Fire Treated / Resistant Plywood as Roof Sheathing 1

[Loui1]

Does anyone know limitations of using fire treated plywood as non structrual sheathing on a roof?

An architect is saying he needs to use plywood on top of my structural metal deck/metal trusses in order to fasten his roofing. He says the sheathing must be fire treated. I've never used a system like this and dont know if it'll eat the deck, etc. Looking on APA, there isnt much info about it.

 

[CJJS]

I have read where the chemicals in FRT plywood will corrode metal. Here's an interesting article concerning this.

http://www.rooftopsystemsengrs.com/interface99A.htm

 

[Loui1]

!!!! Dang !!!!!

 

[jike]

Why don't the architect just isolate it from the deck? Lay a sheet of visqueen down.

 

[Loui1]

Visqueen may help the corrosion problem, but it appears there may be some problems due to solar heating that make FRT wood degrade.

 

[CJJS]

Solar heating in addition to moisture. I guess if you can ensure that it remains dry there shouldn't be a problem.

 

[SperlingPE]

Where is the insulation for your roof?
There is nailable insulation that allows the attachment of other materials.

For fire treated plywood, you have to go to treaters web site or get information directly from them. Plywood manufacturers don't do the treating.

The treatment does affect the structural properties of the plywood, but I am not sure about how it affects attachments or metals in contact with it.

 

[jheidt2543]

SperlingPE is on the right track. You could use nailable insultion if it can handle the loading or use 1/2" thick fiberboard insulation (any insulation that would melt in a fire is not acceptable) as a barrier between the metal deck and the FRT plywood, BUT you must check the fasteners because they too can be damaged by the FRT.

You can use "Deck Mate" screws by Phillips Fastener Products as one solution in FRT lumber, for others go to

http://www.treatedwood.com

for listings of other products.

 

[planitarch]

Fire treated plywood is especially prone to rot without proper ventilation.

In a code seminar I recently attended I heard of a townhouse project (somewhere on the East coast? can't remember) where the attics where not properly ventilated and the rot required a complete re-building of the roof sheathing after something like 5 to 7 years.

A quick google search on the subject turned up;

http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr62.pdf

Of course this might be more an 'architectural' issue, but you might want to consider it in your design.