Advice for strengthening structural mistakes

My wife and I purchased a house with a detached 3-bay garage. On the back side of the garage the previous owners hacked in a 16x30 ft lean-to. The joists are 2x6x16 treated and set on Simpson joist hangers on both ends on 16" centers. The one good thing they did was use 6x6 posts and spanned no more than 10' the long way and 8' the short way, so if you imagine looking at it from the front, there are four posts 10' apart on the outside, and other 4 posts 8' behind those, and nothing under the ledger board attached to the garage. The top ledger board from what I can tell is screwed into the studs framing the garage.

This whole thing was put up with regular deck screws, no nails. None. All the joist hangers are up with regular 3" deck screws. This was pointed out during the home inspection and the inspector said he felt like the structure was stable an safe but that it could be strengthened to make it safer. As of right now, this structure shows absolutely no sign of failure. My best guess is that it's around 5 years old. There is no sagging, all the joists are securely fastened. The roof is shingled and I got up there and bounced around and it feels solid. Obviously I'm concerned about the longer term implications of the structure because I do keep my mowers, trailer, and other equipment under it. I'd also like to use one of the 10' sections for a dog kennel one day.

I cannot afford to take down this structure and do it correctly right now, we just sunk everything into the house. I would like some ideas for strengthening the structure so I can use it long term - if possible. One idea I had was to replace the deck screws in the joist hangers, one at a time, with Simpson structural screws approved for joist hangers. My concern there is that the replacement screws might not get enough "bite" since a hole is already there, and I was also afraid a nail would be ineffective in that case as well. I am also planning to put some posts in right next to the outside garage wall to support the attached ledger board, and then run some members long way bolted to the posts to support the underside of the joists on both ends and in the middle.

Any comments here would be greatly appreciated.

When you say "regular deck screws" do you mean these? https://www.homedepot.com/p/Grabber...-SearchPLPHorizontal1_rr-_-NA-_-203696291-_-N Which look like a galvanized drywall screw? If so, how long are they? These don't have a lot of shear strength, just like drywall screws don't have much. So I could see why you'd want to replace them.

I'd take them out one at a time and try replacing them with a screw designed for the purpose. I suspect if you replace them all you'll get enough bite in the wood to make them connection secure. Especially if your new screws are longer than what you're replacing and they go into framing lumber.

Thanks for your reply. They look to me like they are the 3" Power Pro gold-colored screws like these, or something really similar which I've used on deck boards before. The good part is that with the star-drive head, they are super easy to remove.

They appear to be all 3" screws (I only removed one) which worked because the rims are all double 2x6 (also screwed together). But that also means my structural screws won't bite into new wood unless they are thicker - which may well be the case. But it's also possible a thicker screw won't fit thru the simpson hanger holes. The ones I was considering using are these but I'd have to go out to Simpson's site to make sure they are compatible with the hangers. Each of the joist hangers have 3 screws on each side into the rims and two on each side toe-nailing (toe-screwing?) the ends. That's 10 screws total on each end on each joist. Honestly, outside of using screws, the structure is made incredibly well and is solid. It's the shear strength of the screws right next to the building that concerns me for the long haul. I am plenty comfortable replacing them with structural screws, which would cost me a fortune one time but might allow some piece of mind. And I might be able to find them in bulk elsewhere for a better per-piece price.

Is the garage finished inside if not put a 2x8 between every other stud opposite the ledger nailed or screwed sideways thru the studs. Then drill and screw a lag bolt thru each one into the ledger.
Leave all those screws there and push bend or twist the HDG hangers in there as best you can and only worry about the holes into the ledger. .
There are special HDG hanger nails that are the diameter of a 3" nail but only 1 1/2" long , Nails are better than screws for shear but you have so many you would worry more about the wood splitting than shearing screws.
Before we had hangers we used pressure blocks, They would go in between to rafters and the inspectors want 2 nails toe nailed in the ledger and 2 nails side ways in to the block and 3 nails on each end of the block into the ledger. then after that was built we would go back and put the rest of the blocks and nail everything again. Inspectors like hangers because at a glance they can see a missing nail.
In the middle of the 16 ft put a 2x4 block flush to the bottom of the rafter between every rafter, that stops them from rolling over under a heavy snow load. If you snap a center chalk line you can alternate the blocks on each side of the line to make nailing or screwing easier.
I would bet that everyday there are a 1000 decks and sheds built with 3 inch deck screws so don't sweat it to much.

Got a picture so we can see what your seeing?

I am sorry I do not have pics with me today.

nealtw said:

Is the garage finished inside if not put a 2x8 between every other stud opposite the ledger nailed or screwed sideways thru the studs. Then drill and screw a lag bolt thru each one into the ledger.

Click to expand...

Oh that's an excellent idea and now that you say it I can't believe i didn't think of tackling the issue from inside the garage instead of outside. the garage is unfinished with access to the framing, so while I'd have to move a crap ton of stuff that project could be easily accomplished and that would at least provide some piece of mind for me at the connection point. The builder (which I'm assuming is the previous owner) used the same 3" screws to attach the 2x6 ledger board to the garage studs. So with the sheathing in between, there can't be more than 1" of the screw into the studs. ugh.

nealtw said:

In the middle of the 16 ft put a 2x4 block flush to the bottom of the rafter between every rafter, that stops them from rolling over under a heavy snow load. If you snap a center chalk line you can alternate the blocks on each side of the line to make nailing or screwing easier.

Click to expand...

There are two rows of these blocks flush to the bottoms at 4' and 12' instead of in the middle. That part is OK.

Bill Hartman said:

There are two rows of these blocks flush to the bottoms at 4' and 12' instead of in the middle. That part is OK.

Click to expand...

That's better. in a floor they are no more than 7 ft apart so you would have 2, in a roof when it is called for they are no more than 10 ft. So somebody cared about yours.

yea it's actually a pretty solid job - someone just has a higher regard for deck screws than I do. I'll get that ledger more secure and forget about the rest of it. I have other stuff to do anyways.... Thanks to you and the rest for the responses, they were extremely helpful.