On average, listings lease in the $30'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 went up $3 per sqft per year. That's a 10% rise in rent.
Compared to the rest of the Greater Boston market, the Portsmouth submarket has more expensive rates, and you'll need to pay a premium to be in this hot region.
In the last 90 days, 18 listings have been made available, which means new availabilities most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. About 11% 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 available, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 1,480 sqft. Most buildings in this market are approximately 2 floors. Most buildings in this market were built in 1920 and are Class A.