epitome- Let me say this about building forensics, it is BUILDING forensics, not structural engineering only forensics. Since we SEs are so smart and rarely make mistakes, and the buildings are built exactly per the drawings, there is not much work in the STRUCTURAL only area
There is some truth in that though, so be prepared to broaden your horizons into things you may have never given much thought about, dirty word, architectural details. You know, the "SEE ARCH" parts of your drawings? You will now have to look at those areas now in great detail, and you may not want to do that. So there is definitely an education process to be had there for most traditional SEs, and I am sure Ron can expound on this as I believe he deals a lot with issued due to roofing, waterproofing, flashing, cladding and fenestrations, interior finish distress, etc. There are some good books out there that can serve as a guide, but nothing beats experience, especially in this field.
Most structural forensics that I have dealt with is residential, so structurally speaking, it is not that complicated. But those other issues can get very complicated, especially dealing with roof leaks and moisture/vapor intrusion. Make contacts in other fields if you haven't already so you can pick the brain of architects and other types of engineers.
Your potential clients may be some of your existing clients, as architects and contractors are often asked questions about building problems since the average person doesn't know engineers are that involved in building design or forensics. Let them know you are seeking this type of work.
If you have friends/contacts in the law and insurance fields, this is usually a forensic engineer's bread and butter, they flip the bills for the investigations (as noted by Ron). My suggestion would be to try and get in with attorneys who do a lot of property work, as well as insurance companies in the form of claims adjusters. There is usually a "vender list" and you have to get on them, and this can be a hassle and time consuming, and can be a bit of a political process, that is if you can manage it. Once you are on one of those lists, most companies will cycle through their favorites as they need them. You could end up getting very steady work.
Finally, as Ron said, work both sides of the fence. This looks good to attorneys because it shows you are not biased. I have been asked that question exactly in depositions. So do some work for your neighbors and friends even at a very low cost just so you have the experience, and so you can say you have done jobs directly for homeowners.
Its a long road, and those who like it, usually REALLY like it. It is a lot like detective work, but there are no bells and whistles like on CSI

It is usually far from text book structural engineering. One of the reasons I like it is that exactly...