Obscure glazing is not generally considered a suitable method of mitigating unacceptable levels of privacy in habitable rooms due to the impact on outlook. An alternative method, described in an appeal against the refusal of planning permission for nine houses in north London (DCS Number 200-008-048) might be worth a look on a constrained site.
In this case it was proposed to construct two rows of terraced dwellings some 6m apart with “fritted” glass in the upper floor windows. The inspector explained that “Fritted glass is a proprietary approach which includes a pattern of small circles baked in ceramic on the inside of the glass pane across the whole of the pane. The circles would be 2 mm diameter set in a 2.5 mm grid. These would be black in colour on the inside and, in this case, white on the outside. The technology is designed so that light can pass through the gaps between the circles providing sufficient light within the rooms in question and allowing a view out as the eye filters out the dark and thus recessive circles. However, when viewed externally, the theory is that the eye rests on the reflection of the lighter colour reducing vision through the glass into the room behind, so as to prevent unacceptable levels of overlooking. When compared with “normal” methods of preventing overlooking, such as obscure glazing, the approach is designed to provide higher quality living conditions within the building as the occupants are able to see out.”
The inspector found that the performance of the fritted glass depended on the distance from the window, lighting levels, both internally and externally, and the angle of view: “The closer the viewer is to the window the easier it is to see through into the room behind. When viewed along the length of the windows at an oblique angle the dots apparently joined together to make an effectively continuous translucent covering. However, when viewed straight on it was possible to see through the gaps between the dots to some degree. The degree then depended on the light levels, with the greater the level of light internally the easier it was to see detail within the room.” Overall, he concluded that when viewed straight on more detail could be seen than was normally possible when using obscure glazing.
In the case before him the inspector found that the close face-to-face distance of the two opposite facades would result in unacceptable levels of overlooking. Nevertheless, it might be a solution elsewhere?
The issues of overlooking and privacy are discussed at section 4.136 of DCP Online.