# "Impervious" moisture barrier



## steveray (Dec 18, 2017)

I have a designer specifying a marine poly to fix an oops on some doug fir columns on a Simpson standoff for a commercial gazebo to satisfy the code requirement.

2304.11.2.7 Posts or columns. Posts or columns supporting
permanent structures and supported by a concrete or masonry
slab or footing that is in direct contact with the earth shall be
of naturally durable or preservative-treated wood.
Exceptions:
1. Posts or columns that are either exposed to the
weather or located in basements or cellars, supported
by concrete piers or metal pedestals projected
at least 1 inch (25 mm) above the slab or deck and 6
inches (152 mm) above exposed earth, and are separated
therefrom by an impervious moisture barrier.

What would you accept?
Thanks!


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## Builder Bob (Dec 18, 2017)

Oppppssss.....If you look at the poly, see how long it lasts in UV conditions --- not  ab big fan of the proposal... like some of the flame retardant paint, it requires maintenance on an annual basis per manufactures specs.....However, people are quick to offer this as a solution over FRTW requirements in a type II building.


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## Pcinspector1 (Dec 18, 2017)

Can you get the marine poly on the post ends between the Simpson hanger?


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## tmurray (Dec 19, 2017)

Is it one of the ones that are continuous metal? Like no holes in it? That would be fairly impervious to moisture.

Inside we see poly for this. Outside I see roofing (Type S roll roofing in Canada).


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## steveray (Dec 19, 2017)

Pcinspector1 said:


> Can you get the marine poly on the post ends between the Simpson hanger?



Shirley they didn't put it on there, but they will claim they did....Don't remember exactly which base it is, but it isn't visible other than the 1" standoff, I think it is a dowel in the middle?


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## mark handler (Dec 19, 2017)

would need to see it...


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## Paul Sweet (Dec 19, 2017)

A standoff base is always the best solution.  You have to look at moisture flow in 2 directions.  Moisture flow from the slab into the column needs to be prevented, but moisture that gets into the column needs a way to get out.


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## sergoodo (Jan 3, 2018)

Bituminous water proofing...any liquid applied waterproofing compatible with substrate.  Agree about the UV, needs also to be rated for UV exposure.


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