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Strengthening Ceiling Joists

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I have seen strongbacks running perpendicular to C.J.s in many existing residential houses that stiffens existing C.J.s. Strongbacks are typically 2x10 or like, running along midspan only or along 1/3 points of the C.J. span. You could design beams to act as strongbacks. Of course you need posts to support the beams. This way you do not need to retrofit each and every C.J.s.

 "ebosco(--nospam--at)vogeltayor.com" <ebosco(--nospam--at)vogeltaylor.com> wrote:

I am renovating my two story 1912 dutch colonial which is balloon framed.
The ceiling joists on the second floor are 2x4 members (full 2x4 dimension)
which in some locations span as much as 15'. The mid-span deflection of
these members is 1/2" in some locations and the small depth of the members
gives me little room for adding insulation to the second floor ceiling.

In reviewing the alternatives for improving the situation it seems like a
very stong beam is produced by stacking a second 2x4 or 2x6 on top of the
existing joists. I would connect the two by lag bolting vertically through
the top member into the bottom one. A benefit of this plan is that I could
use the bolts to raise the sagging members slowly over a period of months to
reduce cracking of the plaster.

Has anyone ever seen this approach applied? Any recommendations for lag bolt
frequency? Would it be necessary to add a vertical plywood plate (or plates)
to the edge of the beam to help the two act as one?

This is a time when I wish my engineering experience covered more that
Mechanical, Electrical and Plumbing.

Thanks

Ed Bosco, PE


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