Assuming multi family is a permitable use within the zoning ,
GSE’s will accept the appraisal if:1) appraiser can demonstrate that it is common for the market to have unpermitted GLA /area (provide at least two similar comps with unpermitted GLA/area)2) no value is given to the addition (GLA/area or rooms)3) appraiser states that it was built professionally in workman-like manner (or similar verbiage)4) if there is electricity or plumbing, the appraiser needs to comment to whether or not there are any health/safety issues5) any gas stove will need to have the gas line capped due to health/safetyNote, if the appraiser states the unpermitted area was not constructed professionally in a workman-like manner, the unpermitted area would have to be removed or the property would most likely be ineligible.