When answering this question, the starting point has to be that, if you are comparing the cost of this cover to the cost of standard buildings insurance, you are comparing apples to oranges. Our package is not buildings insurance, it is contract works insurance. We cover not only the structure, but the capital investment in the refurbishment works too (the contract works).
In addition to the fact that we offer an additional head of cover, the simple fact is that a construction site is a much riskier proposition to insure than an occupied dwelling or commercial structure. The potential for loss (particularly under the heads of accidental damage, theft, escape of water and fire) is much, much higher.
Also, in many cases, the insurer is also giving up their right to subrogate against the contractor in the event that they damage the structure and/or works. All of these factors generate upwards pressure on the rating.
It is possible to insure a building project more cheaply, but any premium savings will invariably come at the expense of cover, control and peace of mind.