No, if you are referring to your principal residence where you are living, if the floor fell in and you fixed it, it would not be am improvement, but instead a repair.
You cannot deduct repairs to your principal residence. Repairs means to fix something back to its previous condition/use. Those are general expenses that are not deductible nor do they add to the adjusted basis of the property for when it is sold.
If you make improvements, like a new roof, new carpeting throughout, then those costs can be added to the adjusted basis of the property for when it is sold.
Per IRS Pub 946:
Improvement means an addition to or partial replacement of property that is a betterment to the property, restores the property, or adapts it to a new or different use. Generally, an improvement adds value and extends the life of the property.
