Flashings and ACQ Pressure Treated Lumber

Started by rwalter, June 02, 2005, 12:10:33 PM

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rwalter

Hello,

I am pondering what to use for flashing underneath my sill plates. I am using 2x10 PT sill plates and foam sill sealers. I realize the flashings will be under the sill sealer. Normally aluminum and direct contact with ACQ is a no no. but again it will be under the sill sealer. Copper is pretty expensive and galvinized is a question mark for me. From what I have read about galvinized it seems to be dependent on the zinc content. I know Simpson's had to change the formulation of there galvinize on all there STrong Ties last year. Now I don't have to worry about termites much up here in NY, only water. So what are builders using down south where termites and water are a problem?

jraabe

#1
If your sill is on a concrete foundation you wouldn't normally install flashing under the sill plate. Your PT plate and sill sealer is all you will need unless you are trying to defeat termite tubes. (Your sheathing and siding will normally project down slightly below the sill sealer covering the joint.)

When such a thing is installed it is called a termite shield and not flashing. I don't know if they differ substantially and will let others answer to that since we don't use such things in the NW. However, I would think aluminum with the sill sealer as separator would work fine. It is more easily damaged than galvanized however.


rwalter

John,

The reason I am installing flashing is to keep as much water as possible from seeping behind the dow foam board insulation that is being installed on the outside of the foundation. I am following the building model for a conditioned crawl space at www.buildingsciences.com

See page 8 of the following pdf.

http://www.buildingscience.com/resources/foundations/conditioned_crawl.pdf

michael lopiccolo

 It looks like the flashing also acts like a drip cap,and will be visable even after your siding is up, .In this case you may want to use alum. coil.it comes in 24 inch by 50 ft.baked finish,and in dozens of colors that would match your exterior finish.You can bend it using a brake,to whatever size you want. about 55 bucks per roll. good luck

jraabe

Rwalter:

Yes, I see now what you are doing. Flashing is needed over exterior foundation insulation.

If you have not yet built any of this and are at the design phase, I will describe a detail I've used in similar situations.

Basically you step the foundation wall in 2" on each side and cantilever the sill plates out the same 2" so the wall plane aligns with the insulation below. This works for 2x6 sills but not 2x4.

Then you can cover the foam with either stucco or PT plywood where it needs physical protection. Some builders have even used roll anodized aluminum such as is used by gutter machines. For plywood a little "Z" flashing strip works for the transition.


rwalter

John,

Thanks for the reply. My foundation went in last week and that is exactly what we are planning on doing. We designed the walls to be layed out 2 inches short all around so when we add the 2" foam insulation we will be back to square.  However we might not cantilever the sill plate but instead cantilever the bottom wall plate( 1 1/2") instead (were using 2x6 walls and 1/2" plywood sheeting )  This would allow the 2" foam insulation to run up over the box joists.We will be using 2x10" sill plates on 10" cinderblock built wall.  The flashing I am looking at would then cover the edge as you explained to keep water out.

Here is a picture of the

foundation.http://users.adelphia.net/~rwalter/blockwall.jpg


I am in the process of building a web site for this when I have the time I will post the site.