The house is constructed with 2x4 trusses, 24 inch on center. The trusses span an open area 27 ft long with no support in between so the ceiling is sagged in the middle and the roof ridge is sagged as well.

I jacked up the ceiling to where it should be and installed (2) 2x10’s on each side of the center truss supports in the attic. However, after removing jacks the ceiling came back down almost to where it was previously.

The 2x10’s are approx. 18 ft long with end support only since I don’t want to have a post in the middle of my living room.

My question is:

Will adding more 2x10’s to the 4 existing help and if so how many in total would be required ? Or is there a better solution ? Thank you

  • I get the ceiling, what is happening with the roof? Do you have some pictures? Just FYI even 18" OC ceiling are a mess with sagging, can't even imagine that there are actually 24" OC supports that got sign off on.
    – DMoore
    Apr 24, 2020 at 19:38
  • I'm guessing not pre-manufactured trusses but actually stick framing. I'm also guessing that the house is older, probably 60's or earlier. Bob, can you confirm?
    – Ack
    Apr 24, 2020 at 19:51
  • 1
    Can you take some pictures & post them? If they were trusses manufactured by a reputable manufacturer, they should not sag, unless the load on them is a lot more than what they were designed for.
    – SteveSh
    Apr 24, 2020 at 22:09
  • I had a 24x24 garage built maybe 9 years ago. The trusses span 24 feet. I had the option of going with 2x4's or 2x6's for the truss members. I went with the 2x6's as I knew I was going to be using the area above the garage for storage and wanted the floor to be stiffer than it would have been with the 2x4's. But the 2x4's were OK otherwise.
    – SteveSh
    Apr 24, 2020 at 22:14
  • There's no "so" here. Properly designed/built/installed trusses do not magically sag because they happen to be made of 2x4's, whatever the span. If they were not properly designed/built/installed then they could be made of 2x12's and still sag... You definitely need a structural engineer.
    – Ecnerwal
    Apr 25, 2020 at 3:08

1 Answer 1


Will adding more 2x10’s to the 4 existing help and if so how many in total would be required ?

This is very common for older stick framed homes that were not engineered and the code very minimal. The reason is obvious, it is not constructed strong enough

What you did with the 2x10's is called 'sistering' or 'sistered.' The way that you did it does not add strength to the roof structure as a whole, as you have learned.

Or is there a better solution?

Answered directly and simply


Answered more fully aka 'How' or 'What' is a better solution

It's complicated. It depends on the particulars of your roof framing, the wall layout of your home, and other issues. It involves not just the old framing member sizes, locations, wood species etc, it also includes the connections of the members and other things like constructability issues (how to get members into place at minimal cost)

Generally this is a project for a structural engineer. I'm guessing that you may note like that idea, for reasons. But there is no answers to be found here, from friends, and probably not from contractors, it's simply too complicated an issue.

There is ONE option that might be plausible for your situation: you can make the ridge into a post and beam system. This reduces the rafter spans in half. You'd need a beam of course, and posts, and footings (the existing foundation also surely not able to take these new point loads)

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