I'd contact the division of inspection, explain your dilemma, and offer to work out a solution.

Go in person to the inspectors office. A live person should be able to answer your questions. Call first to make sure you know the in-person rules like office hours and masking requirements.

To remove a pool following Iso (involving a fill) is expensive. Is it well accepted to (or legally permitted) to punch holes at the bottom (not sure if it has already be done or not, but I should be able find out after tearing down the existing deck) and cover it by deck? Anyway I don't have plan to use that land for anything else except for deck...

No plan to sell in near term, but I do want to take this into consideration. Because of rear setback requirement the house cannot be extended to the location where the pool is. Building a detached structure there will look bad as it blocks the view from bed rooms. So I personally think potential buyer either would think a deck be a good idea, or they may possible want to build a pool there. (The worst case is they can pay for filling it and build things on top of it.) Or most people will think otherwise?

If the pool was permitted the filling in of needs to be documented and permitted by the town as well or when they survey the question will come up and you will either be paying a crap ton to do it then and or giving a huge discount for the new owners to do so if they would be willing or able to close on the home.

Wait, the pool is unfilled? Like an empty bowl just sitting under the deck?

Yes, definitely go to your local inspectors office with all of your questions. Something that is accepted may not actually be OK in the ordinances. Check your ordinances and with the inspector before you do anything. Don't take general gossip for granted as to what is permitted or not- get it straight from the horses mouth.

There could be 2 angles to think about a deck over a pool: one is to demolish the pool but not fill it with dirt/stone/etc, another is keep the pool (in town record) and treat deck as pool cover.

Which one makes more sense?

Which one makes more sense?

Ask your building inspector office to find out what is permitted or not.

Thanks you @beesneeds. I will ask building inspector office. I just want to collect more ideas to get myself prepared before I go, as I am new to this area.

@Charles Ross Homes I have to admit, that part of the reasons why I'm reluctant to fill it, is that myself (or future buyer) can have the option to convert it into a underground studio like you said in the future, with part of the "deck" (or ceiling of the studio) being glass.... I have seen something similar in commercial property (like entryway to a subway), but not sure if such thing is realistic in residential...

"I just want to collect more ideas to get myself prepared before I go, as I am new to this area."

Big country, many different areas and codes but none that I can think of that would allow you to build a deck over an existing swimming pool. And a pool that is being debated either filling in or building a dance floor over in my mind is not a pool that will able to be reused as a pool.

If I bought a house and found an abandon pool beneath my deck, I definitely would be more than a bit unhappy. Get it removed, or filled in, and be done with it.

I actually don't mind to disclose to further buyer (which won't happen within 5 years, if nothing unexpected happens) the un-filled pool under the deck, if the deck can be built under a permit - which means its structural safety is confirmed. But @millworkman I'm curious why a deck over pool may not get permit? Isn't it about the same as building a deck at 2 (or 1.5) story high?

You seem to want to fight every suggestion that has been offered!

Contact your local government inspection office or similar.

Also talk to a local Realtor about the advisability of leaving a very expensive albatross for any potential future buyer.

Sheesh.