The most usual case of a multiple storey extension is a two storey house extension but occasionally more may be possible. In addition whilst the height of an extension would generally be equal or less that the original building there may be occasions, for example when the original house is lower than surrounding properties, that a greater height may be possible. As with internal alterations a greater number of storeys than the original building maybe possible even where to the same building height - provided of course there is sufficient latitude within the ceiling heights for this to be achieved. Loft conversions have been a popular house extension, and extension to bungalows and flats for a variety of reasons. Although primarily they make better use of what in most properties is an underutilised space storing the 15 year old television that 'may come in useful' and the teenager's former baby toys. Using the loft may be a relatively cost effective way of creating extra space as the basic structure is already partly in place, it can often avoid requiring planning consent, particularly if only roof lights are used but sometimes even with dormers, gables etc. The extra volume is only measured externally in relation to the permitted development requirements and is often relatively small.
