I would open the windows, put on one of those contractor ventilator masks (the kind used to spray chemicals), and start cleaning - Starting with giving your dad a nice, long warm shower in a shower chair. Then start scrubbing the house. If you can hire a professional cleaning service, so much the better.

I know what you are going through and I feel for you- and your dad! Try to have some compassion for him. He’s gone nose blind to his environment, and clearly needs at the very least a home health care aide, if not a move to assisted living. As my dad started going downhill in his last year, his mail was unopened in piles in his room, bills weren’t getting paid, he didn’t realize he had an incontinence issue, didn’t realize he had a deep bedsore, the place just wasn’t clean. And he was never a slob or ignored paperwork!

It is a labor of love to care for an elderly parent, and yeah, I got to know my dad “really well” in his last year. Didn’t even faze either of us if I had to bathe him. It’s just what you do. However, spending time with him before he died was some of the most satisfying and gratifying moments of my life, and I’m so happy I was able to spend that time with him.

So, gird your loins, and get to work! Best of luck to both of you.

I don't know where you are, but I would contact senior services in the area where your dad lives and see if they can help. It could be a health hazard and they could possibly help find alternative living arrangements, giving you time to figure out what to do about cleaning up. Perhaps there are funds available to help make it livable for him. But do call and see what help might be available.

eta: I'd also contact your fire dept and see if they might have some extra masks you could borrow while you clean. Or the health department might have other ideas.

Can you identify the specific source of the odor? Are there unused sinks allowing sewer smells to come up? You can run water in the drains to stop that by filling the air gap. Is it rotting food? Rotting due to a roof leak or ? Human waste? A respirator/mask is a good idea. You can put some vicks vapor rub around your nostrils to help block it too. Assuming it is not a toxic smell that you should not be breathing. I am sorry for the stress.

Buy a respirator. Open the windows and use fans to exhaust the air.

Is it a hoarding situation or is there a sewer problem?

First and foremost. You need to protect yourself.. Legionnaires Disease is no laughing matter When it comes to cleaning such places. Do some research on it and again. Protect yourself..

One small trick we use is to apply a small amount of Vicks Vapor rub under our nose. Even with a dust mask to help with the odor.

I rehab apartment complexes for a living.. And Honey some of the stuff and smells I experience is unreal.. And people wonder why I have a shower and a washer- dryer in my garage...

Yes they lived like that.. No Joke. People that inspected this place was actually puking before they ever stepped foot in it.. It was that bad..

That is roach dung.. NOT grease..

Nothing but cockroach dung..

Seeing the light at the end of the tunnel..

So be brave, Start at the top and work your way down one room at a time.. Easier to roll a rock downhill than try to push it up.. Same goes for dirt and grim when cleaning something..