Gail:
When you say tax records--are you referring to the actual records on file in the appraisal district (I think that is what you have in Texas) or are you referring to a reporting service like Experian or DataQuick with their system of reporting info? Here in Arizona, DataQuick has a huge problem with their information that they report. An example would be exactly like you have. The county assessor would have two buildings reported on the parcel, the garage apartment as one improvement and the house as the another improvement. DataQuick reports only the garage apartment and none of the other buildings on the parcel; just like the information you have. The other problem in Arizona is regarding basements. The county assessor's in the larger counties total all areas in their computerized data base, basements, garage apartments, guest houses, etc. Then the reporting services, realtors, property owners use that total square footage in reporting sales and marketing the property. Which means if a fee appraiser in using that sale for a comparable there is no information available on the breakdown of how much is in the above grade area, how much is in the below grade or partially below grade area or in the garage apartment or guest house from anybody. Unless the fee appraiser measures both the outside and inside of each comparable, the information on the total square footage of the comparables will be the only thing available to report on the GLA line, which means the total GLA of the subject has to be reported on that GLA line also for comparable purposes. So again what information do you have available for your comparables after you have seen the subject property. What do you think your market's reaction will be to the garage apartment? To the basement? If it is a dank, smelly, damp basement that a typical home owner would use for storage or something, then adjust it out on the basement line, regardless of what info you have on the comparables. If one of your comparables have a one of a kind improvement like a detached workshop or hay barn or something, maybe put it either on the basement line or a different line with a similar adjustment or lack of adjustment.
And the most important thing is to explain, explain, explain so that a reader of your report will understand and agree with your procedure!
By the way just because the assessor/appraisal district never put the home on the tax roll does not necessarily mean a permit was never issued. Maybe building permits didn't exist in 1935 or 1955. Maybe the reassessment when buildings started to be measured and placed on a tax roll didn't start until after 1955. The assessor/appraisal district personnel could have just lost the info in the process and it never got posted. I have seen that happen numerious times in many areas. Assessment records are only a probable indication of ownerhsip and what actually exists--not a proof of either!
When I was in NM, that assessment office only picked up a structure when it was originally constructed, never went back, never checked building permits, etc so the actual size of a structure could be 2-4 times larger than what was in the tax records. They also hadn't been too through when initially picking up information any way, so that 50-70 year old homes had never been on the tax roll and still weren't being taxed. Oh well, the oil companys paid all the taxes in the area anyway and the local governments didn't care if a home owner escaped being taxed since they didn't need the money.
