I m kind of astounded that your hardwood installer would put the new hardwood right up against the existing baseboards that is a total no no for hardwood installation.
How to install wood floor under existing baseboard.
Use 11 4 to 11 2 in long enough to penetrate the molding the drywall and drive at least 1 2 inch into the wall s base plate.
Fill any nail holes and apply any touch up as needed.
In this video i share tips and tricks that i have learned over the years to create.
In my line of work i sometimes have to install baseboard for my customers.
This gap is needed to give the hardwood room to move with changing humidity.
Install the base shoe quarter round molding over the expansion gap created by your new hardwood flooring.
Leave a 1 4 inch or larger gap between the existing baseboard and the new hardwood flooring you are installing.
Then slide the long edge of the flooring under the other baseboard straightening the flooring piece into place.
Nail it to the baseboard not to the floor or subfloor.
Keep the lower edge of the baseboard even with the top of the floor and nail the baseboard into the wall.
Once you have gathered all the tools here are the steps to installing your new baseboard molding.
Use baseboard nails or brads no longer than 18 inches apart for 3 4 inch thick molding.
When attaching the base shoe quarter round nail the molding into the bottom of the existing baseboard and not into the flooring itself.
Nail threshold or transition strips in place where the edge of the floor is exposed.