I would not let a tenant install spray foam insulation in an apartment.

Google ‘green house, red door’ and click images to see what I mean.Personally I’m not crazy about the ‘sea foam green’ as a base color.

You shouldn't have to tear down any walls unless you choose to do spray foam insulation - and that will cost you at least double of the alternatives (not to mention costs of hanging fresh drywall).What I would do is find a company that does blown in insulation.

One time I opened a wall box and the owner had spray flammable expanding foam into all exterior wall boxes to stop ants from coming in. 

All 23 of my residential LLC borrower loans on 1-4's have been SOLD.

We finally got sick of dealing with the rats and cleaning up after all of their poop and pee without our landlord doing a damn thing, so we went to the hardware store and bought some of that expanding foam caulk and filled the holes ourselves.  

-again, the #'s have to pencil.Also in Sean's point about lots in Boston.

I doubt it, you're foaming at the bit and they probably know that too.

It used to have a carpet with a think foam below, but I remove it because it was old and you could heard the noise.I removed the carpet but left the original hardwood floor.

You can shave 20% of your profits off of your taxes before you calculate.