In his later skooldays I tasked No'1 Son & his best mate to clear out a mid terrace we were about to refurb.
Some poor old bloke had spent his final years sleeping on a doss bag in the living room, amongst all the empty Vodka bottles rammed full of nub ends & chip shop paper wrappers. He'd been using a corner of the room as a toilet for some months, pi$$ & s#it everywhere, some of which had seeped into & under the floorboards & into the rubble in the void space.
I never went inside but I'm told on hot day it made your eyes water ! Bless 'em, they filled 4x skips with the stench & never complained once, unlike myself when my 2IC made me chuck a hefty £bonus there way . . . .
There are specialist chemicals you can get, so not to worry Jim, the smell does fade away after a few years but if you search 'Urine Bio Digesters & Odour Neutralisers' I'm sure you'll have it back smelling of roses before the hot weather hits us.