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I have a stamped concrete patio where the step to the bumpout on my house and slab were poured in one piece. They didn't pour concrete under the bumpout, just up against it, leaving a hollow area that tunneling animals make their home.

Voles have found their way under the patio and made a home under the bumpout (and sometimes in to my basement) through this bumpout area. I have a small amount of access under the bumpout now that I have removed the wall and ceiling of a finished bathroom.

What's the best way to permanently keep the voles from getting in to my house through this area? I have easy access to the outer perimeter of the patio, but I wonder if it would be better to seal off the void under the bump out. If I seal under the bumpout, is concrete my best option?

The hollow area under the step has a gravel base and about 4-6 inches in height of air before it gets to 1/4 plywood nailed to the bottom of the joists that support the bumpout. The total hollow area is probably 7 feet long by 1 foot wide by 4-6 inches tall.

I haven't attached pictures because it just looks like ceiling joists that end at a rim joist and plywood nailed to the bottom.

I've tried an exterminator and the voles take the poison, bring it in to my house, and die. This has been going on for 18 months.

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Yes concrete will work just fine. First I would try to determine exactly how the voles entered your basement so I could repair and block it off before I filled in the space. I would also make sure that filling in the space with concrete is not going to prevent water drainage. It might be a good idea to install some sort of drainage pipe.

  • I believe they are digging under the patio and up through the gravel in the void. Once in the void, there are small gaps between the plywood under the joist, the rim joist, and the concrete block of my basement wall. The space I have to work in for this is only as tall as the joist height (assuming 10 inches) . It would be difficult for me to get in there to drill holes in to the old concrete to connect it to the new concrete. Is that a problem? – thatguy Oct 12 '17 at 2:11
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Filling the void with concrete should work well for you, though make sure that drainage won't be an issue as noted above. Alternately, you could add a layer or two of 1/4" galvanized hardware cloth as a barrier. This can be both inside and buried/attached on the outside where they are accessing the void. If you can find any other small locations where they are coming into the house, plug those holes with chore boys. They are copper scouring pads. Don't use steel wool as it will rust and stop being a barrier very quickly. The chore boys last for years.

  • Your thought of a drain makes sense as a backup in case water somehow gets down to this. In theory, with the single pour concrete step above it and my house on the side of it, no water should get down there, but a backup plan is good. How would I do make a drain that keeps the voles out in an area I can barely reach? (It's at ceiling height and only about 10 inches tall). Once I refinish my bathroom I'm not going to have access to this again (I hope). – thatguy Oct 12 '17 at 2:14

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