Firefighters responded to a non-occupied dwelling for a structure fire. Although the fire is being investigated, a space heater was found near the area of origin on the first floor of a newly constructed multi-housing unit. The fire involved the basement and 1st floor. Efforts to extinguish the blaze quickly were hampered by the wood composite I-beams, considered light-weight construction, used in the flooring and having burned through. The sprinkler system hadnt yet been connected allowing the fire to grow significantly before firefighters arrived. Mutual aid was provided by Dover, Exeter, Lee, Stratham and Newmarket at the scene while Newington and Madbury provided coverage in Durham.