Flashing butt joints for fiber cement lap siding


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Old 06-01-21, 05:10 PM
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Flashing butt joints for fiber cement lap siding

So Im about to start doing the siding on my house.
im using 8.25 fiber cement.
the manufacturers (hardie, allura) says to put a strip of flashing behind the butt joints.
Im wondering what folks have used and if they had any problems?

im thinking of using strips of roofing felt and painting it so if it shows up through the joint it will be more discrete.
im also wondering if the paint will degrade the roofing felt
im thinking of the roofing felt because I have a partial roll in the shed.
the Bear Skin joint flashing is like $1 per sheet, which seems a bit pricey, although Amazon reviews seem good.

any thoughts are appreciated.

 
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Old 06-01-21, 06:00 PM
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No, don't use roofing felt. Buy yourself a few packs of flat 6x8 sheet metal roof flashing. You can usually get it in brown or bronze. Keep it 1/4" up off the bottom edge so it doesn't show.

here is an example:
 
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Old 06-01-21, 07:04 PM
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Any particular things about the felt that you dislike or just think the metal is better?
 
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Old 06-01-21, 07:25 PM
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Metal will last forever. Felt won't and is not meant to be exposed to the weather. The felt nowadays is nowhere near the quality of what they used 50 yrs ago.
 
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Old 06-02-21, 05:57 AM
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Had our home sided by Hardy with their own crew doing the install in 2007. They used Tyvek behind butt joints. Visible if they were sloppy but otherwise worked.
 
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Old 06-02-21, 01:47 PM
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Tyvec degrades when exposed to UV (sunlight). No more than 4 to 9 months (depending upon which product) is the max exposure allowed. This according to DuPont.
 
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Old 06-02-21, 02:00 PM
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To be susinct, Tyvek and felt paper are not considered "flashing". Flashing is metal. There may be a few specialty products that are designed and approved to be substituted for metal flashing, but felt and Tyvek are not.

I know people have done it but it's not correct to do so.

See R703.10.2 for the 3 approved methods of joint treatment.
 
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Old 06-03-21, 03:58 AM
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Thanks for the comments.
I will plan to use the galvanized. I saw aluminum was cheaper, but remembered theres the chemical issue between cement and aluminum
thanks again to the posters, but also the board in general for being here as a resource.
 
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Old 07-16-21, 03:44 AM
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Per Hardie’s install instructions metal flashing should be used behind butt joints in lap siding. The install instructions do say that the James Hardie House wrap can be used.
The International Residential Code IRC R703.10.2 requires lap siding to have:
1. A minumim vertical overlap of 1 1⁄4 inch (31.75 mm), and 2. One of the following butt joint treatments:
a) Joint Flashing, b). Caulking, or
c). “H” jointer covers
See the following for full information…
https://www.jameshardie.com/JamesHar...t-flashing.pdf
 
 

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