Never ever put aluminum against treated wood. It will quickly corrode.

I prefer one of the rubber tapes.

This is the first I've ever heard of capping the joists of a treated lumber deck.

I don't have anything between my deck boards and the P.T. joists. That is common here (cold & wet 6 months, then dry 6 months).

I'd use the butyl tape if I was doing it over again. It will damp a loose board too.

If I lived in a hot, wet area like the OP I'd do the tape for sure. Copper is nice but it costs...

FWIW my observations are counter to that. But there, it exists on older treated joists, so, perhaps not much galvanic drive.

I will note that here in the Pacific North Wet I have moss regularly growing on the sides of the decking. :-/

I expect that less wet areas would benefit less from copper than my location.

When I built 20+ years ago, I had no knowledge of any capping products on the market. Not liking the nasty chem of pressure treated joists of the time, I went with cedar and laid out my own joist caps with copper. In between the joists I fab'd up some SS pans. This combo gave/gives me dry space below the deck. It's held up great.

I've never used the tape, but looks like it doesn't do much to protect the joist sides.

I can see the OP adding the tape, butyl as a precautionary measure, but again, it doesn't seem a necessary step for his project. In his original post he states the 5/4 decking was shot but the structural integrity of the deck was sound.

Like many of us I fall into the " while I'm in there " on most projects :D . It's been a while since I have done a decking project so I started looking at DIY websites to see if anything has changed or to look at suggestions on how to make a better mouse trap ;) That's where the idea of covering or shielding the top of the joists came from . Looking at the support structure of the deck from below it looks to be sound with no visual indicators of any problems . The joists are straight with no discernible sag . They could use a pressure washing which I will do before tearing up the 5/4 boards .

If I am going to go through the trouble of tearing up every board and replace NOW would be the time to cover the joists IF I am going to do so . I want this replacement to be the last one I do in my lifetime ! I can see where the butyl tape has merit for sealing around screws and adding some cushion , but because it is basically the same width as the joist it doesn't add any " water shedding " to the sides of the joists . Paul's idea of cutting roofing tar paper 6 " wide sounds like a winner to me , being 6 " wide once stapled in place gravity will " drape " the paper on each overhanging side . Any water that runs/drips down between the deck boards will be shed away from the sides of the joists . Cheap and effective sounds like a win win to me :D

The only reason I am in this position of replacing the deck boards is the previous owner was too cheap or lazy to maintain them :mad: so now I have to clean up the mess . The first major decision I have to make is composite vs. pressure treated . Each has pluses and minuses , the other day I checked out what I consider to be good quality oil based semi transparent stain and it runs $50.00 a gallon ! Multiply that times the amount of gallons needed for this large deck then multiply times redoing it every 2 - 3 years has to be figured into the equation .

I am fortunate there is a pressure treated wood manufacturing facility near me so good quality pressure treated decking is available and the initial install price is much less than composite . But then figure in the maintenance/upkeep and the cost to composite shrinks . But there are so many horror stories out there about composite about it sagging/staining/scratching/expanding due to cut edges not being sealed that scares me also :D I am going to do something fairly soon just don't know what that is yet . Thanks guys

"last one I do in my lifetime"

- how old are you?

Buytl tape is cheap & won't add much time - are ya gonna treat your deck like a fine Porsche or a beater 'stang?
(either one is just fine BTW)

problem with copper is some meth-head tears your deck apart to scrap the copper

Ok, I checked Amazon (not the cheapest source) and 4" wide 24 gauge is <$5/foot delivered. I found mine at a metals scrap yard priced by the pound. (cheap. But likely more than the crack head got for it.;))

Of course that joist tape is ~40¢/ft