NEC3 Option B - Preliminary Item

Good Afternoon,

NEC3 Option B project. All air-tightness works are contractor design, i.e., membranes, tapes etc. (whatever is required to achieve rating) and project in question is a sizable building. The works are measured within the ‘Preliminaries’ element of the Bill of Quantities and during Tender we incorrectly thought the item in question was for carrying out the air tightness testing only and the price we inserted reflected this. On similar NEC3 Option B projects we have worked on all works associated with air tightness (membranes etc.) have been measurable items even when Contractor designed.
Has anyone any opinions on this as work is running into hundreds of thousands and all at our expense.