How to support a 2nd floor deck to fix improperly secured deck ledger

Question

I am in the process of fixing a poorly kept and built 2nd floor Accessory Dwelling Unit/garage apt. The most pressing project is to rebuild/repair the 2nd story deck, which gives access to the apt. The entire structure has T1-11 sheet siding, it's rotted where the deck ledger was improperly attached to the siding and no gap placed between house and the first deck board. I think someone tried to fix this before and replaced rotted wood and reinstalled ledger onto siding again. The deck is slightly sloping towards the house so I suspect when they previously tried repairing they detached the deck from house without bothering with temporary support.

The deck is 12x5, 2x6 joists 20"o.c., 2x8 deck boards. Besides the deck ledger it's supported by 4x4 post on concrete deck blocks 6' o.c.

Any suggestions on how I can support it to fix the deck ledger?

Answer 1

Repair half the ledger at a time. While replacing the first half, let half of the old ledger keep things stable. While replacing the second half, let the new half of the ledger keep things stable. If you put danger tape across the access points to prevent people from walking around up there, the deck boards will be sufficient to hold up the joist weight while you work. Just be sure that the deck board fasteners have good withdrawal strength. I wouldn't trust old nails or rusty old screws.

If you want to use the deck itself as a work platform, then replacing half the ledger with a column at the outermost joist won't quite do it. Taking a conservative value for the Fb of your 2X6s (575 psi corresponding to standard grade Douglas Fir), I get a bending strength of 2.54(0.85)(575psi)(1/6)(5.5in)(1.5in)^2(1ft/12in) = 210ft-lb. The midspan load that reaches that bending strength is found by solving PL/4 = P(6ft)/4 = 210ft-lb for P, yielding P = 140#. It's probably actually okay because as the one 2x6 deflects the other 2x6s would pick up some load and avoid some of the stress on the board you're standing upon (my real estimate is that it's good for 300#), but no responsible designer would tell you that it's okay to walk around up there with that column replacing half of the ledger.