Buying a coop with unapproved renovation?

Only if it's ridiculously cheap and the risk is priced in. Presumably the owner at the time didn't inform the board / get approval because they didn't want to follow the building's (other) rules.

There are often a lot of detailed rules around replacing pipes, waterproofing, soundproofing, etc, and it seems unlikely that the owner would have gone to the effort of complying with those rules without actually getting approval.

Have your lawyer add a clause to the sales contract that requires the seller to obtain written approval from the board for all alterations made to the apartment up to the sale date, and (not just 'seller represents that all alterations have been approved'), and makes the seller liable for payment of any remedial actions required by the board or the DOB.

Have a backup plan.

Agree with Aaron2. This is no small deal. I've seen situations with condo's even where an owner replaced his apartment windows without informing the board. The board found out later and made him replace all the windows as punishment. Ostensibly it was because it was aluminum vs wood like all the other windows. Didn't matter that it wasn't even a landmark building!

If a condo board can do that, a co-op board will have even more power so I'd be careful. Are you working with a buyer's agent? If not, you should really consider a buyer's broker commission rebate to help cover your closing costs (http://www.hauseit.com/closing-costs-nyc/) .. hopefully it's not too late.

What kind of renovation, and what kind of building? Depending on what you're talking about, the risk may be major or minor. I saw this happen in small buildings that went from being laissez-faire to strict as neighborhoods gentrified and property values increased. Depending on the extent of the unapproved renovation, sometimes it was a big deal; other times not. Sometimes even the bigger things end up OK -- the building I used to live in had an illegal basement apartment, an illegal mezzanine, and an illegal roof deck all eventually OKed by the DOB.

I suspect the co-op board won't consent to the sale unless any open items are closed by the seller. (A sale was always the trigger for resolving the longstanding illegal elements in my old building.) The board will probably also require DOB sign-off if applicable. Your lawyer should be able to tell you whether DOB approval is required for the renovations the seller did.

I'm not sure a seller would sign a rider as strongly worded as what Aaron2 suggests (I wouldn't, and I did a legal renovation with Board and DOB approvals), but perhaps he would sign a rider saying that he will obtain sign-offs from the Board, and that you have the right to back out if the Board approval is contingent on any remediation.

Your big risk here may be delay, depending on what's required.

Not clear on why the seller would inform the board about 10 year old renovations. Seems to be calling attention to something no one apparently has cared about for a decade. Since he has called attention to it, I would wait for a written response from the board prior to signing a contract.

agree with @bryantpark - there's a price for everything. only buy this co-op if the price reflects the risk of an un-approved renovation with a co-op board *YIKES*

Hypothesis: someone on the Board knows (or noticed when the apartment was on the market), and has told the seller that the sale won't be approved without legalizing the renovation. This was the case with the illegal roof deck in my old building. People did care, but the board and the unit owner were at a stalemate for years, and the board had no money for legal action. The Board finally had leverage when the person went to sell, and forced legalisation of the roof deck and some remuneration.

In small buildings, there often isn't a paper trail. When we had one unit turn over, the buyer wanted a statement from the Board that the existing washer-dryer was allowed in the absence of any evidence or paper trail that it was approved. We thought that was reasonable and gave him a written OK.

How often to coops or condos go back to enforce renovation rules for projects done by prior owners?

Friends of mine are trying to sell an apartment and the co-op is giving them a hard time about renovations that were done 10+ years ago and by a previous owner!