A cornice sits on the facade of a building above the roofline or crown moulding, which on with flat roofs is at the base of the outer wall.
Generally, the cornice differs from the rest of the building by being made with a more decorative material such as wood or plaster, and/or having a different design. The projecting structure which forms the top part of a wall, whether simply supported or roof-like, can also be termed a cornice. Cornices are not just found on buildings, however. They are used as decorative features on many different types of structures such as bridges and jetties, perhaps most famously on the Parthenon in Greece. Cornices often serve a structural purpose. They may provide a space at their foot for a masonry wall to run or a beam to project which increases stability from an architectural perspective.
A ceiling cornice is a decorative moulding that crowns the top of a room, usually in a rectangular pattern. Ceiling cornices are most often found above window and door openings in a building's exterior wall where they conceal the lower portion of the wall construction from below, which generally would be unsuitable for view.
In interior design, ceiling cornices may be constructed from any number of materials including plaster or wood. Plaster cornices are often used when weight or deflection needs to be kept at a minimum such as over fireplaces or light switches which have to support up to their own weight plus that of people passing through the room. For ceilings with heavy accumulations of dust and dirt, they can sometimes be made from metal coated in a thin layer of rubber, such as that used for making tool handles non-slip.
Ceiling cornices may run continuously around all four sides of the room or just on two opposite sides. Often they only extend across half the width of the room and are referred to as 'quarter', 'three quarter' or 'short' cornices. they are commonly painted to match the skirting boards.Cornices are used to make rooms appear taller or larger, to conceal unpleasant construction details such as the plumbing and air-conditioning ducts, and mask the junction between walls of different heights. They can act as loggias (in other words - covered outdoor patios) for exterior relationships. Cornices can also decorate a structure including giving it an aesthetically pleasing appearance to help in the design process. Cornices are often decorated with elaborate mouldings which may include capping, corbels, brackets, modillions and other decorative elements that extend beyond what is needed structurally. These could be purely ornamental or serve a functional purpose e.g.: by supporting overhanging eaves. Decorative features on cornices may be made from moulded plaster, wood, metal, or other decorative elements.
Modern cornices are often made from wood, extruded polystyrene, or any number of non-traditional materials such as moulding plastics.
A box cornice board is the horizontal trim located at the top of a wall and designed to cover joints between wall panels and to provide protection against water infiltration and throwing rainwater free. Its purpose is also to add architectural detail, in which case it may be called an ornamental cornice or decorative cornice. The "board" part refers to its resemblance in size and shape to a traditional timber board (the type used for boarding up windows when there's a hurricane coming). A system constructed with plywood sheets nailed together over dimensional lumber provides adequate strength, while sheeting made from extruded polystyrene has a low profile and is often used for metal buildings. Other modern materials include vinyl, aluminium, fibre cement board, skirting boards, and various composites of these In some styles of architecture such as Victorian or Art Deco, the projecting cornice may consist of an overhanging boxed structure with moulded decoration or decorative moulding at the outer edge. In traditional domestic architecture, this was frequently constructed from timber. Modern cornices often consist of a lightweight framework with a finished surface on top that gives a smooth appearance to what would otherwise be exposed plywood edges around window openings or other voids in the construction. The material covering the framework is called finish material or "scrim" which is most often vinyl but may be any number of materials, for example.
A cornice return is the return of an architectural element at the end of its horizontal run. Cornices are often functional, especially when they are serving as part of a roof structure such as an architrave cornice. Imagine if the exterior wall of your house was simply butted up to the rafters with no trim or crown moulding to cover it or make it look more finished. It would indeed be "functional", but it wouldn't look very good nor would you get much enjoyment out of living in that building.
For this reason, almost all buildings have some sort of ornamental treatment on their exterior walls with exterior cornices - even something basic like window and door casings can help break up what would otherwise be a plain, hard wall.
The most common ornamental treatment is the use of crown moulding. The function of such a decorative element is to cover rafter tails, which would otherwise be exposed and stick out like a sore thumb on the building. This becomes all the more important when we're dealing with roof lines that aren't flat but rather gables or mansards for example. A cornice return then serves as a way to hide all those structural elements that need to remain hidden from view. It creates design interest and adds an air of sophistication to your home. They are easy to paint.In addition, if you have high ceilings, you can also add a crown moulding or a cornice to cover the gap where the ceiling meets the wall. Doing so will make your room feel taller and more elegant. Of course this isn't possible with every room in your house but if you have a high/cathedral ceiling, it's certainly something to consider.
Modern cornices are often made from wood, extruded polystyrene, or any number of non-traditional materials such as moulding plastics. In the case of more ornate cornices that are made from wood, they can be constructed from a number of different materials, namely hardwood or softwood. Besides those, some people eschew the use of traditional mouldings and go with steel, aluminium or even copper instead. What's great about modern cornices is their simplicity. You don't have to worry about having a carpenter come in and do moulding work for your home. You can buy "off-the-shelf" or "prefabricated" cornice systems that mount onto your wall quite easily with nothing but a few basic hand tools. In terms of how many pieces there are to such a system, it depends on the manufacturer but typically there are no more than 4 or 5 pieces to deal with. It's definitely something you can do yourself. If you're not the type of person who feels comfortable taking on a project like this, don't worry, most manufacturers will gladly provide installation services for their products. Whether you go with an ornate traditional cornice or a modern cornice, one thing that they all have in common is that they are installed on top of your interior wall surface between the interior wall and ceiling. For traditional types of cornices, this means adding crown moulding onto your interior walls at locations where your siding meets the rafters/trusses of your roof structure. Cornices are typically added at window openings for window treatments as well but it really depends on what you see in the style of your home. Other cornice types include, interior cornices, bracketed cornice, cavetto cornice, external cornices, simple cornice, open cornice and close cornice.
While the function of a cornice is almost always to add interest and sophistication, it's by no means an absolute requirement. In most cases you will see a cornice on homes that have stucco or vinyl siding. This might be because most houses with these types of exterior covering usually feature a gable/mansard style roof which means there are tails where the rafters meet the exterior walls and interior walls. For that reason alone, many people choose to add some sort of ornamental detail here. However not all homes with gable or mansard roofs have cornices. Sometimes they're simply built in to the wall structure itself using trim boards. If your home features a flat roof without any slope to redirect water away from the building (such as a shed roof) then there's no real reason to have a cornice. If your home has vinyl or stucco siding, that means it also likely has corner boards. Cornices are typically constructed in the same way as these other types of exterior trim - they're not simply flat slabs of material but rather have some kind of shape or curve to them. As such, these can be made from materials other than wood which is where extruded polystyrene and moulding plastics come in very handy.
Traditionally speaking, homes that feature stucco or vinyl exteriors usually have cornices. However, that doesn't mean that it's impossible to build a home without one - especially if your house features brick walls instead of these materials. For this reason, many modern homes either with brick or masonry surfaces don't include them at all. There are some cases where you may see them on newer homes but they tend to focus on the decorative aspect such as roman architecture, building or furniture element, ancient greek design elements that are necessarily decorative rather than primarily functional commercial buildings in nature since there is no tail section above the exterior walls to support one. This could be for classical architecture or an architectural feature. Surprisingly enough, even some wood-framed houses don't have traditional cornice or interior cornice moulding of any kind whether it's more modern looking or very ornate.