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How To Install Hardi Plank When Base of Wall/Foundation Is Uneven/On Diagonal?

How To Install Hardi Plank When Base of Wall/Foundation Is Uneven/On Diagonal?


Old 05-01-12, 12:50 PM
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How To Install Hardi Plank When Base of Wall/Foundation Is Uneven/On Diagonal?

Ok guys. First off, I am a total ammy when it comes to building stuff. Im mechanical and all but when you start using professional terms I get a bit confused. I also may confuse you when I try to describe something and dont use the right terms. So please bare with me!

I am enclosing an area on my barn to make it my tack room. Originally this space was only covered by the roof of the barn. I had concrete poured when we purchased the property and had them grade the concrete away from the barn so water would drain off of the concrete. So the concrete next to the actual structure of the barn is 1-1.5" higher than the concrete at the edge of the roof line, if that makes sense.

Im at a loss on what to do about starting the siding. Mainly because there is a 1-1.5" height difference from one end to the other. Im going to include pics along the way to show where it started and where we are now so I dont confuse you too much.

This is what we started with (older pic but you can get the idea). The front right corner that is open is where we are enclosing. The concrete grades away from the actual structure of the barn so it slopes going towards the right side of the photo and also slopes going toward the camera

This barn was already built when we purchased the property. Being a pole barn, nothing is level or square. To get a level base line, when my husband and his friend started, they started with the ceiling. Then they framed out the walls and adjusted as needed to again keep everything level even though the "foundation" was not.

This is with the ceiling in and one of the walls up

There is a window and obviously a door. We placed OSB sheathing and covered it with roofing felt instead of tyvek or other house wrap.

This shows the front of the room with the door which is hung level but you can really see the grade of the concrete here as it slopes down from left to right.

Another shot looking out of the door where you again can clearly see the drop

And yet again (just in case! lol) here is where I am installing the vinyl tile and you can see the grade

So I guess my first question is more geared towards PRIOR to installing the siding.

We were told to get Z flashing and place it 1" above the concrete/base plate junction and then place the felt, which we did. However, that means that there is 1" of OSB sheathing under this flashing that is exposed. Obviously OSB sheathing is not pressure treated. What is going to keep that from eventually rotting? We did as told but still do not see the purpose of this when it leaves exposed wood.


What is the best way to place the hardi plank when the foundation is not level? Esp when it comes to the front wall where the door is. Obviously we wont set it level with the foundation but when we set it level horizontally, it will leave a 1-1.5" gap at the bottom on the one end. What is the proper way to tackle this?

Should we trim one of the planks long ways to follow the grade of the foundation so the bottom of the plank will match the angle of the concrete? If we dont and end up with that gap between the bottom of the plank and the concrete, then the above question pertains to this too. How to protect that OSB that is not covered.

On the two exterior walls, there is 4" of concrete above the ground where we could extend part of the plank past the junction of wood/concrete to make it visually appear level. Is that a good way to make it all appear level?

Being a woman, I am VERY visual so understanding how to do this without SEEING it is frustrating! I dont want this "fudged" or done halfassed. Just because its a barn doesnt mean it can not be done properly. Not only do I want it structurally correct, I want it to be visually pleasing to the eye.

So with all that said... help? I hope I didnt make that too confusing. And please keep in mind when answering that again we are not professionals and lamen terms are appreciated! I am very handy and mechanically inclined so if its explained in a way I understand, I assure you it will get done.

Thanks ahead of time and if any more info or photos are needed, please ask.

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Old 05-01-12, 02:40 PM
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Well, I'll take a stab at this and see if I can help.

First, I don't quite understand why someone would have told you to place the flashing 1" above the concrete if it leaves wood exposed behind it. Maybe that's a Florida thing since you get so much rain they think it needs an air space to dry out... I don't get it either.

The sill plate (bottom wall board that lays flat on the concrete) should be pressure treated wood, that will not decay if it gets wet. Second, the sheathing should have been kept up away from the concrete (like maybe 1/2" or so) so that it doesn't sit in water and soak it up like a sponge. If you have to have that 1" gap for some reason, I think I would have covered the edge of the OSB with some butyl flashing tape (like grace vycor plus, protecto wrap, Pella flashing tape, etc) to protect that exposed sheathing from the weather. Then put the flashing on top of that. Sounds odd to me too.

IMO, I would have installed an L-flashing (not a z-flashing), and would have pressed the bottom lip of it into a heavy bead of polyurethane sealant right down on the concrete (no gap) so that the sheathing is completely covered and no water could ever get at it. But that's just me.

Something that should not be overlooked are the instructions for Hardieplank, which require you to keep the first row of siding 6" above grade, or 1-2" above paths, steps, and driveways. I'm not 100% clear on how high your siding will be when you start it, but here is my first thought:

Install what is called a "water table" around the bottom perimeter of your walls. I'd suggest it be made of either Azek (a rot proof pvc trim) or Miratec (a rot resistant treated fiber/composite trim). So picture this 1x6 water table all the way around the bottom of the walls- it will be level on top- but trimmed on the bottom to match any out of level surfaces. A z-flashing (drip cap) would be applied on top of the 1x6. The water table trim would serve 2 purposes. Once it's on, it will establish a level line to start the siding above. (their instructions specify a 1/4" clear gap between the horizontal flashing and the siding.) And secondly, it will raise the siding up off the ground, making the bottom row of siding less susceptible to splash back when it rains.

If you think that is too much work for a shed... and you are okay with having the siding be 1-2" above the cement, then you would cut a taper off the top edge of your first row of siding. (this is so that the finished edge will be exposed to weather, while the cut edge [up] will be covered up by the next row.) It would be as if you placed the siding on the ground, then cut the top edge of the siding level... then raise the siding up 1-2" and install. The ends of that first piece would obviously need to be cut plumb (vertical) as well.
Old 05-06-12, 11:21 AM
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Thanks for the reply.

I went and measured and the two "outside" walls where the flashing lip starts are 4" above the ground and 2" above the concrete. So that seems to be OK. Can we put flashing over the areas where the osb is exposed, under the z flashing? I have the rolled thin metal flashing and flashing tape for around windows and doors.

All of the wood for framing including the plywood ceiling is pressure treated. We placed that "foam" material between the concrete and sill boards, using black jack adhesive. Sorry I forget what its called.

It appears the z flashing was set level and that's why there are areas with like 1" of exposed osb. The good news is that I can install my planks on these two walls without complications as its level and already far enough away from the ground, etc per hardi instructions.

Now lets see if I understand what you are saying about the diagonal area...

Either install the trim for extra protection and to raise the start line of the siding


Taper the first plank to match the diagonal line of the concrete and start this board 1-2" above the concrete. I assume in regards to the cut edge being on top that we would set the cut edge level which will allow the factory edge to follow the tapered angle we cut on top, right?

The area where the osb is next to the concrete is under the barn roof in the aisle but rain still blows in. Am I correct in understanding that we could use the L flashing and sealer material to block off any exposed wood at concrete level in this area?

Hope I didn't confuse you further. We are getting ready to install the trim (was able to get a pneumatic nail gun on craigslist for a good price and picked up 2" finishing nails at home depot).
Old 05-06-12, 11:46 AM
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Yes, it sounds like you pretty much have it. Covering any exposed OSB with flashing would help, but keep in mind if there is splashing, that capillary action can draw water up behind flashing if it doesn't overlap the wood far enough to protect it. Since your wood is pressure treated, keep in mind that ALL fasteners into your PT wood have to be rated for PT contact (they should specifically state that they are recommended for PT wood), which usually means you need hot dipped galvanized nails, stainless steel or some other exterior coating.
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