Floor joists

[Beltzington]

Which senario would result in a stiffer floor, (less deflection) 2*8's 16" on centre or 2*10's 24" on centre.

If you have not considered it, engineered wood joists and flooring are the best available for stiff floors. It will be what I will be using in our new home. Here is one manufacturer, they also have calculators to determine size and placement for various loads. Good Luck.

AdvanTech Flooring, AdvanTech Subflooring, AdvanTech Floor | Huber Engineered Woods

 

[jel1988]

Sorry about the span guys but I checked a floor joist calculator. At a span of 9' 6" 2.8's 16" on centre deflect .209 or L/ 544. At the same span 2*10's 24" O/C deflect .178 or L/641. In all cases 2*10's 24" O/C out perform 2*8's 16" O/C

 

[PILOON]

Just a slight hijacking here, but in the house I just bought has 2x10 joists @ 16" and is sturdy. But I noticed all the Xs with 1x4s in between the joists were never nailed or screwed in the bottom. Should I fasten them on the bottom?

Back to the subject.

YES! they should be fastened top and bottom. If joist is twisted try to get them as close to vertical as possible for best results.

 

[DFB]

Just a slight hijacking here, but in the house I just bought has 2x10 joists @ 16" and is sturdy. But I noticed all the Xs with 1x4s in between the joists were never nailed or screwed in the bottom. Should I fasten them on the bottom?

Back to the subject.

Ya normally with that style of cross bridging the bottoms are nailed after the sub floor is laid allows for the weight to push down on the joist crowns first, if they fit tight probably nothing has warped.

How old is the house?

 

[Billrog]

Deere Dude they are left that way by some contractors until the 2x10's shrink ( dry out) so now would be a good time to nail them solid but keep the 2x10's vertical don't hammer them until their leaning.

 

[duke7595]

If you have not considered it, engineered wood joists and flooring are the best available for stiff floors. It will be what I will be using in our new home. Here is one manufacturer, they also have calculators to determine size and placement for various loads. Good Luck.

AdvanTech Flooring, AdvanTech Subflooring, AdvanTech Floor | Huber Engineered Woods

I'm sure you probably know this but make sure the crown is facing up on each joist. Also, for the few extra dollars it pays to install 16" O.C. regardless the
the size you choose, and no less than #2 grade lumber, hand picked if possible.

 

[newbury]

Sorry about the span guys but I checked a floor joist calculator. At a span of 9' 6" 2.8's 16" on centre deflect .209 or L/ 544. At the same span 2*10's 24" O/C deflect .178 or L/641. In all cases 2*10's 24" O/C out perform 2*8's 16" O/C

Good to know, my point was if it was a short span the difference would be very minor.

Deere Dude they are left that way by some contractors until the 2x10's shrink ( dry out) so now would be a good time to nail them solid but keep the 2x10's vertical don't hammer them until their leaning.

AND if you are trying to nail in cumbersome and tough to get to areas and don't have a palm-air-nailer or similar you might want to get one. They work with even small air compressors like the 3-gal-13-hp-100-psi-oilless-pancake-air-compressor which has been going on sale for $40. I've bought 2.

 

[woodchipper]

Subject is closed, but as I just read the post, I will add that as mentioned, blocking between the joists every four feet will make this floor twice as strong, as the floor live load per square foot will be be distributed over a much greater area. The down force (moment of inertia) beeing transferred laterally to other members. Therefore solidifying the floor, and rendering it much less bouncy in the process.