If you told the man in the street that a boat floating on water can entail the change of use of land he’d probably think you had a screw loose, but see what you make of the following ruling.
The use of a barge in Essex as a clubhouse, bar, and restaurant has been required to cease after an inspector found that a material change of use had occurred (DCS Number 400-018-999).
The appellant maintained that as the barge was a floating structure, it was not subject to planning control, and an additional wooden structure built on top did not require planning permission. The inspector recorded, however, that the judgment in Thames Heliport Ltd v Tower Hamlets London Borough Council  is authority that the use of a vessel on water is capable of amounting to a material change of use of land.
The inspector explained that whether planning permission was required depended on whether or not the barge was a building as set out in section 55 of the Act, and a building is defined by section 336 as including any structure or erection and any part of a building, but not plant or machinery comprised within a building. R (oao Hall Hunter Partnership) v FSS & Waverley BC  is authority that there are three primary factors relevant to the question of whether there was a building; size, permanence and degree of attachment to the ground.
The inspector noted that considerable works had been undertaken to the barge to transform it. She considered that it now had the size, bulk and mass of a building, being two storeys high and much larger than any of the small boats within the marina and boatyard.
The barge had not been moved for at least 18 years and no longer had an engine. Having remained in the same place for a very considerable period of time, the inspector reasoned that the barge had not been used as a moveable vessel. It had been in office use in association with the marina for much of that time, a use which required it to be static and was consistent with a use as though a building. These were all factors indicating its presence as a permanent feature at the marina, she determined. The presence of mooring platforms added to the permanency of the barge in the location.
Of greater significance, the inspector held, was the attachment of utilities. Cables for the supply of water, electricity and telephone ran from the barge underground through the sea wall to the main distribution point, and the barge was connected to a wastewater treatment plant on the quayside.
As a matter of fact and degree and having regard to the size, degree of permanence and physical attachment, the inspector found that the barge should be regarded as a building. She considered the works which had been carried out with regard to the structure were akin to building operations and, as such, amounted to development for the purposes of section 55(1) of the 1990 Act. The works therefore required planning permission by virtue of section 57. She concluded that the matters alleged in the enforcement notice constituted a breach of planning control.
Somehow it all seems so much more plausible when an inspector says it.
For more information on the mooring of craft and floating structures see section 4.3113 of DCP Online.