I am adding an addition to my 1939 Colonial which has a crawl space, 2 1/4" oak floors (running front to back) on a joist system with diagonal 1x6 (I think) subfloor.

The new addition is designed to have a crawl space with 16" engineered floor joists 24" OC and 24' in length (there is no support pilings). They were designed to sit on top of a stemwall but might be shortened a bit to hang on the inside of the stemwall (the stemwall would then be raised 16" to do this). Why? This is another story but simply put to avoid a grading issue towards the house. The joists will run front to back.

I am concerned with the type of subfloor since I have seen different recommendations and want to use 2 1/4 oak to match the original. Georgia Pacifics Plytanium Sturdi Floor subfloor says 7/8" is ok for 24" OC.

What do people think about this set-up?

Thanks in advance

While it meets many local building codes, I do not like spanning 3/4" plywood 24" oc. It will sag, trust me. If your plans are set for 24" oc on the truss spacing, you will need to add another layer of plywood to stiffen it up. 3/8" minimun, I would think. BTW, I haven't seen Sturdi-Floor in a 7/8" thickness. Only 3/4" and 1&1/8".

Thanks for your response. Here is the link to GP's web site

http://www.gp.com/build/product.aspx?pn ... erarchy=pc

It shows a 7/8 but is that really 3/4? I am not a carpenter so never really understand when a quoted size is really the quoted size.

I am bringing a new engineer to tweak the plans and will discuss going to 19.2 OC or 16 OC.

Well, I have finally started the addition and am using the 16" (height) engineered floor joists that span 24' & 12' and are 24" OC. One side hangs on the inside of the stem wall and the other side sits on top of the stem wall. Needless to say the leveling of all the joists is/was difficult because the side sitting on top of the stemwall is up against the original house and I am trying to contine/match my oak floor from the old to the new.

The subfloor was just laid (7/8" OSB). We were going to use 1" because it lined up perfect (old/new subfloor) but the framer decided on 7/8" at the last second on the advice that it was better to be a bit low than high.

There is one very noticeable low spot and a few rough edges where a few sheets meet.

I will ask the crew to fix but expect grief. I have been reading about roof shingles to shim the low spots and presume I can sand the rough edges (where a couple of sheets meet).

Should I demand they remove subfloor sheets and shim from the bottom? Or, because of the long joist spans it will be better to level on top of the subfloor.

Those OSB panels are more than likely glued and nailed. There's no taking them up now. If the 1" OSB was perfectly flat with the existing subfloor, what &*%@^# would think that being lower and uneven is better? But yes, sand the rough, high places and fur up the low places with no more than 3 layers of fiberglass/asphalt roofing. FRAMERS !!!:roll: I guess that's why they call it "rough framing". With many of them, if it's within a 1/2", it's good.

Gary,

Yes, glued and nailed. When you say "fiberglass/asphalt roofing" is that the actual shingle or roofing tar paper material?

The 7/8" vs. 1" advice came from a flooring person...arrgh!

Thanks...I am going to have a few floor folks come in to discuss the installation and fixes. If KLS reads this please email me.