Building A Home Internet Business

We spent about $45,000 this year to convert our attached garage to a purpose built space for our home based business. The improvements were fairly extensive including:

- new doors & windows
- flooring
- new walls and offices
- cabinetry and a 2nd kitchen

This space is used exclusively for our work, including the 2nd kitchen. We operate a 24 hour internet company and needed an isolated space away from the rest of the house to be able to work at all hours.

I know this is a general question ...

Will we be able to deduct the improvements as a single year write-off or are we instead going to have to depreciate/spread the cost of the improvements out over a number of years?

thanks