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Bad Connections - Sistering balcony joist with no back span?

Bad Connections - Sistering balcony joist with no back span?

(OP)
I have been creating assessment reports for exterior balconies here in California. I see a lot of floor joist cantilevered to create balconies. The problem is the framing is Douglas-Fir (not pressure treated or decay resistant). Over time the cantilevered portion of joist decays and the owners hire contractors to create a fix. The repair I see over and over is sistering new pressure treated joist onto the existing decayed joist, but without a back span(no one wants to tear into the interior to run the sistered joist back). I have most recently seen a "reputable large contractor" cut the DF joist back and use screws and or lag bolts to attach a ledger into the end grain of the existing joist (the far exterior end is then supported with a beam and posts). These both seem like really bad connections. The sistering fix must resist the bending moment through the screws ( I've yet to see some supporting calcs when there is an engineer involved) and the ledger fix relies on the exposed end grain of non decay resistant wood. I think the code requires a reduction of (Ceg=0.67) to take into account for the end grain connection being weaker...but still, even if it does calc out now, shouldn't we be concerned that this design relies on the end grain of existing non-decay resisting joist? We have a lot of fog in our area and the moisture in the air often wicks into the end grain and results in decay. Despite my concerns the contractor is continuing to build this way with cost as a justification and has seemed to have found an engineer to sign off on these type of fixes. Does anyone have any experience with these types of connections or know of any resources that may shed some more light on this issue? The NDS and my timber manuals don't seem to address these type of connections....I suspect because they are no good.

I've attached some pictures for clarification. http://gillypepper.smugmug.com/Bad-Connections/

Thanks in advance for any input. I've enjoyed this site for many years!

RE: Bad Connections - Sistering balcony joist with no back span?

Hmmmn. Put a row of 4x4's vertical up against the stucco wall under the new PT header down to a foundation in the dirt below?

And "obviously" this is "not" in any of those California earthquake zones of course......

RE: Bad Connections - Sistering balcony joist with no back span?

I haven't seen that detail used, but I sure as hell wouldn't sign off on it.
If they want to cut off the backspan they need to drop a couple of posts at the end.
Or provide knee braces to the stud wall.
I think it's pretty rare feat to be able to accomplish a moment connection in wood.
Screwing into the end grain with a ledger sure isn't one of them.

RE: Bad Connections - Sistering balcony joist with no back span?

I agree they both seem to be poor connections. I would not sign them.

Garth Dreger PE - AZ Phoenix area
As EOR's we should take the responsibility to design our structures to support the components we allow in our design per that industry standards.

RE: Bad Connections - Sistering balcony joist with no back span?

As long as the 0.67 end grain reduction is taken AND the end grain is solid with no decay AND there is post/beam supporting the outer end AND the p.t. ledger that is attached with screws to the end grain is flashed well enough it should work no problem. I have done a very similar repair a few times and it worked great.

RE: Bad Connections - Sistering balcony joist with no back span?

I like a 5/16"x5-1/8" GRK washer head screw for the connection. Gets 3-1/2" embed with good strength. I up my F.S. a bit to further account for end grain weakness. (3) of those screws in a HF p.t. Ledger will get around 450 lb allowable shear in total, which will work more than fine for an 8' deck joist span, which is most likely more than most cant decks would have been originally.

RE: Bad Connections - Sistering balcony joist with no back span?

I see no issue with the detail so long as it is subject to full calculation and, obviously, is no longer a cantilever.

RE: Bad Connections - Sistering balcony joist with no back span?

(OP)
The weak link is the end grain of the existing cantilevered floor joist (non-decay resisting). I can't help but thinking the end grain will decay since it is exposed to a high moisture exterior.
Thanks for all your comments.

RE: Bad Connections - Sistering balcony joist with no back span?

Then require that it be protected... There are a number of appropriate products, mostly epoxy based.

RE: Bad Connections - Sistering balcony joist with no back span?

It seems like a quick fix and does not address the decay issue that caused the original balconies to fail.

I have never seen a fix where they screw into the end grain of the existing joists. I think key (may I call you key?) had some good points and it can be validated, but it does make some of us cringe.

RE: Bad Connections - Sistering balcony joist with no back span?

NO!

RE: Bad Connections - Sistering balcony joist with no back span?

Scarey

RE: Bad Connections - Sistering balcony joist with no back span?

Hey Ron, Triangled: How about some constructive reason, or discussion, as to why you would not allow this detail?

If the wood you are screwing into is sound (ie: Not at all deteriorated), and the new detail is NO LONGER A CANTILEVER, what is wrong with this detail?

No does not work. Unless Scarey is the last name of another Scarry, I'm not sure what this has to do with this discussion.

RE: Bad Connections - Sistering balcony joist with no back span?

Point Made and Taken CEL!
Thank you!

RE: Bad Connections - Sistering balcony joist with no back span?

Not sure if I am understanding the photos and the OP completely but,
1. Balconies are of course notorious, at least in my considerations, as requiring super care, because by their nature people may accumulate in mass unexpectedly, such as to watch a fire-engine go by, to see a spectacular sunset or or or... 60 psf is a good start, but I like to be even more conservative than that, and that goes for the handrails too.
2. The OP seems to be indicating two observed "solutions". The first "solution" being a system that retains the cantilever and but sisters good wood to the bad at the cantilever only with no new backspan. This absolutely does not work. The new wood provides zero additional negative moment strength at the face of the wall, the commencement of the cantilever....if i am understanding the system correctly.
3. The second "solution" attaches a ledger by means of end grain fasteners and to add post and beams at the tip of the formerly cantilevered balcony. I don't think this is good either, for many of the reasons shared above, and perhaps more, including the lack of a positive lateral connection perpendicular to the wall, parallel to the joists connecting the balcony to the structure.
4. I'd consider either a) attaching the ledger to the cut joist with an upside down hanger with a lateral strap top and bottom from existing joist to new joist, or b), cutting the joists back flush with face of wall and attaching new ledger by lagging it into the existing blocking between the joists.

RE: Bad Connections - Sistering balcony joist with no back span?

Nice; I do like your point four... Definitely would improve the detail a great deal.

RE: Bad Connections - Sistering balcony joist with no back span?


There are many Engineering Handbooks about load capability of nails and lag boltd driven parallel to the wood grain at the end of lumber but I have not seen anything about the load capability when wood blocks are used such as is your case. Before you sign off, find out what type of a load the owner intends to have on the deck. If he says I'll be having parties of over 10 guests with tables, chairs, music and dancing, yeah, I would be concerned even if the calculations prove the system satisfactory. If the deck is not to be used for anything then OK as long as the numbers say it's OK. Racookpe1978 has the right idea about installing 4X4's or I would say, bolt to the wall, supports under the sister beam.

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