How to keep floor insulation dry and safe from pests?

Question

Hi I'm in process of constructing a small house I want to live in. The house will be built on foundation of concrete pilots. Since I want to insulate the floor I am now in process of designing such barrier which will keep the insulation dry and pests (mouse or similar which would get into the crawlspace) away. I have now this construction in my mind (cut below):

===================== - subfloor
||-------------------
|| Joists, spaces filled with insulation
||-------------------
+++++++++++++++++++++ - one way vapor barrier
xxxxxxxxxxxxxxxxxxxxx - chicken wire

What do you think about this solution? Are there any better? I don't want to re-invent the wheel...

Answer 1

See above picture

I would add an electrical outlet in this crawl space and plug in a electronic pest repeller, to make any rodent's life miserable, if they found their way in there.

The other added reason to have at least one outlet down there is for your convenience, if you needed to plug in temporary lighting. Insure that this outlet is GFCI protected as well.

Answer 2

Short answer: Housewrap, then treated plywood.

I built many three- and four-season porches as additions. They were usually on posts. The routine was to frame the floor upside-down, apply housewrap, then install pressure-treated plywood and flip the whole thing over. Then we'd insulate and install the subfloor.

Answer 3

The problem I see with your design is that the "one way vapor barrier" is a vapor barrier, but it's probably also a pretty effective water barrier. In this application, that vapor barrier is going to get cold. And gravity is not your friend, so the moisture that condenses on top of the cold vapor barrier is going to just sit there, becoming a mold/rot problem.

The simple rule is that you put the vapor barrier on the warm side of the insulation. In cold climates, that means to the inside. In warm climates, to the outside. Your profile indicates you're from the Czech Republic, so I'll suggest towards the inside for you.

As you add insulation, you can push this demarcation farther away from the edge. If you have enough insulation, you might be able to put the vapor barrier a few inches from the floor. This might be enough to let you change insulation types. For one example, you might use closed-cell spray foam and then batt insulation to fill the cavities. (This is popular in the southern USA, with the foam to the outside acting as a vapor barrier.) Changing insulation types can help you reduce costs - perhaps you want rock wool insulation facing the bottom, but you might choose to use just a single layer of that plus another layer or two of fiberglass or cellulose above it.

Almost any kind of insulation will be vulnerable to physical penetration by pests (nesting vs eating). You mention using "chicken wire" but most people's understanding of that product is small thin wires with a wide mesh, more than wide enough for mice and other small creatures to pass through. You might consider using a tighter wire product, such as lath mesh (which is steel with a small diamond pattern, used to secure stucco/cement to walls). Be aware that this can be costly - about USD$30 / 4x8 sheet-equivalent near me, versus about $8 for the same area of 1" chicken wire.

Finally, be aware that you need to particularly protect your joist bays from side penetration. It's easy to think about how you will keep vapor in/out of the bays relative to the floor, but think also about how the vapor will be kept out of the sides.

Answer 4

Chicken wire works great to hold the insulation in place. I would ask about the type of insulation you don’t want multiple vapor barriers that will end up trapping moisture. The only caution is make sure if you have copper pipes the chicken wire is not touching or in a few years you will end up with pinhole leaks wherever the wire touches the copper. But other than that chicken wire works great. Chicken wire will not stop even a large rat but if the space is insulated the critters don’t find the small leaks that attract them and if they do get in the insulation it is not ripped down , I have squirrels & mice after putting wire up the floors feel warmer and we have had fewer in the house, this could be from the electronic traps inside and dunk the rat in the barn. Still catch them weekly outside but have only got 1 inside the house since shortly after putting the wire up holding all the insulation in place that had come down, I don’t know how long ago it was put in but a large % had come down.