Loggerhead
The building being knocked down is Percival House which for many years has been the building the airport has used for admin. etc.
The whole of that area is being re-developed to house a massive new hangar for Signature Flight Support. Rumour has it that it can house up to 6 BBJ's at a time. The existing Signature hangar in that area (the North West corner) will also be demolished.
If you refer to my learned friend Buster the Bear's recent post, you will see how this is in line with the airport's intention to develop biz operations even more.