Neither one of the options include removing the old sheet vinyl. This matched my research that with a single layer of sheet vinyl there was no need to remove the old. Since neither of them suggested that, and I'm sure it would add to the cost, that's not really on the table right now. I'm just trying to figure out if a new subfloor is necessary or not.

What GreenDesigns said. How are you going to deal with the transitions to other rooms/halls if you add another layer of subfloor on top of another layer of vinyl? That's building up and now you have a trip hazard because of different heights. If your existing floor is flat/smooth, no low spots, cracks, etc. then I think another layer of vinyl over the existing is the lesser of two evils, but really it should be torn up to do it properly.

The kitchen/dining room only connect to the living room. That room has carpet and the transition is made with one of those metal strips. They would be installing new strips but that would still be the transition. Even if they put in a new subfloor, it will still be slightly lower than the carpet side. Adding a new subfloor and/or building on what is there will actually bring it closer to the height of the carpet and I would think would create less of a trip hazard rather than more.

If not replacing the subfloor puts the project within your budget, keep in mind (if you aren't already) that contingencies should be expected in older house improvements. I'd recommend having a cushion in your budget in case something major is discovered mid-project that would require additional expense to fix.

The installer will have to install new subfloor or emboss the existing vinyl for a properly prepped surface for vinyl. It is important that the surface be as close to perfect as possible for sheet vinyl install.

When we remodeled the kitchen in our 1960’s home last year, the contractor found 4 layers of different linoleun - one layer on top of the other, separated by glue! We had been walking on the top layer for 26 years. It wore fine. The transitions to the hardwoods in other rooms was covered by those metal strips. No one ever tripped.

Technically the new sheet flooring can be installed directly over the old...but there are several things that MUST be in place before that can happen:

1. The old flooring must be clean, sound, flat and well adhered to the subfloor (no tears or lifting)

2. The old floor CANNOT be textured or 'puff' vinyl

3. The old floor must be professionally cleaned to remove any/all contaminants (such as wax, cleaning products, oil, etc)

So long as ALL those items exist, you can lay the new sheet product over the old. My question becomes does your floor meet all 3 requirements?

My next question is why wouldn't they remove the old if your floor does NOT meet all 3. It is fast, easy and usually less expensive (assuming the subfloor underneath is intact) that laying new subfloor/embossing.

I agree that there is no need to remove the old sheet vinyl. You don't need to be concerned with any difference in height (that someone mentioned above) as one layer of sheet vinyl next to carpet won't amount to much at all. Certainly no difference worth noting.

If your current floor does not appear to have any bumps or places that stand out as being uneven, and is a "flat" vinyl, then you should be good. The installer should know to check this out thoroughly - if they are any good. Also, if there is existing moisture damage that you know of, then that part you should take a look at. I had sheet vinyl in my kitchen, and was looking at replacing it with ether new SV, or LVT. I chose LVT, Since I had a nice flat floor, the LVT was to go right over the SV, with embossing leveler applied first.

Unfortunately, because of the complete idiot that they sent to do my install, the company had to redo the job. (Yes, they lost money on this job.) They had to pull all the LVT up, and some of the old SV as well. (Which I wound up thinking was somewhat of a good thing, in my own mind, because I was able to see what good shape the sub floor was in.) The embossing leveler is even more important, I think, if you are getting a "smoother" type of sheet vinyl than what you had previously - most of the new stuff does not have the shine of the old, and the newer finishes will more easily show any uneven spots that the old SV. (SV really is a very forgiving floor covering - it's why it has been so popular for so many years, and also why so many people wind up disappointed in their "new" floor coverings that they replace it with.)

There should be none of the old SV visible through the compound - make sure you ask them about their experience with this. It really is a skill to smooth out and level this stuff. The first guy that did mine did a piss-poor job on that as well, and at the time, I did not know any better.

If for whatever reason, your SV is removed, then lay down a good underlayment like these...

https://www.lowes.com/pd/SurePly-1-4-in-Whitewood-Plywood-Application-as-4-X-8/50124674

http://www.robertsconsolidated.com/products/accuply-premium-underlayment/

https://www.traxxcorp.com/products/matrixx-underlayment/

Read through this article for more info on underlayments for vinyl flooring.

https://bct.eco.umass.edu/publications/articles/wood-underlayments-for-resilient-flooring/

Best of luck. I completely understand your choice of SV - it is hard to beat for wear value and "waterproofness".