concrete over rock

by John
(Kenora Ontario)

Q. I am expanding my house, and one room has the canadian shield rock coming to within 2 inches of the finished floor surface.
how would you recommend I deal with this as there is no room to put down rigid insulation before a finished wood floor.

One thing I was thinking was placing in floor heating cables in the concrete and then pouring concrete directly over the rock to the finished floor height. my concern is will moisture / cold seep through the concrete in the winter? ( Northern Ontario)
another thought was to place a vapor barrier on the rock before pouring the concrete.
suggestions and comments would be appreciated.

A. You should use a vapor barrier Amazon has one you can install under the new concrete floor. This will block any moisture vapor transmission from transferring up through the concrete floor from the sub-grade.

In addition to that you can use RadiantGuard under concrete bubble insulation as it is only about 3/8 of an inch thick. This will reflect the heat and reduce heat loss into the sub-grade. It also acts as a vapor barrier, so with this product you wouldn't need the poly vapor barrier.

This will solve the moisture and heat loss challenges you have because of the rock being so close to the surface

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