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 (vapor block is one brand name) 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 EcoFoil 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.

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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