How to insulate a new, small basement slab pour within an existing slab
Deep energy retrofit combined with extensive remodel of early 60’s modern architecture home overlooking Puget Sound. Using cameras we found drain pipes under the basement slab were compromised. We took this opportunity to remove the slab in these areas as well as over areas where two bathrooms are being built, one existing and one new for the master bath, to accommodate hydronic radiant heat. The idea is to install hydronic radiant slabs in these two areas but we want to isolate them from the surrounding slab as well as from underneath. New foundations drains were installed and no water has appeared in the new excavations in the basement. Even so, we’re reluctant to install the slabs without a waterproof seal between new and old. I’d like some help with the following:
1. Preparation of the ground.
2. Type of insulation (XPS?).
3. Things to be aware of on the hydronic installation (I will be working with a reputable radiant floor company on this).
4. If we should worry about a waterproof seal between the new and old slabs and, if so, what our options might be to create that seal.
5. Other information we should know about this scenario.
In addition, what approach (vapor barrier, insulation, subfloor, etc) should we take for installing 2′ x 2′ tile and carpet on the old slab?
We’re installing a Daikin Altherma system with radiant floors upstairs and hyronic fan coil units and radiant panels downstairs. Since we have a hydronic source, we though we’d use it to heat the floors of the two downstairs bathrooms.
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