24 inch oc engineered lumber floor joist

The home is a 3 story with pored walls for half of basement; 2/5 of the floor system is 16 oc the other 3/5 is 24oc. There is a small deck attached (8x10) to the engineered lumber that is 16 oc with blocks of wood with lag bolts through them. Is that ok? And I thought that if the home was 3 stories that it had to be 16 oc for engineered lumber, this is 24 oc and they have had to have the bathrooms on the top floor leveled out. Any help, I have told the owner that he would need to have a structure engineer come out or have the builder show him the bluebrints that were approved.

Are you inspecting for the owner?

Good Call!

Yes, it is an 11 month inspection.

I would charge an additional fee and do the research for my client. This investigation would include a permit search, interview with the building inspector and consultation with the MFG. of the I joists. Other research possibilities include the builder and local lumber yards that supply MFG. lumber.

You don’t need a structural engineer to determine if they were installed to the specs.

As far as the deck ledger board, it does not look correct in your pictures. I don’t see any strength in the blocking that was installed. Do you have any exterior pictures.

I-joist systems have been around for over 40 years, since the 90’s about 50% of homes use them… I use them about 90% of the time myself…they are excellent however there are issues, such as yours, which have to be accounted for.

With a conventional band or header joist the load is directly transferred to the wall…in this case they are using vertical 2x4 blocking attached to the top and bottom chord of the I-joist which then transfers it back to the wall on down to the foundation.

The problem I see is the transfer of load…, I suspect an engineer would want the blocking fully in contact with the wall so that you not just relying on toe nailing itself and additional ties to the blocking that would account for other forces exerted upon the blocking.

While I applaud Russell’s business model to make $$$ on additional consultation, you do need an SE or an SE stamped set of plans that show this configuration is acceptable… based upon 30 + years of building including using I joist for over 20 yrs, I dont think you are going to find any documentation that shows this configuration is acceptable…this looks like it was done by a “resourceful” carpenter. The client would be better served by paying $200 for an SE to come out and say Yea or Nay.

I have used TJI’s probably more than any Ijoist product…BSI’s are excellent too…you can go here (free of charge ) to see how they allow deck attachments, see page 5.
Remember that each I-joist manufacturer have their own installation requirements.



I think you made a good catch.

You need the identification markings from the TJI or similar manufacturer in order to make a determination.( Example TJI 110, 210, 230, 360, and 560 )

24 on center is an option for some joists but the spans are reduced.
Check the type of joist with appropriate span table.

Thanks for all the help.

Did you use a measuring tape on the wider span joists? Some are placed on 19 1/4", and have mislead me before.
Quick thought, it may be designed for a 19 1/4", and partially installed on 16", then realizing that they didn’t have enough joists, spaced the rest at 24".

Just a thought, for future reference,at the drywall stage,make sure they use 5/8 type drywall, or CD board if available in your region,I have seen lots of 24 inch TJI,especially in the lower levels,basements etc,at times ,the drywall contractor will try to pass off regular 1/2 inch for lower levels,its usually how the estimate ,will sag greatly,my personal preference for lower ceilings on 24 inch center TJI, is resilient channel on 16 inch centers with 1/2 inch drywall,of course this depends on where you are,I have contracted homes in areas which required all 5/8,just a thought, Journeyman Drywaller/ISM/HI

I realize I’m splitting hair here but i think it is worth noting that 1/2" board can be used on ceilings that are framed at 24"o.c. providing, that it is installed perpendicular to the framing, that it does not have a water based texture applied, and that it is not supporting thermal (blown-In) insulation. Of course 99.95% of the homes in my area do have a water based texture. Some builders will use hi-hat at 16" o.c. while most use 5/8" board attached directly to the ceiling framing members. The reference I’m citing here is Gypsum Manufacturer’s Association Specification Manual Ga-216-2007

All true,I am in Alberta Canada,texture is the norm,say painted ceiling and the taper cringes.for me ,for quality I push CD board,even on 16 inch centers,much nicer job for texture or level 4 finish for paint.

There are two issues here, but the main one is the span of the sub-flooring which looks to be OSB and so would have to be close to 3/4" thick T&G to span 24" O.C.

The 2x4 are squash blocks designed to transfer the load from above… a common scenario. What will meet engineering specs and what’s comfortable to walk on (bounciness) are sometimes two different things. It looks over-spanned according to good practice but the engineer will have the final say.



How can you tell the span from what is pictured?

I can’t… When I say over-spanned I mean joists with too great a distance from center to center. Nothing to do with the distance each joist is spanning.

That’s how the term is used in CA and CO which is where I worked as a carpenter.

24 on center is acceptable dependent upon the type of joist used.
Not having the information as to which joist is present, one can not say the installation is improper.