CWI can cause health problems or exacerbate existing conditions, particularly respiratory conditions. This has led to the formation of the Cavity Wall Insulation Victims Alliance (CWIVA). On 3 February 2015 the CWIVA took the debate to the houses of parliament discussing the cavity wall insulation industry.

Issues

Breathing performance; early cavity wall buildings exchange moisture readily with the indoor and outdoor environment. Materials used for repairs must be selected with care to not affect the materials' breathing performance. Cavity wall insulation installed in older buildings can create problems with moisture retention.

Thermal mass In building design, thermal mass is a property of the mass of a building that enables it to store heat and provide inertia against temperature fluctuations. It is sometimes known as the thermal flywheel effect. The thermal mass of heavy structura ...

cavity walls are thick walls. These help stabilize the interior environment of a building better than thinner modern walls. Environmental Influences: The orientation or design of a building may affect the performance of different

façade A façade () (also written facade) is generally the front part or exterior of a building. It is a loan word from the French (), which means ' frontage' or ' face'. In architecture, the façade of a building is often the most important aspect ...

s on a building. Some walls may receive more rainwater and wind than others depending in their orientation or protection to some of the faces.

Moisture Moisture is the presence of a liquid, especially water, often in trace amounts. Small amounts of water may be found, for example, in the air (humidity), in foods, and in some commercial products. Moisture also refers to the amount of water vapo ...

is one of the main problems in materials weathering.

References

External links

* Whittemore, H. L. (1939). Structural properties of a concrete-block cavity-wall construction sponsored by the National Concrete Masonry Association. Washington, D.C.: U.S. Dept. of Commerce, National Bureau of Standards . * Whittemore, H. L. (1939). Structural properties of a reinforced-brick wall construction and a brick-tile cavity-wall construction sponsored by the Structural Clay Products Institute. Washington, D.C.: U.S. Dept. of Commerce, National Bureau of Standards .
Brick Cavity Walls: A Performance Analysis Based on Measurements and Simulations. Journal of Building Physics. October 2007 v31: p95-124
Article must be purchased.
Cavity wall
Energy Saving Trust
Cavity wall insulation (CWI): consumer guide to issues arising from installations
14 October 2019, Department for Business, Energy & Industrial Strategy
Cavity Wall Insulation Victims Alliance
{{DEFAULTSORT:Cavity Wall Masonry Construction Types of wall