Originally Posted by BamaToy1997
Oh I get you on code, and their reasoning behind it. I was just saying that my way, if done correctly, still would prevent moisture from getting behind existing house wrap, and into the building.
I also get the way shingles are laid to prevent rainwater from reaching the sheathing. Of course living in Florida I also know that shingles can still be penetrated. (During 2005 when central Florida was hit with 3 hurricanes in 5 weeks there were over 1000 homeowners who were denied insurance claims because the hurricane winds forced water up underneath the shingles, causing water damage to the homes. The insurance companies classified this as "wind driven rain" and thus denied the claims because their policy did not have a "flood rider" on the policy.
I know this is getting WAY off course, but the point I am trying to make is this, (Take this as EXTREMELY hypothetical, and pretty much near impossible BUT) if rain water were somehow forced behind the siding, and the house wrap was overlapped on top of the flashing, this same water COULD get underneath the wrap and between the house wrap and the flashing. This would allow the water to reach the wood underneath. Now if the house were fully wrapped, and my method was used with the flashing attached OVER the wrap and the deck joist , even if moisture were forced underneath the siding, it would run up the flashing, and get stopped by the house wrap, because the house wrap is BETWEEN the house and the flashing.
Again that is a super hypothetical situation, and in the OPs case it would be a monsoon that would have to cause this, but the people in Florida never expected it to happen either. I can see the code and their reasoning behind it, but I just personally think my idea would offer better protection.
Which is why all roofs should have a felt or synthetic underlayment under all roofing materials
Water behind the siding , running down the exterior of the housewrap goes behind your flashing and is trapped between the ledger and the housewrap instead of being directed outboard of the ledger
In order for water to get behind the flashing as I described installing it , the water behind the siding would travel down the exterior of the housewrap , get to the flashing where the housewrap covers the flashing wall leg and is taped to it , gets behind the tape , travels vertically 4' and goes behind the flashing
Housewraps fell out of favour in our area prior to the introduction of the 10mm rainscreen cavity code because when wood ( siding or ledger in this case ) is in direct contact with housewrap , the pores in the housewrap become clogged with surfacants bleeding out of the wood , in the case of siding that is usually tannins and in the case of the ACQ treated ledger could be the treatment itself
This contamination causes the pores to clog and the housewrap loses it's water shedding ability and is prone to allow transfer of moisture through capillary action
Think of a tent fly when you are camping , the fly will shed water if it is raining no problem until you touch it with your finger , then the water comes through the fly from capillary action , same idea
This is why I prefer 1/2 lapped 60 minute tar paper over housewrap when I build but that is another debate all together