On average, listings lease in the $20's per square foot per year. The Portsmouth region is going through a a rise in rates. In the last 3 months, the median rate rose $2 per sqft per year. That's a 11% increase in rent.
In the last 90 days, 26 listings have come on the market, which means office spaces most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. About 73% of the office spaces in the Portsmouth are subleases, so you might be able to snag a great spot on a short term. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
Even though the median size is 7,810 sqft, there are still 0 listings below 2,000 sqft. Most properties in this region are around 2 stories. Most buildings in this area were built in 1984 and are Class B.