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- To: <seaint(--nospam--at)seaint.org>
- Subject: Galvanized bolts req'd in PT wood?
- From: "Thor Matteson" <thor(--nospam--at)yosemite.net>
- Date: Thu, 11 Sep 2008 20:48:38 -0500
Diane,Another section of the code specifies that only steel or stainless steel is allowed for structural connections (sorry, I forget what section--I'm on 'vacation' right now, away from my codes).
If we are worried that enough moisture will wick up through the footings (or transpire through them) to require PT sills to prevent decay, is that not enough moisture to cause significant galvanic reaction over many years?
I agree with your interpretation of what the code says--I just do not believe that this requirement is adequate for the more aggressive preservative chemicals.
Borate PT lumber is the only type I specify for foundation sills. I do not require galvanized fasteners for borate-treated lumber. I have a big note on all my foundation plans saying if other PT chemicals are used, then *all* connectors that contact the PT lumber must be type 316 stainless steel; framing achors, shear panel nailing, nails driven through the mudsill into studs, anchor bolts, tie-down anchor rods, etc.
I see a huge class-action law suit over this in the future..... yippee. Thor Matteson www.shearwalls.com
Thanks to everyone for the info and thanks also to Jeff and Thor for the = helpful and informative links. IMO, a strict reading of the code gives = you a choice of using galvanized, stainless, silicon bronze, or copper = fasteners w/ PT wood and doesn't specify a need for stainless with the = more corrosive treatments. But the table on pg 4 of the Simpson = Technical Guide T-PTWOOD08 (this table is also in Simpson's hardware = catalog) takes a much more conservative approach, recommending stainless = for all but a few conditions. I am still a bit stunned as I find it = difficult believe the SE community at large is currently specifying = stainless fasteners to the degree recommended in Simpson's table (which = is in line with what Thor mentioned) - yet. But, as I mentioned, I've = been away from wood design for awhile so maybe this is just taking me by = surprise and most folks are already on board with this. Or maybe the = next code cycle will include language that incorporates recommendations = based on Simpson's and other research. =20 =20 Thor, what about the washers for the sill plate bolts (or any bolts for = that matter)? Would you use galv washers with borate treated wood, = stainless with other treatments? =20 Regards, =20 Diane Gould diane.gould(--nospam--at)dgs.ca.gov =20 From: "Thor Matteson, Structural Engineer" <thor(--nospam--at)yosemite.net> To: <seaint(--nospam--at)seaint.org> Subject: Re: Galvanized bolts req'd in PT wood? First, let's decipher the alphabet soup: CCA is chromated copper arsenate--this is the chemical that was "outlawed" in 2004 (it's actually still available for agricultural = uses--I guess the arsenic disappears if a cattle eat it after it leaches out of their feeding trough...) Some of the new treatments are: ACZA--ammoniacal copper zinc arsenate (hmm, still has arsenic...) CC--copper citrate ACQ--ammoniacal copper quaternary CA--copper azole DOT--disodium octaborate tetrahydrate The only one that I specify for mudsills is DOT--it is less corrosive = than CCA was, and it is non-toxic to humans. When ACZA first came out, a contractor friend of mine used some wood = treated with it to build some stairs. He told me that within six months the hot-dipped-galvanized post caps were turning into piles of gray powder. Another contractor on an on-line forum reported that ACQ-treated sills = had reacted with plain-steel anchor bolts within a matter of months to the = point that the bolts had lost about 40 percent of their cross-sectional area. Reports like this from the real world have led me to specify only DOT = for treated wood (where the wood is not exposed to water--the DOT leaches = out if exposed to rain or ground water). Otherwise I specify stainless steel = for anchor bolts, anchor rods at tie-downs, nails that are driven into or through PT lumber, and any framing anchors. Some articles I have seen suggest using Vycor or some other membrane to separate PT lumber from framing anchors. While this could work if = workers *carefully* isolate metal from wood, you still have the issue of nails driven into the PT lumber. I don't see a way around using stainless = steel nails for copper-based treatments. There's more info at my website: www.shearwalls.com/treated_wood.html This issue concerns me a lot; shear wall panel nailing and mudsill = anchors can quietly corrode and we will not find out until a bunch of "new" = houses slide off of their foundations in a future earthquake. Thor Matteson, SE www.shearwalls.com
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