flashing requirements for cement board siding?

[Robert Ellenberg]

I have always specified and used Z flashing at horizontal joints and have assumed it was a code requirement as well as a good practice. However, I haven't created a rain screed space with cement siding before so I considered the Z very important for keeping water out from behind the siding. I am now going to cover the exterior framing with 1" thick foam (OC pink or Dow blue--not bead board) and tape the joints to meet the WRB requirements. Then I am going to add 1/4" thick vertical battens over the studs and 1/4" spacers every 6" on the horizontal joint lines to create a rain screed space for any penetrating water to run down and out. Once my siding sheets are in place I will cover the joints with cement board batten strips.

I was planning to use Z flashings at the horizontal joints but with a proper rain screed space they are not needed. After looking at the code, I'm not sure if they are required or not. R703.8 doesn't require it. R703.10 specifies caulking or batten strips on the joints.

I am also curious to know if anyone can explain the note U next to Fiber Cement siding listed in the table R703.4 next to the WRB requirement. U refers to the WRB exceptions in R703.2 and if you go there, #2 refers you back to 703.4. It appears to be a circular reference without meaning anything.

 

[mark handler]

Install per manufacturers accommodations

Most require flashing

Not everything is in the code

It is also good practice

 

[steveray]

Without specific details or situations, it gets difficult.....But.......To some extent, it gets treated like vinyl siding, all of your water needs to be handled behind it properly, whatever you can do to keep it from getting there, great, as long as it does not screw up the drainage plane underneath....

 

[mark handler]

Install per manufacturers recommodationsMost require flashing

Not everything is in the code

It is also good practice

It is a manufactured product, Install per manufacturers recommodations

http://www.jameshardie.com/pdf/install/hardieplank-hz5.pdf

 

[Francis Vineyard]

Robert that exception might make better sense back in the 2003 edition; Chapter 7 - Wall Covering

Today it means not required on detached accessory structures and approved manufacturer's installation instructions.

Francis

 

[Robert Ellenberg]

Thanks to all.

I wrote J. Hardi and asked them about doing it this way and their response was it had to b ethere because the code required it. I have written them back quoting them all of the code sections and that it is NOT a code requirement but they haven't responded yet.

With a full rain screen I don't believe the Z at the panel joints serve any real purpose and it adds expense and makes the joints much less attractive. The rain screen is such a great proven way to help keep moisture out of walls that I am definitely including them in the future whether I have to add the Z or not.