New Home - Floor Joist 12" or 16" OC?

If you do the math you will need about 25% more joists for 12 inches vs 16 inches.

What is the size of the area you would be flooring? If it were 30 x 50 squared that would amount to roughly 25 more (101 vs 76) 16 foot 2 X12s. Those are about 30 bucks apiece at Home Depot which is about $750 plus hardware depending on how you're mounting/attaching them.

If it gives you peace of mind, it is probably worth it. Make sure you account for the extra weight when sizing your supporting beams though I think that won't be much of an issue.

2X12 fir is about 5 pounds per foot of length.

ETA: Maybe consider spraying in foam insulation?

Good luck with the build

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If it's in your budget, ABSOLUTELY 12" OC. (That is to say make it part of your budget.)

Future you will be very happy you spent the money.

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This this this! If this is your forever home do it right and make your floor solid as a rock.

16" OC is what most codes call for but if 12" OC makes you feel better, then do it.

16" is pretty much the standard for batt/insulation. Going 12" OC would require a lot of extra cutting to fit between your floor joists.

12" is fairly hard to find but I am sure you can purchase it somewhere.

2"x12" seems excessive, the standard for a floor joist is 2"x8", and again, its your choice.

One thing I would highly recommend is to skip fir wooden joists and go with 'pressure treated' floor joists for protection against termites.

Also, get a few gallons of Bora Care, I purchased from domyown.com, and a good sprayer like a RYBIO electric sprayer from Home Depot and spray your floor joists real good.

Furthermore(LOL), get something like Taurus SC and trench around your home.(plenty of YouTube vids on how to do this)

I recently dealt with a termite infestation and those evil little devils can cause some major damage.

Thanks for the recommendation.

Framer said I could get by with 2x10's easy. When I told him I was considering 2x12 on 12" OC he looked surprised . I've just been in a lot of homes where the floor feels soft and I can't stand it. If I have extra money to put into the build I figured the floor system is as good a place as any.

The insulation in definitely something to consider. I'm not sold on the spray foam yet (especially for attics) but it might be something I'd consider for the crawlspace. Seems like it'd make it a lot more air tight.

I've heard of people doubling up on the flooring and making it 1 1/2" instead of 3/4". Seems to me that would greatly increase the load, no?

for the OP. Is your new house in the South? why do you need insulation under the floor?

I'd lean on your builder for advice like this. Trying to glean info from the internet right before a build is going to drive you and him insane.

Spoke to my framer today. He said if I was really doing 12" OC then I should really consider 2x10 instead of 2x12 for the cost. Said by going with 12" OC I could possibly drop down to a No.2 instead of a No.1 as well. So I could get a better price on size and grade. Said that along with the 3/4" flooring would really stiffen it up.

Still unsure on the 2x10's over the 2x12's tho.

Go with the 2x12 and 1" tongue and grove plywood. You will not regret it. Do not do 3/4.

You are paying attention to detail which is a lot better than most do.

3/4" plywood & 2"x10" joists is plenty unless you are going to have a M1A Abrams tank in your home.

Its your castle and your money.

Go with what your framer is suggesting.

I agree with your framer. If you’re gonna do 12” OC, then 2x10 is plenty. Really would like to cut that 15’ span down, though, no matter what you choose.
Also, look into Advantech subfloors. Either 3/4 or 1 1/8. You’ll really like it.