Hello all  I'm looking for words of wisdom and experience here.

My company does highly energy efficient gut renovations but we're about to embark on our first new construction project, which is different for us.  We "inherited" a set of plans and are modifying them to get them to be energy efficient. When we have new exterior walls to build, we typically do 2x6 24" oc with double plates and 16oc floors because my crew does not feel comfortable going to 24" oc for the floor.

My question is what is your typical floor assembly like?  16" oc wood I's, ply subfloor or OSB, finish floor?  Or do you go to 24" and add a second subfloor layer?  Typically how deep are your i's and what is your spacing?

For this particular project we're intending on using 12" wood I's (we have single no spans longer than 20', most less than 15' and total spans of up to 32') and we could space up to 24".  I know all of this is guided by span tables specific to the manufacturer and with what we're doing we are within the requirements for 12" i's, but I'd just like a sense of what new construction builders typically do spacing and depth wise for floors with i-joists that create a floor that feels solid and is easy for the trades.

...and if anyone has done the math, anyone care to offer an opinion on what is the most sustainable floor assembly, given the materials choices and the amount of waste produced?

I'm all ears.

Tanya

Tanya - wood I's are typically 19.25 on center. 24 is good if your spans allow but you may need to go to 7/8" sheathing. Also need to consider the type of flooring going on. If a concrete overlay, the sheathing doesn't need to be as stiff, but if ceramic floor tile, you might have to go with a second layer to get it stiff enough.

The further the joists are apart, the easier it is to get plumbing and heating runs through them.

Make sure the supplier does the calc to prevent the floor from having vibration or bounce and of course meet codes.

where are you?

I built my floor system on 24" centers. I used custom built 4x2 open web floor trusses (3-1/2" wide top and bottom flanges) and decked it with 1-1/8" Advantech sub-flooring. Seems pretty solid to me. My floor trusses are 32' long with the longest unsupported span being 18'6".  The advantage to this approach is being able to run all of my utilities and HVAC through the trusses.  This floor is above a finished basement.

The advantage to this approach is being able to run all of my utilities and HVAC through the trusses

Some people are even boxing in the trusses, sticking a mini-split in there and voila - radiant heating on a budget.