Deck Framing Protection: Section R317.1.3 states ...

[rharper]

pressure-preservative treated wood shall be used when members are exposed to weather without protection from roof, eave, overhang OR OTHER COVERING THAT WOULD PREVENT MOISTURE OR WATER ACCUMULATION ON THE SURFACE... We are proposing to COVER the wood framing with metal flashing or Grace water shield to prevent moisture or water...
Why would anyone object to flashing the wood framing?

 

[Francis Vineyard]

IMO when encased it traps moisture and accelerates deterioration or decay. The Grace Ice & Water Shield is approved for applications in Chapter 9 of the IRC, not as other covering such as canopies, awnings, patio cover, etc.

http://www.icc-es.org/reports/pdf_files//ESR-1677.pdf

BTW welcome to the BCF

 

[tmurray]

Francis nailed it. Depending on your climate it can be a huge issue based on the vapor
permeance of the membrane you want to use. I live in a climate that places the vapor
barrier on the inside of the building and we recently had issues with ledgers failing,
because a contractor was encasing them in a bituminous membrane that acted as a
vapor barrier. So moisture was moving out through the breathable house wrap,
turning to liquid in the ledger and unable to escape. As Francis said, it then caused
accelerated rotting in the ledger and the decks started failing very early.

What is the framing for?

 

[classicT]

Flashing directly in contact with wood framing seems to be a likely source of condensation, which would in turn lead to rot. When subjected to cooling temperatures, the wood would retain heat longer then the metal flashing; thus any moisture (in the environment or wood itself) would tend to condensate between the flashing and wood. If flashing is tight to the framing, this would lead to rot and ultimately failure of the framing.

 

[steveray]

EVERY vinyl sided house has aluminum "flashed" wood....I would have to see the details on this one to make a judgement....FWIW not all PT is all metal friendly...