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Thread: TJI framing
03-16-2009, 06:49 PM #1
I just noticed that an out of town tract builder here uses TJIs for the floor framing but does not use any solid outer banding. Just 2x4s 16" oc on the flat with 1/2 OSB sheathing. Passed code, but I'm a little concerned. Any comments?
03-16-2009, 07:53 PM #2
03-16-2009, 07:56 PM #3
Re: TJI framing
I dunno, did you make any comments?
This one keeps going around the block. As near as I can figure, the engineered rim joist is required because the exterior wall and roof loads are bearing on the ends of the TJI (or whatever other brand) members that might fold or squash. However, on a related note, I rarely see web stiffeners or squash blocks at mid-span points and I have never gotten a good response as to when or where I should. I understand that TJIs cannot support the weight from a roof and second story, and (as home inspectors) we might not be able to discern which interior walls are load bearing and which are not. I would figure that I would at least see squash blocks or web stiffeners at mid-span foundation walls, if not mid-span girders. I make suitable remarks and note that I am not an engineer. I refer them back to the original building plans or to a structural engineer.
Hope this helps.
Department of Redundancy Department
03-16-2009, 10:42 PM #4
Re: TJI framing
Sorry if this drifts a bit....
I had occasion to do Pest/Dry Rot inspection on 10 apartment buildings last month that were 90's construction that was all OSB truss joist built.
Overall, I went away feeling like the building was much less durable than one with T/G decking or real joists and plywood. The OSB just doesn't hold up as well to water problems. And, of course, there's nothing like an apartment building to test the limits of any design. Undetected leaks and other water problems sure take a bigger toll on this style of construction than on the more traditional framing. I went away feeling like I had just inspected 10 big RVs.
I've never been a big fan of OSB. The siding is junk and the framing is not far behind....IMO, anyway.
03-27-2009, 12:42 AM #5
Re: TJI framing
OSB is comparable to plywood. Neither is ideal for high moisture conditions, but OSB has more glue than plywood and is pressed under greater pressure. It's actually said by some to perform slightly better in moist conditions than plywood. One common misconception about plywood is that in "CDX" the "X" means exterior. It's actually "eXposure" as in it can take a little moisture for a little while. For extended moistre you need marine plywood...but no wood product is going to stand up to prolonged exposure to moisture.
Also OSB is different from the old waferboard. Back in the early 90's I don't really remember anyone using the term "OSB" at all. They started making it in the 80's from my understanding, but I don't think it caught on for structural use until the mid 90's. OSB has also gotten better over the years with better adhesives and better quality control.
Of course the reason they use OSB over plywood is the fact that it is that it has similar structural design properties, but costs almost half the price. This is partially becasue it is in some respects a more environentally freindly product. Plywood veneers require large older growth forests to harvest the trunks needed to peel the veneers. OSB is made from chips that can include the branches and practically the whole tree and they can use faster growing species that are often considered unsuitable for dimensioned lumber.
03-27-2009, 07:53 AM #6
Re: TJI framing
I've always been told, even at APA seminars, that the 'X' was for "exterior glue", not "exterior" or "exposure". In addition to the 'X' for exterior water-proof glue there are different exposure categories: Exterior, Exposure 1, Exposure 2 or IMG, and Interior, all based on the glue used and the glue bond resistance to moisture.
"Exterior" plywood CAN be permanently exposed to the weather, but CDX is not "Exterior" exposure. CDX will either be Exposure 1 (most likely) or Exposure 2.
Most requirements for building construction required Exposure 1, which may be exposed to the weather for temporary duration during construction, with the exposed duration time not being specified but often stated as 'days or weeks' rather than 'months or years'.
Exposure 2 or IMG and is designed to be installed in protected areas which are not continuously exposed to high humidity.
There there is Interior Exposure for plywood which is permanently protected by being inside buildings.
I am sure it gets much more in depth than that, but that is a good brief description.