how much bounce is in your floors?

[tesa]

my plans state i can go 12"oc for floor joists using 2X's, thats assuming i don't go with I joists,

we're spanning 20'

i remember my grandma's house was sooooooo bouncy in the kitchen, i remember us kids
would run thru there and make my baby cousin bounce and giggle

tesa

[Beavers]

2x12's on 12" centers can span 20' 7" with a deflection limit of L/360.  That is the maximum deflection suggested for tile floors, so it would be a very solid floor.

Here is a link to the calculator, you can run the numbers based on what kind/grade of lumber you are using and what spacing you want to use.

http://www.awc.org/calculators/span/calc/timbercalcstyle.asp?species=Spruce-Pine-Fir&size=2x12&grade=No.+2&member=Floor+Joists&deflectionlimit=L%2F360&spacing=12&wet=No&incised=No&liveload=40&snowload=-1&deadload=10&submit=Calculate+Maximum+Horizontal+Span#answer

Btw- I used 2x12's 24" O.C. spanning 12' and the floor is very solid.

[tesa]

thanks, i'd like to balance savings with long term stability, 24" oc would be a sweet deal for the lumber budget,
but i'd best stick with the plan

thanks again

tesa

[Beavers]

I wasn't suggesting that you deviate from John's plans. 

I used 24" OC to span only 12'.  The span calculator from the AWC only confirms that the joists called for in the plans would make for a nice solid floor, spanning the 20' for your house.

[tesa]

oh, no, i would never think that

tesa

[MountainDon]

Watch the lumber grade and species when you use the calculator, tesa. I'm not certain but John may have specified select grade... check on that.

Also keep in mind that when talking span distances one measures the unsupported span. In other words with a set of parallel beams you measure from the inside of one beam to the inside of the other beam. Ditto for rafters and ceiling joists.


How much bounce do I have? or my floor in the cabin I should say?    Our floor seems very solid. I can not feel it move. However, it is possible to get one of the glass lamp shades vibrating if it isn't positioned just so. It's the harmonics that set up when we walk across the floor. Other than that it's very solid feeling. It is overbuilt a little going by the calculator.

Here's what I have; 2x10, #2, hem fir, 16" OC... the AWC calculator states it could span 15 ft 2 inches. (The actual span between beams is about 13 feet or about 2 ft less than the calc says is maximum span) It's always better to have some safety factor, pushing things like this to the max permitted can sometimes be less satisfactory.

Using the grade, species and sizes John has spec'd should get you a good base that will allow you to use any floor covering except natural stone (no real marble tiles and the like).

[NM_Shooter]

Seriously consider using 16" centers.... at 24" OC, you will start to get some deflection in the sheet material too.

If you go to 16" rather than 24", you end up having one more joist per 4' section.  This is not a huge price to pay consdering you'll be on it the whole time. 

Your whole structure will be stronger because of it.

I used 2X10 on 16" for a 14' span.  I don't feel deflection, but the floor surface does vibrate like a drum.  I don't have any center supports underneath for dampening.  (I may add some later).

[tesa]

i intend to follow johns call out, i was just thinking in terms of budget how nice that would be, but your right, i want
this to be our forever home, and i want it to be built to last

20'ers 16"oc it is!!

but, if you do the math on my 42' length, at 16"oc it comes out to 31.5 joists, now how in heck am i gonna get that
.5 of a joist, so i guess to make things 12" oc to make the math work out??

tesa

[MountainDon]

It is common to have one odd spacing when laying down joists. I have one bay like that in our cabin. No big deal, that's just the way it works out.

However, just use whatever it is John's plans call for; spacing, species, grades and all, and you will be fine.

[Beavers]

20'ers 16"oc it is!!

Did you run that through the AWC span calculator?  At 16" oc you have use a select structural grade, if you stay with the 12" oc most species pass just fine with the cheaper #2 grade.  Could be cheaper to stick with the 12" oc.

[tesa]

well, my plans call for them to be at 16"oc, but after re-reading them, it looks like he means if i use i-joists

"....full span 2X12 OR I-joists @16"oc"

regardless, i have an updated bid from HD including my rim boards and it is STILL cheaper than using 2x's (apx. $1400)

I joists it is!!

phew, its a good day! one major decission down, and it not even noon yet!!!

tesa