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Need help for flexing floor joists

8 years ago

My 40 yr old house has flexing /sagged floor joists. Joists are gauged 2 x 12 spanning 19 feet set at 16 inch centres. They are above a car garage so I can't install additional supports. They are pine softwood so not much integral strength and have sagged up to 1 inch in the centre in places. Any ideas appreciated

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Comments (6)

millworkman
8 years ago
How long have they been sagging? Is this new or gradually gotten worse over the years? You may want to think of getting a structural engineer in to look at your house if recent. Almost impossible for someone to offer much in the way of ideas from the internet.
PRO
By Any Design Ltd.
8 years ago
last modified: 8 years ago
Two years back we did a barrier free shower in a Historical Home here in Vancouver. The floor joists where 2"x10" full dimension Fir. I needed to cut back 3" for my floor prep and the engineer would not let me. The span If I remember right was close to 18'.

The fix there was sistering all the old joists with 8" LVL's (I was not allowed to install 7"). These can be ordered in 20' easy.

Are you building a room above?

Is there blocking courses in place?
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Thanks for all the tips. Finished the job today. For anyone else who may need to do this, this is how I did it. I cut off the rotted part and cleaned off the old board with tor-bor and let it dry. I used an 8x14 (cut to size) and sistered it to the old board with 8 x 1/2" bolts, construction adhesive and nails. Key was to jack up the new board at the end nearest the center beam so it would fit tight against the sub floor and even with the old joist. I would have preferred to run the new joist across the center beam but getting it on the beam was too much work as it was not an easy fit.
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It appears that the joist has settled somewhat due to the decay. It's not possible to know the extent or effect of the decay, so your safest bet is to sister the joist the full length from plate to girder. Something else might work fine--including doing nothing, but I can tell you from recent experience, if you're planning to sell the home at some point, a home inspector won't likely accept anything other than a full length sistering or a structural engineer's report that an alternative is equivalent.
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"Are you saying you would jack up one inch in one day?" Yes. "For flitch plate, would you only put on one side of each joist?" Yes. "I'm guessing these plates must be custom made?" Only in the sense that you have to have them cut to length.
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PRO
Sombreuil
8 years ago
Sister them with structural-grade fir 2x12's and it will be exactly twice as stiff as it is now. Perhaps even stiffer.
Casey
ionized_gw
8 years ago
There are many ways to reverse the sag. Sistering seems to be the most common. I believe that there was an extensive thread t in one specific forum on Gardenweb in the last few years. Mentioned was a method that involved using metal reinforcement straps along the bottom of each joist. It is a technically more challenging means, IIRC.
PRO
Joseph Corlett, LLC
8 years ago
Dave McIvor:

What is the reason the sag concerns you? Are you planning a new tile floor? If not, I wouldn't worry about the sag.
PRO
Precision Carpentry
8 years ago
I have done this several times.We use a temporary beam and shims to jack and level the old joists and then sister them with new joists connected with some PL Premium adhesive and nails.While jacking the beam make sure to have somebody upstairs keeping an eye on things to make sure nothing is going wrong there.If taking out an inch I would jack it a little over a couple days to allow the old joist to settle in.I don't think I'd try to take an inch out all at once.

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