Floor Joists – Best way to strengthen
House built in 1890s
Gable roof 12/12 pitch, 2×4 rafters, 24″ OC, collar ties 3′ from ridge. 1/2″ plywood sheathing on roof with 1 layer of asphalt shingles. 4 foot high knee walls on each side.
Attic floor joist are parrallel to rafters and are 2″ x 6″ nominal at 16″ OC. 3/4″ Tongue and Grove lath boards with routed plaster keys below with plaster ceiling. 1″ think floor boards in attic.
Attic is currently finished to a minimal standard. It is furnished and used as a Family Room, kids play room.
On on side of the attic the 2’6 joist span about 13′. Not much deflection or bounce at all on this side. Other side of attic is about a 12’6 span, except over the center hall where it is a 16′ span (yes, 16′). As you can guess the 16′ span is where we are seeing deflection.
I will probably end up installing a beam ABOVE the floor joist (and behind the knee wall) to make the 16′ span about 9′-10′.
I did a search on breaktime and read as many posts as I could find about strengthing joists including (1) sistering same size joists (2) sistering larger joists (3) adding same size joists between existing (4) adding metal flinch plate between sistered joists (5) adding metal strapping to the bottom of the joist.
I am planning on getting an engineer to devise a solution, however I’m looking for real life experience on which method is the most cost effective. Does anyone have real life experience with this situation in an older house?
Thanks.
Replies
average case scenario is any engineer yiou hire won't have a damn clue. I like hanging the ceiling from the top. I have a similar situation wherein I have an attic wall[48"tall] in the the middle of a 22 span upstairs area. the attic wall defines one side of this space. I built a temporary wall under the down ceiling and shimmsd it up to give it a little crown, I sheathed both sides of that wall w/ plywood after insulating/ wiring etc. payed attention to nailing schedules fr beams! 16 years, still have 1/4 inch crown in living room ceiling. jim
Mike,
There are many ways to stiffen your floor.
But I think you will be happy with the header. Uh, overhead beam.
For a hallway header, (What, a 4' hallway? 6'?), 2 @ 2x10s sistered would work. Run it 1 bay past each side of the hall and be sure the joists under it are blocked 1 bay past it on each side. Run lateral braces from the top of the header to secure points so it won't tip over. Your AHJ will tell you what size header you need to meet code. (The legal minimum.)
Simpson should have the hangers you need.
SamT
I think that you have chosen well (for the most cost effevtive solution). Double 2x4's (sistered on each side of the existing joists) would also be a good solution if there are only a few of the undersized joists to fix but they would still be likely to cost more than the solution that you propose.
You could take the money you would spend with an engineer and spend it on "overkill" with your beam instead; such as, two 2x12s with 3/4 plywood glued-bolted in between as your "overhead beam. If there is any doubt - put another layer on. An engineer charge will buy a lot of wood.
When we did this on one job we used "mobile home strapping" and hooked a strap to each side of each joist (with each strap going over the top of the overhead beam). Then we drove and glued wedges up on top between each strap and the beam to make sure they were tight.
As someone has mentioned you could plane a little crown into the beam too to pre-stress it up.
We don't know how wide this area is that requires re-inforcing, but your lam-in-place beam of 2x12s doesn't sound like overkill at all to me, more like barely sufficient. iof we're shooting in the daark for overkill, use a shotgun - double barreled - instead of a .22 plinker! Shoot up a doubled 18" LVL with steel flitch 1/2" thick, LOLWhich is to point out why he does need an engineer.My engineer will write up a statement that the beam can be option A, B, or C and leave me to determine which is more appropriate for the budget and crew size and skills.
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Thanks guys,According to the span table I have the 2x6 joists should be OK over a 9' span, which is what I will end up with after installing new beams. Especially considering the joists are 6" not 5-1/2".The size of the beams does not matter as they will be behind the knee walls and will not be seen. So I'm looking for the most cost effective solution, rather than the strongest beam per inch.If I put new beams in they will rest on the exterior walls at the front and back of the house, and also on some interior walls that run parallel to the floor joists (non load bearing). These interior walls are stacked above walls on the first floor, but likely I will have to add some support under them in the basement. This is the part I'm the most concerned about. I'd hate to transfer the load down to the first floor joists and have them sag.As I said I will get help from an engineer, but sometimes it helps to lead the horse to water....
I caught the cost-effective part, butthat will depend on some other things you still haven't said, like how long the beam will be, and whether you work for free or are hiring professionals. Some work uses less exopensive materials, but more labor. Some solutions could span the whole distance without loading those currently non bearing walls, but be more dificult or expensive to insert, spatially.genericly though, normal solid lumber will be the cheaper material.
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Thanks Piffin,Engineers do have their place, you're right. Plus the thing you mentioned "I don't know how wide the span is that needs reinforcing" is a good point too. We haven't got the reality of the situation before us - I was offering an overkill example in some situations, underkill in others. Obviously we can imagine either.
Any lumber yard will have span tables showing how much of what kind of lumber is needed to span your situation. Even your short spans are quite a ways for 2x6s!
When we fix situations such as yours sistering additional 2x6s poses some problems. Over time there is no doubt that all your 2x6s have sagged a bit. So when they are jacked up a bit to align with the new 2x6s we have essentially taken 100% of the load off the old joists and transferred it to the new--until they sag and transfer some of the load to the old joists. Until the new joists sag they are essentially overspanned and a dipped floor is certain.
I would assume the original 2x6s are good for holding up the ceiling and that's about it. Plan the floor with enough beef to support any loads independently of the original framing. A few TJIs will span your longest section without messing with an additional beam if you go up to a 2x8 floor and the new 2x8s sistered to the old 2x6s will beef up the shorter spans and make for a nice flat surface to deck.
Happy holidays,
Don