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pcroom
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# Posted: 22 Dec 2015 06:39pm
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I'm building a 16x16 with a second floor but low enough that it's still under 300sq foot. It's on peirs 9 of them them beams are 3 2x10 the space between them are 6' 10 inches the span between the beams. I was going to use 2x12 for the floor joist is that overkill can I use 2x10 I don't want any sag in the floor. Thanks please help I'm reading to start on the floor!!!
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MtnDon
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# Posted: 22 Dec 2015 06:55pm - Edited by: MtnDon
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Handy calculator for sizing joists and rafters .
You need to know what lumber species are available to you and the grades. Standard floor loads are based on 40 PSF LL=Live load; DL = dead load, the materials. If you plan on heavy tile or stone increase the DL) Std floor deflection (sag) is L/360, where L= joist length in inches. L/360 is maximum for tile. For stone you need less deflection, L/720.
2x12 on 16" centers work for most commonly available species and sizes. The calculator is a nice learning tool.
You have probably seen and read the many caveats against building on piers. They do not meet codes for habitable bldgs and generally for good reasons....
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pcroom
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# Posted: 22 Dec 2015 07:04pm
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I don't understand the calculator I think it's pine from lowes and I don't need a permit for my size I'm building no codes needed. My peirs are super solid tho...
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MtnDon
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# Posted: 22 Dec 2015 08:17pm - Edited by: MtnDon
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Quoting: pcroom I don't understand the calculator
Go to calculator page.
Select the species
Select the size (2x4, 2x6, etc.)
Select the species (if not sure, ask at the store)
Select the grade (ask if not sure.)
Member type is Floor joistDeflection; leave at L/360 for floor joists
Spacing is 16" normally; could be 12" for a stiffer floor, or to reduce joist depth.
Exterior exposure: wet would be for something like a deck that gets rained on; incised is sometimes used on treated lumber. For a normal cabin floor "No" for both
LL & DL I already covered
Then click on the Calculate button. The calculator provides the maximum span and indicates how much on the length at each end bearing point must be sitting on a solid support.
So, using Douglas Fir - Larch, 2x12, #2 on 16" centers the calculator indicates a maximum span of 18'1" with an end bearing of 0.64". Try it. Then change the joist to a different size and recalculate. Then try a different species.... Etc.
If you go to the store or lumber yard and look at the lumber you will see each piece is grade stamped. The main thing to look for is the species and the grade.
If you are interested here's a link to some info on grades that I complied.
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pash
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# Posted: 22 Dec 2015 08:20pm
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If its pine from lowes it is most likely Southern Yellow Pine (syp) and most likely #2. If I am correct in seeing the span is 6'10" then you will be fine. Although, check your terms and such, without blueprints or drawings we cant be sure that it works. One thing I like to do when I build decks/floors is use 12" centers if i dont want sagging or i know that I am putting tile down. It just takes all of the springiness out of the floor and feels way more solid, even if 16" centers were within spec.
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pcroom
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# Posted: 23 Dec 2015 01:48pm - Edited by: pcroom
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Thanks
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pcroom
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# Posted: 23 Dec 2015 01:57pm
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I understand about 16 on center and going closer but what about the length not width. The length betw5my beams 6'10 inches will that sag with a 2x10 the outside board from the weight or should I use a 2x12 it will be a full loft upstairs.
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MtnDon
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# Posted: 23 Dec 2015 02:07pm
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A drawing of the proposed plan would be very nice, showing distances between piers and beams. That leaves no room for misinterpreting what is written. I work better from drawings than words. I may have misinterpreted the beams... are you saying two beams or three beams? I was thinking two, one down each side. I saw the 6'10 and thought that was from pier to pier.... I have not looked at beam size (3-2x10) yet to figure that out. Can't do that w/o knowing more about the upstairs, snow loads....
When you say full loft you actually mean a second floor but with limited headroom to try and sneak around some rule? What will be up there? That will increase the loads on the footings that the piers need.
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pcroom
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# Posted: 23 Dec 2015 02:21pm
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3 beams 9 peirs my beams are 3 2x10 together and the distance between them are 6' 10 inches and we don't get much snow here in Missouri
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MtnDon
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# Posted: 23 Dec 2015 03:30pm - Edited by: MtnDon
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So only three piers under each exterior side wall. That would be stretching things a little thin... that would be 8 feet apart. TABLE R502.5(1) GIRDER SPANSa AND HEADER SPANSa FOR EXTERIOR BEARING WALLS indicates 8'9" spacing maximum for 3 - 2x10 supporting a roof, ceiling and one center bearing floor. But you have a second floor you call a loft. According to the table if both floors had center bearing then 3 - 2x10 would be okay for 7'3" span between piers. But you probably don't want posts in the middle of the main floor. So using 3 - 2x10 and clear spanning each floor would call for the pier spacing to be 5'11".
One more thing.... you state there would be 6'10" between the beams. How was that measured; center of the beam or inside or outside? What is important is how much overhang / cantilever distance will there be at the end of each floor joist? According to code the cantilever should be limited to a maximum distance equal to the depth of the floor joist. If the joist is a 2x12 then that is 12" maximum cantilever.
If you have a center support beam you don't need 2x12 for floor joist stiffness, but you might need 2x12's for the cantilever.
A dimensioned drawing would make a lot of questions unnecessary and prevent misunderstandings.
If you built on a full perimeter block foundation you would not need beams. The entire wall would be supported on the foundation with the load nicely spread. You could clear span both floors with the appropriate joist sizes, species and grades, for example.... 2x12 SYP, non dense#2 will span 16' maximum, dense gives another foot.
Plus the entire structure would be stronger.
What kind of a roof? Design is best done from roof down to the bottom so you know what kind of a load the bottom has to carry and how to safely distribute the loads and get them to the ground.
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pcroom
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# Posted: 24 Dec 2015 01:00pm
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At the ends of my beams I have at the most 6 inches hangover center to center of the beams are just a tad over 7' now if I measure in between the peirs I get a tad over 6'
Ok now going the other direction cantilever wide side is 8" overhang and the over is 10" overHang
And measuring center to center of the beam where the floor joist will be crossing over the beams are 6' 10" and the over side is 7' 3" ops I kind of off there.....
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pcroom
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# Posted: 24 Dec 2015 01:07pm
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What can I do to fix the the beams being so far apart now at 7' 1"
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pcroom
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# Posted: 24 Dec 2015 01:15pm
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In between the piers I have 6 foot 3 inches now thats closer to your 5' 11" number would that work??
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pcroom
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# Posted: 25 Dec 2015 03:07am
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What do u think?
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toyota_mdt_tech
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# Posted: 26 Dec 2015 11:06am
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Quoting: pash If its pine from lowes it is most likely Southern Yellow Pine (syp) and most likely #2. If I am correct in seeing the span is 6'10" then you will be fine. Although, check your terms and such, without blueprints or drawings we cant be sure that it works. One thing I like to do when I build decks/floors is use 12" centers if i dont want sagging or i know that I am putting tile down. It just takes all of the springiness out of the floor and feels way more solid, even if 16" centers were within spec.
I am with Pash here. I know you can go up to 12 feet with 2X8's at 16" OC. But going more HD is a plus. Like Pash said, spring in floor. Another way to remove spring is to to X blocking between joist too. Its time consuming but material cost is minimal.
My cabin (16X18) spans 12 feet with 2X8 and 16" OC and floors are rock solid, zero spring at all. My plans called for SPF (spruce, pine or fir) Most of my lumber was fir. IMHO, douglas fir is some of the best wood for construction.
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Don_P
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# Posted: 26 Dec 2015 12:23pm
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What can I say, I look up torques when rebuilding an engine too.
Span tables for floor parts are in Chapter 5, labeled "Floors" at this link;
http://codes.iccsafe.org/app/book/toc/2012%20VA_Residential_HTML/index.html
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pcroom
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# Posted: 26 Dec 2015 03:06pm
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Thanks
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pcroom
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# Posted: 27 Dec 2015 02:29pm
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Would I be fine I guess I'll just use 2x12 to be safe since no more replys!!!
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pcroom
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# Posted: 28 Dec 2015 10:58am
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???
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Don_P
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# Posted: 28 Dec 2015 09:30pm
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I can't make heads or tails of your writing, post full dimensioned plans and include max snow load in pounds per square foot.
I was driving into WV a couple of months ago, now I don't know if you've ever driven in WV but I'm pretty sure MC Escher got some of his ideas while on a road trip there. So finally, ... yeah I did it, I pulled into a country store and asked directions. The girl at the counter said "You're lost!" and she didn't have a clue how to remedy that situation. But an old man was stepping in the door about then and she said "He knows". After he proceeded to tell me just how lost I was he said "Follow me", and we followed him for 20 or 30 miles over hill and dale. He finally pulled over and explained the rest of the way. I asked where he was going from there. "Oh I was going the other way, But You Was Lost!"
My friend, you need to find that old man to work alongside you, you are lost!
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MtnDon
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# Posted: 28 Dec 2015 10:35pm - Edited by: MtnDon
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  ... like I said back a ways... dimensioned drawing!
A mutual friend who lives in WV has told me he rescues people frequently who have been following their Garmin Navigator down WV mountain roads..... roads that go here & there & nowhere.... 
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pcroom
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# Posted: 2 Jan 2016 03:47am
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I live in missouri we don't get much snow at all but anyways I'm using 2x12 x16. We haven't even got flurries yet and I wouldn't even know how to calulate snow fall on my roof. It's not to hard to figure out what I'm doing from my text.
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jcstinnett
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# Posted: 7 Oct 2017 07:19am
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toyota_mdt_tech
So I am building a basic loft in our lake house. it is a typical 2 story townhome with a vaulted ceiling on the upper floor. there is room for a 14' X 7' basic platform loft. The loft will be supported on 3 sides by the interior walls then I plan on adding a 4x4 column in the center of the unsupported side. There is a bathroom directly below to serve as my bearing wall. My question is can I use 2x8 joists? I'm in Georgia and want to make sure I meet code. I should add that the ledger boards around the outside will be lag bolted and held up by brackets and screwed into the interior wall studs. so it won't be supported by columns around the perimeter. The loft will only be used for sleeping and will have a couple of single beds and a small dresser. I plan on accessing the loft with a spiral stair I picked up.
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toyota_mdt_tech
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# Posted: 7 Oct 2017 09:31am - Edited by: toyota_mdt_tech
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jcstinnett, I am no engineer. I did buy engineered plans for my cabin, pulled the permit and it was all signed off by the county.
I have 2X8 floor joist at 16" OC running 12 foot spans, no girders. The sheeting on top was 3/4 T&G and glued and screwed. I am certain this is minimum, going heavier IMHO is always a plus.
I would listen to the 2 Dons advise, they are pretty savvy with this stuff.
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Just
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# Posted: 7 Oct 2017 11:46am
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In ont. a 14 ft span requires 2 x10 s on 16 in . centers and your ledg
er plate should be cut at least 1/ 2 in. into your wall studs and nailed no screws then ,joist hangers with nails not screws or jack studs going to the floor plate.
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Borrego
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# Posted: 10 Oct 2017 10:24pm
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Hilarious thread! ROFLMAO 
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toyota_mdt_tech
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# Posted: 12 Oct 2017 09:55pm
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Quoting: jcstinnett I should add that the ledger boards around the outside will be lag bolted and held up by brackets and screwed into the interior wall studs. so it won't be supported by columns around the perimeter.
Yeah, that isn't going to work. All the floors load will be on those bolts. No go and no way will any inspector OK that.
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