The upside here can be substantial, so do this carefully rather than fast. Adding a legal unit to a lot zoned for more is one of the strongest value-add plays in real estate. We've seen owners take modestly priced properties on lots zoned for two to four units, add density, and end up with properties worth multiples of the all-in cost over the years. Getting the most legally allowable use out of the land is where the real value gets created. On the tenants: we're not aware of anything that flatly prevents construction while a tenancy is in place, but landlord-tenant law and what you can do during an active lease vary by state and city, so confirm with a local real estate attorney. Alongside the legal answer, run a golden-rule test: would major construction disruption, while the tenant is paying full rent, feel fair to them? That question often points toward waiting out the lease, offering a rent concession, or timing the noisy work. Your options, roughly: - Start now, if it's legally clean and you can do it without stepping on tenant rights. - Wait until the lease ends in October and work on a clear site. - Negotiate an earlier move-out. Before you commit either way, nail down three things: what the finished units will rent for, every build and permitting option available, and the true construction and timeline costs. Know those numbers and the legal constraints first, then choose the path, with your attorney and local building department confirming the specifics.