Building Construction Encyclopedia

⧪ ANCHOR FASTENERS

A small screw-like device that allows you to attach things to a concrete beam, column, slab, or wall. Special anchor fasteners are available for materials like brick and stone. The fastener anchors itself to the base material by pressing on the surrounding material with lots of force, creating enough friction that it cannot be pulled out. You may then attach whatever you like - such as brackets, supports, cable trays, false ceilings - to the anchor, which is normally made of mild or stainless steel. An engineer will select an anchor based on the force that will fall on it. See our page on anchor fasteners.

⧪ BIMETALLIC CORROSION

When you place two different metals in contact, corrosion or rusting can occur. This is because each metal has different electrochemical properties. For example, if you attach a stainless steel bolt to a mild steel member, rusting will occur over time. The solution is to put a neutral material like rubber or plastic in between to avoid or minimize contact between the two metals.

A famous example of this occurred in the statue of liberty, which consists of a copper skin attached to a wrought iron frame. Gustave Eiffel had anticipated this problem, and had put in a thin layer of shellac (a natural resin) between the two metals: however, this had largely worn out by the 1980s, which is when the problem occurred.

⧪ BACKFILL

The previously excavated soil that is put back around building foundations or basements after they are constructed. Soil that is being put back or backfilled must be put back in layers and compressed so that it can properly support the weight of a floor or road above.

⧪ CANTILEVER

A cantilever is an engineering term for a horizontal projection out of a building that is not supported at its outer edge. A balcony that has no supporting columns on its outer edge is an example. A projection that is supported by brackets or cables above or below the projection is also considered a cantilever. The key thing is that there is no support at the outer edge. In terms of structural behavior, a cantilever beam is different from a normal beam, as the cantilevered beam will have tension at the top, and compression at the bottom, which is the reverse of a normal beam supported at both ends.

⧪ CASEMENT WINDOWS

Windows that are hinged on one side are called casement windows. They usually open outside. A casement window can also open vertically, in which case it can also be called a ventilator.

⧪ COLD FORMED SECTIONS

Cold-formed sections are mild steel structural members that are made by passing a thin sheet of steel, usually between 1 and 3mm thick, through a series of rollers until it achieves the desired shape. It is called cold forming because the steel is at room temperature, unlike hot rolled sections (see below). This method produces light steel members like z-sections and c-sections for use in structural framing for steel structures, partition walls, roof purlins, false ceilings, and many other applications. The steel is almost always galvanized to protect it from corrosion. These kind of members are the primary load-carrying elements in light gauge steel construction.

⧪ COMPRESSIVE STRENGTH

Compressive strength is the ability of a material to withstand a force pressing down on it. For example, if you put a 150mm (6") cube of concrete on a hard surface, and put a downward force on it with a hydraulic press, then the compressive strength of the object is the maximum force it will withstand without breaking.

⧪ CONCRETE ADMIXTURES

A concrete admixture is a chemical that you add to concrete while it is being mixed in order to change the properties of the concrete. Some of the most common admixtures are retarders, chemicals that slow the process of setting of concrete so that it can be mixed in a concrete plant and then shipped to the site several hours away in a concrete mixer that rotates the concrete to keep it from setting. Other common admixtures are ones that make concrete more waterproof or make it flow better, or more workable.

⧪ CRAWL SPACE

A crawl space is a space between the ground floor (first floor in the US) slab and the excavated earth below it. It is usually a few feet high. This is common in US residential construction. This space allows a person to crawl inside and access any part of the house, which is very useful when it comes to repairing or replacing pipes and wires of any kind. The periphery is formed by concrete or brick walls, on which the walls of the house rest.

⧪ CURING

Curing of concrete is a procedure done to the concrete while it is setting, or changing from liquid to solid. Curing is done to ensure there is enough water for the chemical process of setting, and to keep the temperature of the concrete within acceptable limits. If curing is not done properly, the concrete may not gain full strength, or cracks could develop. Curing is usually done by placing a layer of thick cloth on the exposed surfaces of the concrete, and ensuring that this is kept wet for the duration of the setting process. It can also be done by spraying water through misting nozzles. Most building standards recommend that curing is done till concrete reaches 70% of its target strength, which can happen in 7 - 12 days for normal concrete mixes. In very dry and windy conditions, the curing period should be extended.

⧪ CURTAIN WALL

A very light, non-structural wall of glass or metal sheeting that is "hung" or bolted to the main structural frame of the building, hence the name. It usually has a frame of horizontal and vertical aluminum or steel members (see mullions and transoms below) on which the glazing or metal sheeting is fixed.

⧪ DAMP PROOF COURSE

A damp proof course is a waterproof layer in brick masonry construction. This layer is installed just above ground level, so that water from the soil does not penetrate into the building. Since brick masonry is porous, it may absorb water from the soil. A DPC prevents this water from rising into the building. The DPC itself is a thin layer of waterproof plaster that is installed between two successive layers (called courses) of brick. It must be capable of withstanding the loads that are acting on the masonry wall.

⧪ DIAPHRAGM WALL

A diaphragm wall is a wall that is constructed under or within the earth. It is constructed by removing just the earth that the wall will occupy, filling the hole with a bentonite slurry to hold the excavated earth surfaces and prevent them from collapsing, and then fill the hole with concrete. Concrete is poured into the hole via a long pipe that goes all the way to the bottom of the bentonite slurry-filled hole, called a tremie pipe. 

The concrete is heavier than the bentonite slurry, so it stays at the bottom without mixing with it and pushes out the extra slurry at the top of the hole, which is then drained away. All the construction workers stay at the surface of the earth, making the work safe - only equipment is lowered into the hole. A diaphragm wall is most often used to create the peripheral walls of large multi-level basements. It is very well suited to this task, as the peripheral walls can first be created, and the earth excavated next so that there is no danger of soil collapsing at the edges of the basement.

⧪ DGU (DOUBLE GLAZED UNIT)

This is a sealed unit consisting of two panes of glass, a metal spacer that runs between the two panes on the periphery, and an inert gas or nitrogen-filled cavity between the two panes of glass. It is important that the cavity is filled with a gas that is completely moisture-free, as this can condense into droplets and obscure the view. The gap serves to provide both heat and sound insulation.

⧪ EAVES

The eave is a term used in roofing. The lowest part of the roof, which projects beyond the walls of the building, is called the eaves. This is in opposition to the ridge of the roof, which is the highest point, usually located near the center of the roof or building. Gutters therefore normally run along the eaves of the roof.

⧪ FALSE FLOOR

A false floor is a light, raised floor that is installed on the main floor with a cavity in between that is used to run cabling and wiring. It is used in corporate offices, where it gives the option of flexibility - since the underfloor cabling is accessible, it can be quickly changed, to suit a new office layout for example. It is also used in computer server rooms because many server designs require the cabling and air-conditioning ducts to enter the server cabinet from the bottom rather than the sides or rear.

⧪ FIRE RATING

The fire rating of an element is a very important aspect of fire safety. The fire rating is the length of time, measured in hours or minutes, that an element can withstand a building design fire without collapsing, either partially or wholly, and without transmitting too much heat from the fireside to the non-fire side. 

For example, if the fire rating of a door is 2 hours, then it is expected that the door system can withstand a design fire for 2 hours, and a person standing on the other side of the door will not be harmed. Building codes in every part of the world are quite explicit on fire ratings; it is these ratings that allow sufficient time for evacuation of the building. The idea is that if materials have high fire ratings, the fire can be contained in a small area rather than spread rapidly. Fire ratings can be given to a number of elements, such as walls, doors, partitions, windows, facades, and suchlike. 

Manufacturers have to conduct tests in independent laboratories to certify the fire rating of their products. Tests have to be conducted on the entire system of the product, for example, a door system includes the door shutter, the frame, the hinges, the door closer, and the fasteners that attach the door to the wall, as the failure of any one of these could cause the entire system to fail.

⧪ FLASHING

No, this is not showing off your naughty bits to an unsuspecting audience! Flashing is a term used in roofing with metal sheets. Flashing is a long folded strip of metal that is usually placed over any joints between sheets, or between sheets and gutters, to waterproof the joint and ensure that water does not leak through. It is also used at the ridge of the roof, and wherever the roof plane turns corners. It is made of the same material as the roofing sheets, except that it is not corrugated like the sheeting.

⧪ GALVANIZING

Galvanizing is the process of covering a mild steel member with a protective coating of zinc. The zinc protects the steel from rusting, both by acting as a physical barrier to moisture, as well as sacrificial corrosion. The sacrificial property of zinc is that in the presence of water, it will rust before the steel does, thereby protecting the steel. There are two ways to coat a member with zinc: in hot dip galvanizing, the member is dipped into a bath of molten zinc. In electrochemical coating, the member is dipped into a bath with a zinc solution, and connected to an electrical system that causes deposition of the zinc on the member. The first method is more effective for building construction. 

⧪ GEOTEXTILE

Geotextile is a type of cloth that is designed to work with soil. It can be used in several ways. First, it can be used to wrap perforated pipes or drains, so that soil does not enter them, but water does, creating effective drainage channels that do not get choked with soil. Secondly, it can be used to improve the properties of the soil if laid in multiple layers (like lasagna) alternating with soil. And third, it can be used to stabilize slopes made of soil.

⧪ HOT ROLLED SECTION

A hot rolled section is a steel structural member such as an I-section, C-section, or angle that is made by channeling molten hot steel through a series of rollers until it achieves the desired shape. Most factory-made steel sections are made with this method. A different method of making light steel sections is cold forming.

⧪ IP RATING

Ingress protection rating. This is an industry standard to classify how well fittings and fixtures resist environmental conditions such as rain and dust. For example, light fittings to be installed outside a building will need a minimum rating of IP65. The rating consists of two numbers. The first number denotes how dust resistant the item is, and the second denotes water resistance.

⧪ INSERT PLATE

An insert plate is a mild steel or stainless steel plate that is placed in a concrete member before casting, so that when the concrete sets, the plate is firmly connected to the concrete. This plate can be then used to attach features like metal railings to the concrete structure by welding. An insert plate will usually have a curved metal rod - called a holdfast - attached to its inner face to securely anchor it to the concrete.

⧪ LAMP

A light source such as a bulb, as distinct from the light fitting, which is called a luminaire. With the advent of LED lighting, the distinction between the lamp and the luminaire has become blurred; in most cases, they are one unit. In the pre-LED age, they were completely separate entities.

⧪ LINTEL

A horizontal beam above a window, door or another opening. It serves a double purpose: first, it supports and holds in place the wall above the window, and second, it serves as a support member on which to fix the window or door frame.

⧪ LITES

A single piece of glass that is cut to the right size is called a lite of glass. Lites are put into windows and doors.

⧪ LOAD BEARING WALL

A wall that carries structural loads in a building. If a wall is a load bearing wall, it is difficult to make changes such as adding openings during renovations. See our page on load-bearing masonry construction.

⧪ LUMENS

Lumens are a measure of the total light energy emitted by a light fixture or source. For example, a 4ft LED tube light fitting will emit about 4,000 lumens.

⧪ LUMINAIRE

A light fitting, as distinct from the light source itself (such as a bulb), which is called a lamp. The luminaire will usually have a few parts: a housing, a reflector, and perhaps a power source.

⧪ LUMINOUS EFFICACY

A very important measure of how efficient a light fixture is at converting electricity into light energy. A more efficient fixture will result in lower power consumption for the same level of light. It is measured in lumens per watt. Good quality LED fixtures will have a luminous efficacy of greater than 100 lm / W.

⧪ LUX

Lux is the unit in which the intensity of illumination on a surface is measured. Lux is nothing but lumens per square meter. Building guidelines specify lux levels for various activities. The lux level is measured at a specific surface, called a workplace. In offices, the workplace will be the office table, while on roads, it will be the road surface.

⧪ MUNTINS

A part of a traditional wooden window. Traditional windows were divided into very small panes of glass, as large lines of glass were difficult to obtain. The wooden member that was placed between these panes and held them in place was called a muntin.

⧪ PERGOLA

A pergola is a shelter formed by a number of wooden beams placed side by side, with gaps in between. It serves to block the sun, creating shade, and acts as a convenient support for creepers. It is most commonly made of wood. It can be attached to the side of a building or terrace or built as an independent structure on columns in the middle of a garden.

⧪ PERMISSIBLE FORCE, ULTIMATE FORCE AND FACTOR OF SAFETY

The ultimate force is the force at which a member will fail. In practice, engineers will usually keep a factor of safety to ensure that the actual forces on a member do not reach anywhere near the ultimate force. So if an engineer specifies a factor of safety of 2 for a member that can take an ultimate force of 200 kg, the permissible force will be 200 / 2 = 100 kg. 

So the permissible force is the maximum force that an engineer will permit (or allow) in a member without worrying that the member will fail. In mathematical terms, the permissible force equals the ultimate force divided by the factor of safety. It is common for structural engineers to specify a factor of safety in the range of 1.5 to 2. Critical components may have higher factors.

⧪ POLAR CURVES

Polar curves are a kind of diagram made by manufacturers of light fittings. They describe the quantity of light emitted by the fixture at each angle from the vertical. They are drawn in section.

⧪ RIDGE

The line running along the highest point of a roof is called the ridge. The lowest point is the eaves of the roof.

⧪ RADIANT BARRIER

A radiant barrier is a thin layer of material, such as polished aluminum film, that prevents the passing of heat through radiation (as opposed to conduction or convection). These materials have a very low emissivity, meaning that they do not allow radiation to pass through. Such a layer can significantly reduce the heat gain (the entry of heat) into a building in hot, sunny climates if it is built in as part of the roof or external walls.

⧪ RETAINING WALL

A wall that is built to hold back a portion of soil to prevent it from falling down a slope is called a retaining wall. Retaining walls are commonly built of stone or concrete. Also, see weep holes below.

⧪ SASH

A window sash is the part of the window that moves, as opposed to the part that is fixed, which is called a frame. The rash usually consists of a frame filled with glass. The entire frame moves as one piece. In a sliding window, the sash slides, in a casement window, it moves on hinges.

⧪ SELF CONSOLIDATING CONCRETE

Self-consolidating concrete is also called self-compacting concrete.

⧪ SETTLEMENT AND DIFFERENTIAL SETTLEMENT

Settlement occurs when the earth below the foundations moves in some way, either because of the load of the building or for some other reason, such as changes in the soil itself. Settlement can cause damage to a building, especially if different parts of the foundations settle (or move) by different amounts. Such settlement is called differential settlement and it can cause cracking, breaking, or serious structural damage. Uniform settlement - where the entire building moves as one unit - is not very dangerous, as the structure is able to maintain its integrity.

⧪ SILL OR WINDOW SILL

A window sill is a horizontal surface or member at the bottom of a window or opening. Often made of stone, it serves as a base on which to fix the window. It must be constructed to prevent leakage of water into the building.

⧪ SHEAR WALL

A shear wall is a vertical concrete member that is used in a building mainly to transfer horizontal loads like wind or earthquake loads safely to the ground. It is essentially a column, but because it is larger - a shear wall could easily be 400mm thick x 3m long - it is called a wall. It is good at taking care of forces that are parallel to its length, so a building will usually require shear walls in both directions. Structurally speaking, a member like a box wall - such as that found around lift shafts - which can safely handle loads in both major axes, is better than a shear wall, which works in one direction only.

⧪ STUD

No, it isn't a good-looking male who has seduced many young maidens...

⧪ TERRAZZO

A traditional kind of floor finish that is made by laying a wet mixture of concrete (made with white cement), marble dust, and marble chips, allowing it to dry and cure, and then polishing it substantially into a flat, level surface so that the chips are seen as flecks of various sizes. The color can be controlled by adding pigments to the concrete and selecting the shade of marble chips. It originated in Venice as a means of converting waste bits of marble into an attractive and economical floor finish. Modern forms of terrazzo use epoxy or chemical binders instead of cement binders, and sometimes substitute quartz, granite or glass chips for marble.

⧪ TRANSOM

A transom is a horizontal cross-member in between two shutters or parts of a window or door. If a door has a glass ventilator above, the horizontal member in between is a called a transom. Its vertical equivalent is the mullion (see above).

⧪ UV STABLE

Sunlight contains ultraviolet light (UV light). This light has some harmful effects, such as sunburn in humans. It also can have some effects on many construction materials, such as paints and plastics. Its effect on paint is to weaken the color of paint, and in plastics, prolonged exposure results in brittleness, which can lead to cracking and loss of flexibility. Building materials that are exposed must be able to withstand this UV light. Those that can are called UV stable, meaning that they do not degrade in prolonged exposure to sunlight.

⧪ VAPOR BARRIER

A vapor barrier is a thin sheet of material that is wrapped around a building as one layer in the skin of the building. Its purpose is to make the building air-tight and prevent air from passing through the skin of the building in either direction. The problem that occurs in buildings that are not air-tight is that air contains moisture. When it passes from a hot to a cold zone, for example from a heated room to the cold external surface of the building, the moisture condenses, making the skin of the building wet. This wetness is bad for the building, and can severely affect the performance and lifespan of many building materials, including many forms of insulation. The vapor barrier prevents this passage of moisture-laden air and eliminates the dampness or condensation of water within the skin of the building.

⧪ VIADUCT

A viaduct is a bridge that carries things from one side to the other, as opposed to carrying purely human traffic. Viaducts can carry rail carriages, materials, or even electricity or supply lines. An aqueduct is a special kind of viaduct often built in Roman times to carry water. It is simply a C-shaped channel, open at the top, usually built over masonry arches to carry water from sources to towns.

⧪ WATERPROOFING MEMBRANE

A thin, continuous plane of water-tight material that is laid over a slab to waterproof it. 

⧪ WEEP HOLE

A plastic or metal pipe laid through a wall that has soil on one side, and air on the other is called a weep hole. It is commonly used in retaining walls (see above). It is put there to allow water to pass through the wall and come out the other side, thereby draining the soil. Wet soil is much heavier than dry soil so the loads on the retaining walls will increase when it is wet.