Floor Joist Beam Spans
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-- |
Floor Joist Beam Spans
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" wrote in message 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-- |
Floor Joist Beam Spans
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 |
Floor Joist Beam Spans
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-- |
Floor Joist Beam Spans
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-- |
Floor Joist Beam Spans
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-- |
Floor Joist Beam Spans
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. |
Floor Joist Beam Spans
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 |
Floor Joist Beam Spans
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-- |
Floor Joist Beam Spans
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 |
Floor Joist Beam Spans
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 |
Floor Joist Beam Spans
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-- |
Floor Joist Beam Spans
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. - |
Floor Joist Beam Spans
Thanks Marson, this is good info and good advice. I am printing it to keep
for future reference. --James-- |
Floor Joist Beam Spans
"James" wrote in message . .. 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 |
Floor Joist Beam Spans
try Cedar county Missouri. No permits required for anything except a septic
system. -- Steve Barker "Michael Daly" wrote in message ... However, I don't know of any place in the western world where building codes don't apply. Mike |
Floor Joist Beam Spans
New Wave Dave wrote:
"James" wrote in message 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. 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 |
Floor Joist Beam Spans
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 |
Floor Joist Beam Spans
Ok, then. If there's no permit required, and therefore no inspection, where
does the code come into play? -- Steve Barker "Michael Daly" wrote in message ... 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 |
Floor Joist Beam Spans
On Sun, 09 Jul 2006 12:18:05 GMT, with neither quill nor qualm, "Steve
Barker LT" quickly quoth: Ok, then. If there's no permit required, and therefore no inspection, where does the code come into play? Common sense, perhaps? Codes are there for a reason. Buildings and projects built to code (or better) are both safer and last longer. -- When love and skill work together, expect a miracle. --John Ruskin (1819-1900) |
Floor Joist Beam Spans
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" wrote in message ... Ok, then. If there's no permit required, and therefore no inspection, where does the code come into play? -- Steve Barker "Michael Daly" wrote in message ... 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 |
Floor Joist Beam Spans
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 |
Floor Joist Beam Spans
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 ? |
Floor Joist Beam Spans
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 |
Floor Joist Beam Spans
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" wrote in message oups.com... 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 |
Floor Joist Beam Spans
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 |
Floor Joist Beam Spans
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 |
Floor Joist Beam Spans
Interesting... where did I say that? "Michael Daly" wrote in message ... 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 |
Floor Joist Beam Spans
On Sun, 09 Jul 2006 19:28:09 -0400, with neither quill nor qualm,
Michael Daly quickly quoth: 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? You've obviously never read any of the NYC or Chicago codes. I think they were written by a pack of rabid union lobbyists and don't even _compare_ to the lovely and light NEC manual. ;) (Disclaimer: I've only seen snippets of those codes and they're wild.) ----------------------------------------------------------------- When I die, I'm leaving my body to science fiction. --Steven Wright ---------------------------- http://diversify.com Comprehensive Website Development |
Floor Joist Beam Spans
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 |
Floor Joist Beam Spans
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 |
Floor Joist Beam Spans
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 |
Floor Joist Beam Spans
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 |
Floor Joist Beam Spans
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: 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 |
Floor Joist Beam Spans
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/fp.../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) a few barn photos at: http://www.terryking.us/photos/barn/2www-barn1-2004/ |
Floor Joist Beam Spans
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 |
Floor Joist Beam Spans
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" wrote in message k.net 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 |
Floor Joist Beam Spans
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. 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. 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 |
Floor Joist Beam Spans
Right, that's exactly what I was saying. "Michael Daly" wrote in message ... 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 |
Floor Joist Beam Spans
On Sun, 09 Jul 2006 02:47:46 GMT, "New Wave Dave"
wrote: "James" wrote in message ... 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. 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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