Expert: Michael Curry - 1/12/2011

Question
Hi Michael!  

I am looking to add flooring in my attic - right now just for storage, but down the road - who knows:)

I will be laying 3/4" tongue and groove OSB.  The attic is fairly large (about 35ft x 60ft) with tons of headroom.  The joists are 16" oc and are 2x8's.  They run the lenght (approx 60ft) of the attic.  There are no additional perpendicular headers the entire length of the attic (in other words, I could shine a light between two joists on one end and see it at the other end).  The joist boards are about 15 feet long each, and at that point they are staggered/overlapped a bit to get the total 60 foot length.  (Hope I am being clear!).

At two sections in the attic they have installed strongbacks (see am trying to learn on my own!  Googled and learned that term a bit ago! )to tie the joists together.  They are 2x4's flat with a vertical 2x6 nailed to the side of each.  The strongbacks run the width of the attic but are not connected to the rafters or anything on the ends.  They are similar to the joists in that each strong back is actually two 2x4's overlapped a bit in the middle (meaning not one 35 foot long 2x4, etc.)

SOOOO (there really is a question here!!).  I understand the strong backs are there to keep the joists in alignment.  But unfortunately they break up the level of the floor as they sit on top of the joists.  If I am putting down the OSB, and screwing it to the joists, is that enough support to keep the joists aligned where I can remove the stong backs?  Or would I have to install some sort of blocking, or, hopefully not, cut joists and install some sort of header.

Thank you!!!

Answer
Hi Steve,

The strong backs are just to keep the ceiling joists straight and are not really structural. Your ceiling was not designed to be a floor and using it that way will probably cause drywall damage below in the larger rooms.
To answer your question: yes the strong backing could be removed and the plywood would keep the joists straight.