I need to replace three 2 x 8 floor joists in my 1916 bungalow. They have been notched, cut and shaved down to less than 2 x 4 and are worthless. I plan on removing them and adding new 2 x 10’s planed down to match the existing size. Once completed, I’ll be adding a small i-beam on posts to take up some of the bounce in the floor.
My question is how best to attach the new floor joists to the subfloor above? The subfloor looks like 1x run at an angle to the joists with oak T&G on top. Can I glue them to the subfloor from below? I came apply continual pressure with a number of jacks and temporary posts that I have, until the glue sets up.
Also, what should I use to shim the joists up tight on the ends? They sit atop CMUs. Someone suggested metal shims, but I am unfamiliar with these.
Replies
Why not just leave the old joists in place, and sister the new ones to them. Glue and nail the new ones to the old ones. Unless you have substantial dry rot or termite damage, this would be easier to do and make a stronger floor.
As for shims, metal ones could be just about any piece of steel the right size. Steel would survive being driven into place a little better, but there's no other advantage. Since you have the equipment to jack the ends up and take the load off while you shove shims in, you can use shims of the same kind of wood as the joists. There's no advantage to having shims stronger than the joists.
-- J.S.
Edited 4/15/2004 8:08 pm ET by JOHN_SPRUNG
You could use Simpson A35 clips to attach the subfloor to the new sistered joists. Use joist hanger nails into the joist and 3/4" #10 round head sheet metal screws into the subfloor.
Glue ISN'T structural...at least, none of the glues you are going to use. It can enhance but not replace mechanical fastening.
Feel free to glue, but you must use a mechanical fastener. Preferrably screws over nails. The Simpson A35 would work, but they're not cheap.
I'd be tempted to use a Kreg pocket hole jig. Anyone have any reason why this would be a bad idea?
Regards,
Tim Ruttan
My father-in-law has a Kreg jig. What kind of spacing would you recommend.
Frenchy's suggestion of toe-screwing without using a Kreg jig was my first thought. Sheetrock screws certainly weren't. However, I suggested Kreg because it would give you perfect control of the depth of screw penetration into the subfloor. Wouldn't want to penetrate the subfloor into the flooring. Okay with hardwood, not so good with linoleum or tile.
David's suggestion that the Kreg screws might split the edge off the joist doesn't seem to me to be a likely problem. The predrilled holes and screws don't have the wedging action that nails have that can cause splitting. You can alternate which side of the joist you drill to further prevent splitting.
As far as a screwing schedule goes, perhaps Piffin can advise. I don't deal with plank subfloors in my neighborhood.
Regards,
Tim Ruttan
Edited 4/17/2004 5:38 pm ET by TRIMBUTCHER
I understand your reluctance to use sheetrock screws, Heck it's not a major issue with me. use whatever screws you wish, I certainly can't claim any loyalty to sheetrock screws, they aren't terribly strong and won't handle much load but the direction of load is in their favor in this instance.
I won't use my Kreg screws in this application because they are very expensive and won't offer any real advantage over simple sheetrock screws.. (in this application..
I would use one screw per plank. plenty enough to avoid squeeking (which is the only thing these screws will ever do)
Is there really a need for toe-screwing here? If the subfloor is securely nailed to the old joists, and you secure the sisters properly to the old joists, then the whole thing is structurally sound. Adhesive as an anti-squeak measure between the subfloor and sisters, and between the old joists and sisters, would be all you'd need. Why risk effing up the finished floor above?
-- J.S.
i'll go along with that!
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And so will I. Thank you all for your advice.
I'd simply sister the new jiost alongside the old and then I'd nail them together well followed by screws(dare I say sheetrock) run in at an angle as if you were gonna toenail.. Sure kreg screws would look nicer but is that important? why not save the time and money and just run some screws in place.
As for the glue idea, My feelings are that unless the old floor was glued (extremely unlikely) you won't gain anything with glueing the new joist in (except maybe a bigger mess) I would put the ends on metal though.. you do not want to conduct the ground moisture up into those beams..
Finally, I don't know that I would go to all the effort to put a 2x10 in.. sure modern 2x8's are smaller but you could easily make up that differance with a strip of plywood or osb on the bottom for nailing purposes
Pocket screws might be a way of fastening to the subfloor, but bear in mind that most pocket screw applications have the drilled hole and the screw parallel to the grain, not perpendicular. The threads are perpendicular to the piece they bite into. A long row of pocket screws down the edge of a joist will probably just split the edge off, either now or later.
Drywall screws are useless in a structural application like sistering joists. They are also pretty much useless for hanging cabinets, which everyone does anyway. They are brittle and have very little shear strength. They are good for hanging drywall. You'll never see an engineered detail connecting framing lumber with drywall screws. The accepted fasteners are good ol' fashioned machine bolts, carriage bolts, or spikes. Glue will help prevent squeaking, so definitely use it against the subfloor.
I think I can disagree here, not that I love sheetrock screws but think about what is trying to be achieved here. there is no real load. All we are trying to do is insure that the subfloor above doesn't move in relation to the new sistered joist (and cause the floor to squeek) the joist is providing the ability to carry the load. Nails are keeping the joist from moving sideways. (because it's sistered alongside the original joist) all the screws will do is provide that last bit of insurance to prevent the subfloor from moving relative to the original sistered joist..
siting right next to the original joist at the very mosy the subfloor has 1 1/2 inch to expand and contract.. In the inpossible event the joist gets wet while the subfloor remains dry (or visa versa) there still is too little wood involvement to provide much risk of a squeek over and above what is already there.
Mind you they did not glue and screw subfloor down at the time the house was built.. What you are attempting to do is bring a vintage floor up to modern code in amybe 1/100ths of the total area involved.. not real practical..
Sorry, Frenchy, misread your original comment. Yes, you could definitely use SR screws from joist to subfloor. In my haste I thought you were saying joist-to-joist. I'd still use deck screws because I think drywall screws break too easy. Maybe that's because I'm so clumsy with my screwguns.
No, it's because SR screws are acheaper grade of meal and not designed for structural applications like this.
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this isn't structural.. it's to prevent movement..
so what causes movement in a floor?
Loads, that's what.
any member subject to loading is structural.
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floor joists that have lasted 90 years are probably strong enough for the loads encountered.. what we are attempting here is to limit the movement of wood relative to other wood in order to eliminate additional squeeks..
(I'm willing to bet there are spots on this floor that squeek already) most likely the close proxiity of a sistered joist won't cause much (if any) additional squeeks. The screws merely ensure that they won't. Kinda a belt and suspender kind of approach..
Well, excuse me for my comment, but I was doing something different than you were, apparantly. See,the first post adressed the idea of replacing them because they are worthless. That means the new ones will be bearing a load. I must have moissed the part where you can have a floor joist that does not handle loads.
stupid me
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Only frenchy would want a cheap snack of sheetrock screws to munch on.
Holy Cow!
Alright, but the next time I'm charging ya.
I'm not a fan of sheetrock screws except where only modest level of strength is called for. Then I like them because they tend to be sharper and dig into wood easier than deck screws do..
I'd go with the sistered 8" stock as well. If you want some extra strength check for full 2" stock at a local saw mill. Probably alot cheaper than kiln dried 2 X10s too. You could lag bolt the old joist to the new or drill and bolt the two of them together. Nails or screws never pull them together like a bolt and ratchet.
Use sub-floor adhesive for fastening the floor to the new joist. A good bead of it squeezed on the underside of the floor before setting the joist should take care of any future sqeeeeks quickly and permanently.
I don't see any advantage of using 2 X10s if you have to knotch them for beams.
My two cents
Gord
Here's a little tip, always remember to predrill for a lag bolt thru the first layer of wood. I drill the size of the shank, ie a 1/2 inch lag bolt gets a half inch hole..
the screw then pulls the second layer of wood tight..
if you don't predrill the first layer any gap you have between boards will remain..
So...predrill for lags in old joist before the new one goes up?
Yes! I wouldn't use anything larger than 3/8ths for floor joists their shear strength is more than enough if you space them properly (about 12 inches on center)
I'd rather use a lot of smaller fasteners than a few large ones. Two reasons,
first redundancy..
If the spot that connects the wood is flawed in any way other fasteners are there to carry the load..
Second,...
You'll get better connection with a number of fasteners than a few.
Now I cheat because I use my air impact wrench and it is but a moments work to run a lag in. if you are going to wrench them in by hand I'd drill a pilot hole once the new joist is sistered in place. Actually a pilot hole is a great idea to use at any time because it makes the fastener hold much better.. If you jam the lag bolt into the wood, the threads and shank need to crush the fibers enough to make room for themselves. Predilling a pilot hole avoids that! use a drill bit about 10% smaller than the root of the lag bolt..
Edited 4/17/2004 11:00 am ET by frenchy