i will be sistering up floor joists this weekend in my old house by adding 2x8s to the existing joists. Got the first few joists jacked up level and I am ready to have at it. I’ve got 18 joists to sister up. My questions is how should these be attached?
Should I screw, nail, lag bolt or use adhesive, or some combo of these?
A neighbor sistered up a few in his basement and used drywall screws, but I thought screws had just about zero shear strength?
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Replies
If they are sagging badly...cut an extra half or 3/4" of crown into them...I'd just use a framing nail gun... (more shear strength anyhow).
Jack...clamp in place while you nail...PL adhesive between might help reduce squeeks.
L
GardenStructure.com~Build for the Art of it!
Use carriage bolts. Tighten them good. Better than nails, nails will squeak. My carpenter sistered with lag screws and glue. As the wood dried, the sisters separated from the original joists. Tightened them up again with bolts. Glue may still reduce squeaks, but little shear strength.
On size, I used 3/8" bolts but am wondering if I should have used 1/2" bolts....I'd welcome opinions on that....
DW screws? You're joking, right?
"DW screws? You're joking, right?"That's kinda what I thought when my neighbor said it. But I'm just an HO, so I thought perhaps his carpentar knew something I didn't. I'm on my way out to buy some carriage bolts.Let the fun begin!
Rather than carriage bolts I'd use hex head bolts so fender washers could be used on both sides of the joists. This way you can really snug things up without burying the head into the joist.
Taylor-
Was wondering what kind of pattern you used with the carriage bolts?
Staggered the bolts around the center of the joists, should have mentioned that. My carpenter relied on 3 lag screws for 5' joists, I replaced with 5 carriage bolts, but he made so many other mistakes I don't trust anything he did. I'm considering upgrading to 1/2" bolts (with glue to hold them in), hence my own question about bolt size. Just don't wanna oversize the holes. I've also used 10d nails in various places when nailing in various connectors to hold these things together. I know it'll make the floor squeak, right now my priority is preventing total collapse.I don't have much faith in glue, having seen the glued sisters peel away as they dried. It didn't help that the carpenter drilled 3/8" holes for 3/8" lag screws....
I just had a structural engineer look at some joist problems (old notch in fioor joist by plumber and notches I had to make for downdraft vent). He had me sister lvls with 16d nails. I said I would also use construction adhesive and he said it would help with shear. He doesn't include glue in his calculations because there are too many "variables" like how much glue I use, whether wood is clean, etc..
Btw in my case I had to extend sister 2'6" past notch one side with 16d spaced 6" and staggered. The other side could only extend 1' so he called for 3" nail spacing.Smile. It could be worse. You could be me working for you.
I guess you're aware of restrictions on notching LVLs, which are pretty tight. Reason I didn't go that route. Sawn lumber is supposed to be more forgiving of bad boy behavior, at least I'm banking on it (I was the good boy).One other word of wisdom: predrilling can reduce the possibility of splitting the wood. Simpson says don't make the hole more than 75% of nail diameter. I found this out after predrilling 85% holes on the advice of a web site. Hey it was all Mr Google could find on the topic, and I am dealing with 75-year-old lumber. Someone should write this stuff down. Breaktime FAQ for well-meaning amateurs?Edit: Yeah the restrictions on notching LVLs are tight alright. You can't notch them! Doh!
Edited 3/26/2005 1:16 pm ET by Taylor
You touched on a few good points, Taylor.
As far as I could understand Mikey said his engineer advised him to sister LVL's to existing notched joists, he didn't have notched LVL's.
If his engineer specified 16d every 6" so your 3/8 carriage bolts every foot sound more than plenty. 1/2 would be overkill IMHO. Hey if Pino's neighbor could use DW screws, anything is better.
Re predrilling. Depends on the species and hardness of the wood, size of the predrilled hole should vary, harder the wood larger the %. I don't know if there is any studies regarding recommendation on predrilled hole sizes for different applications. When I do it it's mainly a WAG. May be you have a better idea.
As I'm sure you know, the rule of thumb for predrilling for screws seems to be 75% for soft wood and 85% for hard wood. Beyond that and you start losing holding power. Perhaps it's similar for nails; I guess it certainly shouldn't be more. In my case, I was scared of splitting my 75-year-old joists. The old wood is a lot denser than even KD modern stuff. I guess the price I pay is a squeaky floor. I may try dabbing some glue in there before the floor goes down. Maybe.Thanks for the reassurance on bolt size, I've been wondering.
Just a follow-up on shear strength: Browse the fastenmaster.com web site and look at technical info for ledger lok screws and they will give a comparison of shear strengths for nails and lag screws. For DF:
16d nail: 131 lbs
5/16" lag screw: 130 lbs
1/2" lag screw: 190 lbs
fastenmaster ledger fastener: 214 lbs
Simpson 1/4" wood screw: 200 lbs (if I remember right)
Assuming carriage bolts have same shear strength as lag screws of similar diameter, I think I'll upgrade to 1/2" bolts.
http://www.fastenmaster.com/pdf/LedgerLok%20SS.pdf
I still don't understand how the Fastenmaster 1/4" Timberlok screws have an "average ultimate single shear value" of almost 3000 lbs. How do I compare this with the above ratings?
In reply to my own question on interpreting shear strength, I thought people might be interested in this reply from Fastenmaster:"The 2995 average ultimate shear value only speaks to the metal strength of the fastener. Fastener shear strength is commonly used as a comparative number between fasteners, and does not usually get used to design a connection. Obviously once this fastener is placed into a wood-to-wood fixture, the wood becomes the weak link. Depending on wood species, moisture content, and safety factors, the actual design value is much lower.
"The new ICC Evaluation Report (ESR-1078) on the TimberLok and LedgerLok fasteners combines all of these factors into one report. After thousands of tests on various wood species and moisture contents, design load tables have been compiled to address most conditions. Go to: http://www.icc-es.org/reports/pdf_files/ICC-ES/1078.pdf"
Edited 4/2/2005 7:42 am ET by Taylor
If I was going to do a lot of them I'd cut 1/2" threaded rod and put fender washers and nuts on each side. http://www.farmtek.com sell threaded rod pretty cheap. They have 3/8" threaded rod in the electric aisle at your local big box.
Bolts that go all the way through are much stronger than nails or screws. Fourteen hundred pound cows break 2x4s like match sticks. Since you are backfilling the holes with steel you are not weaking the wood that much. Half inch really is not that big of a hole in a joist.