Dry waterproofing

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Realizing the cost of remodelling is a painful thing. To mitigate this I have been trying to figure out ways to keep an existing addition on my house. As part of our existing plan this addition was to be torn down because it is sitting at ground level on a slab and has the possibility of being subjected to wind driven rain and/or minor flooding.

After researching dry water proofing I think this will be the way to go. I think the structure itself is still quite sound. We are re-sheathing and siding the entire structure anyhow so I figured why not re-sheath the bottom 4ft of the house with 4x8 sheets of hardi board. Or heck maybe do the whole thing in hardi board. It would still save money in the long run. Then I would paint some kind of sealant or wrap the bottom half in some kind of membrane or paint on some kind of sealent to waterproof it.

The last step would be to attach a brick veneer to the outside for looks. This brick veneer would be built up no more than 2-3ft.

I think this is my best option. Any suggestions?

I'm not in a flood plane and my storm category is a category 3 storm surge in a fema rate code B. My soil is sandy and well drained so water doesn't stand for very long after rains.

[Sweep]

I'm not sure what dry waterproofing you want to use but any waterproofing design must start with a sound substrate which is not clearly described and if the stucture is close to or below grade the waterproofing must force water downward below the floor level into a drain. The seal of the waterproofing to the substrate below grade can be critical because water can rise behind it if the water isn't carried low enough, fast enough.

What is the existing depth of the slab perimeter below grade, the height of the slab above grade, the wall framing, and the sheathing material?

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I'm not sure of the depth below grade of the slab. Above grade its about 3-4 inches or so. The term is actually dry floodproofing. Basically all i'm wanting to do it keep water off the sides of the house at or just above grade. The structure really wouldn't have any kind of pressures placed on it. I'm not in a flood zone. The current wall framing i'm pretty sure is 2x4's. The sheathing material is t1-11 with vinyl siding over it. I'm going to be resheathing the structure in hardi-panels to give it more strength and so it never has to be done again. Then i'm going to put solid-core vinyl siding or hardi-planks over the sheathing.

When I do get a heavy rain water never sits up against the house. But wind driven rain does get sprayed heavily. I think what i'm trying to accomplish is more protection from the wind driven rain then anything else. Even with all the rain we've gotten over this summer down here in sunny S. Florida, no water has made it inside the structure from what I've seen. But my own paranoia insists that I take steps to bullet proof the exterior walls of this part of the house.

[Sweep]

You have started with some misconceptions and carried them to some incorrect conclusions. The design you describe will in no way "bulletproof" the exterior walls of your house. It is, in fact, little improvement over what you have now.

Hardie fiber-cement products are made of wood fiber and cement. Hardi-plank/panel must be treated the same as other wood products on the exterior of your house. It is recommended that you paint it (using their primer) and that it be held a minimum of 6" above grade as required for wood siding by most building codes. Hardie recommends that their product not be allowed to be in contact with standing water. You should buy a piece of Hardi-plank and put it in a bucket of water for a week to learn why Hardie says that.

Installing Hardi-plank as exterior sheathing will have no benefit over the existing sheathing. Since you must protect the wood framing from blown and splashed-back water, on a wall where the framing is too close to the ground, you must waterproof the wall from below grade to at least 8" above grade. This waterproofing would not only protect the framing but the sheathing as well, so new fiber-cement sheathing would serve no waterproofing purpose. It might even be a poor substrate for the waterproofing.

In terms of strength, the T 1-11 plywood should be much stronger than Hardi-board. I don't believe Hardi-panel is even rated as a structrual sheathing panel.

Be very careful when cutting Hardie products. Use their brand blade and avoid breathing the dust which can cause cancer. Clean-up must be thorough and wet, not dry.

A proper waterproofing detail is difficult so close to grade. I would try this method:
• Remove 8" or more of the vinyl siding and clean the exposed sheathing.
• Dig down a few inches and clean the concrete very well.
• Apply W.R. Grace water based primer (WB Primer) to the concrete and sheathing. Let it dry completely.
• Apply a continuous 12" sheet of W.R. Grace Ice & Water Shield or Perm-A-Barrier (modified bitumen & polyethylene self-adhered waterproofing membrane) 4" over the concrete and 8" over the sheathing. Roll all joints and edges with a 2" heavy steel roller.
• Cover the waterproofing membrane (to protect it from UV exposure) with sheet metal and cover as much as possible of the sheet metal with a material that is impervious to water such as horizontal PVC trim (water table) or vinyl siding.

Use only W. R. Grace products but not Vycor, which is too thin. The primer is critical to this design; it will create a strong bond to almost anything. It is usually sold in 5 gallon cans so check with waterproofing contractors to see if they would sell you a smaller amount. There is a product similar to Ice & Water Shield that has an aluminum film on one side. It might do the job if you can find it in a wide enough roll.

This design is not "bulletproof" but it will probably withstand up to a foot of standing water.


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I generally come to alot of wrong conclusions. This is where you come in Sweep. Thanks for setting me straight. I'm not being sarcastic either. Trying to find and honest opinion or answer is really really difficult. Most of the time i'm just throwing out ideas hoping that something will work.

I'm going to be replacing the t1-11 and vinyl sidng with new stuff. Is there anything better than t1-11 for sheathing that i'm trying to accomplish? Even if I use pt plywood? I'm replacing all the sheathing just because it will probably get tore up during other project relating to the remodel as well as when we remove the old siding.

What about the brick veneer idea rather than sheet metal to protect the waterproofing membrane? This would add asthetics as well. Then I would run the new vinyl siding down to the top of the brick. I know I would have to put in a new small slab for this and anchor it to the existing slab but I narrow slab like that shouldn't be a big deal. The brick would only go up about 2-3ft.

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What about Advantech by Huberwood for the sheathing? I know a few builders that swear by it. Plus it has a 50 year warranty. Though I expect it will be expensive.

[Sweep]

It's hard to follow your thinking. Perhaps I don't understand the situation.

The original T 1-11 should be at least 5/8" thick which makes it as strong as 1/2" CDX plywood sheathing. I don't know why you would need anything stronger or why the existing sheathing would not survive the renovation unless it has rotted or you plan to add a lot of windows and doors. Am I missing something?

Avantech says their panels are stronger and more water resistant than CDX plywood but they don't say how much and why would you need such marginally better features?

I assume you mean thin brick tile on a backer board instead of brick veneer wall construction (which is a full sized brick and cavity wall design which would require a galvanized angle bolted to the slab edge and fattening the wall above to the outside over 5 inches which would be prohibitively expensive). Brick tile would have to be installed on a fiberglass-reinforced cement board like Wonderboard or its imitators with a cement based setting bed and grout instead of adhesive. The waterproofing membrane would have to be installed, as described previously, behind the backer board against a solid substrate which means the backer board would have to be installed over the existing (or new) sheathing to whatever height you wanted and the vinyl siding either shimmed out or brought down flush with and flashed to the backerboard (not recommended) Blocking could be placed between the studs but that would not be the best substrate for the waterproofing membrane. I mention all of these possibilities because I don't know the position of the studs relative to the slab edge. Are they flush or set back 5/8"?

In terms of aesthetics I would prefer a "water table detail" at the bottom of vinyl clappboard siding. (see photos) If you do this, then there is no reason not to make it PVC and avoid the high cost and possible future maintenance of imitative brick materials. Brick 2 or 3 ft high would look pretty strange interrupted by the windows and doors.

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I guess the brick might look kinda funny and from the way it sounds a heck of alot of work. I may do a single brick planter box facing the street just for kicks though but that is budget dependent as well. The studs are set back 5/8 I believe not flush with the studs. We are probably putting in a window or two. I guess replacing the sheathing is really dependent on what kind of condition its in. I won't know until I get to tearing the old vinyl siding down. I need to take a digital camera hame from work to take some pictures.

http://www.leepa.org/dotnet/Photo/Photo.aspx?Id=281660&Width=640

Thats a link to a picture of the house. The far left of the house where the carport is will be receiving the dry flood proofing. It's the addition the former owners built in the 70's. You can see the step in the roof.

My future father in law wants to tear it down and rebuild it up to the level of the rest of the house which is on a crawlspace. He used to build houses a long time ago up north. I just want to make it as good as I possibly can because i don't want to spend the money and the structure is nonconforming on the addition end of the house. So if I destroy it in ANY way (meaning demo it) I have rebuild it conforming. Which means I would loose two feet off the end of the house. I don't want to loose two feet because I like my square footage the way it is.

So thats kinda where i'm at. I'm trying to find a way to keep the addition while protect it from wind driven rain and the possibility of a couple of inches maybe as much as 3-4 inches of flooding. I don't think its ever happenned in the past but I don't want it to ever happen.

[Sweep]

I would waterproof it with Ice & Water Shield and cover it with PVC trim unless you can get a zoning variance to rebuild it higher with the same footprint. Can't hurt to ask.

Don't let any plants touch the house.

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I doubt i'll be able to get a variance. And building it higher will probably cost about $50K or more. There is a 30 W x 15 D room behind that carport, florida room (the room with the jalosie windows)), and little room next to the carpot. I'm in the city so they are kinda strict. Nice, but kinda strict.

Why no plants touching the house? I was going to remove all the pants anyhow but why no plants?
Also, what do you think about a small amount of river pebbles (the small marble sized ones) pushed up against the side of the house as a displacer? Not high up at all or anything but maybe about a foot wide.

[Sweep]

Plants get wet and keep the exterior wall wet.

Clean stone at the base of the wall will reduce the amount of dirt and sand that splashes back on the wall from rain.

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Good stuff. At least now I have a plan to keep that structure there. Now all I have to do is gut the interior, re do the wiring, redo the roof sturcture(its currently flat with a 7.5ft ceiling. And a host of other things.

I'm just happy I found a way to keep the structure there. I'll still probably drop $20K on it but I guess thats what you have to pay for location. Its better than the alternative.

When I found the house I had the idea of "find a crappy house in a great neighborhood." Even a crappy house in a great neighborhood is $200K or more.

When I'm done with the place it should be over 2000 sqft. under air. And i'll have a 29x14 great room. Thats big.

Thanks for your help. Its much appreciated. I'm sure I'll have lots of other questions in the future.

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Would you recommend any of the protecto products for this job? I just used the protecto flashing tape for some roof patching. That stuff is very very sticky.

[Sweep]

As far as I can tell Protecto membrane is similar to Ice & Water Shield but it is sticky on both sides. I don't know why that would be an advantage in your situation but it would probably work OK. Be careful how you prepare the concrete for appliction of a self-adhesive membrane. You really should have a primer. Maybe Protecto makes a primer for concrete.

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Yeah I'll definitely prime it first if it will help with the stickyness. I'm researching another idea for my remodelling that may be my strangest (to me anyhow) idea yet. I would lose my garage or carport all together but I wouldn't have to add any footprint at all to my house. I'm meeting with the drafter on the 19th so I'll be passing it by him as well.