|
Posted by Glenn on July 8, 2006, 2:28 pm
2 x 10 spanning 20 foot will sag under their own weight. 2 x 12
would work if the load is really light. You want nothing in the
way of parking. That is reasonable but would it be possible to
have a drop from the ridge every 4 feet with a stiffback? 2 x 8's
would work that way quite well. Even push the envelope with
proper dropping braces using 2 x 6's as that's only a 10 foot span
less the cantilevering effect in the center of continuous joists.
Certainly, the latter would hold a bigger load than the 2 x 12's..
Example: I have a garage that is 24 feet wide. I have no ceiling
in it except 2 x 6 joists (cross ties) every 4 feet. They are
nailed heavily to 2 x 6 rafters on 5 and 12 pitch. I have a 1 x 4
drop nailed onto the rafter at the ridge and dropping down and
nailed onto the joists. To not split the 1'x, I stapled them with
multiple 2-1/2"staples. I have a 6 x 6 - 5 feet long laying
across 2 of them and think nothing of pulling a 8 cylinder engine
on them. I wouldn't even think of doing that even spanning across
four 2 x 12's.
> I plan to build a small garage, 20 feet by 30 feet.
> I want to be able to span the 20 foot width, so that I
> don't have to use interior posts.
>
> At first, I was doubtful this could be done, and I have
> seen comments in these groups that this is not really
> feasible. Yet, I have closely inspected one of the
> yard sheds (with loft) at Home Depot, that is 16 feet
> wide, using 2 x 10 beams on 12 inch centers. It is
> a yard shed, with a small loft. I went up into the loft
> area to see what "bounce" the floor had, and it is quite
> solid, with just a small hint of a bounce (I weigh 215
> lbs). So, I have concluded that spanning 16 feet with
> 2 X 10's is easy, as I have seen it.
>
> But, I know that going from 16 ft to 20 ft wide is
> 4 feet more of span and is 25 % more of a span. I am
> a novice, but I try to find answers for myself first.
> Somehow, I got a span table for Southern Pine lumber.
> The title of the chart is
>
> Maximum Spans: Souther Pine joists and rafters .
>
> This is the full name.
>
>
> The chart also says: 40 lbs psf live load/ 10 lbs
> psf dead load/ 240 deflection / cd = 1.15
>
> I plan to use the loft only for very light storage, but
> these "load" figures seem very low to me. But, once
> again, I have "felt" what a 16 ft span using 2 x
> 10's feels like, and it seems very sturdy to me.
>
>
>
>
> From the chart, it appears that a # 2 visually graded
> (is that what you "usually" find in lumber yards and the
> big box stores??) 2 X 10
> beam on 12 inch centers will span 19 ft, 11 inches.
>
>
> A 2 x 12 beam on 16 inch centers will span
> 20 ft, 2 inches.
>
> -----------------------
>
> Questions: First, am I on the right track ? Does the
> chart seem to apply to my needs and plans? I could email
> the chart (pdf format) to anyone who wanted to look, I
> don't think I should post an attachment here on a news
> group.
>
> Is #2 visually graded, the most common lumber found in
> lumber yards ?
>
> Which would be better, 2 x 10 on 12 inch centers
> or 2 x 12 on 16 inch centers ?? It seems that
> the latter may be a bit cheaper, but price isn't the
> primary concern.
>
>
> What happens if you use a 2 X 12 beam, but put them
> on 24 inch centers instead of 16 inch?? Do you simply
> get more deflection, and less load capacity ?
>
> I know I could use an engineered beam, but I don't want
> that.
>
> Thanks for any tips, experience, and advice !!!!
>
> --James--
| 
Yahoo! 
Google 
Windows Live 
del.icio.us 
digg 
Netscape 
XML Sitemap