compatibility question

[paulmars]

Im installing a galvalume metal panel roof. Supplied steel screws are used to hold the panel clips to the roof wood deck. Some of the wood is rotten and/or termite damaged. So, we have been replacing that with treated wood. I just heard that galvalume is NOT compatible with treated wood. Several sites did say that the peel and stick underlayment is a sufficient barrier to protect the galvalume panels from the treated wood. However, that leaves the screws. Steel is not compatible with treated wood. Several sites say to use Stainless Steel screws, however compatibility charts indicate that SS is not compatible with galvalume. Some sites say that Hot Dipped galvanized screws are compatible with treated wood. Is that true? Zinc is not NOT compatible with treated wood.

Any other ideas what to do short of pulling up all the P&S and treated wood?

paul

 

[metengr]

Hot dipped galvanized screws will work. My exterior deck was installed using pressure treated lumber support structure with hot dip galvanized deck screws and it's still standing.

 

[Ron]

In theory, theory and practice are the same. In practice, they are not! metengr is correct. Additionally, if you need to isolate the sheets from the lumber, common No. 15 asphalt felt will work.

 

[paulmars]

felt paper has been tested and it is not a sufficient barrier. maybe they should have asked Ron instead.

I just pulled the treated wood, it's too risky.

 

[EdStainless]

I have seen testing of 'double weight' galv that shows good life.
Isolation does take more. We used a thick felt product that has a plastic film on one side.
Glad to hear that you took the safe route.

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P.E. Metallurgy, Plymouth Tube