Deck joist repair- Dangerous?!?! Picture

[TSO]

Howdy,
I am looking for advice in repairing a deck main joist that got invaded by carpenter ants after experiencing some rot. Below is an illustration of the problem -



The outer joist is three sistered 2x12x20'. ONly the two outer ones have been affected, just a tiny bit of rot on the bottom where water pooled on the third. The rest of the span is solid.
Because the entire deck structure is enclosed top, sides and bottom with decking and siding, it would be a MAJOR pain to have to rip off everything and replace all three joists. Is ther any splicing or splice/sistering that will do the trick and give enough support?
Thanks

[HayZee518]

I would think that you could sister a 2x12x10 on the middle joist using lag bolts that are countersunk so the heads don't protrude above its surface, then sister another 2x12x20 on top of that one. Use waterproof construction adhesive between all joists. if you have access to the back of the non affected beam, use long carriage bolts and stagger the bolt pattern. you are going to have to remove some siding to make the repair. there's just no way to nail the things up from underneath. I wouldn't trust nails on a joist. bolts are the way to go.

[TSO]

Thanks for the input!
I figured that I could safely lag two new 2x12 on. It would mean removing all the casework on the outside and underside of that end, for the full 20'.

I guess I was wondering if ther was someway to safely splice some new 2x12 on without removing the full length. Thanks to a quirck on the forum, the diagram is below.


Would this provide aneough strength? I don't know how glueing and bolting a splice compares with a solid length, but i don't want to do something unsafe or "non-code". The deck is 14' in the air, and i wouldn't want it to be a hazard.
The 14' is whay I am alos loath to have to do major reconstruction...

[TSO]

Whoops, for some reason....

[TSO]

This time when i tried to post....

[TSO]

The forum said I needed 5 posts...

[TSO]

Before i could attach a URL. Weird. Here's a diagram of what I was saying -

[HayZee518]

yeah you could "cut n paste" a few 2x12s I was just thinking of the weight over the span, that's why I suggested the 2x12x10 and the 2x12x20. Using the adhesive on the joists you will be creating a structural beam. heck, trusses they make now are 2x3's with OSB in between [oriented strand board]

[mrcaptainbob]

Joist repair....

Because of the recommended minimum five foot overlap, would that put the distance between the joint ends at ten feet, Hayzee?

[TSO]

THanks all for the input.
So... is the recommended overlap 5 feet? I could accomplisj that without removing the entire structure end. Will five feet glued and lag bolted give the appropriate span strength?

Thanks

[HayZee518]

I don't see why not. Take a typical ten footer and place it on two end supports so the width is up and down. Now put a sizable weght in the middle. you'll see it deflect down about a half inch. Now put the end in the middle so you have five feet to the end support. jump on it! It won't give much! Same idea here. The adhesive when it cures makes two boards "one piece." AND with three together, you got almost a steel I beam here!

[pushkins]

The minimum safe overlap for a splice in your situation is 5' like previously mentioned.
Remember you cannot drill a hole less than 1.5" from the end of the cut lumber (2.5"-3" is much better) or from either edge. You will want the bolts staggered like HayZee has already mentioned as well.
Don't skimp on the waterproof glue either and apply it in a wiggly line fashion the full length of the replaced bearers.
If it were me, I'd replace the piece for the middle section and then replace the whole outer bearer (glued and bolted).
The way already described will do the job just as well though.

[buckofdurham]

tos,
Would it be possible to install an other pier. Each splice should have a pier under it.