If this small building had a chimney or large cupola to let out steam, it probably was used to house an evaporator for boiling maple sugar. Sometimes, this was an open lean-to. If it was a more buttoned up building, with windows and no chimney, it could have been used as for some other purpose, usually in New England a shoe shop or "Ten Footer" was on the property and used as a way of producing cash in the winter or off hours from farming. To see a post about shoe shops see my post from 9 April 2010 http://nutfieldgenealogy.blogspot.com/2010/04/making-shoes-in-derry-new-hampshire.html
Here are photos of Hank Peterson's sugar house in Londonderry, New Hampshire located on Peabody Row.
New Hampshire Maple Producers http://www.nhmapleproducers.com/
more photos were posted on Friday, 4 March 2011 at this link:
Hank Peterson, maple producer of Londonderry, New Hampshire,
passed away on December 23, 2015. Click here for his obituary:
Published under a Creative Commons License
Heather Wilkinson Rojo, "Sugar Houses in New England", Nutfield Genealogy, posted March 5, 2011, ( http://nutfieldgenealogy.blogspot.com/2011/03/sugar-houses-in-new-england.html: accessed [access date]).