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Spudmasher1
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# Posted: 6 Aug 2012 04:55
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In my attempt to aquire building material, I collected 2x8's to use for floor supports. My cabin plan is 20x20 feet. The base will be built on building block for support, a skid base not on piers.
My problem is these 2x8 are only 18 feet useable material. These were tearouts from an old barn and after pulling nails and trimming the ends they will only be 18 feet.
The way I see it I have several options.
1. Downsize my building plan to 18x20. I really have my mind and heart set on a 20x20.
2. Splice the 2x8 in one of two ways.
A. Butt a 2 foot 2x8 up to the 18 foot section and sandwich splice with side pieces (I'm thinking 30 inch 2x8's each side for strength) to make a 20 foot board or
B. Cut a 5 foot 2x8, line up to add the additional 2 feet I need then nail the boards together. (If I did this, I would have to adjust for nailing my decking on.)
3. Aquire 20 foot 2x8's to replace these.
I started out thinking this cabin was small enough I would just buy all new material. Boy I was wrong. The only way I could do that is find another full time job or stop making house payments on the family home. That's not going to happen.
So I need advise and opinions. Thanks Spuds
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rayyy
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# Posted: 6 Aug 2012 07:04
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I'd say,for all the extra work that two foot is gonna cost you,go with the 18x20 floor plan.You can always add the 2 feet onto the length of the cabin.
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VTweekender
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# Posted: 6 Aug 2012 07:35
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I think splicing as described in 2-A would work fine as long as there is a support under the splices. Plan to set a skid under those splices the length of the building, depending on where you planned to set the skids you may have to cut the 2x8's back further, in other words if you planned on skids every 4 ft then cut to 16 ft and splice in 4 ft.
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GomerPile
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# Posted: 6 Aug 2012 09:33 - Edited by: GomerPile
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You know that a spliced 2x8 will never be the same strength as one that is the correct length.
If you sandwich splice them I would use gorilla glue on the joints and clamp them together to make the glue set well. To transfer load across the splice you have 3 fastener options:
1) Screws (DO NOT USE SCREWS very dangerous they will shear)
2) Nails (10D common nails have 94lb shear strength each, can probably do a 6 inch grid pattern)
3) 1/2" Bolts (very strong but expensive)
You best bet is probably #3 with 4 bolts (or more) on each side of the splice. You will probably find that getting the right wood is cheaper than using bolts. If you are having this work inspected, I would chat with the inspector before spending any money.
I agree with rayyy if you have supports under the splices, then you probably don't have much to worry about.
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fpw
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# Posted: 6 Aug 2012 10:21 - Edited by: fpw
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Splicing works fine, but I would put some type of support under the splice.
These joists are thru bolted.
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TomChum
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# Posted: 6 Aug 2012 11:16 - Edited by: TomChum
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You didn't say how far these joists are spanning, but.....if adding another support is a hassle you wouldn't be asking about extending the boards?
For extending the 18s to 20, I'd choose "B)" - The 5-foot piece sistered on is fine.
Quoting: GomerPile You know that a spliced 2x8 will never be the same strength as one that is the correct length.
Hey GP, sorry but I disagree. If nailed correctly it can be much stronger. If the overlap is glued (with liquid nails adhesive for example), the extended joist will be much stronger than a continuous board (just difficult to inspect). Old wood is an unknown, but old-growth DougFir could be twice as strong as 'new pine'.
Adding adhesive is easy and quick. Watch that too many nails might split the old wood. There might be some joints where a few screws will help to pull a it together tight.
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GomerPile
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# Posted: 6 Aug 2012 11:44
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Tom, I agree that a 2x8 glued together is gonna be super strong and in most applications I would personally nail and glue on a spliced section.
Lets assume you have no glue and only nails. If you manage to get 10 nails on each side of the splice the nails will support 1000 pounds of static load (not bouncing up and down). Add glue to that and is it 2X stronger or 5X stronger? The elasticity of the adhesive will play a large part in how well it deals with dynamic loads.
Imagine a floor with several of these splices (unsupported) under a 600 pount wood stove where the person loading the stove weighs 250 pounds and stacks 100 pounds of fire wood then jumps up and down in disgust as the Patriots loose yet another superbowl to the Giants.... 
At the very least I would worry about sags developing under heavy loads over long time periods.
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Spudmasher
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# Posted: 6 Aug 2012 11:56
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Rayyy adding the 2 feet on the other end is possible. Will have to give that some thought.
VT yes I was planning on a block every splice for support. Good thought on cutting it back to 16 foot. I hadn't thought of that. I have plenty of boards to use.
Gomer no worry about an inspector. Only needs my approval. Dad would give his opinion too. 80 years of experience there. I'd be using a nail gun. Hadn't thought I would need glue too.
Tom these are 18 foot with support blocks under every 80 inches.
Great picture fpw. It always help for me to see something to make it stick.
The lumber is from a 70 year old barn. Boards are heavy and dark in color. Not true 2x8 but 1 3/4 x 7 something.
Thanks everyone for the help. Spuds
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TomChum
Member
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# Posted: 6 Aug 2012 15:41
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For a real-life comparison, the 2X8 floor joists in my house are 85 years old and span ---> 144 inches <----
You're not going to have any problem.
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Martian
Member
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# Posted: 7 Aug 2012 07:47
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Think about cutting them in half and span between your 80" supports since you said you have plenty of them.
Tom
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rancid
Member
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# Posted: 7 Aug 2012 20:28
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22x18 sounds better
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Borrego
Member
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# Posted: 7 Aug 2012 22:09
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Quoting: VTweekender I think splicing as described in 2-A would work fine as long as there is a support under the splices.
This is best. Glue, screw and nail. Strap also, but you'll be fine.....
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Spudmasher1
Member
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# Posted: 8 Aug 2012 03:41
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I feel better about splicing after all the input. I really want to stick with 20x20.
Thanks again everyone. Spuds
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MtnDon
Member
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# Posted: 8 Aug 2012 14:12
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20 x 20 = 400 sq ft
18 x 22 = 396 and 18 x 24 = 432 How about one of those?
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OwenChristensen
Member
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# Posted: 10 Aug 2012 16:19
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I wouldn't build with a center skid in frost country.
Owen
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toyota_mdt_tech
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# Posted: 5 Oct 2015 10:35 - Edited by: toyota_mdt_tech
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splicing works fine, overlap a couple feet on each side of a girder. I don't think a 2X8 can span past 12 feet anyway at 16" centers. So a girder mid way puts you at 10 feet span, either side of the girder, should be good to go. Now how to make it maintain level on outboard skids. I guess a thick a heavy bed of crushed rock under it, packed in place to keep water draining away. Maybe even location, a nole, or high spot then topped with heavy crushed rock bed. The foundation is the most important part IMHO, and so tough to repair or correct after the cabin is all in place.
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Don_P
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# Posted: 5 Oct 2015 22:55
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...Correctly, the splices are 80+" long and rest on two bearing points (the girders are 80" apart, he has 2 center skids). I would cut 4' off the 18's, just past the girder at 160", and save it for header material. Three year old post, I hope he can get it done now 
Nobody suggested alternating spliced ends. If you're going to be bad, at least do alternating weak framing.
To check it, this is a continuous beam overhanging a support, it isn't dramatically out of range using design loading. Don't mistake an elastic construction adhesive for a structural glue, they are meant more as a gasket and have good elastic creep. It will make the joint stiffer under an impact like a footfall but it would slowly creep into a bow under load over time if the glue is used to carry load. Use enough fasteners for the load and the glue becomes gravy.
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Rowjr
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# Posted: 27 Oct 2015 19:30
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Stick to your plan Use 3 center overlaps on both ends and put girders underneath where the splices overlap. Might need more 2 x 8s but more support is always better Check out my cabin design when you get a chance...
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KinAlberta
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# Posted: 21 Nov 2015 01:22 - Edited by: KinAlberta
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I've posted elsewhere on my family's positive experience with two family cabins which sit on concrete blocks dug into soil. One is 24x30 and the other is 24x24. Very minimal movement over 6 decades.
However, now that I'm trying to level them (just slightly) I'm sure wishing my dad and my uncle had significantly "overbuilt" the floor beams and/or lifted the buildings higher off the ground so I could fully access the entire footprints from the undersides. Had they done so, jacking up this or that corner or centre section a 1/2" or so would be a snap. Instead I'm having to consider bringing in a company to professionally level them or sliding additional "way overbuilt" super stiff wood beams under the buildings so I can jack from one side and be assured of lifting the centre (12' in) portions of the buildings.
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OutdoorFanatic
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# Posted: 21 Nov 2015 19:33 - Edited by: OutdoorFanatic
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Splice them staggered about 6'-8' apart, glue them with liquid nails, and shoot the crap out of them with nails. Then glue a 3/4" plywood gusset over the spliced ends and shoot it full of nails.
You'll be fine.
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