rafter sag

I have a roof about 50 years old with a 4:12 pitch and 2X4 common rafters. The problem is at the half way point between the ridge and the top plate on the wall there is about 3/4 of sag. (About 11 feet from ridge to the birdsmouth.)
What is the best way to take the sag out of these rafters? I worry that if I were to attempt to run a brace to the ceiling joist that this would in effect push the ceiling down.
Any ideas?
--

Roger Shoaf

About the time I had mastered getting the toothpaste back in the tube, then
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Roger Shoaf wrote:

Yea, go back and read the answers to the same question you posted two days ago. Don't expect personal responses.
--
Joseph E. Meehan

26 + 6 = 1 It's Irish Math
  Click to see the full signature.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

HomeOwnersHub.com is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.