Do I need to cover the styrofoam on ICF blocks with tar paper ?
ICF stands for Insulated Concrete Forms. Foam insulation is supported with plastic studs, which form reinforcement for the concrete, and studs to screw attach lath for stucco, or other materials. Thick concrete provides a strong, durable building. Note the round clips on the plastic webs. They allow rebar to be clipped on. The plastic studs are 12" O.C.
We have an ICF house to stucco coming up soon. The owner painted the bottom part of the styrofoam with blue stuff, a kind of waterproofing.
As far as tar paper on ICF, I noticed that the house we stuccoed in 2018 had a lot of saturation at the bottom of the wall, up to about 6 feet. I think this was due to a lot of water that penetrated the stucco was absorbed into the foam. Foam will absorb and trap water. I was thinking about using tarpaper in the future on ICF. The disadvantage is that, not only money, but we would need to mark the studs for metal lath, and tar paper sometimes bunches up, and metal trim such as casing bead won't lay flat without some effort. We have a big ICF house coming up, and I like the way the owner did this. Attached is a picture: He painted the bottom of the wall with blue stuff. They use this rubbery paint on plywood for EIFS, but I believe it traps water in the plywood. In this case I think it is a good idea and saves a lot of unnecessary work.
I had a bid invitation to put lath and cement stucco on a commercial addition. The plans called for lath and stucco over blue waterproofing. I had no interest in the job. You see the blue stuff on EIFS applications, and an impermeable material will probably rot the plywood. Plus, I had no interest in something I haven't done before, or even seen.