Levelling floor joists, is sistering OK to do this?

8 Feb 2010
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United Kingdom

I have badly sloping floors in my Victorian flat, due to natural movement apparently, and want to level them before laying oak floor.

Best method seems to be to attach battens on top of joists to bring them level. But as the floor slopes lengthways and widthways and has a few dips in between, this could be a nightmare for mathematical calculation and to cut the battens exactly right. The lowest point would need to be raised nearly 3 inches.

Would it be OK to use the sistering method and attach lengths of 4 x 2 or in some cases 2 x 2 to the sides of joists at the right level?

Joists run lengthways, and longest room is 14 foot but joists run into the hallways, so another 6 foot in length.

If "sistering" is feasible, what length should the attached 4x 2s be, how far apart should screws attaching them to joists be, any other tips greatly would be greatly appreciated.
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