DD,
I'll bet you already know what I'm going to say about this...
A lot of appraisers think that our only job in writing appraisal reports is to give a value; the value opinion itself being the main product of our efforts. Many folks think that if we hedge our values we are building in a safety feature that will protect us and our clients against any appraisal deficiencies or omissions. I disagree. I think our responsibilities extend to disclosing those pertinent elements that have a bearing or influence on our opinions. I think that appraisers will be disciplined for failure to disclose and failure to pursue due diligence far more often than giving a 'bad' value. This would be consistent with an enforcement program oriented toward pursuing factual errors rather than differences of opinion.
As for your suspected unpermitted addition, there are two things that come to mind. I would assume that your client is going to require insurance on the improvements. I would bet that the insurance carrier will not cover unpermitted structural additions or improvements. If a fire or other structural failure starts in the unpermitted (illegal) addition and spreads to the permitted portions, an insurance company is going to be looking to not cover the loss. Either that, or they will be looking at going after whoever represented to them that the improvements were permitted, which may well include the appraiser. In another worst case scenario, say the borrower defaults on the loan and walks. Lender repo's the trashed property and ends up with a loss. That lender now has a 'reason' to chase the appraiser for the loss, under the grounds that 'if we knew there was an unpermitted addition, we would have never made this loan'. The appraiser has no recourse or defense, regardless of their value opinion, because they made an error or ommission of fact by not disclosing the lack of permits and/or apparent difference in workmanship.
I am not suggesting that we need to check every permit out there, nor am I suggesting we need to be competent as engineers or building inspectors (couldn't hurt, though). But we do need to be reasonably familiar with basic construction requirements and note those variances or deficiencies that are readily apparent.
Bottom line, protect yourself and protect your client. If they make the loan after you have notified them of a possible problem and recommended some follow up, then it is no longer your problem.
George Hatch