Blocking to raise plywood siding

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Old 05-30-10, 08:09 AM
S
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Blocking to raise plywood siding

The walls on my 2-story wood frame house are sided with T1-11 plywood siding with no sheathing behind it. Under the gable ends the bottom of the plywood sheets tends to rot because of the low clearance between the bottom of the sheets and the ground (1st story) or where the pitched shingle roof intersects walls (2nd story). The roof area especially is a disaster because the siding ends only about an inch above the shingles, which eventually turns the plywood to mush.

In some places, about six years ago the previous owner had a guy cut out the bottom of the siding and replace it. A couple of observations about these areas: (1) they're already softening at the bottom, and (2) there's no blocking behind the new intersection where the patch and the previous siding meet, so the structural rigidity provided by the siding is compromised. It looks OK cosmetically, but it tells me that if they had replaced the entire sheets they'd need to be replaced again after a few years.

Anyway, I'm replacing the siding and would like to correct the problem by raising the bottom edge of the siding. I've asked similar questions in this forum before but really haven't found a satisfactory solution.

The main problem is that ending the bottom edge of the siding above the existing bottom wall plate (so I can replace the bottom area with a skirt of pvc lumber or something) leaves me nothing to nail the bottom edge of the plywood to. I'm in south Florida so structural integrity and impact resistance are important. Even if I put 2x4 blocking betweeen studs for nailing where the bottom of the sheets end, I'll still have a gap to fill with something, and I'm not aware of anything that has enough impact resistance (for hurricanes) except for plywood. If I use plywood, I'll have to replace the bottom edge every few years.

So I thought I would run this plan by you:

PITCHED ROOF AREAS: In all of the spaces between studs I'd raise the bottom plate with stacked PT 2x4 blocking. Five stacked blocks will give me about a 6" SOLID skirt area below the bottom of the siding). The blocking would be toe-nailed in and nailed together from the top also. I'll end the siding at the top 2x4 block and a wide strip of steel flashing will go from behind the bottom edge of the siding to under the shingles (I'm replacing the shingles next).

1ST STORY WALLS: same thing except I don't need quite so many blocks since the house is on about a 4" pad above grade.

Does this make any sense? I can't think of any other way to have a solid backing for a skirt area/flashing so I can raise the bottom of the siding.

Thanks for any advice!


Steve
 

Last edited by suobs; 05-30-10 at 08:37 AM.
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  #2  
Old 05-30-10, 11:24 AM
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I used to live/work in central fla so I'm familiar with that type of construction. I don't know that this would work but what if you installed cement backer board at the bottom and stucco'd it and then have your siding start above the cement board. I would think you'd want the cement board to overlap the slab - so you might want to embed that part in mortar/thin set. That should help keep the bugs out

I know you would want to add 2xs in the stud wall where the siding will start but not sure I understand about blocking on the roof Any plywood should be behind the flashing and the siding above the shingles.
 
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Old 05-31-10, 05:33 AM
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Originally Posted by marksr View Post
not sure I understand about blocking on the roof.
See diagram below.

Originally Posted by marksr View Post
Any plywood should be behind the flashing and the siding above the shingles.
The plywood is the siding, there's no sheathing as I said. So the flashing would be behind it (also behind the house wrap).

The roof is just the wall above a roof slope. See diagram for what I mean. This wall is under a second story gable end and over another pitched roof. The only thing that's different about it is (a) it's pitched and (b) the bottom plate puts the bottom edge of the siding within an inch of the roof, so whenever it rains the bottom edge gets saturated with runoff.



Originally Posted by marksr View Post
what if you installed cement backer board at the bottom and stucco'd it
Cement backer board on an exterior wall? - not impact-resistant, is it? Even fiber-cement siding doesn't have enough impact resistance without sheathing and will dissolve if the bottom edge is too close to the ground or a roof. In s. FL you can have either 5/8" plywood sheathing with siding (like vinyl, fiber cement, plywood) over it, OR you can have exterior 5/8" plywood (T1-11) without sheathing.
 
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