We are installing the first of our engineered flooring in a hallway and two bedrooms, then we will do the other side of the house. The hallway shows some of the problems to solve. It is 23 feet long with a high spot about right in the middle. It drops off about an 1/8 of an inch evey 2 feet or so. At the extreme ends of the hall the difference from the middle high spot is about 1/2" to 5/8".

In order for the new flooring to be close in height to the stone/tile floors it meets at either end of the hallway, we can raise the 1/2' thick engineered floor no more than about 3/4"-1". So am trying to sort out how to get the floor flat enough and also not have too much height difference where the wood meets the tile/stone.

Here is the solution I need help with: I plan to use 30 pound felt laid from each end to within about two feet of the high spot in the middle of the hall. I may put two layers of felt at the extreme ends so the difference between the high spot is about 1/4". I would use transition to one layer of felt after a couple of feet until just two feet from the high spot. We would then use 1/4 inch plyood to cover the whole hallway.

Although the floor will not be completely flat, the differences are less than they are now. Will this solution cause me creaking or other problems? If so, is there another way to deal with this type of hump in the middle of the floor. My guess is that this will be a problem in other parts of the house too. so sorting out how much out of flat a floor can before before problems develop will be one of the problems to solve everywhere.

thanks