Reply to Terrace OP. Sorry for using the Anonymous label. My apologies!

AdC and AR, thank you. It's good to get different opinions.

I believe the question should not be "......a nice thing to do?.." The Board is not in place to be nice, but to fulfill the fiduciary responsibilities that they were voted in for; in other words, ask rather:
Would reimbursing them, either whole or in part for the square footage used, benefit the coop as a whole?
What happens next time if you don’t reimburse them this time?

Is the penthouse terrace allocated shares? is so, then it is part of their apartment unit and my personal belief would be to pay them an agreed amount based on the space/share allocation. If it were your living room they occupied, you would feel the same, no?
I also believe that at the end of the day, the coop will be benefited by this decision, in that it would cost you more in construction fees if they had to stage elsewhere, a shareholder is more apt to permit access next time it's needed, the staging permits the work to move along faster...

Also, ensure the contractors (at their expense) leave the site better off than it was to begin with..

~AR

I would go for the lawyer's advice if the PL is silent and the co-op is responsible for repairing the penthouse terraces. While the terraces may be for the exclusive use of the residents in the penthouses, in your case the board is taking care of the common good, i.e., the facade and potential liability of the entire building. As AR states, the board is exercising its fiduciary responsibility to meet the requirements of the law and making the builing safe. If the terraces were to be repaired, the co-op would not abate the residents for repairing them. So, let them bite the bullet and take care the good of the entire building too!

AdC