I discovered that the lower half of a 4x 4 supporting my deck is rotting.
Since it's load bearing I can;t simply cut it away. How do I support the
deck while I cut out and replace the lower half and how do I fasten the
replacement to the old upper half?
Ahh feel your pain, son.
Two years ago I discovered that the ledger board on our deck had rotted
at about age 15 because the sods who built our home hadn't used pressure
treated lumber for it.
Fortunately the deck joists were still in good shape. The ledger had
rotted from its back side beacause of moisture trapped behind it.
I supported the house end of the deck with a couple of two by sixes
under a sideways two by six. I just cut those uprights about a quarter
of an inch longer that the exact height and whacked their lower ends
along the landscape timbers which I'd fortuitiously placed lined up with
the deck posts a few years earlier. You could lay a board on the ground
and do the same thing.
The ledger board on our deck was so rotted that it wasn't hard to rip it
out in chunks with prybars. And the same sods who used non PT wood for
it had used regular nails on the joist hangers rather than the proper
"thick" galvanized ones, so the heads popped off most of the rusted old
I lagged in a new pressure treated ledger board with flashing added
behind it where there was none before and my youngest son and a
classmate whacked in new proper joist hanger nails for me.
Fortunately there was a window right below the deck and I was able to
place a padded timber across the inside of that window's frame and use a
"come along" and line to pull the deck towards the house so the ends of
the joists were snug against the new ledger when they drove the nails in.
Had to use an old bumper jack and a piece of two by four to take out the
sag and line up the height of the center joists.
As far as your joining a new 4x4 onto the upper half of the existing one
goes, I presume there's a reason why you can't just disconnect whatever
is attached to the upper end and replace the whole joist, or maybe you
feel that would take work than necessary.
If I had to make the splice you want, a neat way to do it would probably
be to cut away half of each post for about eight inches to form two
mating "L" shapes and join them with a couple of half inch diameter
galvanized carriage bolts, washers and nuts through the overlapping
I'd place the splice as close to the top end as possible, where the
bending moment is least and the bolts less obvious.
If you have any doubts about the strength of whatever you end up using,
DON'T TRY IT and get a professional.
Agree, although I'm not sure why you need a 4x4 on top of the screw jack.
It really depends on what the 4x4 is supporting. If it's a beam, you can
probably just have the screw-jack support the beam. If it's bolted into a
framing member, you can use a 2x board on its side (maybe several of them)
and have the screw jack hold the deck up that way.
Basically it depends on how much of the deck is being supported by that
post. If it's a 4x4, probably not that much, but you still probably want to
support it temporarilly.
Also, I sure wouldn't try to splice a post. Just replace the whole thing
and be glad when its done right.
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