Portsmouth is one of the most densely populated cities in England, with a population of about 188, 000 mainly concentrated on Portsea Island itself. The predominant type of home (54%) is terraced housing, much of which was built during the nineteenth century with the rapid expansion of the dockyard. As a result of this expansion and the restricted amount of land available for building, the housing stock is comparatively old with some 44% being constructed prior to 1919. About 15% of housing is detached or semi-detached, with the remainder being flats and maisonettes.

There are around 77,000 households in Portsmouth, with 68% being owner occupied, 16% owned by the City Council, 5% owned by Housing Association and 11% rented privately.

The large proportion of terraced housing and flats, coupled with the close proximity of the sea, has resulted in comparatively energy efficient housing. However, the age of the stock and low average income, compared to the national average, has lead to a high incidence of disrepair in the private sector. The age and construction of the homes also precludes some highly cost effective improvements to energy efficiency.