British Airways is adapting two hangars at London Heathrow for the Airbus A380, which is due to join its fleet in 2013.
The UK carrier is installing an "eyebrow" enclosure above the airside doors of its West Pen hangar to accommodate the vertical stabiliser of the double-deck aircraft.
This will raise the clear height from almost 23m (75ft) by an additional 3.5m.
While the building can accommodate a Boeing 747 and A319 side-by-side, this will not be possible for the A380. The structure is fitted centrally above the door aperture to allow one A380 to be moved into the hangar.
The separate, virtually identical North Pen is to be modified with a similar construction, giving the airline two bays for its ordered fleet of 12 A380s.
Unlike its European competitors Air France and Lufthansa, which built new hangars for the aircraft at Paris Charles de Gaulle and Frankfurt airports, BA said it was unable to do the same due to the restricted space at Heathrow.
Furthermore, the carrier needed to keep the modifications to a minimum because the two hangars are protected for their architectural merits.
The buildings were constructed during the 1950s and feature internal, arched roof structures made from concrete to avoid any columns on the hangar floor. This made it impossible to elevate the entire roof, a BA spokesman said.
The modification involved the installation of 138t of additional steel structure, with the single largest component - the section that will enclose the tail fin - weighing 24t.
Lifting this "eyebrow" section into place had to be conducted overnight to avoid interference with aircraft landing on Heathrow's runway 27R/09L.
BA said that the hangar modifications are part of a wider property plan to ensure that the engineering base remains a "world class maintenance facility" for the latest aircraft.