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Help for a sagging roof

BarbaraZimmer | Posted in Construction Techniques on April 24, 2013 01:12am

We have an older house with  sagging roof rafters.  The rafters are 22 feet long and are supported by a wall in the middle that sagged because it was improperly supported below.   The lower half of the roof is insulated (below the wall), and the upper half is not insulated.  2×4 strapping goes across the rafters to support the metal roofing.  The roof has about 3 inches of sag in the middle.

Now that we are replacing the metal roofing, we would like to straighten out the rafters to flatten the roof again.  We have put in new footings and beams in the crawl space to prevent any further sagging of the wall,  so what would be the best way to straighten up the rafters?  Should we sister a new 2×6 to the old rafters?   Or is it better to use plywood?  We need to be able to nail down the 2×4 strapping to something, so I am not sure how we could use plywood.  Any advice will be much appreciated! 

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  1. calvin | Apr 24, 2013 07:11am | #1

    Barbara

    With that much sag in the rafters, how much deflection is seen in the floor below?   and do you plan on trying to raise that (or have) ?

    Is the ridge straight, or does that sag as well?

  2. BarbaraZimmer | Apr 25, 2013 01:14am | #2

    The sagging roof

    We don't see any more deflection in the floor below.  We did jack up the wall from underneath and put in new footings, but the sag never came out of the rafters. 

    The ridgeline never has had any visible sag.  We do have a fair amount of snow loading at times, even though it is a metal roof.  The snow does not always slide off right away.

    Barb

  3. IdahoDon | Apr 27, 2013 01:52am | #3

    Sistering new rafters next to the old is the way to go.  2x6's or 2x8's won't be enough.   I'm not going to dig out my load tables, but having done a number of these I would say you'll want to go one size larger than what would be minimum code since you're having to not only support the loads common to your location, but you're also FORCING the existing rafters straight and holding them there against their will.

    In the most extreme cases I've had to use 2x12's to replace 100 year old 2x4 rafters that failed after a heavy spring snow and even then had to slowly jack a number of them into place slowly so the entire roof came up more or less at the same time.

    Something that sounds so simple can be a bear when it comes to actually doing the work.  It's frustrating work until you get a plan that works and a feel for doing it.

    1. BarbaraZimmer | Apr 27, 2013 05:23pm | #4

      sistering new rafters

      The rafters that are up there now are 2x6's.  With the support wall almost in the middle of that span (this is the wall that has been now jacked up and new footings and support beam installed), I don't think the wall or the roof will settle any further.  But when we jacked it up, the sag did not come out of the rafters.  They seem to be permanently bent. 

      The problem now is that the lower half of the roof is insulated, so I don't think we can sister anything to the rafters bigger than another 2x6.  It is an open ceiling inside the house, and I think the total depth of the insulation is 6 inches. 

      It never occurred to us to try and straighten out the original rafters.  We had just thought to sister another 2x6 to them to make the roof look straight again from the outside.  What do you think?

      Barb

    2. BarbaraZimmer | Apr 27, 2013 06:24pm | #5

      The original rafters are 2x6's, and the span is supported about halfway down by a wall (now newly jacked up and with new footings!).  The floors all look fine now, but the sag did not come out of the rafters.  It is as if they are permanently bowed.

      The problem now is that the lower section of roof is insulated, with an open ceiling inside the house.  It would not be possible to use anything bigger than another 2x6 to sister to the existing rafter. 

      It never occurred to us to try and take the bow out of the existing rafters.  We had just thought to sister another 2x6 on in order to make the roof look straight from the outside.  What do you think?

      Barb

      1. IdahoDon | Apr 29, 2013 12:23pm | #6

        It's obvious that what's supporting the roof hasn't been fixed or it would have forced the rafters out straight.  I'm not saying what you did was wrong, I'm just suggesting that rather than putting a patch on a patch on a patch, you want to either add enough rafter to fix the bow, or replace the diagnal braces so the rafters sit where they should.

        The work that's been done to date is what is considered sunk costs (water under the bridge) and if some of it has to be removed to do it correctly than that's simply what needs to happen.  I may not be the right person to take advice from if you're more interested in window dressing rather than getting the framing straightened out.  I'm not saying you're wrong - it just isn't the way I go about it.

        In my line of work one of the most frustrating things is correcting work done by others that is a half ass fix over a half ass fix over a half ass fix.  If the orignal person simply fixed a problem corrrectly all the other patches over patches could have been avoided including me having to rip it all out and do it right.  It must be human nature since that practice isn't going to go away anytime soon, espeically with the remodeling and designing shows stressing doing things cheap and fast, rather than correctly.  Over the last 10 years I've spent probably 2 months a year correcting mis-guided fixes attempted by homeowners and incompetent carpenters so I do benefit from the job security.  :)

        edit:  I had to re-read your original post and not I'm getting the impression that you're talking about adding something to the outside of the existing roof to make the roofline straight?  Those would be called sleepers.  Sistering rafters reffers to adding new rafters directly alongside the existing ones.

        I would turn down a job to add sleepers to correct a roof.  Either correct the framing from the underside, or if the space is finished and access isn't cost effective, rip the roof off down to the rafters and correct it from the top - most likely by sistering on new rafters that are correct for the situation.

  4. IdahoDon | May 01, 2013 03:14pm | #7

    If you still have 3" of sag

    If you still have 3" of sag mid-span in the rafters, which is over a load bearing wall, I hesitiate to say it's better to focus on the roof framing without knowing what caused it..  That interior wall is still 3" lower than the exterior wall?  That's a lot and I don't see you're doing the house any favors by not fixing the real issue - the interior framing, which automatically puts the roof back in the right place.  No?

    To my way of thinking, every $ and hour spent on the roof framing would be better spent correcting the interior framing, which I'm guessing is the real issue.

    When I'm called for a project such as yours where the house has obviously settled unevenly, one of the first things I"ll do is find out how much and where the house has settled.  Laser levels have made this a simple task and often with only a half dozen moves you will know within a fraction of an inch what the foundation and any unsupported interior walls have done over time. 

    All houses settle after being build, some more than others.  In the best cases the entire foundation and any interior footers settle at the same rate so even if the entire house sinks a number of inches as long as everything is uniform there are no issues.

    What often happens is the main perimeter foundation settles settles faster and to a deeper depth than any footers on the interior of the house, so while a house may be relatively level from one end to the other, it can have a roof sag caused by the center-most load bearing footers and walls that have settled less than the rest of the house (depending on the framing).  In those cases the correct fix is to let the center supports down to match the perimeter.  It's far more common for part of a house to remain relatively level, while an entirre side or end of the house sinks and drops off causing a crack in the foundation.  In those cases all the remedial work is spend raising the low parts.

    My best guess without seeing pictures and actual measurements of what the foundation has done, is that 1/3 of your problem is do to foundation/interior footing issues, 1/3 is from out of whack interior framing that wasn't corrected when you installed the new footer and beam, and 1/3 from poor framing practices when the house was originally built which allowed walls to move out of plumb, supports to give, and things to slip a little here and there.

    I just worked on what I reffer to as the "one nail house."   It was built before pneumatic nail guns by an unexperienced and lazy framer who only used one nail where two are normally seen.  The easiest house I've ever worked on to remodel since it comes apart so easy, but the roof framing has settled twice or three times as much as it should have.  If your roof has missing or impropper rafter ties and other poor framing then correcting that is every bit as important as correcting the sag.

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