does anyone know if the irc requires treated bottom plates on partition walls on a slab on grade house? is it acceptable to use white wood with a capillary break such as tarpaper on the bottom?
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17 years ago
does the irc require pressure treated bottom plates on a slab on grade house?
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17 years ago
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17 years ago
The relevant section is IRC2003 R319.1. This section allows the use of untreated sill plates and sleepers if the wood is separated from the concrete by an impervious moisture barrier.
However, it seems to me that the cost of using treated plates in this instance is pretty nominal so why not go ahead and use them? I would think you would spend more horsing around with the "tar paper" than it's worth.
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17 years ago
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17 years ago
Do you specify fasteners that won't corrode at an accelerated rate in the ACQ? The metal connector tie downs and the hanger nails are corrosion resistant with ACQ already, but the sheathing and stud/plate fasteners should also be specified resistant. The shear walls are of particular concern.
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17 years ago
Use actual stainless steel 1/2" all-thread in the slab, and stainless bolts and washers to hold the plate to the slab. Use ceramic screws if already poured slab. Both are used to holdup against chemicals used in current treated lumber. You will need galvanized nails, or non-ferrous or treated screws to hold the treated lumber to the studs. Same reason. There are galvanized nails out there that don't have much zinc, be careful.
Maybe you should invest in your own hired home inspector. The municipal code inspector is not there to protect you by any means.
15# felt is standard under the bottom plate. Don't matter if its standard lumber or treated lumber. It should be 4" wide if the bottom plate is 2X4. The inside should be flush with the inside of the bottom plate. This gives 1/2" overlap downwards outside with the felt paper. This causes any water intrusion to fall below the bottom the plate. Wider bottom plate requires same 1/2" protrusion to the outside and folded downwards. Any sissy framing carpenter's helper can cut #15 felt to the proper width on the roll. And follow the chalk line on the layout on the slab. Its not big deal. I'd go with the treated lumber for the long term. Not because of anything else.- Vote on answer
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17 years ago
If hot dipped galvanized fasteners are needed in nailing into the bottom plate if it's ACQ treated lumber, then there are a lot of builders out there in trouble. I don't know of anyone who is doing that, and i've never seen that spec on a plan. You just try to get a framer to dig out his galvy hand bangers to nail off the bottom plate. It just isn't happening.
I use treated bottom plates as I said before, but I do think it's overkill. if you have enough moisture in your slab to rot your bottom plate on an interior partition, then what about your drywall, not to mention your finish floor coverings? Plus, I have taken apart numerous buildings that had good old white wood against concrete that were fine--including my own seventy year old house which not only has untreated mud sills but has concrete poured between the joists.
RicodJour wrote:
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17 years ago
Sure, use white plastic mudsill gasket material..the polyfoam stuff thats about 1/4" thick X 4" or 6" and comes in rolls
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17 years ago
Yes. Here are a few selected lines from my "Structural Notes":
Sill anchor bolts shall be hot dipped galvanized or stainless steel, 1/2" minimum diameter, with a minimum embedment of 7 inches, unless noted otherwise on Shear Wall Schedule or Foundation Details. Bolts shall be tied in place prior to pouring concrete and shall not be "wet-set" or "stabbed" into wet concrete.
Connectors and fasteners for pressure treated wood shall be hot-dipped galvanized or stainless steel in accordance with IBC Section 2304.9.5.
Hardware for pressure treated wood shall be hot-dipped galvanized or stainless steel in accordance with IBC Section 2304.9.5.
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17 years ago
Unfortunately, that is all too true. However, the bottom edge nails will corrode after a fairly short period of time and that nice shear wall will no longer be of any value. IRC and IBC require stainless steel or hot- dipped fasteners when connecting PT lumber. The framers need to be made aware that if they are not doing this, then they are not following the code. And, building inspectors need to enforce this provision.
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17 years ago
Yep, this is a perfect example of the "law of unforeseen/unintended consequences" and a case where the cure is likely to be far worse than the disease ever was or would have ever been... :(
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17 years ago
Yes, but sheet-metal termite barriers serve both purposes.
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17 years ago
I'd go with stainless or nonferrous as the manufacturers of hardware can't mess this up as easily as galvanized hardware.
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17 years ago
What if they're using "cement coated" nails ? Will that protect the metal from the ACQ ?
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17 years ago
The cement coating is an adhesive and not designed as a protective coating. Will it help extend the life of the nails? Possibly - but possibly is not a desirable result in structural engineering circles.
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17 years ago
Is this corrosion a problem only while the PT lumber is still wet from the PT process, or does it continue to occur after the PT lumber has dried?
I'm retrofitting shear walls on a foundation installed 2.75 years ago with ACQ sill plates. Untreated nails that had been installed in the sill plate over 1 year ago and recently removed show no signs of corrosion. My work so far has been with standard nails; wondering if I need to install SS nails between the standard nails on the sill plate.
Cheers, Wayne
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17 years ago
ACQ is relatively new territory. Wet PT lumber is far more of a problem, but it is unclear at what rate the corrosion will proceed as the wood dries out. Guesses don't work in structural engineering. The few extra bucks for corrosion resistant fasteners is money well spent.
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17 years ago
After making this statement, I realized that I hadn't really been paying attention to the nails I had been removing. So I pulled some nails I had installed 2 years ago, 4 nails from one piece of the sill plate and 4 nails from a cripple stud, and I took a closer look.
The nails from the cripple stud basically looked the same as unused nails, finish wise. The nails from the sill plate did show some signs of corrosion: the yellow/silver zinc dichromate finish was missing in spots, anywhere from 10%-40% of the surface area of the nail, and they all showed a few spots of brown rust at the point.
Based on this level of corrosion, if I want the nails to be structurally sound in 50 or 100 years, do I need to use corrosion resistant nails?
Thanks, Wayne
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17 years ago
Wayne:
AS I said in an earlier post: my specifications require the use of corrosion resistant fasteners when connecting to PT lumber. So, I recommend that you use HD galvanized nails when putting together any pieces attached to PT lumber.
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17 years ago
Bob,
Just a side note. I no longer use the term "HD" galvanized nails. I had a client that asked my advice about building a deck and I told him to use HD galvanized nails. The next time I saw him, he was using zinc coated nails on his deck. When I pointed out to him that these were not the ones I specified, his reply was: "Yes they are,... they are from Home Depot!" (HD)
As my father used to say: You can't make anything foolproof, 'cause fools are too ingenious.