How do I stop water leaking from a concrete slab porch into the rooms below?

Question

My front porch is concrete and is above a portion of my garage, laundry room, and a basement bathroom. The house is in Zone 6b: -5 to 0 F. The rooms are not finished and I am not sure of the ceilings construction (see photos). I initially thought the same concrete slab makes the floor of the porch and ceiling of the rooms below, but there is some lighting in these rooms. Possibly there's just conduit embedded in the concrete and this is still true. If it helps, my house was built in 1940 and has a block foundation which this concrete slab sits on.

My concern is I have two cracks in my ceiling that run the width of this slab. Both of these cracks leak anytime there is moisture above, despite the porch looking to be painted relatively recently (I just purchased the home).

The first crack is in the bathroom:

The second is in the laundry room:

And here's the porch, what's above:

I'm concerned about this because the bathroom crack has obvious signs of damage to the concrete/plaster. It give when I push on it around the crack and I'm sure I could easily chip it away. Also, I would like to finish the bathroom, maybe even the laundry room, and would like to hang drywall or something without concerns of moisture getting through. Finally, it's worth noting, that this home has a home warranty and if I can anticipate any costly repairs that might be covered, I'd like to move now.

So my question is, is this a big concern, ad either way, how can I fix this? Thanks.

Answer 1

Concrete always cracks and is porous to water. What you have is a roofing question. The only line of defense is what's above the concrete, and it better be elastomeric to account for crack expansion and contraction.

These rooms are likely not insulated. A spray foam roofing material applied above the concrete may be just the answer. The foam will easily absorb the crack motion below, AND give you quite a bit of R value per inch in insulation. You'd then need to build a new porch surface on top of the foam.

Or look for products designed for walking rooftop decks. Rubber Membrane Flat Roofs (EPDM) for example, you'd basically glue a giant sheet of rubber on top of the porch. You'd get no insulation, but your water problem would be solved.

Yes there are crack injection kits meant for radon or foundation work. You could inject the two cracks you know about today. But you can't inject the crack that will form next winter. Your only sure solution is a membrane roof on top of the deck.

Answer 2

You can turn your porch into a covered porch, putting a roof over it.bor like Brice said, you can install roofing membrane to the floor of your porch just like if you were roofing a flat roof, but that will look ugly, so you would also probably want to build a deck on top of the porch to hide the membrane.