2030 plan - stiffer floors

Started by Chuckca, June 20, 2005, 03:30:34 AM

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Chuckca

Could post and piers be added to the center of the first floor span to stiffen the floor....I think 19' is the outer limits of 2x12 doug fir #2 or better...adding a couple of PP's seems to make sense....Comments please!

John Raabe

Yes, I wouldn't span 19' with DF #2. It would have enough strength but you may not be happy with the deflection (experienced as bounce).

For stiffer floors, either move up to engineered joists, go to select structural 2x12s or do an interior bearing as you suggest.
None of us are as smart as all of us.


rwalter

#2
John,

At what  level of deflection do you normally design a floor joist to withstand?  I thought I have read in one of your previous posts that you normally look for at L480 deflection or higher. Is that correct?
According to the American Wood Councils span calculator it has #2 Doug Firl spanning 19' 11" at a L480 deflection at a 40/10 live/dead Load on 12" OC or L600 deflection at 18'4" 40/10 live/dead load using 12" OC.


http://simurl.com/basgec  

Note: Changed calculator to short URL  -GK



Just curious.

Thanks

John Raabe

#3
In most cases floors are designed for 1/360 deflection. This is code level design.

In longer spans however that can still add up to some noticeable movement and companies like Truss Joist started recommending several years ago that TJI floor systems be designed to their "High performance" standard of 1/480.

For shorter spans such a standard is overkill but at 18' to 20' and longer designing to 1/480 will feel more solid to more people and builders find they have fewer call backs. This is never a question of strength you understand, just "bounce".

PS - That is a good on-line span calculator! You can use it to check spans of PT lumber when used outside for a deck (incised lumber, wet service conditions, 60 psf live load). It is unusual for most charts to cover such conditions. Thanks for the link.
None of us are as smart as all of us.

rwalter

#4
John,

Yes I really like this calculator myself its the best one I been able to find. I used this to design my cabin that I am in the process of building right now. I used 3d Architect to design a 20x32 cabin based on the Providence design on your 3d Architect help section.  I am using 2x12'  Doug Fir for the floor joists so your comments concerned me. My foundation has been built 2" short on every wall to allow for polystyrene insulation on the outside walls. I also used 10" block and 2x10"PT sill plates so my span is 18' 1".  That should meet and L600 Deflection using #2 or better Doug Fir. I checked the stamps on the Doug Fir and some say structurally select, but I'll have to check them all though I am not sure what they all are stamped.

http://pg.photos.yahoo.com/ph/webworldcomp/album?.dir=5d35&.src=ph&store=&prodid=&.done=http%3a//photos.yahoo.com/ph//my_photos


John Raabe

Looks like you have a good solid foundation there  (and a spirited helper!)

You are building a quality project and the floor system should be quite solid and satisfactory.

Keep us up to date with your progress. Many folks here will be interested in sharing your experience.
None of us are as smart as all of us.