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My house has a full flight of poured concrete stairs (covered with decorative stone) that runs parallel to (and butts up against) an exterior wall. enter image description here

The interior wall had water stains at the basebord, some distortion in the laminate floor near the baseboard and the distinct odor of damp, decaying wood.

I pulled the baseboard off and cut away the drywall 12 inches up for the entire length of the wall. The sill plate is damp and one stud at the bottom of the stairway shows signs of rot or termite damage. The insulation was damp at the ends but not at the 12 inch mark.

Currently, there is nothing between the poured concrete for the stairway and the studs. No plywood sheathing, no plastic, nothing. It looks like at some point in the past there was something there. Two of the studs have scraps of plastic sheet between them and the sill plate. I cannot tell if the plastic sheet was on the interior or exterior side of the studs. On the exterior side of the studs near the top end of the stairs there is plywood sheathing about 12 inches wide, but broken off in a ragged edge. It is waterlogged.

My best guess is that there was/is a leak between the stairs and wall near the upper end of the stairs. The water is flowing down the concrete and then running along the sill plate toward the corner of the wall. At some point in the past the interior wall was removed and the plastic sheeting and plywood sheathing were ripped out and then the interior wall was restored. Obviously, this is not the right solution.

My question is two-fold:

  1. If this were new construction, how would one construct a stairway parallel to an exterior wall.

  2. How can the wall as currently constructed be repaired such that water infiltration cannot occur in the future.

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    You have a tough problem there. It should of been built with multiple layers of flashing and ice and water shield. I would of never attempted to put stone on top. It is too hard to control water after it gets in seams.
    – justin j
    Nov 28, 2015 at 17:08
  • What is under stairs? Is it floating or solid concrete to ground, How high?
    – justin j
    Nov 28, 2015 at 17:10

3 Answers 3

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When concrete is poured so that it will be in contact with a wood part of the building allowances should be employed so that moisture is prevented from becoming trapped and is able to escape quickly. The wood wall that abuts to the concrete stairs should have been isolated with a vapor barrier. The most commonly and easiest to use would be 30 lb. roofing felt tacked along the stair/wall face. Metal flashing and self-sticking flashing would also prevent water from contacting the wall. An isolation or expansion joint would have helped any water that did find a way in to eventually evaporate. Repairing the concrete from contacting the studs is difficult. If there was any space between the surfaces a barrier could be retro-fitted. I'm not sure how feasible it would be to start cutting back the edge of the steps to create a space for repairing the wall? If you could that would enable the installation of treated lumber and water shields (flashing and felt). If not than all that can be done is to silicone caulk the wall/concrete joint, but water will still get in through the concrete by condensing.

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    Water is most likely getting in through joints in rock capping and making its way under rock and against house. I don't know what grout lines look like but trying to seal them is a gamble and freeze thaw cycle will make it hard to stay sealed. Silicone will help but will not stop all water. Wall needs to be sealed at house at concrete layer not rock
    – justin j
    Nov 28, 2015 at 18:07
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As you seem to already know, you have a real mess on your hands.

The answer to question 1 is that the wall would first be built properly, with wood sheathing, a water-resistive barrier of tar paper or Tyvek, and a scratch coat of stucco. Then the staircase's structure would be bolted through the wall into the studs and the decorative stone would be mortared to the scratch coat of stucco around the staircase. Then brown and/or and color coats of stucco would be applied over the remainder of the scratch coat.

The answer to question 2 is as follows:

Contact a structural engineer and and arrange for all the wood in the area to be safely and completely removed without compromising the structure. Then I would paint the concrete visible from the interior with RedGard. After that, I would build a plywood panel that fits in the area, cover it with standard tar paper, and tip it up into place against the RedGard-painted concrete and the stucco on all sides of it. After that, You can install new studs in the wall and re-drywall.

With such an assembly, water in the concrete will be prevented from entering the interior by the vapor-barrier RedGard paint, and any that does make it inside for some reason will hit the tar paper and drain away from the interior.

Needless to say, this is probably not going to be a DIY job and I encourage you to hire a professional and get a building permit.

I'll also mention that if the rest of the structure is built the same way--stucco over studs with no sheathing or water-resistive barrier--then you have a building that was fundamentally built wrong and you might want to explore the possibility of removing all the stucco and installing proper wall sheathing and a water-resistive barrier. If that's not an option, paint all of the stucco with mineral-based sealer such as sodium silicate or potassium silicate. Apply several layers. Resist the urge or advice to use latex paint or other polymer-based masonry sealers, as they are not vapor-permeable and any water that gets inside will be trapped and rot the wood. If the stucco is already painted with latex paint, removal is your only practical option.

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As you seem to already know, you have a real mess on your hands.

Indeed. You almost certainly need a permit to do the work detailed in the other answers. A structural engineer is a must. Sorry.

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