SHEET ZINC between 6X6 Wooden Column and Poured Concrete / New Deck w Storage Space underneath 1

[SalemCat]

I've got a 20' X 22' poured Concrete Foundation in my backyard. It's very strong; very stable; and has cured for 20 years. I had planned to built a 2-1/2 story Post-and-Beam Addition, but time flies, and needs change.

My new plans are to built a nice Deck over it, with Storage underneath. The Storage Space will have a Concrete Floor, and will be highly insulated. The Space will have neither Heat, nor Plumbing, nor Windows. It will have Electricity, and will be Vented by means of Built-In Fans that will automatically respond to situations of high heat or high humidity. The Water Table is quite low, as I live on a small hill, and we've never had a groundwater issue with this space nor my adjacent home.

The structure will depend on 6X6 wooden columns, spaced on 4' intervals Center-to-Center, with substantial 6X6 and 4X4 bracing. The Deck Floor will be supported by 20' Engineered Wood Joists, spaced 16" CTC. The Roof/Deck Floor will utilize Plywood Sheets covered by a heavy waterproof membrane, that several manufacturers offer for situations just like mine. The Sheathing will also be Plywood, covered with Vinyl Siding. I will be using lots of screws and adhesive - very few nails (for long term I do not trust nails).

I have no concerns regarding the strength of this structure, as I plan to exceed Manufacturers recommendations and Local Codes. I hope to never, ever have any need to maintain this for a good 30 years.

MY QUESTION: I'd like to use solid ZINC Sheet, .062" THK, underneath / between the wooden 6X6 support Columns and the Concrete, to prevent Wood Rot. I do not want to use PT Lumber, as I will be doing 99% of this construction on my own (if I possibly can), and PT simply weighs too much. (I don't like the feel or look of PT either.) The connection will, hopefully, never get wet if my workmanship and flashing are appropriately done..

Will solid Zinc Sheet between wood and concrete prevent wood rot ?

 

[JAE]

Why don't you just use a Simpson Strong-Tie column base?


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[racookpe1978]

I suspect rather than a cool, sheltered, thin, dark, not-quite-dry (humidity, if not direct rain and snow/sleet) (did I mention sheltered and dark?) place where pets and people cannot clean and chemically treat will not yield wood rot, but plenty of bugs, mice, oppossums, and other slithery critters. If laid right over the concrete, rats and bigger pest can't (maybe) reside, but cockroaches, termites, silverfish, and ten billion other biologics will. Grow, breed.

Simpsom strong-tie clips and brackets in treated wood have worked for me for the 30 years I've used them outside.

 

[SalemCat]

I will be using Simpson (or Simpson-Style) Hangers on the connections between the Rim Joists and Floor Joists (both likely by Weyerhaeuser), so I'm not adverse to them. I expect I'll be using many overhead.

On the Foundation, however, I'm looking for an extreme solution. We don't get High Winds or Tornadoes here in Salem, Mass (at least not often!), but when I place these 6X6 Columns I'm looking for permanence.

On either side of each 6X6 Column I want to use a 6X6 Knee. These will support the Column, and tie it to the Foundation. A 3/4" Bolt will hold each Knee to the concrete (the Bolts fixed into the concrete), and a 3/4" Bolt will pass thru both Knees and the Column (a sandwich). There will be substantial Washers under all Nuts.

I want to avoid using a Sill at all, as what I'm considering is more akin to Timber-Framing than Balloon Construction.

I did not mention, but it is important, that this Foundation is a Full Perimeter Foundation, designed and able to support a 2 or 3 story building (likely would hold more than that). It's not a Slab, and the Rim is a good foot or more off any Soil. There are also French Drains that were installed with the Foundation, which have been doing a remarkable job of keeping the entire area dry.

My plan is to pre-install all Knees, and then when the time is right, I (or I and a Helper), will be able to quickly raise the Columns to an upright position. The Helper can then leave; I'll install the Bolts, and I'll be well on my way.

So I just don't see what a Simpson will do for me right here. And a Zinc Barrier will have an added benefit of keeping any moss in check, though even now, after 20 years of just sitting there, there is no moss on the Foundation anyways.

 

[JAE]

A Zinc barrier flat on the concrete between the wood and the concrete will not stop rot in my opinion - per racookPE1978, there will still be moisture in there.

The Simpson bases are permanent and should work for you. If you are looking for something a little more "pretty" then you can sketch out a 1/4" steel plate assembly similar to the Simpson products and have a steel fabrication shop make them for you. The key is to stand the column off the bottom of the surface where it gets wet.

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[SalemCat]

I think you're right - that if the base of the Column gets wet, it will rot. The Simpson products, ultimately, will not prevent rot - though they may slow it considerably. And that no metal, nor resin, will stop rot if the wood is still getting wet. For that matter, when the zinc coating wears out on the Simpson, it will fail as well.

(Years ago I bought some Galvanized Steel Sheet at Home Depot, and folded it up to made a Water-Diversion Device at the base of a Plastic Gutter DownSpout. In just a few years it became a hopeless sieve of rusted foil. Now I'm not saying that had a good coat of Zinc on it (obviously it was very thin), or that the result should be compared to a Simpson Product, but I'm betting that zinc-on-steel simply slows a process that never ends)

As the base of my columns will be protected from the weather on the outside by a continuous envelope of OSB Sheathing and Vinyl Siding, I've now concluded I don't really need Zinc, Steel, or any Barrier to separate the Wood from Concrete. And that was what I was concerned about.

And on the inside, the Column to Concrete junctions will be largely exposed for aesthetics, so if there is any ongoing problems with moisture it should be readily apparent. I simply need well-designed and implemented Exterior Flashing.

 

[jayrod12]

The simpson stand-off bases (similar to the one you show) do a good job of delaying the moisture long enough for your lifetime.

IF you are going to heat and insulate, why not just build stud walls? Seems so much easier.

 

[SalemCat]

Stud-Walls - yes, a sensible choice. Nothing wrong with them. But the large timbers and joinery visible inside will be much more attractive to my eyes.

And I like doing something different; something interesting to me. It's just for myself, and I want to enjoy the experience.

For example, here's just a few pics of my Water Heater replacement of a couple of years ago. My old heater was failing, and I was always unhappy with the installation. A professional plumber had done it. He was quick, inexpensive, and did a perfectly adequate job. I'd use him again, if I must.

But the small room the Water Heater occupies was a tangle of piping going every which way, with very few supports. Pipes rattled; were routed in the middle of the room. They were in the way; you had to duck under them. All this made any maintenance a chore.

I re-routed much of the piping. Got it out of the middle of the room, back to the walls, where it is now fastened securely to the concrete. I installed extra valves, and flex hoses. Replaced the crumbling exhaust as well.

Now I have a Gas Water Heater installation that pleases my eyes, is simple to inspect and maintain, and eventually, easy to replace with no more effort than twisting a few valves and turning some fittings.

This is the kind of work I wish to do on my Deck and room underneath. Vanity work, that takes time, that would cost a fortune to have done.

 

[jayrod12]

Fair enough.

A standoff base and reasonably good waterproofing detailing should buy you 25-50 years of life (neglecting termites as they are highly location dependent).

You likely wouldn't find anything to help connect your angled timbers to the concrete that isn't custom fabricated. Since you seem to be less concerned with cost as long as the final product is clean then I would suggest getting custom made 1/4" thick steel bases that surround the entire column base and are water tight, then get them galvanized.

I would also be suggesting utilizing some sort of beam that allows you to space your posts out more provided the foundation can take it. We could not comment on that because you haven't actually given any details on the foundation besides saying it's robust (which is a relative term, some people think a 4" slab is robust)

3.5 feet clear between posts doesn't leave much room for 6x6 or 4x4 bracing. How tall are you planning on this storage area being?

 

[SalemCat]

 

[SalemCat]

(A standoff base and reasonably good waterproofing detailing should buy you 25-50 years of life (neglecting termites as they are highly location dependent).) We don't have Termites around here - yet. But I've using Stainless Steel Termite Mesh, anyways. CLICK HERE Contrary to the Web Site's disclaimer, I am fairly certain the Patent expired years ago. (I actually did some real research on this, and am personally certain it is expired. But I'm not a Lawyer, just some guy on the 'Net.) It seems enough Mesh will cost me $200, give or take.

(You likely wouldn't find anything to help connect your angled timbers to the concrete that isn't custom fabricated. Since you seem to be less concerned with cost as long as the final product is clean then I would suggest getting custom made 1/4" thick steel bases that surround the entire column base and are water tight, then get them galvanized.) The Angled 6X6 Knees (2 per 6X6 Column Base), will be fastened to the Concrete and also the Column with 3/4" Galvanized Threaded Rods or Bolts. They will be accessible from inside, and can be loosened and re-tightened if need be. I could actually remove any Knee at any time, simply by unbolting it. Not sure why I'd want to, though.

(I would also be suggesting utilizing some sort of beam that allows you to space your posts out more provided the foundation can take it. We could not comment on that because you haven't actually given any details on the foundation besides saying it's robust (which is a relative term, some people think a 4" slab is robust)) I'm placing the 6X6 Columns 4' Center-to-Center. This makes attaching 4X8 OSB Sheathing on the outside and 4X8 OSB Flooring really easy. I'm planning on using fairly deep (12") Engineered Beams as Floor Joists, which exceed Weyerhaeuser specs for a 19' span, to keep them spaced at 24" CTC. That way at least half the Joists could be centered directly on a Column. The others will hang from the Rim Joist, using Simpsons or equiv. I'd like to measure the actual width of the foundation, but it's covered with snow. I've got drawings of the Foundation filed away, but am too lazy right now to go retrieve them. Anyhow, the Building Inspector here passed the Foundation for a 2-1/2 story addition, years ago, so I can't see an issue with a simple 11' high Deck.

(3.5 feet clear between posts doesn't leave much room for 6x6 or 4x4 bracing. How tall are you planning on this storage area being?) From Floor to Ceiling will be somewhere between 8' (Code minimum for Living Space - though this will not be Living Space) to 9'. This height does not include area within the Joists (nor should it). This keeps the entire Structure within reach, for me, using only low Scaffolding.

Finished, I'm hoping this Deck and Storage area to serve, also, as a bit of a SAFE ROOM. Someplace my family can cocoon during Hurricane - or worse. Our main Home is nothing special - just a Raised Ranch tossed up by a Developer on a severe budget in the 1960's. Sometimes I marvel the homes in my neighborhood are holding up as well as they have.

Another issue I'm still figuring out, is how to effect the Braces necessary between the Engineered Wood Joists. I want something that looks good from below (so no common steel diagonal joist braces), but will not be a time-consuming nightmare to fabricate. I may simply buy an additional Joist or two, and cut it up to use as Bracing. It will match, look good, and be strong.

 

[jayrod12]

Do you need braces for the floor joists? Ideally, the sheathing should provide the compression chord bracing, I guess in an uplift scenario you need bottom chord bracing, but that depends on the design wind speed in the area. Some form of solid blocking at mid-span or third spans would likely do the trick.

If were willing to frame stud walls between your large timbers, then the walls could still act as shear walls and you wouldn't need the cross braces.

 

[SalemCat]

(Do you need braces for the floor joists? Ideally, the sheathing should provide the compression chord bracing, I guess in an uplift scenario you need bottom chord bracing, but that depends on the design wind speed in the area. Some form of solid blocking at mid-span or third spans would likely do the trick.

If were willing to frame stud walls between your large timbers, then the walls could still act as shear walls and you wouldn't need the cross braces. )

When you take a good look the Weyerhaeuser Web Site CLICK HERE you'll understand why these TJI Joists need to be braced. They're light, they're strong, they're straight and true. But they would twist and fail if not installed precisely as specified.

I had not mentioned this before, but other than the 6X6's, which are fairly inexpensive and not difficult to acquire straight and true, I'm using as little sawn wood as possible. Even in my limited experience I've totally had it with the typical 2X4, and other common sawn wood. They're generally twisted, bent, full of knots, or have huge patches soaked in pitch - just awful. In the past I've had to sort through huge piles of them to find just a few I was happy with. I don't know how the pros can stand it. Carpentry is hard enough without dealing with crappy wood - which isn't cheap, either !

Also, I want my Storage Space to be completely free of support columns inside. I use Commercial Wire Shelving on Casters to store items, and the freedom to roll them around, and configure them as I like, is important. I've got more than a few Shelving Units storing stuff in a rented Storage Facility already, and the amount of stuff I can cram in, and still be accessible, astounds me.

 

[JAE]

Design wind speed for the area - depends on your area but you did say "safe room for hurricanes" above. The uplift could be tremendous so yes - you'd need some serious blocking, significant hold-downs and straps, and I don't think Simpson column bases would provide you with enough hold down capacity.



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[Ron]

"Watertight" at the base of a wood column is not a practicable achievement. It is better to have some ventilation at the bottom such as provided by the stand-off bases. You can coat the saw-cut end of the timber with an asphaltic coating that will help to protect the open, porous exposure of the sawcut.