All contracts, options, or other devices not based upon a substantial consideration, or that are otherwise employed to permit an unlicensed person to sell, lease, or let real estate, the beneficial title to which has not, in good faith, passed to such party for a substantial consideration, are hereby declared void and ineffective in all cases, suits, or proceedings had or taken under this chapter; however, this section shall not apply to irrevocable gifts, to unconditional contracts to purchase, or to options based upon a substantial consideration actually paid and not subject to any agreements to return or right of return reserved.History.

Use an open-cell spray foam.

I would first check to see if the coin collector device on the machines have been tampered with and if that's not the case, just kindly ask the tenants if either there is new lower price Laundromat that might have opened up or are they no longer satisfied with using your machines.

If you have multiple wythe of brick, you should be able to either affix 2- 4" (in layers of 1", 1.5"  or 2") of foil faced polyisocyanurate rigid insulation (tape all seams and stagger the seams of each layer), or spray the inner surface with 2 - 4" of closed cell spray foam insulation.  

In 2018 Baltimore County is requiring carbon monoxide alarms / detectors to be:hardwired with a secondary battery backup (similar to smoke detector requirements in Balt County now)battery must be sealed, tamper resistant, and must last for a minimum of 10 yearsconnected to an on-site control unit that monitors the carbon monoxide alarm remotely so that a responsible party is alerted when the device activates the alarm signal and receives its primary power from a battery or the control unit(Ref: Baltimore County Notice with details)The one in bold specifically concerns me.

@David WolfWhen we purchase an old building like this we just start chewing away at updating it bit by bit: this summer we had half of a 120 yr old duplex vacant for two months, so we gutted it back to the studs, put 3" of closed cell insulation, EnergyStar windows and doors; moved a few walls around and refinished the floors.

Just go and get starter one if you don't have everything setup you might want to put on there (Business name if you are going to setup an LLC, website since you don't have that yet, a business number aside from your home or cell, a fax number... etc.).

Typing from my cell.

I expect to hear it turns out well.And as an aside - I have 2 cell phones, a work phone and a personal phone.

Signs will appear on all sorts of water using devices, and on the water heater and heating system.