deck rebuild question - what to cover joists with ?
 

The deck on the back of our house is structurally sound but the 5/4 deck boards are shot . Previous owner waited way too long to do maintenance so I now have to replace . Have not made up my mind yet on pressure treat vs. composite but that is not my question here . I have read on some forums that some guys are installing some type of " joist covers " to the top of the joists before putting down the decking . I guess the theory is the covers shed water away from the top of the joist so it can just drip on the ground . Kind of makes sense to me . But what are these covers called ? Are they made of thin metal or aluminum or vinyl/PVC or ??? I am picturing something in a 8 ' length that is lightly nailed in place before installing the deck boards . Or maybe a material in a roll ?

I already have good edge flashing where the joists meet the house , I am specifically talking about the tops of the joists . Or is this a total waste of time and $$$ and just get on with R&R ?

It's just butyl tape. Search for 'joist tape' to find more but if it's anything like windows, it's not if but when it lets water in, it'll keep the wood wet and accelerate the rotting process.

https://cdn.shopify.com/s/files/1/13...g?v=1553790449

I just recently completed my lower deck and bought 10 rolls of this material
https://www.energyconscious.com/grace-vycor-deck-protector-4-x-75-roll-45639.html?fee=5&fep=3512&gclid=EAIaIQobChMI3IX588-R5AIVsCCtBh2QwQ5LEAQYBCABEgKqlPD_BwE

We use 28 GA painted sheet metal (aluminum can be used as well) fabricated in a "U" shape.

+1 to Bugs, Vycor

You can also use rolled roofing under lament (tar paper). Cut it in 6" strips and tack it to the top of the joists then nail the deck planks down. Simple cheap done.

If it ain't broke...

My 29 yr old original deck and structure is sound.

But I know you....

You won't just replace the deck boards like I would ;)

I used annealed copper flashing strips (~4" wide) to top the joists on a deck I built 20 years ago.
Each over-hanging side is folded down maybe 15-30 degrees. This keeps the joists very dry. Whereas any of the wrapped solutions have water running down the joist sides, and clinging.

I've been very happy with my solution. It's aged well.

First off thanks for the replies . I am now a little smarter than this morning 😉. The deck is exposed to morning sun then is shaded in the afternoon . The deck is about 10 ' above ground so adequate air flow from underneath . Paul in humid Florida do most builders cover the top of the joists ? The butyl tape or roofing paper once they get wet I would think would promote mold/decay ? KC yeah I over analyze everything !!!

You could probably nail a copper wire along the top of each joist. Copper and fungus don't exist.

Copper and fungus; just like unicorns.

:D

Rick,

In Florida most builders go the cheapest and fastest method possible and unless the owner tells them to put something on the top of the joists they won't do it. It's all about keeping the first cost of the house as low as possible and let the next guy pay for replacing the deck.

When I pull deck boards up, and I have pulled up every nail :( that rears it's head...replaced with 3" deck screws....the nails are tough to extract and my sub-deck has nothing but solid structure. Don't you have an attic to insulate in Aug instead ;)?

Do something extra....only if'n ya need to....

Lay Z Boy :)

I've never heard of this being done - although I do understand what it is trying to avoid.

In my county covering the deck joists is required by code. Also, all joists must be pressure treated.

OK, there are the exceptions. Do they exist freely in nature? Does this same wood degradation reasonably affect PT deck joists?

Apparently Island911 believes copper in the extreme does. Or is his copper non reactive and could be substituted with any wrap-over covering?

I admit I jumped in too soon with my comment and after your response I delved in. W/o citing a bunch of studies involving micronized copper and nanoparticles, I think the idea of a copper strip is even more effective chemically speaking than a copper cover because the strip will leach into the edge of the joist whereas a cover is going to be in place mainly for it's longevity. Water in his case is apparently not intended to soak into the wood but rather be expelled.

I take my theory from the roofing business where copper and zinc are used to mitigate lichen by killing the fungal side of the complex structure.

Amial, me thinks you know a whole lot more than I ever will, but tell me, is a copper wire on top of a joist exposed to moisture a complete waste of time and material? Tell me if it has no redeemable value or let it go.

If the deck is properly pitched and you have adequate airflow, don't see why you would need anything? Which appears to be the case? Not sure how old the deck is but, if it lasted this long and you say is in good shape, then I would say just put down new deck boards.

Zeke, buddy, you misunderstand me - I was just poking fun at your choice of words. I think you meant to say "copper and fungus don't co-exist". I'd lay odds you know more than I ever will! SmileWavy

The thing is, the same conditions that took out the decking are there, on the joists, exposed in the deck spacing. Even treated joists look nasty at every gap.

Capping the joists is doing your future self a big favor; assuming your not a flipper.

I like the copper for a few reasons. First, as Milt sez not much grows in contact with copper, Second, annealed copper is very easy to work with. (Al flashing is typically cold rolled) Third, copper patina is dark(fades away) whereas Alum is shiny.

Good point , I can only assume the deck was built in 1996 or later as the house was built in 1996 .

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