Vinyl tile or sheet flooring is often used in bathroom and kitchen applications, typically over a plywood underlayment. A composition type board will expand when wet, so these are not recommended for use in these areas, where there is moisture and humidity. Instead, the underlayment should be of 5/8 inch thick plywood, sanded and plugged, which is made for underlayment.
If you have hardwood flooring in adjacent rooms meeting the edge of the vinyl floor in the kitchen or bathroom, it can be tricky to get the two surfaces to lay flush with each other. For 25/32 inch thick hardwood, which is the most common thickness, if you use vinyl tiles of 1/8 inch thickness laid over 5/8 inch plywood underlayment, both floors will be about even.
If you are using 1/16 inch thick vinyl sheeting, though, you’ll need to lay a few layers of building paper between the plywood and the sheeting to flush the two surfaces up. Making up a small sample of the plywood/building paper/vinyl stack-up with scrap material will let you check your leveling against the hardwood floor before installation.
If you plan on using the existing vinyl floor as a base on which to apply newer vinyl flooring, it can be done. Ensure the old vinyl flooring has good adhesion still and is not curling up or warping. Then you will need to apply a coat of embossing leveler before installing the new flooring.
For vinyl flooring which runs around the doorway jambs, extend the underlayment in one piece by making cutouts for the jambs, rather than creating a separate peice. This will lessen the wear on the vinyl; there is lots of foot traffic in doorways, and you want as rigid an underlayment as you can get to support the vinyl. Vinyl is prone to weaken and crack in unsupported, high traffic areas.
Your underlayment should be nailed through the subflooring and into the floor joists, using spiral flooring nails. This prevents the nails from working their way out of the wood under vibration or thermal expansion, conditions which will force the nail head to push through the vinyl floor. 15 pound felt laid between the subflooring and the underlaymet will also help alleviate this problem. At locations other than floor joists, ring shank nails should be used.
For a squeak-proof floor, mastic or construction adhesive glue can be spread on the subfloor with a notched trowel, before the underlayment is applied to it.