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Floor Joist Beam Spans
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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--
| |
|
| 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.
"James" <jnipperxxx@nospamfdn.com> wrote in message
news:WeKdnfNI7Z2OcDLZnZ2dnUVZ_tKdnZ2d@comcast.com
> 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--
| |
| MDT at Paragon Home Inspections, LLC 2006-07-08, 5:25 pm |
| > 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.
As a theoretical matter, to maximize span for a given floor thickness
the entire floor structure should be designed as an engineered
structure, with sub-flooring, fasteners schedules, adhesives,
dimensional and engineered members, etc. specified together. By
adjusting these variables a structural engineer can spec designs for
residential floor spans of 3O'+ using readily available components.
As *practical matter*, my first question would be: "What does the
local building department require?". Your question may be answered
right there, and there might be some surprises - for example since you
now have a load bearing second floor, you may find substantial footings
are required below the exterior walls.
My second question, if you are permitted to build as you please, would
be "What is a reasonable design criteria considering the loads that
might reasonably be placed on the floor by subsequent owners?"-
keeping in mind that they may stack old newspapers up there...
Once you know those numbers (load sq/ft and allowable deflection), as
specified by local code or derived by common sense, you are ready to
start thinking about materials and techniques.
Michael Thomas
Paragon Home Inspection, LLC
mdtATparagoninspectsDOTcom
| |
| marson 2006-07-08, 5:25 pm |
| have you considered wood i joists? bring your plan to a lumberyard and
they will do the design for you. or google "truss joist macmillan" for
example to find simple span tables) i joists are easier to install
(lighter), straighter, and can span longer spans. comparably priced to
sawn lumber.
| |
|
| This place is so remote, they have never heard of a building inspector.
And yes, I will have 36 inch depth, 12 inch wide poured footings around
the perimeter of the garage.
Thanks !!
--James--
| |
|
| Thanks Glenn, very interesting. No, I want to use straight horizontal beam
joists, and had questions about a spannig chart for Southern Pine wood.
--James--
| |
|
| You will need to have it engineered and they will tell you what you
need to do. In order to get a permit you will need plans and the plans
will need tom have an engineers stamp on them! If it is not required
you should still get it done or at least approved by a PE.
That said on This old house they had a span they needed to raise the
ceiling on. They cut the joists from 12 to 10" and bolted steel plate
cut to size they also had sag and used the edge of the steel to judge
when the floor was level using floor jacks to jack the ceiling. I
would think with the steel plates on both sides of 2x12's you should be
fine. But the snow load will also have an effect as well as the roof
pitch!
I had a barn built with a 60' clear span. it had 2 with beams bolted
together.
Engineered trusses should take care of it for you
More than you ever wanted to know
http://www.alpeng.com/wood_truss_info.html
W
James wrote:
>
>
> 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--
| |
| Michael Daly 2006-07-08, 5:25 pm |
| James wrote:
> This place is so remote, they have never heard of a building inspector.
Then build anything you want and watch and see if it collapses. However, I
don't know of any place in the western world where building codes don't apply.
BTW - your insurance agent may have something to say about this, too.
> And yes, I will have 36 inch depth, 12 inch wide poured footings around
> the perimeter of the garage.
Which means nothing without knowing what the soil is like.
BTW 2x10 would not be legal for that kind of span as a _floor_ where I live.
Without checking, I don't think 2x12 would work either - 2x14 sounds about right.
Mike
| |
|
| No, as stated in my original post, I don't want engineered beams. I will
use either 2 X 10 or 2 X 12 beams. My questions related to the
reading of the Maximum Span Chart for Southern Pine.
To those of you who say it can't be done, it appears that the Chart says
otherwise.
My footings will be ok.... don't worry about them. My questions relate to
the reading of the Maximum Span Chart for Southern Pine.
Thanks !!
--James--
| |
| MDT at Paragon Home Inspections, LLC 2006-07-08, 5:25 pm |
|
James wrote:
> This place is so remote, they have never heard of a building inspector.
> And yes, I will have 36 inch depth, 12 inch wide poured footings around
> the perimeter of the garage.
Sounds like you are headed in the right direction: thinking of this as
a serious structure, not just an up-sized "garage" on a pad + loft
space. I'm not an engineer, and I try hard not to play one the net, but
I *do* know that some of the scariest things I've seen in new
construction in my area result from architects and/or builders who land
jobs to build 'McMansons" and just assume that the materials and
techniques that worked for a living room with a 22' clear span can be
"up-sized" to work at 26' even 30 or even 35' - there is a 4M
dollar house not too far from me where the second contractor on the
project worked with an engineering firm for six months to stabilize
such a structure, essentially erecting a permanent structural steel
frame inside the existing footprint to literally keep the building from
collapsing.
Michael Thomas
Paragon Home Inspection, LLC
Chicago, IL
mdtATparagoninspectsDOTcom
| |
| MDT at Paragon Home Inspections, LLC 2006-07-08, 5:25 pm |
| > No, I want to use straight horizontal beam joists, and had questions about a spannig chart for Southern Pine wood.
See the first table here, for a 20' span garage w/ floor above:
http://www.savvyhomeadvice.com/articles/tji.htm
Michael Thomas
Paragon Home Inspections, LLC
Chicago, IL
mdtATpragoninspectsDOTcom
| |
|
| Michael, thanks for the link, that is very helpful !! From that page, it
pretty well confirms for me that the 2 x 12 on 16 inch centers is
precisely what would work in my planned structure .
Thanks again !!!!
--James--
| |
| marson 2006-07-08, 8:25 pm |
|
James wrote:
> No, as stated in my original post, I don't want engineered beams. I will
> use either 2 X 10 or 2 X 12 beams. My questions related to the
> reading of the Maximum Span Chart for Southern Pine.
>
> To those of you who say it can't be done, it appears that the Chart says
> otherwise.
>
> My footings will be ok.... don't worry about them. My questions relate to
> the reading of the Maximum Span Chart for Southern Pine.
>
> Thanks !!
OK, sorry i posted earlier about ijoists--i missed your comment about
not using engineered lumber. i have worked with 20' SYP 2x12's before.
hope you have a good back!
reading the span tables is pretty straightforward, and in spite of what
the naysayers say in this thread, at 30 psf live load, you can span 26,
yes 26 feet! with a select structural SYP 2x12 at 12"oc(good luck
finding that!). that is what the tables at southernpine.com say. the
real questions are what is your live load and what is the grade of your
lumber.
where i live, duluth minnesota, the city posts what live load you
should use for various rooms, attics, storage, etc. on their website.
if in doubt, follow the codes, even if you don't have plan review or
inspection.
As for grading, I have seen mostly machine stress rated lumber when
using structural lumber, but what you get is inconsistent in that there
are mixed grades in the same unit. I wouldn't trust home depot
however, since they can try to make their prices seem lower by actually
supplying a lesser product. if you can go to a real lumberyard, do so.
you can probably order select structural SYP if you want, though be
prepared to pay for it. a good lumberyard will have someone who knows
all about what grades are available.
btw, SYP used to be the common structural lumber, but in the past few
years, only doug fir and hem-fir have been available here.
-
| |
|
| Thanks Marson, this is good info and good advice. I am printing it to keep
for future reference.
--James--
| |
| New Wave Dave 2006-07-09, 3:25 am |
|
"James" <jnipperxxx@nospamfdn.com> wrote in message
news:svGdnZtSeY14zi3ZnZ2dnUVZ_qGdnZ2d@comcast.com...
> Thanks Marson, this is good info and good advice. I am printing it to
> keep
> for future reference.
Consider a built-up beam at the mid-point ABOVE the joists and then bolt
the joists to the beam using angle iron ala . . .
http://www.pbase.com/speedracer/image/2622653. We've successfully
applied this technique on a handful of jobs always, as in this picture,
removing a wall after the beam and angle irons are in place. These
happened to be 2X6 joists.
--
"New Wave" Dave In Houston
| |
| Steve Barker LT 2006-07-09, 3:25 am |
| try Cedar county Missouri. No permits required for anything except a septic
system.
--
Steve Barker
"Michael Daly" <michaeldaly@foo.bar> wrote in message
news:sLednXjwdLnEhS3ZnZ2dnUVZ_qydnZ2d@magma.ca...
However, I[color=darkred]
> don't know of any place in the western world where building codes don't
> apply.
| |
| RicodJour 2006-07-09, 3:25 am |
| New Wave Dave wrote:
> "James" <jnipperxxx@nospamfdn.com> wrote in message
>
> Consider a built-up beam at the mid-point ABOVE the joists and then bolt
> the joists to the beam using angle iron ala . . .
>
> http://www.pbase.com/speedracer/image/2622653. We've successfully
> applied this technique on a handful of jobs always, as in this picture,
> removing a wall after the beam and angle irons are in place. These
> happened to be 2X6 joists.
The OP is talking about a 20' span and a 40 pound live load. That'd be
about six or seven hundred pounds load on each connection, so it could
be done with a couple or three suitably sized bolts, but stepping over
a beam in a space you're using for storage isn't exactly a desirable
feature.
To the OP: most people that have objections to engineered joists
usually cite fire concerns, but as you're using the space for storage
and not habitation that's really not a big issue. So what's the
problem with using engineered joists. You might want to price the
floor assembly both ways before you make your decision. Lumber prices
haven't exactly been going down recently.
R
| |
| Michael Daly 2006-07-09, 3:25 am |
| Steve Barker LT wrote:
> try Cedar county Missouri. No permits required for anything except a septic
> system.
>
Not requiring a permit and not having a building code are two different things.
Mike
| |
| Steve Barker LT 2006-07-09, 9:25 am |
| Ok, then. If there's no permit required, and therefore no inspection, where
does the code come into play?
--
Steve Barker
"Michael Daly" <michaeldaly@foo.bar> wrote in message
news:MoWdnWuce5I7GC3ZnZ2dnUVZ_o-dnZ2d@magma.ca...
> Steve Barker LT wrote:
>
> Not requiring a permit and not having a building code are two different
> things.
>
> Mike
| |
| crhras 2006-07-09, 1:25 pm |
|
Code is the law and permits and inspections help the compliance and
enforcement of that law. There are many situations where laws are not
enforced yet it is still in your best interests to comply with them.
April 15th comes to mind.
"Steve Barker LT" <railphotonut@not.hotmail.com> wrote in message
news:1u6sg.4752$qi5.1587@tornado.rdc-kc.rr.com...
> Ok, then. If there's no permit required, and therefore no inspection,
> where does the code come into play?
>
> --
> Steve Barker
>
>
> "Michael Daly" <michaeldaly@foo.bar> wrote in message
> news:MoWdnWuce5I7GC3ZnZ2dnUVZ_o-dnZ2d@magma.ca...
>
>
| |
| RicodJour 2006-07-09, 1:25 pm |
| Steve Barker LT wrote:
> Ok, then. If there's no permit required, and therefore no inspection, where
> does the code come into play?
Code is the minimum acceptable construction. Why would anyone want to
build something that failed to meet such a low standard?
R
| |
| HerHusband 2006-07-09, 1:25 pm |
| James,
> 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.
A few years back we built a 24'x28' garage. I wanted a completely open
lower level, and a fully usable attic (i.e. No truss webs). I never
expected to put any real weight in the attic.
I used regular #2 Douglas Fir, 2x12 joists at 16" OC to span the 24'
width of the garage. I added solid 2x12 blocking every 8 feet along the
span. I used 2x6 rafters at an 8/12 pitch and ended up with about 7 feet
of headroom running down the center of the attic.
Yes, with a 24' span the attic floor is a bit bouncy, but not nearly as
much as I expected. If you stand in one place and bounce up and down you
can feel it, but it's not really detectable in normal walking. Still, I
wouldn't want to store an engine block or a library of books up there.
Mostly, we just use the attic to store items like long PVC pipes, empty
stereo/TV boxes, holiday decorations, etc. But, I do have a few heavier
items up there too.
I could have easily strengthened the floor by doubling up joists or going
to 12" spacing.
> that is 16 feet wide, using 2 x 10 beams on 12 inch centers.
We used 2x10 douglas fir joists at 16" OC in some parts of our house.
That's close to the maximum span for doug fir, but the floors still feel
quite solid.
> I know I could use an engineered beam, but I don't want that.
You could use wood I-joists and easily span 24' or more. They're light,
straight, and about the same price as 2x12's around here.
Alternatively, you may want to check with a truss company for "attic
trusses". These can easily span 24' and still have a usable room in the
middle of the attic. I decided against these because of cost, and because
I was mostly working alone. It would have been very difficult to install
trusses by myself.
Take care,
Anthony
| |
|
| Thanks for the input Anthony, and your experience is interesting and on
point.
From all the input received here, I now have no doubt that I can span 20
feet easily, using #2 southern pine 2 X 12 beams , on 16 inch
centers.
I remain curious if anyone can still answer these remaining questions that
were in my original post:
--------------------------------------------------
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 ?
| |
| RicodJour 2006-07-09, 5:25 pm |
| James wrote:
> Thanks for the input Anthony, and your experience is interesting and on
> point.
>
> From all the input received here, I now have no doubt that I can span 20
> feet easily, using #2 southern pine 2 X 12 beams , on 16 inch
> centers.
I'd have doubts. http://www.cwc.ca/design/tools/calcs/SpanCalc_2002/
Choose US species and the loads you indicated - you can't span 20'
easily or even barely. Your house, your call.
R
| |
| crhras 2006-07-09, 5:25 pm |
|
I agree for the most part. Howerver, here in Chicago ocasionally it seems
that the code was influenced by politics and requires things that don't make
sense and only serve to put more money in someone's pocket.
"RicodJour" <ricodjour@worldemail.com> wrote in message
news:1152466671.888899.311660@p79g2000cwp.googlegroups.com...
> Steve Barker LT wrote:
>
> Code is the minimum acceptable construction. Why would anyone want to
> build something that failed to meet such a low standard?
>
> R
>
| |
| Michael Daly 2006-07-09, 8:25 pm |
| crhras wrote:
> I agree for the most part. Howerver, here in Chicago ocasionally it seems
> that the code was influenced by politics and requires things that don't make
> sense and only serve to put more money in someone's pocket.
>
So, because of a few odd bits in the code, you reject it all?
Mike
| |
|
| R:
Well, I must respectfully disagree. In addition to assurances from folks
here WHO HAVE DONE IT, as stated in my OP, I have walked on a floor made
with 2 X 10's spanning 16 feet. There was no bounce. Surely I can go
to 2 X 12's and span 4 more feet.
The chart you pointed to is neat !! Thanks !! It does indicate I would
have to use 12 inch centers.
--James--
I'd have doubts. http://www.cwc.ca/design/tools/calcs/SpanCalc_2002/
Choose US species and the loads you indicated - you can't span 20'
easily or even barely. Your house, your call.
R
| |
| crhras 2006-07-09, 9:25 pm |
|
Interesting... where did I say that?
"Michael Daly" <michaeldaly@foo.bar> wrote in message
news:QK6dnebncraWDCzZnZ2dnUVZ_rqdnZ2d@magma.ca...
> crhras wrote:
>
> So, because of a few odd bits in the code, you reject it all?
>
> Mike
| |
| RicodJour 2006-07-09, 9:25 pm |
| James wrote:
>
> Well, I must respectfully disagree. In addition to assurances from folks
> here WHO HAVE DONE IT, as stated in my OP, I have walked on a floor made
> with 2 X 10's spanning 16 feet. There was no bounce. Surely I can go
> to 2 X 12's and span 4 more feet.
Respectfully disagree with what or whom? The Canadian Wood Council?
Let me know what they think of your research - walking on an entirely
different floor system and asking people on usenet.
If you want to revise your criteria to justify what you seem set on
doing, please feel free. Instead of having 40 PSF as your live load,
go with 30 and there won't be a problem. Just be aware that storage
can frequently exceed live loads commonly found in a house, and rather
quickly.
> The chart you pointed to is neat !! Thanks !! It does indicate I would
> have to use 12 inch centers.
Right. Or go with a higher grade of wood. Before you count your
chickens though, find out if you can get SYP framing lumber where you
are for a reasonable price. In my neck of the woods framing lumber is
either Hem Fir or Doug Fir. You can get 2x12 in pressure treated
lumber but you do NOT want to do that. Besides the greatly increased
cost, for no reason, you would have to use different connectors and
fasteners and there would be substantially increased shrinkage.
Instead of going through all of that extra effort, why not rethink your
objective, realize that indeed it has all been done before, and select
a commonly available wood such as Hem Fir Select Structural on 16"
centers. Most likely that will be your best alternative.
You should also check out some of the other design tools online at CWC.
For example, they have DimensionCalc which will tell you that your
2x12 framing lumber will shrink about 1/4" as it dries. That is area
of construction commonly ignored by all too may professional designers
and all amateurs.
R
| |
| RicodJour 2006-07-10, 3:25 am |
| RicodJour wrote:
>
> Right. Or go with a higher grade of wood. Before you count your
> chickens though, find out if you can get SYP framing lumber where you
> are for a reasonable price. In my neck of the woods framing lumber is
> either Hem Fir or Doug Fir. You can get 2x12 in pressure treated
> lumber but you do NOT want to do that.
That doesn't read correctly. Make that you can get 2x12 SYP in
pressure treated...
R
| |
| Michael Daly 2006-07-10, 3:25 am |
| crhras wrote:
> Interesting... where did I say that?
Ok, what are you saying? Some parts of the codes are crap. Big deal - those
parts are not relevant.
Mike
| |
| Michael Daly 2006-07-10, 3:25 am |
| In-Reply-To: <xZadnb0_WPO9LSzZnZ2dnUVZ_vGdnZ2d@comcast.com>
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James wrote:
> Well, I must respectfully disagree. In addition to assurances from folks
> here WHO HAVE DONE IT, as stated in my OP, I have walked on a floor made
> with 2 X 10's spanning 16 feet. There was no bounce. Surely I can go
> to 2 X 12's and span 4 more feet.
You seem to rely more on beliefs than code data. You find 2x10 ok for 16 feet -
how does that translate into 2x12s ok at 20 feet? He has pointed you to one set
of code limits and it shows your ideas are not satisfactory. What you need to
do now is check your local code and find out what the requirements are.
Where's Hammurabi when you need him?
Mike
| |
|
| The longest allowable span I could find on line was 18' 5" -18' 11"
using 2 x 12 size of #2 douglas fir 12 nches apart.
Maybe you could inset a foot on each side with posts versus down the
middle and span the 2 remaining feet on each end.
RicodJour wrote:
> James wrote:
>
> I'd have doubts. http://www.cwc.ca/design/tools/calcs/SpanCalc_2002/
> Choose US species and the loads you indicated - you can't span 20'
> easily or even barely. Your house, your call.
>
> R
| |
|
| The longest allowable span I could find on line was 18' 5" -18' 11"
using 2 x 12 size of #2 douglas fir 12 nches apart.
Maybe you could inset a foot on each side with posts versus down the
middle and span the 2 remaining feet on each end.
RicodJour wrote:
> James wrote:
>
> I'd have doubts. http://www.cwc.ca/design/tools/calcs/SpanCalc_2002/
> Choose US species and the loads you indicated - you can't span 20'
> easily or even barely. Your house, your call.
>
> R
| |
| terry@terryking.us 2006-07-10, 9:25 am |
| When I built my large modified-post-and-beam barn/garage I went thru
the same gyrations of tables and codes, all of which came up with
different numbers.
All approaches use a 'safety factor' between the point of probable
failure (read 'broken') and 'working loads'. The factor varies from 4
to 7, and other 'basic' numbers like Modulus Of Rupture (MOR) has
different 'opinions' in different publications. So the results vary...
I got the Wood Handbook from the US Forest Service: Huge file at:
http://www.fpl.fs.fed.us/documnts/f...3/fplgtr113.pdf
and spent hours understanding the formulas etc. It may be worth it to
you to do this... as you seem to want to dig in and do your own work
based on your own understanding, rather than all the conflicting
'experts'...
I don't have any neat design package, but I'll send you my .123
spreadsheet if you want. I think Excel will open it... Basically you
just need the values for:
MOR (Modulus of rupture) you want to use, with some safety factor,
and the acceptable PSI for the end bearing area (end of beams on
supports)...
Here's a look at the raw numbers for hemlock. Get any other wood out of
the handbook.
---------------------
Hemlock Density: 50.00 Lb/ft3 Grn 28.00 Lb/ft3 dry
Hemlock Weight (Lb. Per Board Foot) 4.20 green 2.30 dry
Hemlock Modulus Of Rupture (psi) 6400.00 green 8900.00 dry
Safety factor 4.00 green 6.00 dry
HEMLOCK: Safe Working Loads: GREEN DRY
Hemlock Working Stress-Beam 1600.00 psi 1483.33 psi
Hemlock Parallel (Post end) 950.00 psi 1050.00 psi
Hemlock Perpendicular (Beam Bearing) 360.00 psi 650.00 psi
----------------------------------------------------------------------------------------------------------
(Need a fixed font to see these)
As you can see I used a safety factor of 4 for the green hemlock I was
using, and that naturally increases to a factor of 7 when dry. So I
was OK with my 6400 pound Yukon driving on the first floor, and it'll
have a better safety factor now, 2 years later. And I haven't put much
load on the second floor yet....
The nice thing about a spreadsheet is you can try out different size
beams and see the resulting MOR numbers and decide on your safety
factor.
I just designed and built a 12by12 deck on our Cabin that is about 14
feet above ground. Most codes require 100 Pounds Per Square Foot for a
'Party Deck Load"... California requires 150 PSF in a few towns, as I
understand it, after several people were killed in a deck collapse. I
used 150 PSF, and had to go to an 8by8 beam on the outer edge because
of a 12 foot span. That beam costs $50 here in Vermont. I was able to
make tradeoffs on joist size, span and so on. I added a center support
beam to keep the joist span to 6 feet, which made a huge difference and
allowed 2 by 6 PT joists.
ANYWAY, you might decide to do all this, or not.... and use some
tables,
I checked all my barn calculations against tables and they were
close....
Have fun!!
Regards, Terry King ...On The Mediterranean in Carthage
(Back ...In The Woods In Vermont for the Summer)
terry@terryking.us
a few barn photos at:
http://www.terryking.us/photos/barn/2www-barn1-2004/
| |
| Bob Morrison 2006-07-10, 1:25 pm |
| In a previous post James wrote...
> 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.
>
Use engineered lumber I-joists. 14" TJI 210 @ 16" o/c should be about
right.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com
| |
|
| Good advise but if it is just storage as stated, I would go for a
drop in the center as I described earlier and then not even be
concerned about weight. Even stronger and a whole lot cheaper.
Not to mention dropping from 14" to 6 or 8 gives a lot more head
room.
"Bob Morrison" <SpamFighter@junk.com> wrote in message
news:MPG.1f1c06cd47a25d57989bbc@news.west.earthlink.net
> In a previous post James wrote...
>
> Use engineered lumber I-joists. 14" TJI 210 @ 16" o/c
> should be about right.
>
> --
> Bob Morrison, PE, SE
> R L Morrison Engineering Co
> Structural & Civil Engineering
> Poulsbo WA
> bob at rlmorrisonengr dot com
| |
| HerHusband 2006-07-10, 1:25 pm |
| > Is #2 visually graded, the most common lumber found in lumber yards ?
Typically, yes. I request kiln dried lumber when available, but it's rare
to find kiln dried around here for anything larger than a 2x8 or so.
> Which would be better, 2x10 on 12 inch centers
> or 2x12 on 16 inch centers?
Taller joists usually result in a stronger floor.
> What happens if you use a 2X12 beam,
> but put them on 24 inch centers instead of 16 inch?
A much shorter span rating, and you have to use thicker plywood to span
the 24" joist spacing.
>
> I'd have doubts. http://www.cwc.ca/design/tools/calcs/SpanCalc_2002/
> Choose US species and the loads you indicated - you can't span 20'
> easily or even barely. Your house, your call.
A 20' wide building with a 2x6 supporting wall at each end would result
in a 19'-1" free span. That leaves several options:
Assuming a 30 Live/10 Dead (sleeping areas/attics)
2x10 at 12" OC = 19'-10" span
2x12 at 16" OC = 21'-1" span
Bump the load rating to 40 Live/10 Dead (all rooms)
2x12 at 12" OC = 21'-9" span
On the other hand, if the attic isn't tall enough to walk through and
we're talking limited light storage, you could size the "floor" as
CEILING joists.
Assuming a 20 Live/10 Dead (Drywall, No rooms, Limited storage)
2x10 at 16" OC = 20'-9" span
2x10 at 12" OC = 23'-11" span
2x12 at 16" OC = 24'-4" span
Obviously, it depends on what James plans to store up there, but I'd
probably opt for 2x12's at 16" OC.
Anthony
| |
| crhras 2006-07-10, 5:25 pm |
|
Right, that's exactly what I was saying.
"Michael Daly" <michaeldaly@foo.bar> wrote in message
news:gaednQx6kOLBTyzZnZ2dnUVZ_rudnZ2d@magma.ca...
> crhras wrote:
>
> Ok, what are you saying? Some parts of the codes are crap. Big deal -
> those parts are not relevant.
>
> Mike
| |
| jusair@arn.net 2006-07-11, 3:25 am |
|
crhras wrote:
> Right, that's exactly what I was saying.
>
>
> "have you considered using a 2 or 3 2x 12 s nailed to each other and crowned spanning the 20 ft in the center of the 30 ft span then run joists perpendicular to the beam giving you a span of only abot 14'9 or 14' 7.5
| |
|
| On Sun, 09 Jul 2006 02:47:46 GMT, "New Wave Dave"
<DjMcB@houston.rr.com> wrote:
>
>"James" <jnipperxxx@nospamfdn.com> wrote in message
>news:svGdnZtSeY14zi3ZnZ2dnUVZ_qGdnZ2d@comcast.com...
>Consider a built-up beam at the mid-point ABOVE the joists and then bolt
>the joists to the beam using angle iron ala . . .
>
> http://www.pbase.com/speedracer/image/2622653. We've successfully
>applied this technique on a handful of jobs always, as in this picture,
>removing a wall after the beam and angle irons are in place. These
>happened to be 2X6 joists.
Nice picture.
I had a 30 year old house with cracks running across the ceiling and
did what you did as an addon to stop the sagging.
|
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