Metal SIPs are a great way to build with a material that is virtually termite proof. But when it comes to subfloors it seems you are back to having a structural item far less resilient than everything else. I've seen fortocrete but that is out of the question unless funds are unlimited. I don't trust Magboard (at least not yet). That leaves plywood or OSB. I wanted to know what others prefer using. I was looking at 3/4" sturdifloor as opposed to standard CDX. Does that seem a worthwhile improvement? I've not had the best impression of OSB but perhaps it is much more improved these days. Is anyone using OSB? It appears Advantech is much better than what I remember of OSB. I was thinking of coating whichever with Thompson Water Seal.

Torben;

 we investigate every new product that comes out looking for a non-wood subfloor. I am agreement with you on fortocrete and am not comfortable with Mag board either yet. I have done installs with advantech skins and found the edges will swell just the same as regular OSB, there is also nylo-board (too expensive)        so far have not found anything better than 3/4" T&G plywood, it will take many rains

Sorry Chris,
I beg to differ. My experience has been just the opposite. I have far less problems with Advantech OSB than with plywood. Note that generic T&G osb and Advantech are NOT the same thing.

I prefer a thin layer of concrete on metal decking or a Advantech OSB.  I have found that one coat of latex paint works better to protect the OSB from water than Thompson Water Seal.  In order to save money on good latex paint, use old latex/acrylic paint you already have or buy returned paint at your local paint store.  The color of the returned paint does not matter since it will soon be covered with another floor.

I do try to use latex/acrylic and not oil paint.  As long as the paint is compatible, various colors can be mixed in a five gallon bucket to get one color - usually gray or some other dark color.

The procedure I use consists of the following:  Sweep the floor clean before any walls go up.  Have one person to pour a narrow line of paint from the five gallon bucket onto the floor while another person uses a roller with a long handle to spread the paint.  Just be sure to apply the paint thick enough to seal the seams also.  Another benefit to using paint is that the floor will be easier to sweep while the house is under construction.

By the way, I think a dirty or messy site reflects poorly on the builder.  Keeping the site clean on a daily basis is easy to do and it keeps a lot of hidden dust from getting into the duct work which can lower the efficiency of the HVAC.  If the site is not kept clean on a regular basis, then be sure to replace the HVAC filter about twice the first month of operation and have the HVAC coils checked for cleaning after the first year.

Wes;

once the Advantech is cut the edge is no longer protected, our experience was with Advantech SIPs and all square edge Advantech is not sealed, it is an option........... our experience was horrible! after one rain the factory edges swelled making spline installation difficult. But I have never had an issue with plywood.

The trouble we have had with plywood floors from rains is that the top ply will separate from the 4x8 sheets.  Many times we have replaced whole sheets of plywood.  (Tough job since they are glued and screwed.)  A light rain does not seem to bother the plywood.  Standing water is when we have our problems.  After a good rain in my area, some builders or framers will drill 1/2" holes through the puddles to drain the water to the crawl space or basement.

Chris, Do you use regular CDX or something more like Sturdi Floor?

Torben;

Sturdi Floor ............... I have had jobs rained on for 2 weeks during the rainy season with no problems

Thank you Chris! That is what I was leaning toward but 2 weeks of rain... I will definitely use Sturdi Floor. I saw a side by side comparison of Advantech with Sturdi Floor at the builders show that made me question my preference for plywood. Hearing about how it swells at cut locations.... that is good to know.

Chris,
I think I see the difference. I have never seen square edge Advantech. All we use is 23/32 T&G Advantech subflooring, which is sealed on all 6 sides. Our experience with this product has been excellent.  Including one project that had over 7 inches of rain on the deck with no significant problems.