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Roofing/How to fix truss-less sagging roof


I have an older house, ~100 years, and the roof structure is starting to sag pretty good. It is about 20 ft across and 10 ft high, but the problem is that it was never built with any webbing. It is constructed only of 2x4 top cords.

I was thinking of doing this, to try and fix the sag with an attic truss system:
use a temporary 2x4 or 4x4 to cross the two top cords around mid height and jack it up (using a 4x4 post spanning the joices to spread out the load on the floor)
this should push the bow out and i would install 2x4 braces at about 4 ft heights at 90 degrees and another brace at 45 degrees in (what would be) a crawl space. Also i would install a cross brace around the peak, maybe 7 ft off the floor.

I guess my question is, if this would work, and if it might, what should I use for securing the braces to the existing framing.

thank you.

Sorry I didn't reply earlier.

If the sag is too much you might not be able to bend the wood back to where it started. It takes time to sag like that and it could take upward pressure for a long time to get it to go back.

If one side is stronger than the other the red horizontal piece will start to tilt as one side moves upward more than the other.

This could turn into a truss type system but there are forces at work that need to be calculated. At the bottom of the truss system you need a horizontal member which is the ceiling part. What is that made of? The lower blue pieces will start to push down on that ceiling member. Will that hold the additional force?

The weakest part of the rafters will be the center point so it would be better to put in the blue horizontal piece at mid-line of the rafters but that will take away height in the crawlspace.


As far as attaching the pieces you can use anything - nails, screws, bolts or plates


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Brad Zacharia


All aspects of residential Roofing. This includes shingles and flat (low slope) roofs. I have knowledge in the installation as well as the design of roofs from an engineering standpoint.


I have been doing roofing for 40 years. This was my father's business and I took it over in 1980.

I have written responses to artcles that I felt needed a response to and those responses have been published in roofing trade magazines.

BSEE Drexel University

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