commercial tenant's right under WA state landlord tenant act, lost business because of landlord's repairs made space unusable

The answer largely depends upon what your lease says. There is no commercial landlord-tenant act in Washington.

Commercial leases in which the landlord has maintenance or repair obligations relating to the tenant's premises typically exclude any right to any consequential damages (business loss) and typically specifically say that such disruptions are not a violation of the lease. However, commercial leases can be quite lengthy and complicated, so you should have a knowledgable real estate attorney look at it.

PLEASE BE ADVISED: This answer and any information contained herein is not intended to be treated, and should not be construed, as legal advice. Rather, this answer is offered solely for general information purposes. This answer does not create an attorney-client relationship, nor does it create any kind of legal relationship, duty, or privilege. This attorney is licensed only in Washington.

As stated by another commentator, your lease must be reviewed. Additionally, under Washington common law, you might have an argument that the landlord interfered with the covenant of quiet enjoyment. If the landlord breached the lease or the covenant of quiet enjoyment, the tenant might be entitled to damages.