Shimming works, but if the trusses are really twisted or bowed, I’ve had better luck just sistering full-length 2x’s. It’s a pain pulling boards, but it saves time later when you’re not chasing squeaks or dips. Up here, shortcuts just don’t hold up—freeze/thaw will find every weak spot.
Not sure I totally agree with pulling all the boards just to sister every truss.
I get the logic, but if the twist isn’t too wild, I’ve had luck just shaving down the high spots and shimming the low ones. Full sistering’s solid, yeah, but it’s a lot of extra lumber and time, especially if you’re just dealing with a couple problem trusses.“It’s a pain pulling boards, but it saves time later when you’re not chasing squeaks or dips.”
Up here (northern Ontario), we get brutal freeze/thaw too, but I’ve seen decks hold up fine with careful shimming and making sure everything’s screwed down tight. Only time I’ve had real issues is when guys try to rush or use junk shims. If you’re picky with your layout and double-check for level as you go, you can dodge most of the headaches without tearing half the structure apart.
Guess it depends how bad the trusses are and how much time you’ve got. If it’s a new build, sure—sister away. But for a quick repair or if you’re short on material, shimming’s not always a shortcut in my book.
“If you’re picky with your layout and double-check for level as you go, you can dodge most of the headaches without tearing half the structure apart.”
That’s been my experience too, especially on older decks where you’re just trying to get a few more years out of them. I’ve always wondered, though—when you’re shimming over a wide span, do you ever run into issues with the shims compressing over time? I had one spot by the stairs where things settled after a couple winters, and I had to pull up a few boards to redo it. Maybe it’s just the type of wood I used...
“I had one spot by the stairs where things settled after a couple winters, and I had to pull up a few boards to redo it.”
That sounds familiar... I used cedar shims once thinking they’d hold up, but after two rainy seasons, they squished down like a bad sandwich. I’ve had better luck with composite shims, but even then, wide spans seem to find a way to sag. Maybe it’s just the nature of old decks—nothing stays put for long. Ever tried using strips of leftover metal flashing as shims? Not pretty, but they don’t compress.
Ever tried using strips of leftover metal flashing as shims? Not pretty, but they don’t compress.
Yeah, I’ve done the flashing shim trick a couple times—definitely not winning any beauty contests, but it does the job. I hear you on cedar shims turning to mush. Composite ones hold up a bit better, but like you said, those wide spans just want to sag no matter what. Sometimes I wonder if old decks are just stubborn by nature... seems like you fix one spot and another pops up.