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Old 03-08-2012, 11:53 PM   #1
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floor joist (seaming two sections)


i need to sister two 2x10 floor joists due to termite damage.
the span is 14 ft but due to space limitations/pipe obstructions it will not be practically possible to get a solid 14 ft length in place. if i do it in sections and than make a mending/seaming plate with another 2x10 extending 2-3 feet beyond each side of the seam held in place with carrage bolts will this suffice?

is there any formula or calculation which would dictate how much overlap the mending plate should have to give the same structural integrity?

thanks

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Old 03-09-2012, 12:17 AM   #2
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floor joist (seaming two sections)


Most the time the tremites have to get into the joist from one end or the other, eating there way to the point where you can see the damage, so most of it is hidden.
So you may be attaching to a compromised section of wood.
No way to suggest a way to get a whole length in without being there to look at it.
Best bet is to just try and get the very longest piece you possible can in there.
You did get a termite treatment, right?

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Old 03-09-2012, 12:43 AM   #3
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floor joist (seaming two sections)


the termite damage is from 20 years ago, i want to put a heating oil tank in the corner where the floor joist is located so i want to do this repair before the tank goes in otherwise the tank will be way too much of an obstruction. you are correct about the termite damage being hidden/beam compromised. i would say that the beams are basically paper at this point, unfortunately installation of a 14 ft section will not be possible. do you think the seaming is technically viable or a waste of time? the location is in the corner of the house, not under any bearing wall etc.
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Old 03-09-2012, 01:04 AM   #4
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floor joist (seaming two sections)


any pics? those always help a lot. maybe someone can then offer a work-around, like ending the new 2x10 at a header going to ones on either side.... or something....
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Old 03-09-2012, 02:28 AM   #5
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floor joist (seaming two sections)


I am im mo way an expert but put this idea out there for others to comment on.

How far up the beam are your obstructions? could you possibly put a 2x6 on each side?
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Old 03-09-2012, 07:42 AM   #6
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floor joist (seaming two sections)


It is definitely possible to splice (the word seam is usually used for roofing material) two short pieces of dimensional lumber into a longer piece. This is not commonly done because it almost always requires an engineering stamp on the splice plate (the plate refers to the construction element that ties the two short joists together). The following link shows a method used by a FACTORY to manufacture long joists using shorter lumber. This technique essentially uses a metal truss plate, which unfortunately cannot be used by a DIY person because proper installation of the plate requires an expensive tool.

http://www.builderonline.com/high-pe...a-fresh_3.aspx

However, it is possible to achieve a similar result using an overlap piece of dimensional lumber and an appropriate bolt pattern. The overlap is generally pretty substantial, could be as much as 3 feet either side of the splice (6 foot overlap board), and the bolts are typically 1/2 inch galvanized bolts with nuts and washers, typically not carriage bolts due to the need for proper torquing of the bolts. The engineer works out the required length based on moment transfer and shear requirements, then works out the required bolt spacing pattern based on a fairly complex mathematical analysis that takes into account shear failure of each bolt and shear failure of multiple bolts. The bolts are never the limiting factor, it is almost always the strength of the wood in shear, i.e. you have to prevent tear out of the wood around the bolts.

I know this sounds needlessly complex, you just want a simple answer, unfortunately this is not a simple analysis, which is one reason I have only seen it done once in the field. Most folks simply find a way to install a new, full length joist, and be done with it.
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Old 03-09-2012, 09:51 AM   #7
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floor joist (seaming two sections)


Any advantage to using steel joists?
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Old 03-09-2012, 01:13 PM   #8
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floor joist (seaming two sections)


Quote:
Originally Posted by Marvel View Post
Any advantage to using steel joists?
Good idea. Sure there is advantage; steel will carry more load for a given height, as you can get any number of flange widths and thicknesses, as well as web thickness.

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