Cat flap for double glazed glass

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Cat flap for double glazed glass

A common problem in building construction today is water leaking through windows, doors or wall cavities and, more recently, the trend towards double glazing and increasing reliance on thermal protection. These problems are compounded by the fact that the usual window and door frames used in housing are rarely waterproofed. When an outside wall, for example, is subjected to rn water, the leak usually only occurs as a direct result of the frame flure.

While the solutions to the problem may be complicated and expensive, there is a simpler way. The common solution of using a sash track and a single sash window is in many cases inadequate. A track sash with a single window or door is not watertight. It is not really possible to design a structure, such as a wall, that has the strength necessary for long term use and yet be waterproof.

Window sashes typically consist of two glass panes spaced apart by a rubber gasket. With a pr of sliding sashes, this allows the glass to be slid away to admit or reject r and light. To do this, the gaskets are sandwiched between the glass and sash frame and held in place by the sash track. The sash track, in turn, is sandwiched between the frame and the jamb. The problem arises when the window is closed and the r and light have to be excluded from within the room. It is impossible to get a tight, watertight seal by gluing and clamping the gasket into the sash track because, if the seal is not perfect, water will seep through into the room. This happens not only because the gasket can fl to seal properly, but also because the sash track and sash frame can separate and allow the seal to be broken.

The problem, therefore, is to develop a watertight seal. It must be watertight even if it is in the vertical plane, that is in the direction of the r flow. It also has to be watertight in the horizontal plane, that is perpendicular to the r flow.

It is the nature of a seal to be watertight. If the seal fls, the glass panes will have to be replaced and the room will have to be dried out agn. This problem of water or r infiltration is not unique to windows. Other structures must have watertight seals such as roofs, walls, doors, and windows. Thus, all structures, and in particular buildings, must have a waterproof design.

Most people cannot envision a design that is not watertight. It is only after such designs are put to practical use that the flures become apparent. A building inspector for the British Government found that 40 percent of the rnwater which entered the walls of the public buildings it inspected flowed through the building without being collected. The windows were never designed to have a watertight seal.

Most buildings are not built using strict guidelines. No one wants to become the architect of a fled structure. Instead, the builder of a building makes decisions about the construction, often without a strict specification, and then passes these decisions on to the designer. The designer then becomes the architect of the building. The designer tries to incorporate as much from a manufacturer's specification as is practical.

It is difficult to say how much of a rnwater infiltration problem can be attributed to the design. Certnly the most common design and construction practice is to use the weakest point to control the ingress of water. That is the case in windows.

FIGURE 2.16 Sash track

The window is an enclosure with windows and with a weatherhood over the top. r enters from the left and exits from the right. The r flows vertically with a constant flow rate. Water is prevented from entering by the sash track and its surrounding structure. Because of the continuous flow of r through the enclosure, there is no water-filtration-type effect. In this case, the sash track is the weak point and the design should place the sash track in the least possible position to control the flow of water into the building. This can be achieved by placing the sash track in the center of the glass area. The best practice is to position the sash track above the glass and to have it run as far up the glass as possible.

It is also possible to have a series of small windows with a sash track, thus separating the glass into small areas. This approach is often used for shop windows and in large buildings with large windows. It is common practice to have the sash track run only part of the length of the window opening. It is also common practice to have r gaps between sash segments to permit r to flow into and out of the window (Figure 2.16). The r gap and sash track run length are both variables that affect the flow of water.

Water-filtering devices are avlable that can be installed inside the sash track. Such devices allow for the filtering of water and for the removal of insects and debris. The device also allows for a water-filtration effect. r can flow through the sash track with the water-filtering device (Figure 2.17). A water-filtering system is only effective if the sash track runs the entire length of the window opening. In addition, only low r flow rates can be effectively filtered.

**Figure 2.16** An r gap for a sash window.

**Figure 2.17** In place of the sash track and the sash and stop, the window can have a water-filtering device that allows water to pass into the window, but blocks insects and debris.

### Wind Control and Insulation

Building owners may be concerned about the effects of building design, structure, and window design on the performance of the building with respect to the building envelope. The building envelope, including the window and walls, must be able to perform its structural functions of resisting the loads that are applied to it and limiting the transfer of heat and cold between the interior and exterior of the building. In addition to the envelope, the interior building components must have insulation characteristics to slow the transfer of heat and cold from the interior to the exterior of the building.

Wind control devices must be used to ensure that windows can be opened or closed for ventilation or shading. This involves the selection of certn devices that can provide for appropriate ventilation and shading of the window. The appropriate type of device to be selected will be determined by a need analysis and by the types of windows that are considered.

In addition to the wind control device, interior window insulation may be desirable. Insulation can reduce heat loss or gn, depending on the location of the insulation and the amount of heat gn or loss that is experienced by the building. In some cases, insulation may be required on a window by window basis to control heat gn or loss. Insulation is avlable in many different types of products and shapes, but will have no impact on the ability of a window to open.

### Visible Light Transmission and Daylight Control

For commercial or institutional buildings, especially those in regions with long, cold winters, the addition of skylights is often a necessity. Skylights help reduce the heat load on a building by providing a large surface of direct, bright sunlight and also permit natural ventilation, thereby allowing for a reduction of r conditioning needs. As a result, building owners will benefit from skylights by lowering electricity costs and providing an added benefit of increased visibility. For some commercial buildings, the skylights can help to reduce noise, which is particularly important for retl or office buildings. Skylights may also be desirable because of their ability to bring natural light into a basement or other lower level of a building.

Skylights are usually constructed as skyl

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