Waterproofing ground level door over slab

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Old 02-14-12, 02:59 PM
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Waterproofing ground level door over slab

I'm hoping someone here can give me a straight answer on how to resolve this situation. Also hope I put this in the correct section. Here goes:

There's an older home here in town that I've been thinking about purchasing. Problem is it has a ground level back door. Entire house sits on a concrete slab, and the slab extends out maybe 14 feet past the back door to form a patio along the corner of the house. Currently the patio portion is enclosed, keeping the water away from the back door. What I'd like to do is remove the flimsy enclosure and redo the back door so there's no chance of water coming into the house. Been thinking of tearing out the door and pouring a 2" concrete threshold in there, and then installing a new door over that. With a thick rubber mat inside it shouldn't be too much to step over. Also, I could cut the slab outside and install a wide drain and gutters over top. Does that sound like enough to make certain NO water comes in if I go this route? Been told be one contractor to drill holes in the slab where the door currently sits and put in metal rods in to keep the new concrete slab secure after it dries. Been told by another that metal rods aren't necessary, just a bonding agent and flashing over the new threshold. And I've been told by another guy that 2" of concrete won't hold over time. I keep asking if a paint-on waterproofing product would help, but I can't get a straight answer. Bottom line is I'm worried the water will somehow sneak under the new threshold and come into the house if I do this, and I don't want to deal with water problems all the time. Can someone explain to me the proper way to do this--or if it's even possible? Maybe I wouldn't even need to raise the door with proper drainage? Thanks.
 
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Old 02-14-12, 03:18 PM
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So you are sure that the level of the slab inside is exactly the same level as the slab outside? Set a 2x4 on the floor inside and a 2x4 on the pad outside and set a level across the threshold to check.

As you probably know, cement should ALWAYS be lower outside than inside to prevent blowback. Something you didn't mention is what type of floor covering you have inside... and how thick it is. Am I correct in assuming that you are not planning to remove the exterior cement?
 
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Old 02-14-12, 03:39 PM
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XSleeper:

No, I'm not absolutely sure the the slab is the same height on both sides (I haven't bought the place yet, and there's a door in there now), but it sure looks level with the naked eye.

The floor in there now is carpet. I would want to pull it out and put vinyl plank flooring, which I know is going to take away more interior height. Been holding out on making an offer on this place because of this door situation. Looks like it may've been setup for a wheelchair or something.

Yes, I'd keep the exterior concrete there. Maybe put in a drain.
 
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Old 02-14-12, 06:03 PM
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Well, if anything, when the door gets changed out, I'd suggest not raising the threshold, but instead put down a Jambsill sill pan, then put the new door on top of that. The sill pan spans the entire rough opening and will have an interior lip to keep water out. The new door should get sealed to the interior lip of the sill pan, but the rest gets left open to allow for drainage. If the sill pan gets sealed down good, (using a good polyurethane sealant underneath) nothing will come underneath it.

I'm a bit leary of raising doors up much above the finish floor at all. The way they are built nowadays, prehungs already have a 1 1/4" threshold to step over, (when installed at the finish floor height) and some people don't like THAT, because they complain about tripping, having to step over it. I think it's perfect, since you have enough clearance for even the thickest rug.

So I think the sill pan is your answer- you may just have to adapt it a little bit for your particular situation.
 
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Old 02-14-12, 07:59 PM
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Thanks for the reply, XSleeper. I just read through a few old threads here and seen you recommending a door sill for them as well, and all had similar situations with ground level doors.

When you get a few minutes, could you please explain the process of doing this properly. I'd really like to do this myself, but I've never done it before with a concrete slab.

If I pull everything out and start with a clean, flat slab, what material would be best for a sub-sill? Would pressure-treated wood do here, or one of those pvc slabs? (The door sill pans I've seen all have a front lip that points down, so I'm assuming one needs to install it over a sub-sill.) Also, because this is going right over concrete, would I use a polyurethane sealer under the sub-sill AND screw it down to the slab? Then, say, cover the whole thing with a flashing, then another layer of polyurethane sealer, and then the sill pan, followed by the new pre-hung door, sealing only the inside backing to the wood frame of the door?

Thanks again for your help.
 
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Old 02-14-12, 08:15 PM
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Your sill pan will likely have the lip in front. If your slab is flat (no step down) then you'd just slice that lip off. (score it with a utility knife then bend it back and forth until it breaks off) In either case, you will be relying on the sealant beneath either the sill pan (or your subsill) to keep out water so there really is no difference... and you'd be relying on the inner flange to keep any water that gets into the RO out.

The front lip of the flange really works best when it hangs over the front of a raised slab, or over the wood framing on a house. Adding framing to your opening really accomplishes nothing other than raises the door up... raise the door up too much and you will need to cut into the header on top. Now if you find out that your slab is pitched back toward the house... and you need this subsill to help act as a dam... well that might be a different story. In that case, you'd want to replace the slab!

If you do want to insert a subsill (like I said before, I wouldn't recommend it + it doesn't necessarily need it) I would use solid PVC, such as Azek 1x6, trimmed to length and width to fit the rough opening exactly. Glue it down with polyurethane caulk or PL polyurethane. (I usually will apply 2 or 3 large continuous beads all the way across the opening) Place the subsill into the sealant and anchor it to the slab with a few tapcons. Then apply additional beads of sealant on top of that, assemble the sill pan following their directions.

And yes, I'd apply one bead of sealant to the inner bottom corner of the sill pan so that when you set the door in place, the inside is sealed to the inner flange.

There are many brands of sill pans available depending on where you live. You can find them online, or a big box store near you might have their own brand that they sell. Most are 3 piece, preformed corners and a middle section that is cut to length and glues everything together.
 
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