If you have oak up there I would be thinking about a way to display it and not put up a ceiling . I cant imagine the oak beams you described not being strong enough for the job. They have worked for 100 years they will be doing the job in 100 more. Don't even think about nails.
Jimmie
lol. oh they do the job, they're just bouncy. too much span for 7-1/2" of wood. And after 6 years, we're tired of looking at them.
thanks for the reply.
I built my shed using mixed hardwood 2X4 rough lumber from sheet-metal skids - and I had to drill for virtually EVERY SPIKE.
15.5 feet. That's crazy.
I did some beefing up. I first jack each joist, then add stiffening. I hand nailed, and bolted, and screwed. Did not PL Premium. Good thing to do. My first floor joists are 2x10 12 foot long. I found stiffening works with only a 5/8 inch sheathing cut from 4x8 sheet. I was not really worried about stiffening, mostly trying to get rid of the sag. Best done over a long time period with the jacks. I didn't need to go from end to end on the joists, just middle.
When I hand nailed, I first drilled holes. Also with bolts. I had to try and pull together warped boards. Nailing is otherwise sufficient, but add glue. Check above joists. You may need some shims.
Greg
When I paid a structural engineer to confirm what I already suspected was true, he advised, 16D CC nails 16" OC, 3 in a vertical row and 2 in the middle of the OC repeated on the other side in an alternating pattern. This was BNG (before nail guns) and I drove every one of those suckers by hand. In oak I would pre-drill with a 1/8" bit because of splitting hazard.
Adhesive is great, lots of contact area to spread the load. But adhesive can be really messy and two rows of SDS screws is plenty of shear transfer.
t4-
Nails are very good for shear transfer (no slop in holes like bolts) but that 100 year old oak may not accept them readily.
Depending on the sister joist geometry, the SDS screws may or may not need to take much shear load. It all depends on the load path. If the sister joists bear up against the floor sheathing and the sister joists bear against the ledger (with or without blocks), then the screws will carry very little shear.
If the sister joists only bear on the ledger & not against the floor sheathing, the SDS screws will wind up taking load out of the original joist and into the sister joist.
Getting the sister joist to bear cleanly & continuously against the floor sheathing will be difficult. The SDS screws (or adhesive) will do the important job of getting the old & new joist to work as two springs in parallel.
Lateral support of the new joist is a secondary task for the screws, composite action is the primary.
cheers Bob
cheers Bob
Bolts require a hole tat least as large as the bolt shank, this makes a sloppy fit. Lags (SDS) screws need a pilot hole (screw root diameter or smaller), makes for excellent shear transfer..... no slop.
cheers Bob
Joe's suggested fix is a very good one.
I "top" sistered my living room ceiling / attic floor joists, orignally full sized 2x4's that I "glued into" 2x8's using a slow cure epoxy paste (Sikadur 35?). I just mushed them together and let them cure, no clamping. I tested a trial sample and the "glued up" 2x8 failed at a bottom chord knot before the glue budged.
The Sikadur 35 is a heavy paste that allows a bond line as thick as
1/8".cheers Bob
I doubt even a "good" nail gun (NR83) will do the job but a palm nailer will.
Steve's situation is an issue of stiffness not strength. Too much bounce means he needs to add stiffness and that relates mostly to joist depth.
Per the joist calculator mentioned recently in another thread, a 15' span needs a 2x10 of decent timber or a 2x12 of lesser material.
If my calcs are correct, Steve's original joists sistered with new
2x8's will be stiffer than a 2x10 by 13% but t only be 55% as stiff as a 2x12.cheers Bob
Steve-
"too much span for 7-1/2" of wood"
totally true.......
Depending on how much bounce you want to remove, you might consider using an engineered wood product.
snipped-for-privacy@f1g2000yqi.googlegroups.com:
Engineered timber is a possibility depending on what Steve wants to do.
The bottom line is, 2x8's are not deep enough...... 2x10's would be better.
cheers Bob
How can you measure stiffness without testing the plank? Do you use an accepted norm? This stuff is beyond me, except I can see how glue would work well with sisters. I always clamp glue, but never used epoxy.
I use a lot of drywall screws and lag bolts to slap stuff together. My brother was a general and I listen to him for some things. He told me once that 2 nails can be better than 6 screws for resisting shear in some circumstances. Don't remember what we were talking about, maybe roof hurricane tie-downs.
--Vic
Of course stiffness can be determined by testing but stiffness can also be calc's based on the joist geometry & material. Especially in Steve's situation where he's interested in boosting stiffness.
An idea of the existing stiffness can be calc'd as well as for the proposed sister. Added 50% might help, adding 100% or more would be better. WIthout an idea of where his floor is compared to "idea" he might be over killing or way under shooting.
Take a look at this joist calculator. You can "play" with the joist size, timber species & timber grade and see how the allowable span changes.
" He told me once that 2 nails can be better than 6 screws for resisting shear in some circumstances."
that's a pretty general statement, I know for a fact that a single
1/4" SDS will take the place of a handful of nails. His statement tends to be more correct for small screws but IMO screws (SS) are better in a lot of locations (exterior exposure & esp open patio covers) since over time they will not rust and encourage rot or lose strength. Galvanized timber connector nails will last a long time, SS ones even longer but #10 SS screws in the same application will last a long time plus provide better withdrawl resistance.I know nails are shear fasteners and better than screws in shear but over the years I've seen those shorty connector nails rust out / rot out in patio covers to the point that I changed my tune.....
what good is a screw that's rust away & help rot out the wood? IMO better to drill out the hanger nail hole and use a larger dia SS screw (larger root diameter) than stick with nails that I know will cause the failure of the entire system.
I always clamp (or screw) when using traditional glues. When I top sistered my ceiling joists there was no easy way to clamp so I used epoxy paste that was forgiving of joint gaps. I pretested a sample made with rough timber, dirty just brushed off. The sample failed at 175 psi shear when a knot in the bottom member failed.
Based on my crappy sample, I knew that my sistered joists would perform better since I wire brushed both faces of the glue joint and none of the bottom chord members had large flaws. Plus, based on my calcs, my shear demand was WAY lower than 175 psi more like less than
50 psicheers Bob
That's handy. Reason I asked is I put 2 extra ceiling joists in my garage when I bought this place. How it was built didn't seem right. 6' centers in some places. Probably built in 1959. Those joists are 21' 2x6 and from what I can figure basically just tie the top sills together and square. Good place to hang lights and the door opener too.
Anyway, I've seen too many garages fall out of square. Besides that I wanted to put plywood up there as a storage platform. When I ordered the joists from HD I said pine, because I thought that's what the old ones were. They said they only had Douglas fir that long, so that's what I got. Precut the angles, jigsawed a hole in the fascia, and slid them onto the plates. Nailed them in. Patched the fascia hole. A couple years later I put up alum gutters, soffit/fascia.
Put a few 4x8 x1/2 plywood up there and started storing stuff, nothing real heavy. Boxes of Christmas decorations and the like. Garden tools in the winter, snow shovels in the summer, etc. Then I told my kid to get rid of the 4 tires he was keeping in there because the alloy rims were "special," or put them up on the platform. I was tired of them getting in my way. He did that. 2 stacks of 2, alongside each other. A couple years later I was chatting with my 80-year-old neighbor in the garage and he pointed out one of my new joists was sagging. He's retired building trades and has the eye for it, but when he pointed it out I saw it. Tires came down and it sprung back up. 6" won't take much load over 21'. I learned that quick. But I'm still tripping over or moving those tires.
I started using them to put together 8' workbenches at least 30 years and they're good for that. You can knock them down if you have to, though I never did any of 6 or so I built. No real load on the screws. Solid as the day they were built,
Fasteners are a science in themselves. I wouldn't do anything structural without expert advice on fasteners.
You did your homework.
--Vic
Bob, just wondering your if your calcs take into account the existing wood is 100+ year old oak.Usually these timbers were made from heartwood. It is surprising to me it is not rigid enough already. I would look to see if it is in fact the joist that are giving when he walks on them and how they are giving. The problem could be that the flooring is not strong enough to properly distribute the weight from joist to joist. Lack of a proper subfloor could cause this which is a common condition in old homes. Just something else to think about.
Jimmie
oh, believe me, when you walk across the west one third of the room and the china hutch on the east wall jingles, it's the joists moving. And no 7.5" of wood of any vintage or species is good for a 15.5' span. I redid the lower level with 2x10's and put a support beam down the center of THAT span. Of course it wasn't a problem to do, since the joists are only 8" off the dirt!
Vic, those "joists" you describe from the 1959 garage are not joists. They were not designed or installed to resist bending loads. They are "tension ties" to resist the spreading force generated by the roof. To span 21' as a joist you would need at least a 2x10.
I stand by my comments on drywall screws. They are easily the most mis-used fastener in America. They are not the appropriate fastener for anything other than drywall. Hacks use them to hang kitchen cabinets.
cheers Bob
:
Jimmie-
The wood is not the problem. The joist depth & span are the issues. Steve made no mention of the subfloor construction and, yes, the subfloor construction can influence overall floor behavior but it's pretty much a secondary effect.
Steve could "box out" his wimpy joists with a lots of blocking, lots of glue and a structural skin on the bottom surface of the joists to create composite action floor. This would increase the floor stiff and get adjacent joists to share load. It would be a LOT of work and still probably not work as well as sistering especially if Steve used deeper sisters.
A number of year ago I worked on a floor vibration problem. It involved a kitchen and living space over a 25' garage. Unfortunately, the joists were spec'd as 12" floor trusses. They skimped on the depth to stay within a city overall building height limitation. The condos were three story.
The 12" floor trusses were too flexible, should have been at least
14". A real PITA to fix.cheers Bob
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.