Renovation insurance

I am writing an article for Homebuilding and Renovation magazine about renovation insurance.

I need expert comment on the following :

Why does standard home insurance not cover renovations?
What does renovation insurance typically cover? (i.e. buildings cover, contract works cover, unoccupied property, public liability insurance, theft of tools/equipment)
Examples of life life scenarios where renovation insurance will kick in.
How much does renovation insurance cost for typical projects (i.e. extension, loft conversion, basement conversion)?
What impacts the cost of renovation insurance?
When should you take out renovation insurance? (i.e. before work begins)
Does renovation insurance cover you if your builder goes bust?