What is meant by outside and inside surface area ratio of a window frame?
In Constructions database when a window is defined a Frame can also be specified. The frame dimension is defined in relation to the window unit as a frame factor % and the outside/inside surface area ratios so in this way user has the flexibility to define different types of frames that may be present in the building design
The frame percentage of a glazed construction specifies the fraction of the drawn window area taken up by the frame.
A frame percentage of 10% on a window of 1 m2 means, 0.9 m2 is transparent glazing with 0.1 m2 attributed to the frame.
A window frame, however, will tend to have a complex cross-section and project out from the plane of the glazing. This means the exposed surface area of the frame will tend to be greater than the frame area as initially prescribed by the frame percentage. A surface area ratio can therefore be provided to account for the increase in surface area arising from a complex frame geometry.
A surface area ratio of 1.2 applied to a window frame of area 0.1 m2 will result in an effective surface area of 0.12 m2.
The surface area ratio is defined as, the ratio of exposed surface area to the area of frame in the plane of the glazing. In most cases a frame will have a uniform cross-section along the length of an edge. If the frame is approximately rectangular in shape then we can calculate surface are ratios as shown below.
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Case
A The frame lies in the plane of the glazing and does not project out beyond the window itself. Surface area ratio is 1 / 1 = 1
B The frame has a width of 1 unit and projects out from the plane of the glazing by 1 unit. Surface area ratio is (1+1) / 1 = 2
C The frame has a width of 2 units and projects out from the plane of the glazing by 1 unit. Surface area ratio is (1+2) / 2 = 1.5
