does the irc require pressure treated bottom plates on a slab on grade house?

Posted by marson on October 23, 2006, 4:50 pm

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?

Posted by bodega on October 23, 2006, 5:02 pm

I just completed an addition to my wife's commercial daycare and was
required to use treated wood for a bottom plate on a concrete slab. I
did this in Auburn,WA which is in King Co. but I would check with
you're local authority where you get your building permits.
marson wrote:
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Posted by Bob Morrison on October 23, 2006, 6:22 pm

In a previous post marson wrote...
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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.
--
Bob Morrison, PE, SE
R L Morrison Engineering Co
Structural & Civil Engineering
Poulsbo WA
bob at rlmorrisonengr dot com

Posted by marson on October 23, 2006, 7:09 pm

thanks once again Bob. I definitely agree that you should use treated
bottom plates. In this case, someone in our company framed partitions
without and I'm just wondering if I have to them go back and change
them. The building inspector didn't even know if it was in the code or
not!
Bob Morrison wrote:
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Posted by Jonny on October 23, 2006, 9:39 pm

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.
--
Jonny
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