Solid Hardwood, Engineered and Laminate Flooring - Small uneven area before nailing hardwood

At the end of my 3' wide hallway the plywood subfloor boards meet evenly.
Then, in the last 12 inches of the hall the subfloor seems to dip 1/4 inch lower. I need that area to be level as I'm going to nail prefinished hardwood flooring. Because it's a small area someone told me shim the hardwood floor in that area. Others suggested pouring a leveling agent. I can't get under the subfloor. Any suggestions??

Secondly, after the floor is even should I lay 15lbs. tar paper even though there is no moisture problem?? Why am I going to lay the tar paper??

Thanks

I'm going to kick this over to the Wood & Laminated Floors Forum, you'll get more detailed advise from the pros there that do this type of work daily. I've laid a couple of laminated floors for customers against my recommendation to the customer, personally I like a real hardwood floor, Red Oak is my personal favorite, but that's simply a matter of personal taste & the fact that the laminates IMO won't hold up well over the long haul.

The felt paper is laid as a moisture barrier & is specified by the NOFMA in their installation guidelines. So in the interest of not getting sued & just in general covering my behind & making my insurance guy happy ;), I always follow manufacturer's guidelines.

From the text of your post, it's my opinion that your subfloor wasn't properly installed & prepped prior to starting this installation. I would probably go with a leveling agent, but it's hard to say without actually seeing it firsthand. I am confident that the resident pros will be able to better help you out.

You should use wood singles to level.The singles are a foot long and goes 1/4" to nothing.As for the tar paper I wouldn't use it because 1st of all you can't see the beams to try to nail on them and 2nd if you get a good spill the water has no where to go but up to your hardwood!!