Most listings are in the $20's per square foot per year. The Portsmouth submarket is seeing a a rise in rates. In the last 3 months, the median rate increased $5 per sqft per year. That's a 31% increase in rent.
In the last 90 days, 26 listings have been made available, which means new listings are probably going fast. You'll want to be prepared to make an offer immediately. There aren't many listings below 2,000 square feet available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,310 sqft. Most buildings in this market are around 2 floors. Most buildings in this market were built in 1978 and are Class C.